domain: spi phys

text:
Jean-Michel Melkonian

Jonas Hamperl

Quentin Berthomé

Jean-Baptiste Dherbecourt

Rosa Santagata

Myriam Raybaut

Antoine Godard Dphy

Optical parametric sources from the SWIR to the LWIR for standoff gas sensing

Keywords: lidar, absorption spectroscopy, infrared, greenhouse gases

We present our activities on the development of narrow linewidth tunable optical parametric sources and their integration in lidar systems. In particular, we present different implementations of the nested cavity optical parametric oscillator (NesCOPO) that enables tunable single-frequency emission from the SWIR to the LWIR, when pumped by a fixed or a tunable wavelength laser beam. We show how to amplify the output energy and while preserving the spectral linewidth to perform standoff detection of greenhouse gases and toxic chemicals with direct detection lidars.

INTRODUCTION

Standoff detection of chemical species -particularly in the gaseous phase-is of interest for atmospheric research and Earth observation (monitoring of greenhouse gases), industrial process monitoring, defense and security (detection of chemical warfare agents or chemicals considered as such), and safety (leaks of hazardous gases). To this end, infrared absorption spectroscopy is probably the most powerful tool to identify chemical species since most polyatomic molecules display characteristic absorption features linked to their vibrational and rotational modes and thus to their chemical structure. Quantification is also possible provided that the absorption cross-sections have been measured beforehand.

For long range detection (from 100 m to several tens of kilometers), the choice of wavelengths is bounded by atmospheric transmission windows, roughly located between 2 and 2.5 µm (short wave infrared, SWIR), 3-4 and 4.5-5 µm (midwave infrared, MWIR) and between 8 µm and 13 µm (longwave infrared, LWIR).

Passive methods, relying on spectral analysis of absorbed solar or thermal light, by selection with optical filters, angular dispersion with grating or prisms, or interferometers, are now well established, having given rise to many commercial products and several spaceborne instruments. On the other hand, active methods, such as absorption lidars [START_REF] Orr | Infrared LIDAR Applications in Atmospheric Monitoring[END_REF], provide a measurement independent from the optical background, while the spectral selectivity can be enhanced by using wavelength-tunable, narrow-linewidth lasers.

In spite of the increasing variety of devices emitting infrared light (solid state lasers, rare earth doped or supercontinuum fiber lasers, semiconductor quantum cascade lasers, optical parametric devices), it is still a challenge to emit a narrow linewidth radiation with a large wavelength tunability, especially when high peak powers are involved.

In this paper, we will review our recent work on narrow linewidth tunable optical parametric sources and their integration in lidar systems, for diverse applications such as methane leak detection for industrial safety, ground-based and airborne carbone dioxide and isotopic water monitoring, and detection of chemical warfare agents.

Principle of differential absorption lidars

In this work, we focus on differential absorption lidars (DIAL) that use attenuation and time-of-flight measurement of light pulses backscattered after propagation in the atmosphere (Figure 1). Return light flux is directly detected by a photodiode, in contrast with coherent lidars that use heterodyne schemes (usually to retrieve wind speed from the Doppler shift). In its simplest form, a DIAL emits two laser pulses consecutively at two different wavelengths. One *jean-michel.melkonian@onera.fr wavelength is in coincidence with an absorption band for the targeted species called λ ON , and a second wavelength is on a minimum of absorption called λ OFF . The laser pulses, after passing through the target gas cloud, are backscattered by the aerosols (dust or water droplets), collected by a telescope and focused on a photodetector. The gas concentration at distance is then retrieved from the ratio of the ON and OFF backscattered signals at time such that /2, where is the speed of light. Spatial resolution along the line of sight is usually limited by the detector bandwidth ∆ , so that Δ ≅ /2Δ . If light is backscattered from a solid target, spatial resolution is lost and the ratio of the ON and OFF signals is equal to the integrated optical depth along the line of sight (IPDA configuration for Integrated Path Differential Absorption LIDAR). For the same distance, the IPDA signal is typically 10 4 higher than the DIAL signal. Obviously, additional ON wavelengths are required for identification of more than one molecule, or if atmospheric species present infrared spectra overlapping with the one from the target. Additional OFF wavelengths can also be useful for better subtraction of the baseline on large spectral ranges, using a polynomial fit. Note that wavelength tunability does not need to be continuous, because for most applications the measurement of the shape of the absorption line is not necessary to retrieve the concentration (unless pressure and temperature are unknown and suspected to vary greatly). Figure 1. Simplified principle of molecular detection with a differential LIDAR.

Challenges for absorption lidar emitters

As for any lidar, a DIAL emitter should deliver a high peak power laser beam with a good pointing stability and a low divergence. In addition, the light spectrum should match the absorption spectrum of the target molecules, i.e. it should be very narrow and centered at a very precise wavelength, and at least tunable over two wavelengths for the ON/OFF differential scheme to work. This last requirement can take very different forms depending on how many different species are addressed, the complexity of their chemical composition, air pressure that has a strong impact on the absorption linewidth, and the abundance of the target species relatively to the one of other species with similar spectral features. We have listed nonetheless a few typical requirements in Table 1, to appreciate how difficult it may be to meet them all at once.

Two extreme examples can be found in remote sensing of CO 2 from space, and chemical warfare agents (CWAs) detection. For the former, a pulse energy above 50 mJ is required to get enough signal from Earth reflection after at a 10 km altitude, while the wavelength stability must be better than 1 MHz to get the required precision, taking into account the effect of pressure with the altitude [START_REF] Ehret | Space-borne remote sensing of CO2, CH4, and N2O by integrated path differential absorption lidar: a sensitivity analysis[END_REF]. For the latter, an ON/OFF tunability of 50 cm -1 and a global tunability of ~500 cm -1 are required because CWAs display broad spectral absorption bands, and what is the more, in the LWIR.

To be able to address these different challenges, we have developed generic optical architectures based on downconversion of light in nonlinear crystals under laser pumping, as described in the next section.

ENABLING TECHNOLOGIES

Quasi-phase-matched crystals

To generate radiation in the mid-infrared, we use frequency down-conversion of the pump in non centro-symmetric crystals, using second-order χ (2) nonlinearity, so that → + , where is the optical frequency and the indices p, s, i stand for the pump, signal and idler respectively. Efficient conversion occurs when the signal and idler waves propagate in phase with the nonlinear polarization created by the pump, which is naturally prevented by chromatic dispersion. Birefringent phase-matching, which uses the dependence of the index of refraction to compensate for chromatic dispersion, is a method that can be implemented in all anisotropic crystals. We use it for large aperture crystals in nonlinear amplifiers, such as KTiOPO 4 , ZnGeP 2 , and CdSe. However, this method does not give access to the highest coefficient d 33 of the nonlinear tensor which is associated to identical polarizations, and the efficiency is further reduced by spatial walk-off between the waves, which is another consequence of birefringence. Besides, birefringence phase matching is not possible is cubic crystals such as ZnSe or GaAs, despite their high χ (2) non-linearity.

In all our nonlinear oscillators we now use quasi-phase-matched (QPM) crystals, in which the nonlinear coefficient is periodically reversed to cancel the phase-mismatch whenever it reaches π. This allows using waves with identical polarizations (a.k.a. Type 0 phase matching) and a single propagation direction. This writes:

--- 0, (1)
where k is a wavevector and Λ is the QPM grating period. QPM has been a decisive technology to be able to use small beam sizes and hence low laser energies. QPM offers unique phase matching engineering possibilities, such as multiple periods and fan-out gratings for changing the wavelength by translating the crystal, or aperiodic grating to widen the acceptance bandwidth (Figure 2). We will give practical implementations of these three kinds of gratings in the next sections. In addition, wavelength tuning can be achieved by temperature control of the crystal. Periodic reversal can be provoked in ferroelectric crystals such as MgO:LiNbO 3 or Rb:KTiOPO 4 by domain propagation under a strong electric field (resulting in MgO:PPLN and PPRKTP respectively), or in cubic crystals such as GaAs by patterning using lithography and etching and then epitaxy regrowth (resulting in OP-GaAs). The materials have not been listed in an exhaustive way.

Figure 2. Three types of quasi-phase matching designs actually used in lidar emitters.

QPM can also be implemented for waves of different polarizations. In the case of crossed signal and idler polarizations (a.k.a. Type II phase matching), the acceptance bandwidth gets much narrower than for identical polarizations, which can be of great use to generate narrow linewidth radiation near the degeneracy /2. Since spatial walk-off remains zero, a longer crystal can be used to compensate for the lower nonlinear efficiency. In Figure 3, we compare the acceptance bandwidths of PPLN pumped at 1.064 µm for an idler wavelength near 2.3 µm for type 0 and type II phase matching: the contrast is striking. This is why we often chose type II for our emitters operating close to degeneracy (at least when the idler is below 3 µm). Another solution is to put a volume Bragg grating (VBG) inside the NesCOPO cavity: this element clearly hinders the wide tunability of the NesCOPO, but the spectral filtering is so efficient that the crystal can be used in Type 0 QPM (Figure 3). and normalized reflectivity of a VBG for comparison (2.5 mm thick, 400 ppm index modulation, reflectivity is 79%).

Another interesting case is backward QPM, in which one of the generated waves propagates in the direction opposite to the pump (one ⃗ is replaced by -⃗ in Eq. ( 1)). Although proposed very early, this has only been experimentally demonstrated recently thanks to PPRKTP, because the small required QPM period of about 500 nm would make the domains merge in PPLN [START_REF] Pasiskevicius | Mirrorless optical parametric oscillator[END_REF]. A backward OPO oscillates without mirrors, it has no longitudinal mode just like a DFB laser, and the spectrum of the backward wave is transform-Fourier limited. However, wavelength tuning of the backward wave needs a tunable pump wavelength, because it is quite insensitive to temperature.

A peculiarity of QPM is that if the crystal is not cut right after a domain border, the three waves will not be in phase anymore, so a special trick is necessary if one wants to cascade several QPM crystals, as will be discussed below.

The nested-cavity optical parametric oscillator

Pulsed OPOs are not notoriously known for generating narrow-linewidth, diffraction-limited beams. This is because of the absence of spectral and spatial selection in the cavity, and the use of short cavities (to build up the field during the transient travelling of the pump) and large beam sizes to carry more energy. We have solved this problem by designing a low-threshold oscillator with embedded spectral filtering [START_REF] Godard | Nested Cavity Optical Parametric Oscillators -A Tunable Frequency Synthesizer for Gas Sensing[END_REF], and amplification of its output in large aperture crystals (see next section).

The nested-cavity optical parametric oscillator (NesCOPO) is based on a dual-cavity doubly resonant scheme where the signal and idler waves oscillate in separated cavities, as depicted in Figure 4. Pairs of mirrors M2-M3 and M1-M3 are related to the signal and idler cavities, respectively. A double-pass pump beam is made possible owing to the gold-coated mirror M3. Such a configuration is suitable to achieve a low oscillation threshold and to prevent back conversion toward the pump after reflection onto M3, providing that the relative phase between the three interacting fields is maintained at its optimal value in the backward direction. This condition can be fulfilled by cutting the crystal after a domain end, or, in a more practical way, by adjusting the transverse position of a wedged PPLN crystal. In this case, the OPO gain bandwidth is halved while the threshold is divided by four compared to the single-pass scheme.

Adequate differentiation and separate adjustment of both signal and idler cavities enables single-longitudinal-mode emission because only one single exact coincidence of signal and idler modes is obtained within the parametric gain bandwidth (see Figure 4, right). This is analogous to the mechanical Vernier effect.

In marked contrast with injection-seeded OPOs, whose tunability is restricted to the one of the seeding laser, usually a DFB diode, the NesCOPO tunability is only limited by the phase-matching properties of the crystal, which is much larger. When a quasi-phase-matched crystal (QPM) is used, the wavelength boundaries are only limited by the transmission curves of the mirrors, because QPM allows defining several phase-matching setpoints in a single crystal (see Sec. 2.1).

Mode-hop frequency tuning of the radiation can be obtained by adjusting only one parameter (signal or idler cavity length, crystal temperature, change of QPM period by transverse translation of the crystal, or pump frequency) whereas fine continuous tuning is obtained by adjusting simultaneously two parameters so as to maintain the doubly resonant oscillation on the same mode coincidence. The choice in the adjustment parameter actually defines the span and speed of wavelength tuning:

• Change of QPM period by crystal translation (~ 1 sec): to change the target spectral range by a few cm -1 or up to several hundreds of cm -1 , e.g. to switch the emitter between species (i.e. CO 2 → H 2 O); • Change of crystal temperature by thermoelectric heating/cooling (~ 1 min): to set the QPM wavelengths to their targets, as in a calibration process, and/or to extend the spectral ranges offered by the different QPM periods;

• Signal or idler cavity length by piezoelectric actuation (~ 1 ms): to switch between close wavelengths (fitting within the acceptance bandwidth of the oscillator crystal, which is typically 1 cm -1 ), e.g. to perform a differential ON/OFF measurement; • Pump frequency tuning (time depends on laser technology): any of the aforementioned uses;

• Signal and idler cavity length: to scan several wavelengths across an absorption linewidth. The huge wavelength versatility of the NesCOPO has a downside though: the wavelength must be measured very precisely. On the other hand, as it operates on a single longitudinal mode within a spectral window that is know from the crystal QPM period and temperature, a full spectrum analyzer is not necessary. A combination of Fizeau interferometers [START_REF]HighFinesse lambdameters[END_REF] or Fabry-Perot interferometers [START_REF] Des Aulnois | A new way of controlling NesCOPOs (nested cavity doubly resonant OPO) for faster and more efficient high resolution spectrum measurement[END_REF], an integrated Fourier Transform Spectrometer [START_REF] Le Coarer | SWIFTS: on-chip very high spectral resolution spectrometer[END_REF], or mode beating with a frequency comb [START_REF] Dherbecourt | Design and pre-development of an airborne multi-species differential absorption lidar system for water vapor and HDO isotope, carbon dioxide, and methane observation[END_REF] are all suitable methods.

Note that if the gain bandwidth is especially large, the Vernier effect will fail to select only one coincidence: thus is why we have to resort to Type II phase matching when the signal and idler wavelength are close to the degeneracy point (2.128 µm for 1.064 µm pumping). We also investigated the use of a VBG as the output coupler M3 for the idler wave, to reduce the spectral acceptance of the cavity and be able to use a Type 0 PPLN crystal. The NesCOPO operated on a single longitudinal mode and could be tuned over 15 nm thanks to a transverse chirp of the Bragg period [START_REF] Kabacinski | Wavelength tunable, single-longitudinal-mode optical parametric oscillator with a transversally chirped volume Bragg grating[END_REF].

Optical parametric amplifiers

The general architecture of our emitters is the one of a Master-Oscillator-Power-Amplifier (MOPA). The spectral and spatial characteristics of the beam are defined by the master oscillator (the NesCOPO described in Sec. 2.2), and are preserved through amplification, provided that pump lasers have adequate spatial and spectral features, and that full saturation is not reached. The superiority of this approach was experimentally demonstrated by others 14 years ago [START_REF] Haakestad | High-pulse-energy midinfrared laser source based on optical parametric amplification in ZnGeP2[END_REF]. In our SWIR/MWIR emitters, we start from a commercial diode-pumped, injection-seeded Nd:YAG laser to pump a NesCOPO, usually based on PPLN, with less than 1 mJ of energy at 1.064 µm (Figure 5a). The rest of the laser energy is used to pump several crystals (usually PPKTP), separated by a signal/idler dichroic mirror to mitigate backconversion effects occurring when the three waves are not in phase at the input of a crystal, or when the pump becomes depleted near the center of the beam. After that, LWIR radiation can be generated by difference frequency in a crystal such as ZnGeP 2 , as we have shown previously and will not be detailed here [START_REF] Melkonian | Long-wave infrared multi-wavelength optical source for standoff detection of chemical warfare agents[END_REF]. The MOPA concept can be transposed further into the infrared by choosing adequate optics and crystals (Figure 5b). However, the scarcity of high-energy singlefrequency 2 µm lasers make the LWIR energy more difficult to scale up. Experimental implementations of these architectures are given in the next section.

EXAMPLES OF LIDAR EMITTERS

2 µm emitter for ground-based water vapor isotope ratio measurements

So far, no DIAL instrument has been able to quantify the relative abundance of the water isotopologue HD 16 O, which would require collocated measurements of both the main isotopologues H 2 16 O and HD 16 O. Such a measurement would lead to improved understanding of processes governing the global hydrological cycle, with the prospects of improving the accuracy in the predictions made by atmospheric general circulation models [START_REF] Steen-Larsen | Evaluating the skills of isotopeenabled general circulation[END_REF][START_REF] Hamperl | Differential absorption lidar for water vapor isotopologues in the 1.98 µm spectral region: sensitivity analysis with respect to regional atmospheric variability[END_REF]. To this aim, we realized a parametric source operating at 1.98 µm and performed a first demonstration of probing H 2 16 O and HD 16 O.

The emitter architecture is of the "2 µm MOPA" type described in Figure 5a. It is an improved, more ruggedized, version of our previous MOPA setups [START_REF] Melkonian | Long-wave infrared multi-wavelength optical source for standoff detection of chemical warfare agents[END_REF][START_REF] Raybaut | High-energy single-longitudinal mode nearly diffraction-limited optical parametric source with 3 MHz frequency stability for CO2 DIAL[END_REF][START_REF] Dherbecourt | The NAOMI GAZL multispecies differential absorption lidar: realization and testing on the TADI gas leak simulation facility[END_REF]. A picture of the setup is shown in Figure 6. The parametric source is based on a NesCOPO combined with OPA stages, pumped by a commercial injection-seeded Nd:YAG laser (Innolas), delivering 12 ns-pulses at a repetition rate of 150 Hz. The NesCOPO uses a MgO:PPLN crystal in type II phasematching (crossed idler and signal polarization), and emits single-frequency radiation, tunable in a 1 nm-window around 1982.5 nm (signal) suitable for addressing H 2 16 O and HD 16 O (the idler wavelength lies around 2298 nm but is not used for the measurement). The OPA uses several rubidium doped, periodically poled, KTP nonlinear crystals (PPRKTP). These crystals combine a high damage threshold (> 4 J/cm² with coating), a high nonlinearity (d eff > 9 pm/V), and the possibility to be poled through thick aperture (up to 5x5 mm²) [START_REF] Zukauskas | 5 mm thick periodically poled Rb-doped KTP for high energy optical parametric frequency conversion[END_REF]. With a pump energy of 70 mJ, and idler rejection between the last two crystals (total interaction length of 30 mm), it was possible to obtain a signal energy in the range of 6-9 mJ at 1982 nm. (c) λ ON / λ OFF recorded wavelength switching for HD 16 O measurement

The NesCOPO emitted wavelength is pulse-to-pulse modulated and recorded with a High Finesse WS6 IR wavemeter (Figure 6c). For each targeted species (H 2 16 O and HD 16 O), such pulse-to-pulse wavelength modulation is necessary to emit the two wavelengths (namely λ ON and λ OFF ) in and out of coincidence with the absorption line. This is performed by adjusting the NesCOPO cavity length using piezoelectric transducers. A transverse profile of the output beam after passing through a beam expander is shown in Figure 6b. It is Gaussian with a measured M 2 <1.5 and a divergence fullangle of 300 µrad. The emitter is mounted on a carbon fiber bench (CarbonVision) to minimize temperature induced deformation. Even so, the pump beam is continuously monitored by two cameras to monitor beam pointing drift during the day as the lidar is tested in an unregulated temperature environment.

The lidar receiver consists of a 10-inch, custom-made Newtonian telescope which focuses the backscattered radiation onto a 900 µm-multimode fiber, whose output is imaged onto a commercial InGaAs amplified PIN photodiode of 300 µm diameter. The signal is pre-amplified and digitized with a high-speed 12 bit oscilloscope card, for a total NEP of 1.3 pW/√Hz and a bandwidth of 3.5 MHz (50 m longitudinal resolution). The telescope full-field-of view angle is 1.2 mrad.

DIAL tests along a horizontal path were conducted on 16 April 2021 in Palaiseau, France. The upper panels of Figure 7 show the recorded ON/OFF lidar signals expressed as signal-to-detection-noise ratio (SNR), with a dominant noise contribution from the transimpedance amplifier. The lower panels of Fig. 77 show the retrieved volume mixing ratios (VMR). The signals were averaged over 30 minutes successively for each species. For H 2 16 O, a reference was provided by an in-situ Picarro G2401 analyzer, located in the vicinity of the lidar instrument. We recently integrated the DIAL emitter in a mobile truck combined with a zenith-looking telescope in order to measure vertical profiles of H 2 16 O and HD 16 O in the lower troposphere. We will compare the DIAL measurements with those obtained by a Raman lidar and in-situ sensors in order to quantify instrument errors and biases and compare them with theoretical simulations [START_REF] Hamperl | Differential absorption lidar for water vapor isotopologues in the 1.98 µm spectral region: sensitivity analysis with respect to regional atmospheric variability[END_REF]. Future work will also consist in increasing the extracted power of the transceiver for higher sensitivity.

2 µm emitter for airborne measurements

Although the possibility to measure greenhouse gases from air and space with lidars is expected to come with significant benefits such as measurement independency from solar illumination, the technical and scientific challenges for this kind of mission are highly demanding. In this section, we give an overview of our ongoing efforts to increase the technical readiness level of a lidar that is intended for multi-species detection in airborne operation. These technical developments are being carried initially for an ESA TRP project (GENUIN) and now running in the frame of the EU H2020 LEMON project [17] in collaboration with climate research laboratories. The lidar is designed for vertical DIAL measurement of water vapor and its isotope HDO, as well as carbon dioxide.

The infrared emitter is based on the combination of two NesCOPOs with a single optical parametric amplifier line as illustrated in Figure 8. The pump laser is an injection-seeded, diode-pumped actively Q-switched Nd:YAG laser based on a stable resonator and a Nd:YAG amplifier, yielding 15 ns long pulses and operating at a 150 Hz average repetition rate. The NesCOPOs are pumped by a beam extracted directly from the oscillator to ensure a high beam quality in the focused far field. In the first NesCOPO, the QPM condition is tuned to get the emitted signal in the 1982 nm window suitable for water vapor and HDO isotopic ratio sounding. The idler wave is generated in the 2290 nm window suitable for CH 4 probing. The second NesCOPO QPM condition is tuned for signal emission in the CO 2 2051 nm window (R30 absorption line). A specific pumping timing is applied to operate in double-pulse mode (i.e. 75 Hz double-pulse emission) with a 500 µs delay. This way, each OPO can be switched from the OFF to the ON line within 500 µs, which is much shorter than the coherence time of the atmosphere, even under a strong wind or a strong turbulence. The idler beams are coupled out and combined with dichroic mirrors to be sent to the OPA line. The OPA line is composed of cascaded Rb:PPKTP nonlinear crystals with transverse aperture of 5 x 5 mm². The OPA has been designed to amplify the extracted idler energy from the NesCOPO from ~20 µJ to several tens of mJ (gain > 30 dB). We chose to keep the same beam diameter size of 2.9 mm diameter in all crystals, to reduce the footprint of the pump distribution stages, and limited the fluence to 2.5 J/cm² to eliminate the risk of laser-induced damage. To switch from CO 2 to H 2 O, the PPRKTP crystal temperature has to be changed by 25 °C. The idler wave is removed after each crystal as it is an efficient way to reduce saturation and back-conversion effects, optimizing the extracted signal energy and M². The OPA is pumped by the 1.064 µm beam after amplification in a Nd:YAG rod to reach 200 mJ energy per pulse. Special care has been taken with the thermo-mechanical management of the laser and OPOs in order to withstand temperature changes and the expected aircraft environment (ATR 42 aircraft from the SAFIRE fleet). The housing is made from a single block of aluminum with thicknesses validated by the laser manufacturer. The NesCOPO cavity is inside an opto-mechanic assembly built around a low expansion glass frame with stringent mechanical alignment tolerances. The NesCOPOs are located in the same housing as close as possible to the laser oscillator in order to minimize pump beam pointing fluctuations. The housing is mounted on a specially damped carbon breadboard via isostatic mounts. The design has been validated by FEM simulation of thermal deformations and vibrational modes, and a CAD view can be seen in Figure 10.

Figure 10. Overall emitter layout on carbon breadboard, together with emission beam shaping and energy calibration systems.

The same care has been taken with the receiver of the lidar. The telescope, that includes a 35 cm diameter mirror, has been manufactured by a specialized company, and will be integrated in a carbon and steel frame mounted on dampers, designed to withstand the vibrations of the plane.

For this lidar, we chose an innovative wavelength measurement solution, which should provide a much better precision than the traditional one based on Fizeau interferometers. It consists in using a GPS-disciplined and CEO-stabilized frequency comb and beat note analysis in order to retrieve the optical frequency. To perform this optical beating, a leak from the OPA stages is extracted and sent into a second harmonic generation (SHG) stage in order to match the spectral range of the frequency comb.

More details on this lidar have been given in a recent publication [START_REF] Hamperl | High Energy Parametric Laser Source and Frequency-Comb-Based Wavelength Reference for CO2 and Water Vapor in the 2 µm Region: Design and Pre-Development Experimentations[END_REF].

LWIR emitter with a tunable pump laser

The leading idea of this emitter design was to downconvert to the LWIR directly from 2 µm laser radiation, using the "LWIR MOPA" design of Figure 5. Indeed, the optical efficiency of this solution is, in principle, twice the one of the "2 µm MOPA+DFG" design. This development has only been possible thanks to the commercial availability of 2 µm optical components and systems such as thulium and holmium doped lasers, 2 µm optics, 2 µm single mode fibers and fibered components, InGaAs detectors, InGaAs spectrometers, etc.

First, two single-longitudinal-mode lasers were developed specifically for OPO pumping, using thulium doped yttrium aluminium perovskite (Tm 3+ :YAP) as the laser medium. The first version was passively Q-switched, and emitted 36 ns long pulses with an energy of 170 µJ at 1940 nm [START_REF] Grisard | High energy single frequency passively Q-switched 2-micron microlaser in thulium-doped yttrium aluminium perovskite[END_REF]. Later, a 125 µm étalon was added to make the laser run on a single longitudinal mode (unpublished). Later, an actively Q-switched, wavelength-tunable laser was developed [START_REF] Berthomé | Actively Q-switched tunable single-longitudinal-mode 2 µm Tm:YAP laser using a transversally chirped volume Bragg grating[END_REF]. It emits 60 to 80 ns long pulses with an energy of 250 µJ at a 1 kHz repetition rate, with a TEM 00 mode and a M² factor below 1.05. The laser runs on a single longitudinal mode thanks to the combination of a volume Bragg grating (VBG) and a 4-mm uncoated YAG étalon. The output wavelength is tunable from 1940 nm to 1960 nm by translating the VBG owing to a transverse chirp of the Bragg period in the VBG. However, since the étalon is not moved synchronously, the laser tunes by hops of one cavity free spectral range (0.65 cm -1 ). Secondly, we developed a LWIR version of the NesCOPO, by using OP-GaAs [START_REF] Grisard | Quasi-phase-matched gallium arsenide for versatile mid-infrared frequency conversion[END_REF] as the nonlinear medium. The difficulty to manufacture the crystals did not leave time for coating the M 2 mirror directly on the crystal facet, so we used an external mirror instead (Figure 12). For the same reasons we did not polish a wedged output facet to control the nonlinear phase (see Sec. 5). Nonetheless the NesCOPO could be arbitrarily tuned to any desired wavelength by combining piezoelectric actuation and temperature control, the spectral purity was almost Fourier-transform-limited, and a spectrum of ammonia near 10.4 µm was recorded [START_REF] Armougom | A narrowband infrared source based on orientation-patterned GaAs for standoff detection of chemicals[END_REF]. One of the positive outcomes of these experiments involving the first version of the Tm:YAP laser was the very good reproducibility of the results over the years, secured by the long lifetime of components in the infrared and the good opto-mechanical implementation made by the partner company. The complete optical setup of the LWIR emitter is shown in Figure 13a. Approximately 25 µJ are used to pump the OPO, 90 µJ for the SFG/SHG stage (described later), and the rest goes into the OPA. In the second version of the pump laser, a parametric amplifier (OPA), active Q-switching and wavelength tunability have been added. Active Q-switching was requested to increase the pulse energy to 250 µJ to have at least 120 µJ left to pump the OPA, increase the average power to reduce the integration time of the wavelength meter, and increase the repetition rate for lidar measurements. Also, active Q-switching allows synchronization with other lasers, for simultaneous wavelength emission or further amplification of the LWIR with another pump laser. Tunability of the pump wavelength (provided by a VBG mounted on a linear piezoelectric stage) has been added to tune the idler wavelength on a broad range faster than temperature control.

Figure 13b shows the idler wavelength tunability triggered by the pump laser tunability. The idler/pump tunability slope ⁄ is very close to 1. It is thus expected that the NesCOPO will tune by mode hops over the same amount as the pump in average, i.e. 0.65 cm -1 , with an added, unpredictable deviation allowed by Vernier mode selection within the parametric gain bandwidth, which is about 14 cm -1 wide for a 6-mm-long OP-GaAs crystal with a double-pump pass. More precise characterizations are in progress. Of course, the more traditional tuning methods described in Sec. To measure the idler wavelength, we could have used a commercial wavemeter based on Fizeau interferometers, as they are also available in the LWIR. Instead, we chose a more compact and less expensive solution based on sum frequency generation (SFG) of the pump and signal wavelengths towards 1 µm where a silicon based spectrometer can be used.

The pump frequency can also be measured by second harmonic generation (SHG). The idler wavelength is then retrieved from the equation: ! -"! . Over short time periods, the wavelength of the pump is much more stable than that of the idler, which is likely to be tuned, switched, or servo-locked by the user. So only the SFG needs to be constantly recorded, so that the idler wavelength is deduced from: 2 # -"! .

Sum frequency generation was obtained in a 20-mm-long MgO:PPLN crystal with an apodized, longitudinally chirped poling (APPLN). The purpose of the chirp is to increase the acceptance bandwidth to avoid having to move or heat the crystal when the idler wavelength is tuned. The crystal was manufactured with 6 different aperiodic QPM tracks with different center period and chirp rates, to minimize the risks related to the exact prediction of the conversion efficiency, which scales down with the acceptance bandwidth. The chosen chirp was 0.25 µm/mm, yielding a SFG bandwidth of 150 cm -1 around 2.5 µm. SHG of the pump is then the consequence of off-phase-matched conversion in the crystal enabled by a high pump fluence. Achieving the same in a PPLN would have required a length of no more than 2 mm, resulting in a very low efficiency. In a birefringence phase matched crystal, finding a giant acceptance would have been a stroke of luck and in any case the small beam sizes would have been incompatible with walk-off. This is a good example of the many possibilities offered by QPM that we introduced in Sec. 2.1.

More details on this emitter will be presented and published elsewhere [START_REF] Berthomé | Widely tunable LWIR parametric source[END_REF].

We recently integrated the first version of the LWIR emitter in a complete lidar system mounted on a wheeled camera dolly. We used the lidar to detect chemical warfare agents on French military ground. The system proved to be very robust, and we now aim at duplicating the LWIR source to emit ON/OFF pulses in a row.

CONCLUSION

Standoff gas sensing with lidars is a very demanding niche for laser technologies, with sometimes conflicting requirements. The wavelength must be very stable and be tuned over a large range ; the radiation should be pulsed and the linewidth be very narrow and stable over the pulses ; the pulses should be emitted closely in time while there is very few metrology tools for pulsed radiation ; the laser should emit several watts and fit in a shoebox.

In an attempt to meet these needs, we have developed parametric down-conversion sources that are versatile enough to meet the requirements of many different applications: ground-based and airborne greenhouse gases monitoring (aiming to get spaceborne one day), methane leak detection, and chemical warfare agents detection. They rely on state-of-the-art technologies such as quasi-phase matched materials, single-frequency lasers, frequency-agile lasers, infrared spectrometers, and on the partners developing them.

We are constantly looking for new solutions to simplify the optical setup without compromising the performance.

InGaAs and HgCdTe avalanche photodiodes, new quasi-phase matching schemes, upconversion detectors, tunable fibered lasers, compact frequency comb lasers, infrared semiconductor lasers, are some examples of possible game changers for gas detection lidars. The good health of the photonic industry is also a stepping stone of our developments.

Figure 3 .

 3 Figure 3. Calculated spectral gain of PPLN for type 0 and type 2 phase matching (single-pass low signal parametric gain),and normalized reflectivity of a VBG for comparison (2.5 mm thick, 400 ppm index modulation, reflectivity is 79%).

Figure 4 .

 4 Figure 4. Principle of the nested cavity optical parametric oscillator (NesCOPO).

Figure 5 .

 5 Figure 5. Two MOPA architectures for SWIR (or MWIR) and LWIR generation.

Figure 6 .

 6 Figure 6. Experimental bench of the parametric laser source. (b) Transverse beam profile at the laser bench output.(c) λ ON / λ OFF recorded wavelength switching for HD16 O measurement

Figure 7 .

 7 Figure 7. Raw (no energy normalization) averaged DIAL signals over 30 min and retrieved VMR for H 2 16 O (a) and HD 16 O (b).

Figure 8 .

 8 Figure 8. Simplified optical layout of the 2 µm emitter for airborne operation. (PBS) stands for polarizing beam splitter, (λ/2) for half-wave plate, and (BP) for Brewster plate.

Figure 9 .

 9 Figure 9. (a) Signal beam energy and M² calculated at the output of the OPA line as a function of pump energy in the first OPA stage. The configuration is composed of two stages with two PPKTP crystals in each stage and idler filtering. The total pump energy distributed in the OPA line (stage 1+2) is 200 mJ. (b). Picture of 4 PPKTP crystals.

Figure 11 .

 11 Figure 11. Q-switched Tm:YAP lasers developed by partners (Thales R&T and SME teem photonics) for OPO pumping. Left: passively Q-switched. Right: actively Q-switched Tm:YAP laser with a transversally-chirped VBG enabled wavelength tunability.

Figure 12 .

 12 Figure 12. Schematic of the NesCOPO cavity used for LWIR generation. Right: picture of an OP-GaAs crystal with two different QPM periods.

Figure 13 .

 13 Figure13bshows the idler wavelength tunability triggered by the pump laser tunability. The idler/pump tunability slope ⁄ is very close to 1. It is thus expected that the NesCOPO will tune by mode hops over the same amount as the pump in average, i.e. 0.65 cm -1 , with an added, unpredictable deviation allowed by Vernier mode selection within the parametric gain bandwidth, which is about 14 cm -1 wide for a 6-mm-long OP-GaAs crystal with a double-pump pass. More precise characterizations are in progress. Of course, the more traditional tuning methods described in Sec. 2.2 are still operative.

Table 1 .

 1 Typical challenges for DIAL emitters.

	Parameter	Typical value	Most challenging
			requirement
	Pulse energy	1 mJ	50 mJ
	(peak power for 20 ns pulses)	(50 kW)	(2,5 MW)
	Pulse duration	< 100 ns	< 20 ns
	(equivalent range resolution)	(15 m)	(3 m)
	M²	< 2	< 2
	Number of laser lines	> 2	> 8
	Wavelength linewidth	< 1 GHz	< 100 MHz
	Wavelength stability	< 20 MHz	< 1 MHz
	ON/OFF wavelength tunability	0.7 cm -1 (20 GHz)	50 cm -1
	ON/OFF switching speed	> 100 Hz	500 Hz
	Wavelength tunability	Several cm -1	500 cm -1
	for multi-species detection	(not continuous)	(not continuous)

ACKNOWLEDGEMENTS

The authors would like to thank Julien Totems and Patrick Chazette (LSCE, France), Cyrille Flamant (LATMOS, France), Nicolas Blouzon and Nicolas Geyskens (DT INSU, France), Corinne Evesque (IPSL, France) Bruno Grouiez and Laurence Régalia (GSMA, France), for their contribution to WaVIL, the H 2 O/HDO lidar.

They are also grateful to Jan Fabian Geus and Michael Strotkamp (Fraunhofer ILT, Germany), Andrius Zukauskas, Kjell Martin Mølster, Carlota Canalias and Valdas Pasiskevicius (KTH, Sweden), Lukas Nagy, Oliver Pitz, David Fehrenbacher, Hanjo Schaefer, and Dirk Heinecke (Spacetech GmbH, Germany), Paul Denk and Norbert Graf (Innolas, Germany), Marine Dalin and Vincent Lebat (Onera, France), for their contribution to LEMON, the airborne multispecies lidar.

The authors show appreciation to Basile Faure, Grégoire Shouaité, and Marine Favier from teem photonics, Arnaud Grisard and Eric Lallier at Thales R&T, and Bruno Gérard at Thales III-V lab, for their long-lasting cooperation in building MUSTARD and SPICE, the LWIR emitters.

This work has been funded by French Agence Nationale pour la Recherche ANR under grant N° ANR-16-CE01-0009 (WaVIL), European Union's Horizon 2020 research and innovation program under grant agreement N° 821868 (LEMON), Direction Generale de l'Armement (DGA) and ANR under grant ANR-11-ASTR-016 (MUSTARD), DGA under contract 172906033 (SPICE).


Nolwenn Mingant
email: nolwenn.mingant@univ-angers.fr

Hollywood in North Africa and the Middle East: A History of Circulation Chapter 12 Preliminary draft

and strategy, offering a case study on relationships between American and non-American interests in the early twenty-first century globalized world of cinema.

First Contacts: The Warner Bros. Deal

When the Abu Dhabi authorities decided to enter the realm of production, they immediately turned to what they considered as the "mother of all media hubs," Hollywood, or as Ed Borgerding put it, "the capital of the entertainment business." (Borgerding 2017). In September 2007, a few months after its creation, Abu Dhabi Media Corporation, thus announced the establishment of a film partnership with Warner Bros, with a $500 million fund for film production, and a $500 million fund for videogame titles. This production deal was, in fact, the corollary of a real estate deal between Warner Bros., a subsidiary of Time Warner, and Abu Dhabi real-estate company ALDAR. The deal, which included a theme park, a hotel and multiplex cinemas in the sheikdom, was originally engineered through personal relations, as Hollywood producer Hunt Lowry's attention was brought to the region's potential by a friend of his, working as a lawyer in Abu Dhabi. Lowry, who had previously worked with Warner Bros. was to become the chief executive of the announced joint venture in the US. iii Middle Eastern alliances were not unheard of in Hollywood. In the late 1990s, Saudi investors had already shown their interest in investing in the American film industry. In 1996, both Prince Mohammad and Prince Waleed had contemplated making a bid for MGM; Prince Al Waleed, in particular, has been involved in the media sphere, with stakes in EuroDisney, NewsCorp., Italy's Mediaset and Planet Hollywood. iv By 2007, Hollywood was more than ready to welcome foreign financing. Hedge funds and private equity, which had largely financed films a few years before, had drastically pulled out, both due to the lack of substantial returns and the credit crunch. v The subprime crisis gave Abu Dhabi's authorities the opportunity to "buy in at the bottom of the cycle." vi An alliance with an Abu Dhabi company made particular strategic sense for Warner Bros. who had developed a strategy of international involvement both in multiplexes notably in Great-Britain, Italy, Japan, and in local-language productions, for example in Japan, France, Germany and India. vii In spite of the attractive potential of the Middle Eastern alliance, American executives had a number of reasons to feel cautious. Past deals with Saudis had fallen through, and stories of shady middlemen and broken contracts circulated. viii One worry in particular concerned the film's content. Both the conservative mindset of the Gulf region and the fact that Abu Dhabi Media company was a state-owned company could mean content restrictions and, in effect, censorship. ix The creation of Imagenation Abu Dhabi in September 2008, as a state-funded company, with a less official and more film-friendly name could be seen as a step to gain more confidence from the Hollywood partner.

Creating the structure, building the network

After this failed attempt to establish Hollywood contacts, a first constructive phase in the history of Imagenation Abu Dhabi occurred between October 2008 andFebruary 2011, under the leadership of Borgerding and Al-Mazrouei. The company's mandate was commercial. Its mission was "to support the film industry and local talent by making movies that have commercial potential, to assure the sustainability the industry will need if it wants to survive on its own." xiii The imperative of sustainability led the team to focus on productions that were considered highly profitable, "award-winning films which are commercially successful and appeal to audience across the world." xiv As no film production expertise existed in the country, Borgerding pursued a two-pronged strategy. First, he brought in two German executives, Financial Officer Stefan Brunner and Head of Development Daniel Tully, to create the company's infrastructure, in congruence with the knowledge transfer strategy applied in many other industries in the Gulf country (Mingant 2017). Then he sought out strategic alliance with US independent companies. Such companies were even more open than the Majors to the injection of Emirati capital, as, in the late 2000s, they were suffering from the economic crisis, the closure of Hollywood Majors' specialty divisions and drastic cutbacks in development spending. xv In the US, partnering with Imagenation was thus viewed as an opportunity, enabling independents to work with only one financing partner xvi or obtain resources to expand into acquisition and distribution. xvii The press presented the signing of those deals as coups for the US companies xviii and referred to Imagenation as "deep-pocketed," xix an expression to make Hollywood mouths water. For Imagenation, working with independent companies was a guarantee that they would be given the creative control they sought. Imagenation was actually very selective, allying only with companies that had a strong economic or symbolic capital 2017), not only answered Imagenation's economic mandate, but also brought symbolic gains, as a detailed analysis of the four partners shows.

A subsidiary of the American non-profit scientific and educational organization National Geographic, whose core idea in the belief in "the power of science, exploration and storytelling to change the world," xx National Geographic Films had notably produced the Best Documentary Oscar winner March of the Penguins (2005). The deal had the artistic legitimacy of being arranged through the head of National Geographic Films, Canadian producer Jake Eberts, who had founded Goldcrest in the 1970s and had gained international recognition with Ghandi (1982) and Chariots of Fire (1981). xxi The films co-produced with Imagenation were not to be nature projects but "real-life storylines about humans (…) in the vein of 'Ghandi,' 'The Killing East, which it represented in a positive way, and was able to bring strong financial contribution to the projects were a factor of trust in the relationship (Borgerding 2017). Films co-produced with Participant Media explored such sensitive issues as US foreign policy (Fair Game, 2010), segregation in the US (The Help), fracking (Promised Land, 2012) or the threat of world epidemics (Contagion). These films often received critical acclaim, such as the Octavia Spencer's Best Supporting Role Oscar (The Help) and Gus Van Sant's Berlin Film Festival International Jury Award (Promised Land).

Hyde Park was created in 1999 by Ashok Amritraj, a famed Indian tennis players who became a Hollywood producer in the mid-1980s. For Borgerding, as a producer with established connections both in Hollywood and in India, Amritraj was "Hollywood plus." xxiv The deal covered two types of productions: the $250 million fund would lead to the production of twenty English-language films over seven years, while additional financing would be provided for local-language (Arabic, Hindi) and cross-cultural films. xxv While English-language production would fulfill Imagenation's economic goals, Hyde Park's "cross-cultural ethos"

Independence or Integration?

Knowledge transfer, however, does not necessarily run smooth, and Imagenation's second local production stands as a warning tale. Shot in March 2011, Djinn was blighted by the lack of skilled local personnel. Significantly, Garin noted one year later that "[t]here are less than 5 people qualified to make feature films in the UAE." li Imagenation's answer was to bring in most of the talent from the English-speaking world: American genre director Tobe Hooper, American screenwriter David Tully, German producer Daniella Tully (Imagenation), producers Jaye Gazeley and Robert Crippen (FilmWorks), and American director of photography Joel Ransom. Emiratis were given secondary and consultative positions to learn the trade: Nada Shouma as dialogue coach, Mohammed al-Otaiba as shadow director, and Nayla Al Khaja as cultural consultant. lii In the same way, supporting roles were given to local TV celebrities (Saood Al Kaabi, Ahmed Abdullah), but the two leads were given to two expatriates: Londoneducated Bahraini Khalid Laith and London-, New York-and Paris-educated Lebanese Razane Jammal. liii The Emirati personnel did not feel integrated and resentment developed, liv to the point that Nayla Al Khaja resigned, declaring "I was the only Emirati on set -all the key players weren't. (…) it's just that you couldn't call it an Emirati film." lv To this lack of local input corresponds a lack of local flavor. While the film was shot in Ras Al Khaima, lvi a well-known location, the story takes place exclusively inside a building. As Culture Crypt notes, "Save an establishing shot or two, the entire movie may as well have been lensed on a soundstage in Cleveland." lvii Language was also an issue. With all the key personnel being non-Arabic speakers, English language is preeminent in the film. This could impact not only reception by the audience, but also acting, with CultureCrypt critics pinpointing the good performance during the Arabic scene, but the "deadened dialogue delivery in English (which) chills the chemistry between characters." lviii In the end, the focus on a young Emirati woman who craves to go back to New York gives this "Emirati" film a very American flavor. With the film remaining in post-production for more than two years, rumors circulated that UAE authorities had taken offense at the way the country was represented, notably regarding witchcraft. lix With Djinn, Imagenation fell into the trap of completely outsourcing the production of a local film to foreign personnel, thereby producing with an unidentifiable film, adapting an Arab legend to American and Japanese horror conventions, lx severely cut to answer the supposed expectation of a broad audience lxi and, in the end, satisfying no one. lxii What Djinn demonstrated was the necessity for Abu Dhabi personnel to acquire knowledge fast in order to break from the dependence on Hollywood. Emiratization, i.e., the progressive replacement of expatriate personnel by UAE personnel, has thus become a priority (Mingant 2018, 289). This is probably one reason behind the choice of Michael Garin. As a member of the board of Central Media Enterprises (CME), Garin was instrumental in changing the face of the Eastern European broadcaster leadership, reducing by half the number of executives from the English-speaking world and putting the company in the hands of a Romanian executive. As Garin himself noted, "And that's what Abu Dhabi aspires to -having its businesses run entirely by Emiratis." lxiii By 2014, 55% of Image Nation's personnel was Emirati, and their goal is to read 75% by 2017. lxiv In the end, Garin, who describes his mandate as "developing people before developing movies," lxv envisages that, once the industry has reached sustainability, Image Nation will become obsolete: "As I always say, Our mission is not to build Image Nation, our mission is to build the nation." lxvi As the name of the company implies, the aim is the give the nation the possibility to develop its own images and representations. The Emiratization in personnel is intended to lead to Emiratization in style and content. This was foregrounded as early as 2009 by Borgerding, who noted that, just as there were Egyptian, Hollywood, Bollywood and Danish styles of making movies, there could be an "Abu Dhabian" or UAE style. lxvii Interestingly, although Image Nation managed to balance foreign and Emirati influences on recent productions Rattle the Cage (M. Al [START_REF] Al-Ansari | Yasin on breaking ou with 'Zinzana[END_REF] and

The Worthy (A. Mostafa, 2016), the Hollywood influence on the UAE film style will probably continue long after the last American advisor has left. Hollywood cinema remains, indeed, the golden standard for international-audience-oriented films, both for executives intent on the concept of production value, lxviii and for a young generation of filmmakers, such as Majid al Ansari whose film references are not auteur films from the Middle East, but Baz Luhrmann, David Fincher, Guy Ritchie, and Asian cinema (Mingant 2018b, 176-9). lxix Besides, despite the strong discourse on autonomy, Image Nation's strategy is, rather, to fully insert in the global film world. Imagenation does reach out a hand toward regional talent and proposes discussions on a potential "Arabwood," whose engine would be Abu Dhabi. lxx In actual fact, however, the company had not reached out to historical filmmaking nations of the Arab world, such as Egypt or Morocco, either to emulate their models or to establish collaborations. Image Nation's strategy has been a top-down application of model from the English-speaking world. One key model they wish to emulate is New Zealand, a small nation film industry which had quickly gained recognition as a viable production center, in the aftermath of The Lord of the Rings trilogy (Peter Jackson, 2001, 2002, 2003) and is now fully integrated in the globalized film industry (Leotta 2015, 29). Far from challenging the current global film rules, Image Nation has sought to integrate the existing ecosystem. When the company was created in 2008, it entered a film world where globalized practices and contacts had already become entrenched. For over a decade, the international audience, which had hitherto been the bread-and-butter of pre-selling independent companies, had become a priority for the Hollywood majors. Foreign topics, locations, talent and financing had increasingly found an open door into the film Mecca (Mingant 2010). Imagenation both benefitted from this context and participated in intensifying this capillarity.

In this game, Abu Dhabi has one particular card that it could play to establish itself in a unique position: its central geographic and cultural position between East and West. This vision is visible from the start, through the partnership with Indian-American producer Ashok Amritraj, the 2009 Hyde Park/Singapore's Media Development Authority deal, the collaborations with Dharma Productions (My Name is Khan, 2010) and Reliance (The Hundred-Foot Journey, 2014). In 2016, Image Nation rekindled an Asian strategy that had been left aside by signing a $300 million film and television fund pact with state company Intercontinental Communication Center. With some of the projects being international-oriented Englishlanguage films, the deal will enable China to intensify its entry into Hollywood. But the deal can also work to the advantage of Hollywood companies intent on penetrating the Chinese market. It is a two-way bridge. As Garin noted, "There is now a second route for Hollywood into China, by heading East through Abu Dhabi." lxxi Image Nation's assets are not only its funding capacities, but also its knowledge of, and relationships in, Asia. It is ideally positioned to become a place for Hollywood companies to bring Asia-related projects that might not be Hollywood and Asia to write its name in permanent ink on the global film map.

i "Image Nation greenlights soccer comedy, " Variety.com, December 13, 2012. ii "Abu Dhabi bets big on media, pic pacts, " Variety Daily, October 13, 2008. iii "Deal to put Warner in Abu Dhabi," Los Angeles Times, September 27, 2007. iv "Sheiks rattle but don't roll, " Variety, March 22, 1999. v "Abu Dhabi invests in Hollywood," Los Angeles Times, September 4, 2008. vi Ed Borgerding, quoted in "Abu Dhabi Puts more cash on the line in Hollywood," The New York Times, September 3, 2008. vii "Deal to put Warner in Abu Dhabi," Los Angeles Times, September 27, 2007. viii "Sheiks rattle but don't roll, " Variety, March 22, 1999. ix "Abu Dhabi invests in Hollywood," Los Angeles Times, September 4, 2008; "Abu Dhabi Puts more cash on the line in Hollywood," The New York Times, September 3, 2008.

x "Abu Dhabi Puts more cash on the line in Hollywood," The New York Times, September 3, 2008.

xi "Abu Dhabi Puts more cash on the line in Hollywood," The New York Times, September 3, 2008.

xii The real estate deal also fell through and the Warner Bros. park was never built with Aldar.

xiii "Stefan Brunner, the COO of Imagenation Abu Dhabi," video posted May 17, 2010. http://ireport.cnn.com/docs/DOC-445348 Accessed March 6, 2017. xiv "Abu Dhabi lanches $1bn film company," Screen International, September 5, 2008; "Abu Dhabi invests in Hollywood," Los Angeles Times, September 4, 2008.

xv "Imagenation, " Variety, November 3, 2008;"Duo Draw Abu Dhabi Coin," Daily Variety, October 8, 2009. xvi "Skoll Score: Indie Nabs Mideast coin," Daily [START_REF] Variety | Islamywood: Guess who financed & produces Valerie Plame' movies?' debbieschlussel.com[END_REF] xvii "Nat Geo in film reorg, " Variety, December 27, 2011. xviii "Indie nabs Mideast coin," Daily [START_REF] Variety | Islamywood: Guess who financed & produces Valerie Plame' movies?' debbieschlussel.com[END_REF] xix "Bridging the Gulf," Variety, June 29, 2009. xx National Geographic, 'About us,' http://www.nationalgeographic.com/about/ Accessed March 6, 2017.

xxi Borgerding Ed, former Imagenation chairman, Skype interview with the author, 13 mars 2017. xxii Jafaar, Ali. 'Imagenation, ' Variety, November 3, 2008. xxiii Participant Media, "About us," https://www.participantmedia.com/about-us, <accessed March 6, 2017>. xxiv Quoted in "Hyde Park digs Abu Dhabi pics, " Variety Daily, November 3, 2009. xxv '''Killer'' Deal for banners, Daily Variety, February 22, 2010; "Gere, Frace pour a ''double,''' Hollywood Reporter, April 29, 2010. xxvi "Imagenation deal fuels cross-cultural slate, " Variety, April 29, 2010. xxvii "Cultural Groove," Daily Variety, November 6, 2009.

(

  Borgerding 2017). The early years of Imagenation Abu Dhabi were thus years of Hollywood alliance building. The company signed a $250 million production deal with Participant Media in September 2008, a $100 million joint venture with National Geographic in October, a $250 million deal with Hyde Park Entertainment in November, as well as a development deal with veteran Hollywood producers Walter Parkes and Laurie McDonald in October 2009. In five years, Imagenation produced seventeen pictures. These strategic alliances, made through personal connections (Jake Eberts, Jeff Skoll) or chance meetings (Walter Parkes) (Borgerding

Fields

  ' and 'Syriana.'" xxii The National Geographic-Imagenation alliance led to the production of Amreeka (2009), which raised the issue of discrimination against Middle Eastern immigrants in the US, and The Way Back (2010), a World-War-II-prisoner-of-war-escape drama unfolding in breathtaking landscapes. Participant Media, which had been created in 2004 by former eBay president and philanthropist Jeff Skoll, aimed at making "entertainment that inspires and compels social change." xxiii At the time, the young company had produced immigration drama The Visitor (2007) with Overture Films, Afghanistan-themed drama The Kite Runner (2007) with DreamWorks, US-Afghan foreign policy drama Charlie Wilson's War (2007) with Universal, and had won an Oscar for the environmental documentary An Inconvenient Truth (2006), produced with Paramount Vantage. Participant Media had also marketed its film with internet social awareness campaigns. That Participant had made a number of films based in the Middle

  xxvi would have more symbolic value. With Hyde Park, Imagenation envisioned itself as creating a bridge between Hollywood, the Middle East and Asia, and in October 2009, the two companies strengthened their alliance by forming a $75 million joint fund with Singapore's Media Development Authority, a state agency. Their first film was to be Street Dancing, a dance competition story, mixing styles and cultures and set in New York and Singapore. xxvii As of 2019, none of the films announced with the Singapore MDA authorities had materialized. During this first phase, the deal with Hyde Parks resulted only in the production of two Hollywood-style action films: post-Cold War thriller The Double (2011), starring Richard Gere, and Marvel comics sequel Ghost Rider: Spirit of Vengeance (2011) with Nicholas Cage. The last alliance was a development deal. Walter Parkes, a producer since the mid-1970s, and Laurie MacDonald, former production vice-president at Columbia, had joined Spielberg's Amblin Entertainment in 1993 and helped create DreamWorks. xxviii Their production records included such well-known Hollywood successes as Gladiator (2000), Men in Black II (2002), and Catch me if you Can (2002). These credentials reflect Imagenation's global strategy to enter the world of commercial filmmaking by collaborating with the top players. This agreement thus gave the Abu Dhabi company entry into the financing of Men in Black III, alongside Columbia and Amblin, and Flight (2012) alongside Paramount. These four strategic alliances served a number of purposes. First, they enabled the team to actually bring the company into existence, by giving it direct access to projects in development. Secondly, they allowed Imagenation to set foot into Hollywood and to gain business credibility. They established Imagenation as a long-term financial partner for Hollywood firms and allowed its entry into working relationships notably with the DreamWorks/Amblin and Participant/Summit networks. These alliances also brought two symbolic gains. By allying with top Hollywood talent, Imagenation could rapidly obtain artistic credibility. This would create a virtuous circle, in which more quality projects would be offered to them. But symbolic credibility went beyond the film world, and these alliances held a strong soft power value: the fact that a Middle Eastern state-owned company would finance socially committed films, especially the Participant films, went counter to the backwards image often associated with the Gulf countries. It was a clear answer to those fearing Gulf-financed films would have to self-censor on sensitive issues. From the start, Imagenation assured that it was open to producing controversial material, as long as it did not insult Arabs. xxix Beyond economic gains, Imagenation's Hollywood connections were thus bringing in soft power gains for Abu Dhabi. In the long-term, Borgerding's plan was to enhance Imagenation's creative control and turn it into a development company working on a project-per-project basis with Hollywood majors (Borgerding 2017). The company had also started developing two local films: Sea Shadow and Djinn. In early 2011, when Mohamed Mubarak Al Mazrouei, a close adviser to the Emirati rulers, replaced Mohamed Khalaf Al Malzourei as chairman of the Abu Dhabi Media Company, xxx the board did not validate this strategy. Khalaf Al Mazrouei, Borgerding and Brunner were dismissed in February 2011. xxxi Refocusing on the UAE, Clarifying the Relationship to Hollywood In the US, the backing of Hollywood films by a Middle Eastern company raised some eyebrows. Conservative commentators warned that a conspiracy was being hatched by Abu Dhabi to take over Hollywood. They saw it as no coincidence that anti-Bush film Fair Game should be financed by a Middle Eastern sheikdom and anti-fracking movie Promised Land by an oil producing country. xxxii They also denounced Imagenation's anti-Israel stance both in its films (Amreeka) and in the choice of its partners (Mel Gibson in The Beaver, 2011). In the words of conservative blogger Debbie Schlussel, Abu Dhabi would be producing "pure propaganda" with the collaboration of "LaLaLand" executives irresistibly attracted by "the smell of IslamoCash." xxxiii Although the commentators rightly assumed that Abu Dhabi had created Imagenation to serve an ideological purpose, they were mistaken in the type of agenda pursued. Though Imagenation would clearly deny financing to any film presenting Arabs in a negative light, xxxiv it was never created with a view to change Hollywood's representation of the Arab world (Borgerding 2017). From the start, Imagenation's ideological focus has been centered not on Hollywood itself, but rather on using Hollywood to advance Abu Dhabi's economic and soft power interests, a focus which became clearer as the company reorganized under the leadership of Mohamed Al Mubarak, chief executive officer at the Aldar real-estate company, as chairman, and Abu Dhabi Media co. board member veteran American media executive Michael Garin as CEO. Renamed Image Nation, the company was divided into two divisions-Image Nation Abu Dhabi, head by former UAE diplomat Mohammed Al Otaiba, and Image Nation Internationalto "better balance (their) local and international activities." xxxv Al Mubarak and Garin were given full funding to devise a five-year business plan that would better respond to the Abu Dhabi leadership's objectives. xxxvi In essence, the focus "went from Hollywood-centric to Abu Dhabi-centric and UAE-centric." xxxvii Image Nation International paired down its Hollywood investment, with a production slate privileging films in the $10-20 million budget brackets and niche-market oriented, such as Latin American-themed horror film Out of the Dark (2014), multicultural restaurant feud The Hundred-Foot Journey (2014) and social activist biography Cesar Chavez (2014). On the other hand, local production was stepped up, with the release of four films between 2013 and 2016 (Djinn, From A to B, Rattle the Cage, The Worthy) and the development of two more projects (On Borrowed Time, Going to Heaven). The new focus on the UAE and its priorities was also visible through two other types of programs that Image Nation started to involve in: documentaries and television. In 2014, Image Nation started a documentary division, headed by Danielle Perissi, in order to "tackle issue (sic.) that are important locally and also globally." xxxviii In effect, the topics of the documentaries are either UAE-themed social issues in As One: The Autism Project; the story of the 1990 UAE football team in The Lights of Rome or related to the UAE foreign policy such as Every Last Child, a documentary linked to the UAE's Pakistan Assistance Program for the vaccination of Pakistani children despite Taliban opposition and partly targeted at the Pakistani community in the sheikdom. xxxix The documentary division is thus a continuation of the soft power strategy already mentioned. xl Image Nation's entry into the world of television and broadcasting was also motivated by the new emphasis on local considerations, notably the use of local production infrastructure. Image Nation thus branched out in reality TV content (Beyond Border, 2013), broadcasting (with the launch of the Arabic-language, free-to-air television channel Quest Arabiya, in partnership with Discovery Communications, in June 2015), xli and TV serials Justice: Qalb Al Adala (2016). xlii The new attention to UAE interests also led Image Nation to step up its local training program (the Arab Film Studio, Mawaheb) by developing relationship with the Dubai Film Festival's Enjazz grant program, as well as the French FEMIS film school. xliii The Hollywood alliances signed by the first leading team also evolved. Participant did not renew its agreement after it expired in 2013 and considered an alliance with the Doha Film Institute. As the deal has fallen through, Participant has remained open to collaboration with Image Nation. xliv While Image Nation lost the close relation that had led to most of its production in its first years, it strengthened its relationship with Hyde Park, which absorbed National Geographic Films and extended its Parkes + McDonald/Image Nation for another five years. xlv Image Nation also clarified its relationship to Hollywood, which was more clearly asked to deliver economic and educational dividends. Economically, Image Nation's two branches are inextricably linked, the raison d'être of the international branch being to earn the money that will be spent by the Abu Dhabi branch. Image Nation has thus reversed the relationship, with Hollywood productions such as Tom Hank's The Circle (2017) and Mattel's Barbie (2018) now more clearly acting as cash machines to subsidize Emirati projects xlvi and jumpstart the local film industry. Of even more strategic importance is the expected educational gain, the ability to train Emirati personnel who, in the long run, will build this sustainable film industry. xlvii The connection to Hollywood is thus valued as an educational opportunity, like the partnerships with the Dubai Film Festival and the FEMIS. As Garin noted in 2014: "We have the talent and we have the financial resources. (…) What's lacking in our region is experience and mentors." xlviii Experience gains are achieved by turning Hollywood into an internship provider, through the Production Company Internships and the On-Set Internship programs. xlix Early recipient of the Mawaheb program trained on the Indian set of the Best Exotic Marigold Hotel (2011) and at Participant's US offices. Mentoring occurs as American professionals provided input on UAE projects, such as established genre filmmakers Peter Safran and Steve Schneider teaming up with Ali Mostafa for end-of-the-world story The Worthy (2016), or original L.A. Law (20 th Century Fox Television, 186-1994) scriptwriter William Finklestein and former HBO Europe drama head and showrunner Marc Lorber presence in the Justice: Qalb Al Adala team. l With the strategic change of 2011, Image Nation International has clearly put Hollywood to the service of the Abu Dhabi branch, as a provider of funds and an address book.

  made in the US. Producing team Parkes and MacDonald thus brought the He Named me Malala documentary project (2015) about the young Pakistani education activist and Nobel Peace Prize Laureate Malala Yousafzai to Imagenation partly to benefit from their cultural expertise due to "religious political sensitivities" of the topic. lxxii Another example of the type of program for which Image Nation can act as a bridge between East and West is the reality show Chance of a Lifetime (2014-2015), developed by Hyde Park, in which twelve young filmmakers from the UAE, India and Singapore make short films related to the United Nation's priority global causes. In a truly globalized fashion, the show was coproduced by Hyde Park-Image Nation, the United Nations, the UCLA Burkley Centre for International Relations and Variety magazine, and broadcast on Participant's Pivot TV in the US and the National Geographic Abu Dhabi. lxxiii Just as the Gulf countries had been commercial hubs in the pearl era of the 19 th century (Piquet 2013, 48), Image Nation is now betting on growing collaborations between

x

  It also meant that Abu Dhabi authorities intended to be considered as equal partners. A few months earlier, in February 2008, the replacement of Abu Dhabi Media Co. Chief Executive, Riyad Al-Mubarak, by American Ed Borgerding, was accompanied by a return to the negotiation table. A former Disney International executive hired to defend Abu Dhabi's best interests, Borgerding immediately objected to the lack of creative role granted to Imagenation, in a deal that tended to relegate the company to the single role of investor (Borgerding 2017). xi In the long run, Warner Bros. proved unwilling to give Imagenation Abu Dhabi access to its most valuable properties and the deal fell through. xii Although to this day Warner Bros. is still listed as a partner of the company's website, this short-lived alliance led to only one production: family movie Shorts in 2009.