Rémi Colom
email: remi.colom@univ-avignon.fr

Ross Mcphedran

Brian Stout

Nicolas Bonod

Modal analysis of Mie resonators: Pole-expansion of scattering operators

Most of the resonant photonic structures behave like open cavities for light where light is trapped for some time before leaking or being absorbed. Their modes are called quasi-normal modes and are associated with complex eigenfrequencies ωn = ω n + iω n , ω n characterizing the rate at which the energy leaks from the structure. As a consequence, one can show that the fields of these modes diverge far away from the scatterer. This is problematic when one attempts to develop a theoretical description of the resonant interaction between light and resonant photonic stuctures in terms of their quasi-normal modes. Moreover, the existence or not of a non-resonant term in addition to these resonant contributions is still an open problem. Here, we address these two problems by deriving pole-expansions of the scattering operators of resonant optical structures. We evince the existence of a non-resonant term and we solve the problem of the divergence by studying the scattered field in the time domain and by using the causality principle. The quasi-normal mode expansion that we obtain will be of a great use to study light-matter interactions since it allows to determine the optical response of a photonic resonator both in the time and frequency domain.

Introduction

The resonant interaction between light and nanoscale photonic structures is a fundamental process in photonics. Examples of such resonances are plasmonic resonances hosted by metallic nanostructures, whispering gallery modes also called morphological-dependent resonances occurring in small index dielectric microspheres/microdisks or low order Mie resonances featured by high-refractive index nanoparticles. One can explain the existence of such resonances because nanostructures behave like open cavities for light. These cavities consequently suffer from significant leakage of electromagnetic energy due to scattering into their environment. Besides scattering losses, some optical resonators such as plasmonic resonators can also suffer from additional absorption losses. Resonances in photonics consequently all share a common mathematical description. They can in fact all be considered to be modes of open optical cavities often referred as quasi-normal modes or resonant states that are associated with complex eigenfrequencies ω n = ω n +iω n where ω n < 0 if the time-dependence of the fields is e -iωt . These modes also fulfill the outgoing boundary conditions and thus asymptotically behave like e iknr = e i ωn c r when r → ∞. This condition coupled to the fact that ω n < 0 yields an exponential divergence of the eigen-vectors. This divergence has long been known as "exponential catastrophe" [1] but METANANO 2019 IOP Conf. Series: Journal of Physics: Conf. Series 1461 (2020) 012025 IOP Publishing doi:10.1088/1742-6596/1461/1/012025 2 is one of the main problems one faces when attempting to derive a theoretical description of the interaction between light and resonant photonic structures based on their quasi-normal modes. Such a quasi-normal mode expansion would however be of a great interest to strengthen the understanding of the enhancement of light-matter interactions near a resonant photonic structure [2]. Here, we will derive such a modal expansion and we are consequently going to address these two major problems: (i) Does the scattered field only contain resonant terms or is there also a non-resonant term? (ii) The second problem is related to the already mentioned exponential catastrophe: how is it possible to expand the scattered field on a set of exponentially diverging fields? We will start by establishing the pole expansion of the scattering operators characterizing the optical response of a resonant scatterer. This result will allow us to address problem (i). We will subsequently study the optical response of the scatterer in the time-domain and we will show that some considerations based on the causality principle will allow us to address the problem of the "exponential catastrophe". The usefulness and the accuracy of the QNM analysis will be shown by studying the optical response of a dispersionless spherically symmetric scatterer.

Results: 2.1. Pole expansion of scattering operators:

Let us consider the case of light-scattering by a 3D scatterer of dielectric permittivity s in the frequency domain. An excitation field E exc (kr) that is usually a plane wave or a superposition of plane waves interacts with a scatterer. This process produces a scattered field E scat (kr) that is radiated away from the scatterer. In the case of 3D scattering, it is more adapted to expand these fields on the set of regular (M

(1) n,m (kr),N (1)
n,m (kr)) and outgoing VPWs (M

(+) n,m (kr),N (+) n,m (kr)): E exc (kr) = E 0 n,m e (h)
n,m (ω)M (1) n,m (kr) + e (e) n,m (ω)N (1) n,m (kr) (1)

E scat (kr) = E 0 n,m f (h) n,m (ω)M (+) n,m (kr) + f (e) n,m (ω)N (+) n,m (kr) (2)
The definition of (M

n,m (kr),N

n,m (kr)) and (M

(+ n,m (kr),N (+)
n,m (kr)) is provided in [3]. It is particularly useful to introduce the T-matrix that relates the scattered field to the incident field. For a spherically-symmetric scatterer, the T-matrix is diagonal and its coefficients are equal to

T (i) n (ω) = f (i) n,m (ω) e (i) n,m (ω)
where i = e or h. The total field outside the scatterer is equal to the superposition of the excitation field and the scattered field: E tot (kr) = E exc (kr)+E scat (kr). One can also make the choice to express the total field as a superposition of incoming E in (kr) and outgoing fields E out (kr): E tot (kr) = E in (kr) +E out (kr). E in (kr) and E out (kr) may be expanded on the set of incoming (M

(-) n,m (kr),N (-)
n,m (kr)) and outgoing (M

(+) n,m (kr),N (+)
n,m (kr)) VPWs. One can introduce the S-matrix that relates the outgoing field to the incoming field and its diagonal coefficients can be shown to be equal to

S (i) n (ω) = 1 + 2T (i)
n (ω). In this study, we want to describe the light scattering by a nanoparticle in terms of its quasi-normal modes. It is thus necessary to establish a link between the quasi-normal modes of a scatterer and the scattering operators i.e. the S and T matrices. Since quasi-normal modes are the sourceless solutions of Maxwell equations, the QNM eigen-frequencies necessarily correspond to the poles of the S and T matrices i.e. the conditions for which a scattered field can exist without any excitation field. A quasi-normal mode description of light-scattering by a nanoparticles can consequently be obtained by deriving the pole expansion of its S and T matrix coefficients [4,6,7,8]. We derived this pole expansion for a dispersionless spherically-symmetric scatterer and found the following expressions [3]:

S (i) n (ω) ≈ e -2ikR   S (i) n.r. + M α=-M r (i) n,α ω -ω (i) p,n,α   (3)
T (i) n (ω) ≈ S (i) n.r. e -2ikR -1 2 + e -2ikR 2 M α=-M r (i) n,α ω -ω (i) p,n,α (4)
where ω

(i)
p,n,α are the poles of the S and T matrices and correspond to the eigen-frequencies of the quasi-normal modes of the scatterer. r

(i)
n,α is the residue associated with the pole ω (i) p,n,α whose expressions are provided in [3]. S (i) n.r. is the non-resonant term and is equal to

S (i) n.r. ≡ 1 + M α=-M r (i) n,α ω (i) p,n,α
and is calculated by using the sum rules reported in [3,5]. The poles

ω (i) p,n,-α are equal to -ω (i) *
p,n,α . One clearly sees that these formulas predict the existence of a nonresonant term for both the T and S matrix coefficients. This expression consequently provides an answer to question (i) in the introduction. These formula are quite useful since they allow for an accurate prediction of the optical response of a scatterer in terms of a finite number of eigenfrequencies ω (i) p,n,α . Thanks to these formulas, resonances in the optical response of a photonic structure may be easily explained thanks to a small number of modes. This is illustrated in Fig. 1 where the dipole electric partial scattering cross-section of a ε = 16 spherical dielectric scatterer is shown. Overall, a very accurate prediction of the partial by taking M = 50 i.e by taking into account 100 poles.

Exponential catastrophe and scattered field in the time domain:

In the previous section, the existence of a non-resonant term was established. Now, let us consider the problem of the exponential divergence of the quasi-normal modes. Since these modes satisfy the outgoing boundary condition, their field is proportional to e i ωn c r when r → ∞ as a consequence it exponentially diverges far away from the scatterer. One could think that this divergence forbids the derivation of the scattered field on the set of quasi-normal modes. In [3], we showed that it was possible to derive such an expansion when one considers light-scattering in the time domain. In fact, if the excitation field is causal, meaning that it possesses a cutoff in time, one can establish that the scattered field admits a divergence-free modal expansion of the scattered field. In order to obtain such a divergence-free expansion of the time-dependent scattered field, we start by expressing the frequency dependent scattered field using the pole expansion of the S and T matrices previously obtained. We then evaluate its inverse-Fourier transform by means of the residue theorem. We thus found that there are two types of terms in the time-dependent optical response of a scatterer: a non-resonant term that possesses the same temporal envelope as the excitation field and resonant terms that correspond to the convolution between the excitation and exponentially decreasing terms.

Conclusion:

Here, we have reported our results concerning the quasi-normal mode analysis of the optical response of Mie resonators. By deriving pole-expansion of the scattering operators, we evinced the existence of a non-resonant term in the quasi-normal mode expansion of the scattered field. We also achieved to derive a divergence-free expansion of the time-dependent scattered field by using the causality principle.

Figure 1 .

 1 Figure 1. Comparison between exact calculations (solid black line) and the quasi-normal mode expansion (dashed red line) of the electric dipolar scattering efficiency for a ε = 16 dielectric spherical scatterer. The quasi-normal mode expansion is carried by setting M = 50 in Eq. (4).

Acknowledgments

Research conducted within the context of the International Associated Laboratory ALPhFA: Associated Laboratory for Photonics between France and Australia. This work has been carried out thanks to the support of the A*MIDEX project (no. ANR-11-IDEX-0001-02) funded by the Investissements d'Avenir French Government program, managed by the French National Research Agency (ANR).


Isabelle Sancho May

The Splendor and Misery of Confucian Officialdom in Chosŏn

Korea: the System of saga toksŏ 賜暇讀書.

I would like today to present to you a very interesting feature of Chosŏn Korea that I have been interested in for many years while studying the history of Korean scholar-officials:

the saga toksŏ.

I first came across the expression saga toksŏ, somewhat by chance, when I was writing my PhD dissertation on Korean Neo-Confucianism and had to write -feverishly and in a hurry-countless biographical footnotes about numerous scholar-officials of the beginning of the Chosŏn period. I then noticed that most of them, especially the important and influential ones in the realm of intellectual and political history, were granted something called "saga toksŏ" during the early stage of their careers. Literally, the expression means "to be bestowed leave to read books," but at the time I did not fully understand what actual practices that expression precisely referred to, and only noticed that it was rather frequent in the early centuries of the new Yi dynasty that ruled over the Korean peninsula from the late 14 th century to the late 19 th century.

A few years later, I became interested in the topic again while studying a well-known text written by the author I have been studying for almost ten years now, Yulgok Yi I, an outstanding Neo-Confucian of the Chosŏn period. This text, called Tongho mundap (Questions and Answers at the Eastern Lake), was written during a monthly assessment and submitted to the young king Sŏnjo in 1569 by Yulgok when he was on saga toksŏ. It is precisely the emblematic remaining text of a saga toksŏ. So after some research, I found out that saga toksŏ might be understood and explained in modern terms as "sabbatical leave,"

"ongoing training" and even an "induction program." Considered as a privilege, it was bestowed from time to time by Chosŏn kings upon some of the most successful candidates of the highest civil service examination. Without any equivalent in China or Japan, where such a practice had neither a formal and institutionalised form nor a specific name like in Korea, the saga toksŏ can also be regarded as one of the most salient Korean attempts to put into practice all together the ideals of Confucian kingship, officialdom and Learning.

On the one hand, it is a symbol of the ideal quest for a balance of power between the kings and the bureaucratic elite -a constant problem in the course of Korean social and political history, and on the other hand, it provides us a few interesting insights into the reality of the culture, sociability and ideology of the Chosŏn period.

*****

It is generally accepted that the system was created in 1426 by king Sejong, advised on this matter by Pyŏn Kyeryang 卞季良 (1369-1430), then Academician at the Office of Royal Decrees (Yemungwan). But 1426 is only the first official record that can be found today in the Annals of Chosŏn and the actual start of that practice remains uncertain.

Illustrating the Sage monarchy advocated by Confucianism, the system of saga toksŏ, is strongly linked to the figure of the "great king Sejong" (Sejong taewang; 1418-1450), commonly regarded as the very embodiment of the sage ruler in Korea.

It is especially related to two features of his reign:

1. The restoration, in 1420, of the Hall of Worthies (Chip'yŏnjŏn), originally created in Koryŏ

Later renamed Hongmungwan (Office of Compositors) or Oktang (the Jade Hall), this

Hall of Worthies was in charge of the preservation of books and archives, as well as the composition of official texts and notes ordered by the king. This important organ, which was the pen -or rather here the ink brush-of the State, was part of the so-called Samsa (the Three Ministries), that is to say the heart of the central government, with the Office of Inspector-General (Sahŏnbu 司憲府) and the Office of Special Counselors (Saganwŏn 司諫院)

! In fact, the system of saga toksŏ was meant by king Sejong and his advisors to palliate the failures of this Hall of Worthies where appointed officials were too busy composing texts to study for themselves and truly be worthy of the name "Worthies".

The growth and development of the Classics Mat Lectures (kyŏngyŏn 經筵)

These lectures, primarily intended to inculcate the Classics and historical texts to the king, were one of the common means of checking the actual knowledge of government officials on a regular basis. Besides, most of the Royal lecturers in charge of these lectures were appointed at the same time at the Office of Compositors, and the leading ones were even members of the Royal Secretariat or the State Council.

! Therefore, the main issue raised by the institution of the saga toksŏ at the time of king Sejong in the 15 th century was the management of the bureaucracy, and in a Confucian perspective the management of "talented men" that should be recruited through examinations (and not only by recommendation), and appointed at the core organs of the administration. This exceptional sabbatical leave embodied ideal Confucian kingship and was the expression of royal patronage over the source of all legitimacy: Learning.

-The system was most probably applied from the 15 th to the 18 th century, so it lasted roughly 340 years. However, there were many interruptions because of:

-the lack of interest from autocratic or "bad" kings (according to the Neo-Confucian -economic difficulties due to crop failures, epidemics, food shortages or natural disasters (Any unnecessary expenses at court were curtailed for a while, as a conspicuous sign of royal compassion).

-During the three and a half centuries of its existence, the total number of the recipients might have been about 250 to 300 according to remaining sources, among which two thirds (i.e. 200) were granted sabbatical leave before the end of the 16 th century, that is to say when the system reached its peak.

-As for the average duration of the saga toksŏ, it ranged from 3 months to 1 year at least, and 10 years at the most (which only happened once).

The Main characteristics of the SAGA TOKSŎ

No specific selection criteria

The selection criteria changed a lot over time and were not defined in any official record. The exact number of recipients per selection, their ages and skills, the duration of the leave, the number of selections per reign are still pretty much unclear.

Yet, we can be sure about one thing: when the system began in the 15 th century, all the recipients successfully passed the Higher civil service examination (mungwa), the most difficult one, which was held at the palace in front of the king. Contrary to the several other lower civil service examinations that played the role of assessing one's knowledge and reinforced social status, this higher examination opened up the door of a successful career in officialdom and strongly bore witness to one's commitment to serve the king.

This also means that none of the recipients passed the military examinations, even though military officials were still held in high esteem under certain reigns in the first half of Chosŏn (especially Sejong's reign).

Besides, there was only one case of a recipient who was selected through recommendation without passing any kind of examination, which clearly indicates that more objectivity in selecting men at court was sought after.

! One major aim of the saga toksŏ was indeed to reduce the influence of masterdisciple bonds among the scholar-officials, to reduce the number of recruitments by cooptation or recommendation, and thus to create a strong sense of exclusive loyalty towards the king. Conversely, by showing that they were eager to promote and patronize the most talented laureates by bestowing upon them special privileges, kings actually acted like ideal Confucian rulers who were supposed to be supreme educators and sponsors of young talents.

A closer look at the rankings of the recipients of the saga toksŏ in the Higher civil service examination shows that all of them were among the highest positions:

A. The recipients who passed the so-called 'regular examinations' (held every three years, at a fixed date, about thirty laureates) represent more than half of the total number Among these 142 men:

-16.9% were placed first (changwŏn) -30.3% were placed in the first-ranking group (kabgwa 甲科; from the first to the third top laureates) -62% were placed in the first and second groups combined (kabgwa + ulkwa 乙科;

from the 4th to the 7 th top laureates) B. And, as for the total number of recipients (around 300 men) who passed either the regular examinations or the exceptional examinations (where the number of laureates was not determined), one can notice the same proportions -17.4% were placed first -37.7% were placed in the first group -74.3% were placed in the first and second groups combined

The age of the vast majority of these men was between 20 and 30; even though, after the 16 th century, there were a few people in their forties and even in their fifties.

However, generally speaking, it can be said that the original aim of the system was to promote young and talented men in order to create a breeding ground for future accomplished high-officials with a strong sense of commitment to the king.

No compulsory curriculum

The recipients were rather free to choose the texts and topics they would like to study.

But still, in practice, the curriculum was quite consensual: Confucian Classics, histories, Chinese and Korean poetry.

It is however worth noticing that in a charged diplomatic context, mainly with China, the stress was clearly put on literary and poetical compositions in classical Chinese.

Excellent literary skills were indeed absolutely necessary for successful diplomatic encounters and exchanges.

But, in the 16 th century, with a growing number of Neo-Confucian literati (sarim) present at court, the stress was rather put on Neo-Confucian texts, and literary skills were considered as a pleasant but minor pastime. For most of them, true learning should be made of ethical cultivation and Neo-Confucian readings.

3. Selected men officially remained at their posts (! so the leave was not that "sabbatical")

The recipients of saga toksŏ kept receiving their emoluments, which means that they were often called back to perform their functions, for they were not replaced at their posts during their leave.

They could also be sent on missions in the provinces or be promoted.

In some cases, a few recipients never carried out the saga toksŏ in spite of being selected. And some others who had already been on leave were not counted among the new recipients and were not listed in the records.

Besides, some recipients did not want to go on leave and asked to be sent back to official work. Beyond the prestige of being selected, these men were apparently unmotivated to study more than they did for the civil service examination.

Lastly, in some cases, the leave was cancelled because of the lack of sufficient knowledge or the misbehaviour of the recipients.

All of this created considerable and recurring problems, especially when the number of recipients increased.

No strict rules to assess the work in progress

This was a constant and rather serious problem, for it raised the question of how relevant and efficient the whole system was in the long term.

The rules varied widely with each reign. Generally speaking, a report had to be submitted three times a month and the recipients were expected to accept monthly assessments (wŏlgwa) with the officials appointed at the Office of Royal decrees.

However these assessments were not really mandatory, for the officials could not be removed from their offices, except in exceptional circumstances. In fact, they could get exceptional leave in the case of family or health problems, and while in mourning. And of course, one could say that they were somehow relieved of their duties when they were either executed or sent into exile, which happened quite often under certain reigns.

Some proposals to address this concern were made from time to time.

For example:

-an attempt was made to divide the recipients into 2 groups; while one group was studying, the other one was sent back to office, with a turnover every 3 or 6 months.

-on the contrary, a reduction in the number of recipients was also tried.

-lastly, there was one attempt to let, in a month, the recipients work for 10 days, study for 10 days and write a report about their studies during the last 10 days.

As for the results of these assessments, they mainly consisted in circumstantial poetry, of which only a few traces still remain. There is however one remaining work written and printed in the 16 th century at the Reading House, but this is a dictionary of Chinese characters.

The recipients were placed under the supervision of the Director of the Office of Royal decrees (taejaehak 大提學) as well as the king himself

As I have already mentioned, the saga toksŏ was mainly instituted to reduce the influence of master-disciple bonds, as well as regional and factional ties, and also to put an end to recruitment by cooptation and recommendation.

But, the goal of a more objective selection of talents was not met in practice. It turned out that the personality and personal choices of the Director of the Office of Royal decrees (Yemungan) were crucial. The Director short-listed a few candidates and convinced the king to select his favourites.

Material and human resources needed by the scholar-officials at the Reading house/Toksŏdang were provided by the palace supplies office

There is one account of the material resources and products available for the recipients:

a text in the collected works of Yi Chik 李植 (1584-1647), chosen for sabbatical leave in 1626.

Cf. 李植, 택당별집 澤堂別集, 卷 5

According to Yi Chik's account:

-12 scholar-officials were selected and given residence at the Reading Hall.

-They were divided into 2 groups.

-Each man was given a specific topic and had to write a text that would be graded by the Director of the Royal Decrees, who would show the results to the king.

-3 times a month, they took a test in front of the king and were graded. According to their ranking, prizes were, in order: a tiger skin, a leopard skin, spices or condiment, black pepper, precious wood.

-All of the recipients were fed and housed. For one month, they were given 15 sŏk (grade for the salaries of officials, 石) of rice and 15 sŏk of beans.

-For each man, the palace kitchens (내섬시 內贍寺) supplied per day: 1 bottle of alcohol, soy sauce, vegetables and fuel.

-1 saddled horse was at their disposal in case they needed to go out -2 boats were also prepared for their outings and banquets -Music instruments could be borrowed from the palace -They were also supplied with 9 servants and 8 maids -and 80 slaves cultivated the land specially allocated for the Reading house.

-If they happened to have some fuel or rice left over, they were authorized to exchange them for money to buy more food, alcohol or any other personal needs.

But life in the Toksŏdang was not always that comfortable. Indeed, things changed drastically from the reign of Kwanghae kun (1608-1623) in the early 17 th century, because of the king's lack of interest for the saga toksŏ. For example, only 4 servants were in charge of the Reading house and the portions of rice and cereals were sharply reduced.

The question of the costs of the saga toksŏ had been a longstanding issue at court and explained why that practice happened to be interrupted many times.

But criticism of supporting a few scholar-officials was not only about economic matters. A great deal of criticism was expressed about the extravagant and amoral nature of the saga toksŏ, which set a bad example for the common people. As said before, numerous banquets punctuated by boat trips and enlivened by courtesans and musicians were held on a regular basis at the Toksŏdang, with all expenses paid.

The majority of the recipients had successful careers afterwards, except in cases of a troubled political climate

An analysis of the highest position attained by the recipients during their career shows that, out of 300 men:

-217 became higher level officials (당상관/ 정 3 품)

-37 became senior high-ranking officials -52 became Directors of the Office of Royal decrees (and they were in charge of selecting the recipients of the saga toksŏ)

→ So, most of them were close to decision-making power and close to kings.

Besides, it is worth noting that many of them were appointed to diplomatic affairs at some point. For example, between the 15th and the 17 th centuries, 16 out of 18 high-ranking officials in charge of dealing with Chinese emissaries had been in saga toksŏ.

The geography of the saga toksŏ

The saga toksŏ used to be located in various different spots in the capital Hansŏng (Seoul), but it was fundamentally related to a specific space dedicated to learning and occupied by literati: the Reading house (Toksŏdang 讀書堂), also later called the Reading house at the Eastern Lake (Tongho Toksŏdang 東湖讀書堂)

-But at the beginning, under Sejong's reign, the selected officials stayed at home. The sabbatical leave was then called 재가독서 在家讀書.

-But soon, considering that the scholars were not concentrated enough, being constantly distracted by guests, friends or pupils going back and forth, the decision was made around 1442 to make them study in Buddhist temples high in the mountains, outside of the capital.

That form of sabbatical was called 산사독서 山寺讀書.

-장의사 藏義寺 temple between 인왕산 (종로구 옥인동) and 삼각산 (강북구) + 진관사 津寬寺 temple in 삼각산 (today's 북한산)

-But also, from 1483: the 龍山寺 temple in Yongsan -But, as Neo-Confucian ideas quickly gained ground, it was soon considered improper for

Confucian scholars to study in Buddhist temples. It is however also noteworthy that, apparently, some of these respectable literati committed petty theft in the temples, leading to complaints by the monks. So it was under Sŏnjong (1469-1494) that, after being interrupted for a while under the previous reign, the saga toksŏ gained a specific place. That was the creation of the Toksŏdang

The construction of the Reading House went through several stages.

In 1492, the idea of building a special place was postponed, because of financial problems. So a decision was made to renovate a Buddhist temple in Yongsan, only inhabited by a "depraved" monk (married and the father of a little child) who was to be defrocked and chased away. The work started in 1493 and the Reading House, a still partially renovated building, was inaugurated by the king himself on the 12 th day of the 5 th month of 1493. Then, the recipients of the saga toksŏ moved in, right after the removal of the statue of Buddha.

But at the end of the reign of Yŏnsagun, the building in Yongsan had fallen in ruins and the system of saga toksŏ was suppressed.

Then under Chungjong's reign, from 1506 and 1512, a deserted monastery inside the city located next to the palace in today's Chongno area was used for saga toksŏ. It is the 정업원 淨業院. This monastery was built under the new dynasty but was soon deserted because of the decision to empty and relocate all Buddhist temples and monasteries away from the centre of decision-making and the capital city. Finally, in 1622, after many discussions, the recipients of the saga toksŏ were officially allowed to stay and study at home, for as a matter of fact they seldom went to the 한강별령.

The construction of the

Afterwards, the 유하정 流霞亭 house in Oksu was probably used a few times but not very often, for the building was the private property of a royal prince.

To sum up = the system of the saga toksŏ was fairly flexible and unsettled. It mainly depended on the men in power and the good will of successive kings. This feature was both its strength and its weakness. On the one hand, the saga toksŏ paved the way to distinguished careers; and in the 16 th century in particular, it was part of the cursus honorum of many important scholar-officials.

But on the other hand, especially starting from the 17 th century, it became more and more a pointless sinecure and even a secondary reward for services rendered during factional strife. So over the centuries, it tended to be reduced to an empty name without any tangible reality or specific set location.

The whole system ended up being suppressed in the 18 th century.

A few more topics related to the saga toksŏ

The imaginary geography of the Toksŏdang

The Toksŏdang was also a place for sociability and social contact for the selected scholar-officials who received visits. Besides, being selected was an official recognition of personal skills, especially at the beginnings of the system. The name, the ranking and the date of their selection for the saga toksŏ were engraved on a wooden board hung on the northern wall of the main hall of the Reading House.

The feeling of belonging to a privileged elite, enjoying a special status in officialdom was reflected by the desire of commemoration and celebration, especially in the 16 th century. Some traces of this desire remain today in a few paintings that have survived the vagaries of history and the ravages of time. These paintings are between landscape painting and what is called the "literati's meeting painting" (계회도 契會圖).

It is worth remembering that the development of this specific genre is linked to the increasing presence of self-aware Neo-Confucian scholars at court in the 16 th century. This kind of painting was often ordered when the recipients of the saga toksŏ wanted to celebrate themselves at banquets, and a copy was distributed to each participant.

The main focus of these paintings is less the landscape than the very gathering of talented men staged in the landscape. Reading and learning are the main themes underlined, for they reflect and define the very raison d'être of the literati gathered in the Toksŏdang.

Let me first specify a few formal characteristics of this 계회도 painting.

The painting is divided into 3 parts, 3 different grounds:

-on the top is written the title of the painting in seal script -in the middle there is the painted scene of the literati gathering -at the bottom is written the basic information about the participants

In the case of the painting dating from the 16th century, the scene of the gathering blends in with the surrounding landscape of false realism (in fact, the mountains can only be seen when one is standing on the opposite bank of Oksu and facing the Toksŏdang from a very far distance).

The basic aim is to locate the gathering of literati at the very heart of a fantastical landscape performing a geomantic function. The choice of building the reading House at the place called the Eastern Lake is in that sense very meaningful. It is nestled in deep mountains, along the river, next to other mountains; this environment was carefully chosen, for the recipients of sabbatical leave were supposed to merge with and breathe the vital energy, Ki, of the place they were living in to study properly. In Neo-Confucianism, the cultivation of this energy is part of the ethical process and both the physical and mental training required for true Learning.

The Reading House at the Eastern Lake was a very propitious site for the circulation of vital energy; it was located on a confluent and was just in front of the ferryboat crossing the Han river. In the 16 th century, the banks of the Han were a lively literary space with a proliferation of poetic activities meant to reflect that circulation of Ki.

By contrast, I would like to show another representation of the Reading house, dating from the 17 th century.

One can notice at first sight that the painting arrangement is drastically different:

There are no more mountains, no river, and there is a magnification of the scholarly gathering.

The use of colours highlights the individuals and the details. This sort of painting differs from that of the 16th century emphasizing the blurred identity of the scholars who were depicted as only being part of the nature that they, somehow, beautify.

The Toksŏdang and the strengthening of the identity of the Neo-Confucian scholar-officials

The saga toksŏ was affected in many ways by the troubled -and sometimes tragic-history of the literati at the beginning of Chosŏn.

Let me remind you of two significant events:

1. The first traumatic event is set in the 15 th century, right after the coup by future king Sejo: The vast majority of scholar-officials who had been bestowed saga toksŏ under Sejong were eliminated. This meant that Sejong's efforts to cultivate talents were unsuccessful and the system of sabbatical leave itself was threatened from its very beginnings.

2. The second traumatic event took place under the reign of Yŏnsan kun: the literati purge of the year muo (무오사화 戊午史禍). During this purge, the corpse of Kim

Chongjik 金宗直 (1431-1492), the former leader of the Neo-Confucian scholars at court, was dug up and beheaded in public.

All of his disciples, who had been selected for the saga toksŏ under Sŏngjong were The core message of Yulgok is that a king needs capable men to rule a country.

Confucian kingship depends on a balanced interaction between the king and his ministers. But the decisive factor in the success of this interaction is the qualities of the scholars-officials who are the king's advisors. Governance should not only be driven by collective decisions and the balance of power, but what's implied in the text is that a king is nothing without his advisors.

Yulgok notably explains that the reason why good governance had not yet worked in Korea was the lack of a relevant ideology (that is to say, Neo-Confucianism). He also adds that Sejong failed to embody ideal kingship, in spite of his good nature and his many skills, for he was not surrounded by the right people.

!This is a perfect example of Neo-Confucian rhetoric, but it is also a very good illustration of a certain sense of moral superiority from the Neo-Confucian scholarofficials.

So to sum up, in a monthly assessment of his work in progress at the Reading House, Yulgok goes beyond what was required and inculcates the king with the basic ideas about the proper balance of power, where the advisors are, in fact, the true teachers and the king is only one part of the "prince/minister" duo.

Forms and expressions of royal patronage

As has been explained before, officially, kings were the only ones who could judge the work in progress of the recipients of the saga toksŏ. Besides, these recipients could not be dismissed or intimidated. So, playing the role of patrons or sponsors, kings -especially those who were not well-versed or interested in scholarship-often had to express their patronage by offering them banquets and gifts.

The most usual gifts were: wild animal skins (tiger and leopard skins), books, paper, ink brushes, but (what might seem more surprising at first sight) alcohol and alcohol cups.

The royal reward of alcohol (sŏn'on 宣醞) was in fact a common practice and was especially important in the case of saga toksŏ.

→ In fact, an alcohol cup happened to symbolize the whole system, just like the Reading house.

The story starts in 1493, when Sŏngjong bestowed an alcohol cup, called 수정배 水 精杯, to the recipients of the saga toksŏ for the inauguration of the Toksŏdang.

In 1504, during the purge of year kapcha, king Yŏnsan kun abandoned the Classic Mat lectures and axed the Hall of Worthies (집현전), but he also had the cup 수정배 transferred from the Reading House to the Sŭngjŏngwŏn 承政院 (Royal Secretariat). He thus confiscated and sequestered the very symbol of the saga toksŏ, the pledge between a king and his ministers.

The cup then disappeared in the turmoil of Japanese invasions. It was said that it was finally found in China, bought and brought back to Korea with great care. Indeed, at that time the Reading House had been destroyed and the cup was the only remaining symbol of the saga toksŏ and the idealized and glorious past of the Korean monarchy.

Afterwards, bestowing an alcohol cup upon the recipients of the saga toksŏ became common practice:

-Chungjong (1506-1544) offered a silver cup in 1542, made from a Statue of Buddha that was ordered to be melted down for the occasion -Myŏngjong (1545-1567), his successor, also offered a cup, but with the shape of a cicada -the symbol of moderation Such a recommendation doesn't seem unnecessary, for under his reign, -, in 1548, a recipient was dismissed, for he spent long days of leisure boating and drinking wine -and in 1555, some other scholars lost the privilege of saga tokso because of their immoderate consumption of alcohol (not to mention the time spent on archery, then in vogue at the Reading House...) -In the 18th century, Sukchong (1674-1720) also offered several cups for alcohol made of precious metals.

-and Yŏngjo (1724-1776) as for him offered 3 cups asking for poetry, but without much The main differences of this system, compared to the saga tokso are:

-It was located within the palace -The rules were strict and clearly defined in an official text: the Munsin kangje chŏlmok 文臣講製節目 -The selected officials had to quit their positions and attendance was compulsory -They were given holidays twice a year, at fixed dates (the 3 rd day of the 3 rd month and the 9 th day of the 9 th month) at the Yuhajŏng (part of the Kyujanggak starting from 1781) where they were entertained by royal order (courtesans, banquets, etc) --> The aim of this system was to improve the previous system of saga tokso then fallen into disuse. So one might say that the 초계문신 was the swan song of an idea born with Sejong and that was to die with the second sage king of Choson, Chŏngjo.

CONCLUSION

The saga toksŏ is fundamentally related to what is commonly called the "Confucianization of Korea." The system was initiated by Sejong and ended with Chŏngjo; and these are the two figures of sage rulers of Chosŏn Korea in the Confucian historiography.

Taken as a whole, one can say that the system didn't work very well, mainly because of the inevitable discrepancies between theory and reality, and because it basically depended on the men who were successively in power.

In my opinion, the saga toksŏ is a good illustration of how the idea of a Confucian state can be both praiseworthy in theory and hardly enduring without being distorted while put in practice. It is an illustration of the splendor and misery of Confucian officialdom and Confucian kingship in Korea.

  historiography): Sejo, Yonsan kun and Kwanghae kun, who did not necessarily care about cultivating and fostering talented scholars -the lack of interest of scholar-officials themselves -criticism and jealousy from other scholar-officials -the replacement of kings or periods of regencies -literati purges and factional strife -popular uprisings -foreign invasions (Japanese invasions and then Manchu invasions from the 16th century onwards)

  Tongho Toksŏdang (the Reading House at the Eastern Lake) started in Oksu in 1515 and took two years to be achieved. This part of the Han river was called the Eastern lake because of its location at the intersection between the Han and its affluent the 중랑천 中浪川 During the Japanese invasions, the Reading House at the Eastern Lake was totally destroyed by fire. So in 1609 a decision was made to temporarily relocate the Reading House at the 한강별령 漢江別營, a ramshackle military building in Yongsan on the banks of the Han river A historical footnote is that the area was very famous and full of history, for it was the former location of the 제천정 濟 川 亭 house where Chinese emissaries were accommodated under T'aejong and Sejong

  강혼 姜渾 (1464-1519), 신용개 申用漑 (1463~1519), 이의무 李宜茂 (1449-1507), 조위 曺偉 (1454-1503), 최부 崔溥 (1454-1504) -executed: 권경유權景裕 (?-1498) 권오복 權五福 (1467-1498), 김일손 金馹孫 (1464-1498), 이종준 李宗準 (?~1499) Besides, among the other recipients of leave under Sŏngjong's reign, let's cite: -이경동 李瓊仝 was sent in exile during the purge of the year kapcha 갑자사화 甲子士禍 (1504) -이승건 李承健 (1452-1502) was relieved of his duties -조지서 曺之瑞 (1454-1504), 최부崔溥 (1454-1504) were beheaded In total: 13 out of 20 recipients of the saga toksŏ under Sŏngjong met a cruel fate under king Yŏnsan kun. However, 3 of them later participated in the 중종반정 中宗反正 (the bringing of Chungjong to the throne) in 1506. This common history of martyrdom and a certain sense of victimhood greatly helped to shape and strengthen a strong sense of identity and community among some scholar-officials, especially the Neo-Confucians. And the most famous text remaining from the saga toksŏ illustrates this self-consciousness. ! Tongho mundap 東湖問答 1569 by Yulgok (1536-1584) Let me remind that Yulgok came first in the higher civil service examination in 1564, under the reign of Myŏngjong, and was selected for saga toksŏ 3 years later in 1567, the first year of Sŏnjo's reign. The text was submitted to the king at a monthly exam at the Toksŏdang in 1569. The king was only 17 years old and Yulgok was 34. The text is set up as a dialogue, in a question and answer form, between a host and a visitor. The host can most certainly be understood as Yulgok here, and the visitor as the king. → So the text depicts a fictional encounter but it also consists in a mise en abîme of the actual situation at the Reading House, where the king pays visit to scholars. This setting of course reminds of the figure of Mencius who used to teach various kings, and it also suggests a master disciple relationship between Yulgok and the young king Sŏnjo. Contrary to the ideal of the Confucian king who must be the supreme teacher, here the teacher is the scholar who benefits from a special award to study. The text is rather long (more than 16000 Chinese characters) and is divided into 11 parts of different lengths. Part 10 : 教人之術 Part 11 : 正名為治道之本 Each part is organized around a question put at the beginning by the visitor to the guest. The question is simple but the answer is more elaborate and didactic. At the end of each part, a short sentence reminds us what the question is and summarizes the answer.

success 4 .

 4 A comparison between the saga toksŏ and the system of 초계문신 抄啓文臣 implemented by Chŏngjo Reminder: Just after ascending to the throne in 1776, Chŏngjo created the Kyujanggak 奎 章閣 to gather together a few skilled scholar-officials with strict rules In 1781, he ordered the State Council to select 20 talented men among the officials under age 37. The curriculum was the four books, the five Confucian Classics and the Records of the Great historian (Shiji). Tests were held twice a month and officials were either rewarded or punished depending on their rankings at these tests.