Jean-Claude Thoenig
email: jean-claude.thoenig@dauphine.fr

RESCUING PUBLICNESS FROM ORGANIZATION STUDIES

Keywords: organizational analysis, publicness, organized, organizing, public administration

Does publicness still make sense as an issue for further research? Classic organizational sociology (or standard theory) has provided a breakthrough for understanding public administration and management, but has not fully explored the agenda. Publicness is analytically characterized by the ownership of two production functions: efficiency (outputs), effectiveness (societal outcomes). While similarities may exist between public and non-public entities on some aspects of their organizational models, the effectiveness function they are accountable for is quite specific. Such a perspective allows public administration and organizational scholars to explore new perspectives such as organizing and organized (or the agenda of extended theory).

Is it still worth to study the public sector and public administration with modern organizational theory and analysis lenses? The real world keeps struggling with issues and demands that require the intervention of some sort of public action no market mechanism or charity initiative would be able to achieve. And yet knowledge production about organization, organized and organizing seems to have become rather dull whenever publicness is considered as a specific inquiry domain.

Perspectives such as agency theory and neo-institutionalism, just to name a few, influence quite strongly public administration studies. By comparison organizational sociology inspired research has lost part of the importance it had for the discipline in the late 1960s and the 1970s.

Even mainstream organization studies as a field are not inspired or driven by public organizationsz as much as they are by other objects such as private management or economic regimes such as firms and markets. Publications and colloquia suggest that most of the time public agencies are used as empirical illustrations to explore broader facets of general organization theory. They may also fuel knowledge and approaches covering rather specialized areas or narrow defined domains such as those dealing with health, education, police or social welfare.

Nowadays the proportion of papers submitted to international conference specialized in organization studies and that specifically dealt with public sector organizations and administration is rather low. For instance it has declined from 42% to 7% when comparing four EGOS colloquia held in the 1980s to four held between 1999 and 2002 (source: personal archives). Doctoral theses dealing with public setups at large and public administration in particular are less numerous. In a country like France, in which organizational sociology contributions had a major influence between the late 1960s and the 1980s, the total number of dissertations has declined by more than half since the 1990s while organization studies on firms and not for profit setups have at least tripled (sources: Ministry of Higher Education). Even professional journals in Europe as well as in the USA show a relevant decline of interest. Factors explaining such a lack of academic enthusiasm and creativity may be several.

Value added return would be stagnating when not declining about knowledge on public organizations. Their study would tend to replay old tunes such as the bureaucratic paradigm.

Life cycles and fads should also be blamed for. To write contributions to supposedly dominant or fashionable schools of thought such as network theory, path dependency or critical studies would make access much easier to academic careers and journals.

Professional education institutions such as business schools offer more and better job opportunities than sociology, public administration and political science departments do. This coincides with a time when humanities are facing a lasting identity crisis [START_REF] Horowitz | The Decomposition of Sociology[END_REF]. With the exception of New Public Management related issues, research funding has also massively dropped in many countries, at least when compared with other topics.

Another line of argumentation refers to a lack of awareness junior researchers as well as some of their teachers manifest about fundamentals in social sciences.

Scientific lessons and work published before the 1980s are simply ignored, hindering cumulative progress. Doctoral students when not their teachers sometimes evidence quite weak or biased undergraduate exposure to the fundamentals of disciplines like sociology and political science.

The purpose of the paper is to argue that publicness still makes sense as an issue for further research. Its first section questions whether grounded organizational knowledge has really explored publicness in an exhaustive manner. For instance classic organizational sociology -defined by a standard theory or definition of its domain [START_REF] Thoenig | How Far is a Sociology of Organizations Still Needed?[END_REF]) -has provided breakthroughs as a Verstehen perspective, as a body of conceptual and methodological frameworks. At the same time it did not fully explore and address the agenda about public organizations as such.

To consider publicness as an issue may benefit from a perspective suggesting that public organizations are organizations of a specific nature because, unlike firms, churches or voluntary associations, they are in charge of policy effectiveness, of a production function that generates societal impacts. While similarities may exist between public and non-public entities on some aspects of their organizational models, the effectiveness production function public agencies and other governmental bodies are accountable for is quite specific from an action as well as from an order standpoint. This research agenda finds inspiration in policy studies and suggests a theory of governmental agencies of its own that provides a fruitful angle or framework to test the publicness dimension. To study policies simultaneously as processes and as contents offers a fruitful access or analytical entry to inquiry on public organizations. Knowledge gaps remain that should be of interest for political scientists, public administration and other related social science disciplines.

Rise and decline of organizational sociology.

Publicness defined by the formal status of the organization remains a questionable and fuzzy criterion. A variety of legal statuses and territorial areas handle public affairs in modern societies. Governments at various levels, from urban communes to the United Nations, rely on complex and highly differentiated sets of formal organizations they control [START_REF] Thoenig | Public Sector Organizations[END_REF]. The separation line between public and private does not appear easy to draw descriptively.

The reference to formal status provides no solid ground for another reason.

Civil service in the Common law tradition as well as public administration in the Roman law perspective do not control in a monopolistic way the handling of public affairs, from law and order, fire protection and environmental protection policies to education, land use and social welfare. Hybrid institutional designs and fuzzy legal statuses are common practice. Some public agencies operate in a market related manner and even compete openly with private firms. The state acts as a profit-oriented owner. In several sectors such as social welfare governmental authorities subcontract collective good mandates and allocate public funds to not for profit associations, the latter getting most of their budget from taxpayer money, not from charities or clients-users. Some nongovernmental entities such as firms, associations or citizens play an important role in delivering collective goods, quite often without being formally mandated to do so. The state is far from having exclusive ownership and control of public affairs, from the definition of the issues to be addressed to the design of actual solutions and their implementation.

To assume that reporting to some state or governmental authority provides a sufficient property of their uniqueness may lead scholars to ignore the contributions made by sociology of organizations. Within half a century the scientific status of public sector in organizations studies has dramatically It ranked organizational issues at the top of priorities to be researched and managed. Leading figures like Aaron [START_REF] Wildavsky | Speaking Truth to Power: The Art and Craft of Policy Analysis[END_REF], a political scientist by training, considered contributions made by organizational theorists such as Martin [START_REF] Landau | Redundancy, Rationality, and the Problem of Duplication and Overlap[END_REF] as major inspiration sources. Unfortunately, in the late 1980s, political and organizational Verstehen of public phenomena lost some ground. Competing disciplines came to the forefront that gave more visibility to normative perspectives. Policy analysis and policy design inspired by axiomatic approaches that blend microeconomics, agency theory and quantitative-only types of data took over. In some cases they forgot analysis underway and preached managerial recipes linked to ideologies such as rational choice.

Publicness as an issue was taken over by two alternative paradigms: perspectives inspired by market and firm references, new versions of old critical or even anti-positivist postures. While ideologically New Public Management and Postmodernism do not share much in common, both tend to question when not deny the specificity of public organizations as social constructs. The former argues that market principles and private firm type of management have to be used as benchmarks. The latter considers that the public sector is just one facet of a much broader trend or picture that is at work across societies such as undesirable organized principles and organizing processes oppressing contemporary mankind, enabling capitalism and globalization to rule the world.

In some extreme versions, critical theories even argue that organizations are phenomena or artifacts that are illusions, not topics for knowledge.

Defined by Max [START_REF] Weber | Wirtschaft und Gesellschaft[END_REF] as a major step toward modernity and rationality in act, bureaucracy gradually became a scapegoat and a problem to fight. It is ironic to see that, more than sociologists, economists such as Kenneth [START_REF] Arrow | The Limits of Organization[END_REF] and Oliver [START_REF] Williamson | Markets and Hierarchies: Analysis and Antitrust Implications[END_REF], to name a few, were pioneering in characterizing the properties of firms as a distinctive type of organization. Such contributions, the ways of reasoning and the pro-market flavor they promote, have influenced quite strongly public organization studies for the last part of the twentieth century. Rational Choice and Public Choice approaches define new frontiers about public sector enterprises. Efficiency is substituting legalism as source of legitimacy. Management, not administration, provides the reference for political regimes applied to the public sector. New Public Management, legitimated by international institutions such as the World Bank and the OECD, inspired many if not most public funding allocated to programs on administrative reform in the public sector.

What classic standard theory left unachieved

Classic organizational sociology has in fact partly failed. Most of its leading figures have dealt with publicness related matters in an ambiguous manner. In fact all the promises have not been or could not be delivered. Various endogenous reasons may explain the relative decline of classic organizational sociology applied to governmental agencies.

One may be linked to the term of bureaucracy.

The founding father himself did not help when he published in the 1920s his theory of bureaucracy as a formal organization. On one side it inspired an ambitious and fruitful research program that started in the early 1950s with contributions from pioneers such Robert Merton (1952), Robert Dahl andCharles Lindblom (1953) and Peter [START_REF] Blau | The Dynamics of Bureaucracy: A Study of Interpersonal Relations in Two Government Agencies[END_REF]. It lasted at least for twenty years.

On the other side it opened the door to an ambiguous positioning of the term of bureaucracy. Three meanings overlapped and still do: a descriptive and conceptual one that could apply to any organization, whatever its legal status would be, a way to name any agency controlled by the state, and a pejorative meaning linked to big government, red tape and frustrations of users. Despite attempts to avoid confusion made by authors like Victor [START_REF] Thompson | Modern Organization[END_REF], despite analytical and conceptual frameworks defining the model and its latent functions by Robert [START_REF] Merton | Bureaucratic Structure and Personality[END_REF] or Michel [START_REF] Crozier | The Bureaucratic Phenomenon[END_REF], classic or standard sociology of organizations was to some extent trapped by the polysemic status of bureaucracy.

The motivations that were driving the personal agenda of some scholars were identical to the disappointment and the worries that had inspired Roberto [START_REF] Michels | Political Parties[END_REF] about the becoming of socialist parties and trade unions in European democracies in the early part of the 1900s. Trotzkyist activism during their youth influenced political critiques of New Deal institutions by Philip [START_REF] Selznick | TVA and the Grass Roots[END_REF] or motivated Martin Lipset and his colleagues ( 1956) to understand why it was possible to avoid the iron law of oligarchy and to maintain a high level of democratic life to develop within a American trade union. From U.S. southern states libertarian such as Theodore Lowi to Eastern liberal backgrounds such as Graham Allison and Robert Dahl, the spectrum of sources of inspiration and social debate leading to organizational studies was quite wide. The economic crisis of the early 1930s followed by the management of the Second World War efforts and consequences had boosted the growth of government. Various models of Welfare State were starting to develop on both sides of the Atlantic Sea.

To some extent sociology of organizations studying governmental organizations, but also political parties and even firms, became perceived as focused too narrowly on field studies and model buildings that were bureaucratic and therefore pathological. Alternative solutions or better types were not spontaneously associated with its knowledge. This opened the way to other approaches or disciplines, considered as more in line with modernity.

Another reason of the unachieved delivery by standard theory is linked to postulates that have not been verified accurately.

Such is typically the case with the existence of the differences, if any, between organization in the public sector and organization in other sectors. A striking aspect of the program classic sociology of organizations has achieved is the relative incomplete or ambiguous answers it has provided to public organization as a specific phenomenon. For instance handbooks and encyclopedia that had been published since the late 1950s [START_REF] March | Organizations[END_REF]March 1965) did not devote any specific chapter to the issue. This reflects a broader phenomenon.

A widely shared opinion by organizational sociologists was that differences existed. Private firms were assumed to be less rigid and more able to listen to their environment. The reason is that they have to survive in competitive markets, while public agencies face less changing and unpredictable environments. Public agencies are postulated to be more efficient than private firms when economic and political development is required. Fred [START_REF] Riggs | Bureaucratic Politics in Comparative Perspective[END_REF], for instance, argued that developing countries need public sector to come to prominence because of a polity "unbalanced" between their strong political system and their weak public administration sphere.

Nevertheless comparisons are not always based on technically solid ground.

While some examples are quite disturbing, evidence shows in a consistent way that, for instance, the existence of a specific and strong form of administrative sector does not explain, all other things being equal, why development is or is not generated. Ordinal differences on various parameters such as formal properties or modes of functioning of organizations were attributed to the fact that they are profit oriented, not for profit or governmental. The Aston studies underlined that size was a key cause [START_REF] Pugh | The Aston Programme[END_REF]. Other studies suggested that bureaucratization measured by the levels of formalization, centralization of authority and complexity in the division of tasks is in many cases quite strong in leading business firms and, comparatively, quite low in public agencies [START_REF] Dupuy | L'Administration en Miettes[END_REF]. State bureaucracies are not by nature prone to rigidities in the way they actually function, other types of organizations being less stalled as a matter of principle. Today the agenda is quite open to further research.

One point is striking about the interface between sociology of organizations and publicness. Knowledge produced by the discipline owes a lot to the study of public sector agencies. But publicness has not been its key concern as a social phenomenon.

In Europe and even more in the U.S.A., pioneering contributions by sociologists have studied public agencies, but as empirical tests for the validity of a broader paradigm. Herbert [START_REF] Simon | Administrative Behavior. A Study of Decision-making Processes in Administrative Organizations[END_REF] observes how city park managers decide about new projects. The doctrine of absolute rationality is fallacious when considering human behaviors in organized settings. Philip [START_REF] Selznick | TVA and the Grass Roots[END_REF] studies how the Tennessee Valley Authority created by President Franklin Roosevelt is exposed to secondary institutionalization processes at the level of its grass roots units.

This tradition made immense contributions to knowledge about organizations in general and firms in particular. Agencies operating in the public sector have provided breakthrough discoveries. Concepts such as cooptation, power and control, theories such as culturalism, functionalism and redundancy and overlap, have received wide attention. Studying two public welfare agencies Peter [START_REF] Blau | The Dynamics of Bureaucracy: A Study of Interpersonal Relations in Two Government Agencies[END_REF] discovered that employment security and autonomy are conducive to a positive attitude toward change. Michel [START_REF] Crozier | The Bureaucratic Phenomenon[END_REF] derived his explanation of the way national cultural norms embedded organizations from monographs on the French postal agency and the state owned manufacture of cigarettes. James March and Michael Cohen (1974) developed the garbage can model primarily from observations about how American universities are governed. The list seems endless of many of the prominent figures in the discipline from Amitai [START_REF] Etzioni | A Comparative Analysis of Complex Organizations[END_REF] and his discovery of the phenomenon of compliance to Charles Perrow and his social-structural approach (1970).

Very few organizational scholars have tackled the publicness issue. Peter Blau and Richard [START_REF] Blau | Formal Organizations[END_REF], for instance, formulated a typology differentiating commonweal (or public), business, service and mutual benefit organizations.

Nevertheless most of the time, public organizations were treated as illustrations of a more general type of meso social configurations called organizations. Any organization, including the firm, is embedded by power dynamics and functions as a political arena made of strategic behaviors [START_REF] March | The Business Firm as a Political Coalition[END_REF]. Today perspectives bringing the institutional phenomena back in are widely endorsed by business schools and applied to economic regimes and firm management.

Conformity and legitimacy imperatives explain why similar institutional forms diffuse across organizational fields. The irony is that many pioneering studies of American sociological institutionalism [START_REF] Thoenig | Institutional Theories and Public Institutions: Traditions and Appropriateness[END_REF] had studied public sector related phenomena: the diffusion of new patterns of organizational management across cities [START_REF] Tolbert | Institutional Sources of Change in the Formal sSructure of Organizations: The Diffusion of Civil Service Reforms (1880-1935)[END_REF], elementary schools [START_REF] Scott | Environmental Linkage and Organizational Complexity: Public and Private Schools[END_REF], etc. How far the public status makes or does not make a difference with firms or with not for profit statuses still remains an open research question.

Taking advantage of policymaking studies

Public administration as a discipline has taken over bureaucracy as an issue at a time when classic organizational sociologists left it. Quite many perspectives have explored it under various angles [START_REF] Meier | Bureaucracy in the Twenty-First Century[END_REF]. The fact is that the organizational dimension itself remains quite marginal. Other approaches are dominant.

Compared to knowledge generated by organizational sociology, New Public Management, postmodern view and agency theory are perspectives based on poor models when not questionable premises. Neo-institutionalism deals with administrative reforms leading to non-learning processes in public organizations, as if organizations would not be autonomous change actors.

Network approaches are to some extent an exception. As approaches they borrow quite much from recent breakthroughs made by organizational theory applied to business and to political sociology.

What is also striking is that the linkage between bureaucracy and publicness has not been solidly established in organizational terms.

The distinction between private and public, between profit, not for profit and governmental management, has been addressed since the emergence of public administration as an academic discipline. The 1970s and 1980s coincided with the publication of several reference papers [START_REF] Rainey | Comparing Public and Private Organizations[END_REF][START_REF] Lynn | Managing the Public's Business[END_REF][START_REF] Rainey | Public Management: Recent Research on the Political Context and Managerial Roles, Structures and Behaviors[END_REF][START_REF] Yates | The Politics of Management[END_REF]. Suggesting that public management is harder than private management, Graham [START_REF] Allison | Public and Private Management: Are They Fundamentally Alike in All Unimportant Respects?[END_REF] lists similarities and differences. On top of ownership, public organizations are supposed to be different because of their exposure to the political arena or to their dependence to governmental funding (Warmsley and Zald 1973). Barry [START_REF] Bozeman | All Organizations are Public: Bridging Public and Private Organizations[END_REF] defines publicness as the fact that government more than market factors influences action-taking and contexts in which organizations operate, whatever their legal status is.

Strong evidence based on sharp organizational analysis is lacking as a literature review suggests it [START_REF] Rainey | Public and Private Management Compared[END_REF]. Normative discourses still prevail such as ethics, public interest in Common Law countries, intérêt général in Roman Law states, or accountability. Despite the fact that New Public Management and the early 2000s seem to consider the case as solved, the private being the ultimate reference, the opinion still prevails that publicness makes a difference, as emphasized by authors such as Jonathan Boston (1995).

The influence of institutionalism, old or neo, and the reference to political economy remain quite influential. Not much inquiry has yet been provided to test the validity and plausibility of the assumptions. Lists and criteria remain rather descriptive or institutional. And not much effort has been made to build an analytical framework that would really cover more key organizational characteristics and less management focused properties.

A few authors have wisely suggested openings to explore the publicness agenda that organizational studies should take into account [START_REF] Schubert | The Public Interest. A Critique of the Theory of a Political Concept[END_REF][START_REF] Goodsell | Public Administration and the Public Interest[END_REF][START_REF] Ranson | Management in the public domain[END_REF]. For instance public interest should be considered as embracing subjective interests as well objective goods. Public organizations deal with political agendas. The state is not an integrated system but is made of a plurality of more or less autonomous actors. Policy effects are a key action concern. Policymaking matters from a process as well as from a content perspective. It discusses hypotheses standard organization theory had ignored for years -the distinction between the formal organization and its environment, asymmetric and transitive relationships inside monocentric hierarchies, etc. To define heuristic approaches becomes a challenge organizational studies should consider head on.

In the late 1970s and early 1980s several public administration scholars left organizational sociology stricto sensu and joined political sociology or science, but without dropping their research interest for governmental agencies and publicness as such, on the contrary. Pioneering studies in Europe [START_REF] Mayntz | Public Bureaucracies and Policy Implementation[END_REF][START_REF] Thoenig | Public Transportation Policy Making in France as an Implementation Problem[END_REF] as well as in the USA [START_REF] Pressman | Implementation[END_REF][START_REF] Bendor | Parallel Systems. Redundancy in Government[END_REF][START_REF] Chisholm | Coordination Without Hierarchy[END_REF]). Exciting dialogues between policy studies and organizational reasoning derived from the study of constitutive polices such as intergovernmental studies and decentralization of territorial affairs (Rhodes 1982;[START_REF] Thoenig | Territorial Politics[END_REF]). Studying policies is a stimulating way to explore organizations with different lenses or from a different angle.

A fruitful approach of publicness to consider for organizational knowledge purposes assumes that public organizations are social systems driven by and accountable for two production functions, and not just for one, as it is the case for firms and voluntary associations [START_REF] Thoenig | L'Analyse des Politiques Publiques[END_REF]):

• operational outputs. This function relates to inner efficiency, to the production of specific goods and services that can be easily identified and numbered;

• societal change outcomes. This production function handles the delivery of effectiveness. It deals with rather mid-term, indirect and less quantifiable effects.

TABLE 1. TWO PRODUCTION FUNCTIONS

Administration in general refers to the way resources or inputs such as money, personnel and raw components are linked to visible outputs or finished products such as the number of cars manufactured or the volume of oil refined. The purpose is either to minimize the resources used to achieve a certain amount of production or to maximize production for a given amount of resources allocated.

Economists describe such a coupling as an internal production function. The goal to achieve by the hierarchy is efficiency. The tools available are techniques and procedures such as accounting, cost control, human relations, logistics, etc.

The time horizon is conventionally defined and not a matter for debate. Budget cycles are of one year, productivity inside a plant is measured by conventional standards, etc. The nature of public efficiency remains an organizational research question.

Productivity, client satisfaction, costs are criteria among many others to consider. It also has been argued, well ahead of New Public Management, that efficiency as a normative reference remains too often success-oriented [START_REF] Landau | The Arrogance of Optimism: Notes on the Failure-avoidance Management[END_REF]. Other doctrines of efficiency are at work in public management such as failure avoidance. In this case reliability, and not optimality, provides their foundation. Organizational redundancies and overlaps of jurisdictions may downgrade microeconomic performance proxies and increase the annual cost structure. But whenever a major accident, catastrophe or unrest happens, whether meteorological, technical or social, the system supplies enough slack and reliable sources of know-how to minimize the consequences.

Except for some minor legal differences (status of the employees, appropriation and accounting rules), public agencies face similar administrative contexts than those private firms acting on the market are dealing with. Inner management looks alike in both worlds. But, and this makes the whole difference, public sector organization administration has a second production function to take into account, that private organizations have not. This function is called effectiveness. It is not internal to the institution but external. It is embedded in a societal fabric of some sort. Therefore it is more complex to administer a public organization than a private one.

Effectiveness refers to the way specific outputs or finished products, goods and services, are causally linked to policy outcomes and societal impacts they are supposed to generate. These outcomes and impacts are of a special nature as compared with outputs and products. No consensual timeframe states when to make such assessments, how and with which indicators.

The public organization has no monopoly to define them a priori. More or less volatile groupings express non convergent opinions about them, select those that make sense for them, judge, evaluate more or less spontaneously whether specific societal impacts are a success or a failure, and whether they may be attributed to a specific policy endorsed by a specific public institution.

To assess the level of publicness, it is less important to consider whether on not an organization is owned or controlled formally by the state, but it becomes more relevant to check whether it has discretion to define its own criteria of success and its ultimate goals. Inside the same country publicly owned agencies may differ quite much. Some function as if they would be private firms, setting their own goals and criteria of efficiency, without being accountable for any effectiveness function. Others are accountable de facto for both production functions. They are supposed to be somehow efficient while being also effective. How organizationally the balance between both production functions is achieved, and with which consequences, are questions still to open to further research.

An analytical framework

As a concept publicness is characterized by four main properties:

• ownership of societal impacts

• policy mandates legitimized by governmental authority

• multiple and divergent indicators of success and failure

• no spontaneous self-evaluation.

A public organization manages a policy which ultimate goals are defined and assessed by third parties, some governmental authority when not a set of differentiated stakeholders, public and private.

Public organizations do not legitimize by themselves only the goals or impacts of the policies they handle. Third parties do, usually the political authorities that govern the domain and are legitimized to act. They allocate monies, appoint people, fund the acquisition of equipment, etc. Two classes of outcomes are expected to be induced. Negatives are to eliminated or have not to happen that otherwise would disrupt society -crime, poverty, fire protection, water and air pollution, etc. Positives should be supplied, outcomes should be provided to induce improvements or to satisfy aspirations that otherwise, if nothing would be done by the government and the state, would not be supplied by civil society spontaneously -cultural development and access to arts, local economic development, access to job markets, etc. A public policy is not just the policy of a public organization. Polities shape and governmental policies legitimize a set of collective norms and actions about societal change to which public enterprises are expected to conform. Exogenous reasons and achievements frame effectiveness. They provide the essence of a public enterprise.

Evidence shows that the power of political authorities may vary . They may not always seem to be proactive, but their non-acts are acts that matter and have consequences. Impacts to achieve are most of the time not defined in details and a priori. Political rationality or electoral cycles may lead governmental authorities to avoid commitments about long term and quantitative goals.

Political executive and legislative bodies care more for symbolic impacts and immediate support from public opinion and less for actual consequences in the long run. Agencies may even be left by their own so that they substitute in a technocratic manner their own know-hows, routines and interpretations of the goals to reach. In certain circumstances more cynical motives may be at work.

Governmental authorities pass new laws and make new policy announcements while being aware of the difficulty to get them enforced on the field. Such is the case for symbolic policies. Their real stake is to produce support from public opinion, and not lasting impacts on daily practices. Their latent message sounds like "do not worry, we care". But, at the end, accountability and initiative remain attributes of the political arena.

Public organizations play a societal role that goes far beyond their technical function of providing goods and services. They shape society, polity and the ecology, they construct and influence purposively their environments.

Reinforcing their legitimacy to act and impact society is one of the key uncertainties they face.

A public agency may have to maintain certain categories of roads in a specific geographic area. To do so it can deliver itself all the outputs that are part of its mandate. It may also subcontract their production to private suppliers. In any case the raison d'être of its internal production function or efficiency is not to expand its road maintenance market share or to deliver a profit that maximizes the satisfaction of its owners or principals. What really matters at the end is that traffic safety does not downgrade, that transportation fluidity increases, that the politicians who head the public jurisdiction do not get blamed by local constituencies.

In any case such societal impacts are not obvious to define. Public organizations face a world in which ambiguity is the name of the game. How far the impacts or outcome are direct consequences of causes such as the outputs delivered by the agency remains not always easy to assess. On top of that, political rationality, which implies the possibility open to political policy makers not to be held responsible for their past decisions whatever their actual impacts have been, makes the environment of public organizations quite volatile and uncertain

Embedding public agencies socially and politically is a way to induce effectiveness. To a certain extent backward mapping and re-interpretation of rules are quite common practice at the level of so-called street bureaucrats [START_REF] Elmore | Backward Mapping. Implementation Research and Policy Decisions[END_REF].

Publicness implies that agencies are confronted with two kinds of knowledge sources.

One is related to the structure of its formal organization. Organizations in general are social constructs aimed at achieving some collective reliability out of risky actors such as individuals and small groups. How to make different logics of actions compatible to produce a certain type of goods and services is perhaps the most fundamental question academic research addresses since many years.

Key properties of an organization such as centralization of authority, asymmetric and linear relationships, specialization of tasks and jurisdictions, procedural as well as substantive decision rules design a structure of knowledge, a theory [START_REF] Thoenig | How Far is a Sociology of Organizations Still Needed?[END_REF]. They anticipate consequences to be generated. They prescribe what will happen when specific acts are produced, when such and such governmental interventions are made in a stated area and in certain manner.

Knowledge is perfect when no fault occur, when the formal solutions for the operations to conduct are always correct. Organizations supply certainty and reliability.

Another source of knowledge derives from the policies themselves. Policies also are theories, but of a different nature than organizations. Any policy blends some normative with some factual premises. Death penalty is a judicial policy.

Its raison d'être can be formulated according to two quite different premises.

One is moral or ideological. The penalty may be legitimized as a form of societal duty, of ethical revenge. Those who have killed have to pay for their crime with their own death. Such values are set or shared a priori. They are not testable and open to verification. Another set of premises legitimizing death penalty are factual. Such is the case with deterrence. Future events are expected to differ from past ones. Potential killers shall be afraid to commit a crime of the same class. Consequences can be traced, tested empirically and evaluated later on.

Factual premises are hypotheses [START_REF] Landau | The Proper Domain of Policy Analysis[END_REF]. A policy proposes a set of acts and non-acts to alter some existing context or mode of conduct. It is intentional, as it expresses the will of a policy maker. It is designed to attain in the future some goals or outcomes by producing today some outputs. Policies are therefore describing or postulating in a more or less implicit manner three components; a desired state condition, a supposed present condition, a set of means to change the present condition in the future. They assert if-then linkages.

Policies are supposed to control and direct future courses of action in a world that is uncertain and risky. The function of their empirical claims is to eliminate errors.

Facts suggest that errors are common and that dysfunctional phenomena are widely present.

A first one is linked to errors of the theory on which the policy is relying. The latter may be built on wrong effectiveness assumptions about social, economic and ecological phenomena. Wrong assumptions are made about the factual situation today and the probability to generate the future desired state. For instance death penalty does not deter killers. Policy makers ignore reality on which they intervene and have wrong representations of the conducts to change and the dynamics to mobilize for that purpose. More accurate use of scientific knowledge dealing with the specific policy domain -for instance criminologymay provide tools for better effectiveness.

A second one derives from dysfunctions in efficiency. Inner management may be poor, formal structures may not be adequate. Implementation is a key point.

Governmental authorities rely massively on organizations to implement them.

Evidence consistently shows that this transfer is not easy to achieve in a smooth Rules and formal structures are solutions aimed at solving problems defined in advance, the different units inside the agency being expected to conform. At the same time the organization is supposed to produce and handle information about its environment and the impacts of its knowledge structure. Information means surprise, anomaly, a signal that something goes wrong about action taking and the knowledge structure itself. Evidence suggests that publicness hinders the use of errors as incentives to correct knowledge structure.

Like many private and not for profit organizations, public agencies usually show a high level of knowledge. The problem derives from the fact that the more an organization has knowledge the less it has information, the less it generates and handles errors as a lack of adequate knowledge and a piece of information. An error becomes a sin to avoid, a pathological state to hide, not an opportunity to learn, a signal to make sense of for future action taking. When error happens people are often punished while errors are not spontaneously corrected.

Unlike other classes of organizations, and because of their effectiveness production function, public agencies face another obstacle in correcting errors and using information. As mentioned above, and in a majority of cases, external impacts indicators are fuzzy and ideologically loaded, objectives are uncertain, time horizons are controversial and unstable, causal linkages between a specific policy and a specific set of outcomes are not linear and difficult to establish.

Even rudimentary self-awareness is lacking.

Policy evaluation is neither spontaneously induced nor obvious to achieve. The idea to manage an evaluation of effectiveness is an ideal goal difficult to achieve, an utopia [START_REF] Thoenig | Evaluation as Usable Knowledge for Public Management Reforms[END_REF]. Evaluation and organization are somewhat contradictory. Public agencies as organizations do not, most of the time, evaluate their own activities [START_REF] Wildavsky | Speaking Truth to Power: The Art and Craft of Policy Analysis[END_REF]. They do not correct errors and surprises that are generated either by the action theory that its organizational structure implies or by the societal theory implicit in the policy it is mandated to implement. They rely instead on their knowledge to identify societal needs to One major contribution to publicness study an action perspective supplies is empirical.

In most policy domains problems are addressed and handled by more than one formal agency. In other terms what happens in one sector is the consequence of what many policies and public bureaucracies do, whether intentionally or not.

Unemployment is the consequence of multiple governmental acts and non-acts, from locating low income housing to fiscal incentives and training programs.

Several policy sectors and agencies combine to influence its rate and structure.

More generally a specific policy induces consequences and impacts not only for the specific problem it is designed for, but also for other problems and the way other policies operate and impact society. Therefore cases are quite exceptional when a specific formal organization exerts a full monopoly and exclusive ownership on a policy jurisdiction.

Observation suggests on and on that public agencies are not working in a autarkic manner. Public agencies and the state are just one among many actors, sometimes much more powerful and relevant than others, sometimes much less.

These observations imply lasting consequences for organizations studies. A state of the art survey of literature [START_REF] Thoenig | Public Sector Organizations[END_REF]) classifies public organizations according to the degree to which their inner functioning is impermeable or sensitive to outer dynamics and factors. Four types are listed:

• an inward-orientated type. The organizational functioning cuts itself from its environment.

• an environment sensitive type. Functioning takes into account outside stakes, groups and issues by showing local flexibility capacities or by institutionalizing cooptation processes, whether formally or informally.

• an outward-driven type. Because the organization is highly dependant from outside forces such as professions or resources such as information, centrifugal dynamics matter more than its authority hierarchy.

• an inter-organizational set embedded type of functioning. The formal organization does not provide the backbone of its integration. It is regulated by some broader and rather stable network or collective action system of which it is part. Organizing refers to the way separate actors linked by some form of interdependencies build a pattern allowing recurrent behavior and action certainty. Which normative schemes and behavioral processes are set up and diffused? How and why are action taking and division of work quasi-negotiated? [START_REF] Thoenig | Public Transportation Policy Making in France as an Implementation Problem[END_REF].

Organized refers to the way social configurations grow and evolve that are not coordinated by one center, but by a multi-centric core. How do shared social norms -rules on rules, or secondary rules [START_REF] Reynaud | Les Règles du Jeu[END_REF]) -emerge and get constructed that shape appropriate ways to behave and to design operating rules -or primary rules -emerge? What integrative mechanisms are at work such as indoctrination, domination, regulation or self-interest based opportunism? How is social integration achieved when no clear-cut limits define the boundaries, the limits memberships, when relationships between the various parts are not transitive and when asymmetry between levels is very low? What are performance abilities of such and such types of organized set up?

These issues had been ignored by organization studies for many years. Basically focused on organizations as formal forms of human activity cooperation, they took for granted that to explain social phenomena inside a public agency, it was sufficient to observe what was happening inside its legal or formal limits, in some cases by adding the users as a source of observation. A few pioneering studies had suggested that ignoring the wider action set may be a constraint for the advancement of knowledge in organization studies. They identified social constructs such as grass roots cooptation of local elites and institutionalization [START_REF] Selznick | TVA and the Grass Roots[END_REF] or exchange of favors between field agencies and local politicians (Crozier and Thoenig 1976). Support and conflict with civil society lobbies and social milieus were analyzed as organizational vectors for public sector agencies. Policemen, social workers, tax collectors, just to mention a few, have a public service mission enforce detailed rules and codified procedures.

Their success or their failure depends nevertheless to a degree that may not be irrelevant from access to and support from local resources provided by outsiders: to get intelligence, to identify users, to get help from relays and allies, etc. Despite such exciting findings public organization studies surprisingly did not really switch to other research designs until policies and quasi organized action systems would open up a different approach.

A corollary of such a breakthrough is methodological. If it is true that formally autonomous organizations may depend from others when handling a certain problem or implementing a certain policy, then it implies that it is such a specific problem or policy that structures a form of organized structure and They induce empirical consequences. And they are generated by organized settings. Some progress has been made about cognitions in firms [START_REF] Michaud | Making Strategy and Organization Compatible[END_REF]. Public organization studies have still some way to go in this respect.

The relevance of publicness should be tested, for its own sake as well as an analytic tool. Its added value is worth considering as long as it contributes to the advancement of general organization, organizing and organized theory, but also to the understanding of public administration and policies in multi-level societies.

  a major debate. Old institutionalism inspired by formal-legal approaches such as public administration theory in North America and science administrative in Europe started to decline in an apparent irreversible manner. More rigorous observation of organizational functioning and behaviors have taken the lead. Notions like the state and the public administration have become analytically poor or disappointing. They hide differentiated specific local orders. Action boundaries keep fluctuating. Publicness should not to be considered as a given or an axiom but as a problem for enquiry. Sociology of organizations also challenged Marxist inspired perspectives. Meso level phenomena such as organizations should not any longer be considered as mere superstructures. Class struggles and vested interest dynamics do not explain the whole story about how ministries and public agencies operate. Organizations should be approached as specific orders and locally embedded action systems. The end of the 20 th century coincides with a spectacular change, as if sociology of organizations has indeed lost momentum. Other theories have taken the academic lead. Sociological perspectives have been marginalized by other disciplines or paradigms. An illustration is provided by public management education. Public management as a specific domain had developed in the USA in the early 1970s.

  manner. It remains a source of risk and waste. Policy studies even suggest that up to two thirds of the failures originate because of what happens during the implementation or administration phase. Implementation, being achieved by organizations, is prone to routine and to biases. The formal organization as a source of error geometrically increases the number and intensity of errors. For instance discretionary behaviors of street level enforcers, when not repressed by their supervisors, may lead to failing policies. A law exists but it is not fully enforced. It is a consequence of a policy error as much as just a matter of administrative mismanagement. The specific organization governmental authorities ask to implement the policy does not take ownership and deliver. Do public organizations correct their errors? To manage simultaneously two production functions makes public organizations a complicated context to handle. Inner dysfunctions may generate outer dysfunctions.

  serve and effective means to deliver them. Efficiency and effectiveness are relevant as long as their criteria and achievements are in line with the knowledge structure. If not they make not much sense. The public organization prefers to discard them as action drivers. Policies are basically self-perpetuating.From organization to organizing and organizedTheoretical and conceptual frameworks are not by themselves ends. They provide means. They are useful as tools to explain certain problems, and obstacles to understand others. Publicness as defined above offers a heuristics to explore public action and the way public organizations contribute to it.Studies of public organizations gain a lot from maintaining close contact with policy analysis. They improve Verstehen approaches of what governmental authorities do and the public issues that are addressed. Bringing policymaking and polities back in enables academic research to deal with content, and not to focus only on process. It also widens the picture. Daily routines, formal structures and inner functioning of agencies are also parts of a more global action arena called policy-making.

Formal

  organizations are not the only way to fulfill certain outcomes. Other social configurations and processes such as organizing and organized do offer alternative solutions. Making different logics of action compatible in a lasting way and without major difficulties can be achieved otherwise than by a hierarchy of authority principle. Policy adjustments and cooperation between separate when not rhetorically antagonistic public agencies and private operators may even be easier to induce without using formal coordination structures across them. Mixing policy analysis and organization analysis leads to identify and analyze other forms of social voluntary cooperation: informal cooptation, cross-regulation, redundancy, collective action, networks, etc. Public organization scholars were to some extent ahead of private firms. It is later in the 1980s that the latter gave birth to attention given to similar mechanisms linking operators acting on economic markets such as joint ventures, strategic alliances, etc. Such a research program started in the late 1970s. Two key social processes were brought to light by social sciences: organizing, the organized.

  are the implications for organizational values such as the pursuit of general interest and for the content of professional skills inside public agencies? Are administrative bureaucratization and narrow action codification mere pathological obstacles or are they necessary counterparts to make participative democracy work? • Do organizational cognitions matter? Classic organization sociologists have ignored them. Policy evaluation research has given more attention to it. Stakeholders express normative judgments and mobilize prejudices when considering that a policy fails or succeeds. State agencies protect themselves from centrifugal forces and particularistic requests emanating from civil society and polity by building barriers such as professional norms and moral identity references such as the general interest. The nature of such phenomena is clearly cognitive. These criteria should be observed in act, and not just as a collection of discourses or a set of so-called cognitive maps. Shared cognitions or common languages for action are neither argumentation nor rhetorical artifacts. They also cannot be confined to local expressions of exogenous and global phenomena such as class ideologies or professional cultures.

  Their acts and non-acts not the only ones that matter to solve a specific issue carried by the governmental agenda. Many organizations with another legal status -voluntary organizations, private firms, charities, etcintervene, formally or informally, as subcontractors, as policy implementers, as problem solvers, etc. Political science defines such sets by metaphors and terms such as policy arenas or communities. Local economic development, social welfare, health, crime and law, public transportation, are just a few policy areas

among many that see coalitions at work. The lesson is that public issues and their treatment should not be considered in a stato-centric manner. Public policies are collective problems, involving many institutions and organizations.

organizing activity between a set of actors, that generates this set and provides interdependence for cooperation. In other words the content and the context of a problem or a policy design inter-organizational types of social configurations.

Usually rather implicit, they nevertheless may be quite well established, durable, etc. One public agency therefore may be part of many such inter-organizational settings. Action and order requirements are quite complex to address in a organized manner, at least more than classic organization sociology inspired by Max Weber's formal model had thought of. Bureaucratization tells only one part of the story in public sector and public action.

Further research is still needed to explore in a more systematic way a wide variety of questions. Three may be worth mentioning:

• Are specific kinds of organizational configurations coupled with specific policy tools such as monies, rules or institution building?

Various typologies are available that classify policies according to criteria such as the degree of coercion they exert on the groups and individuals whose practices and statuses they want to modify [START_REF] Salisbury | The Analysis of Public Policy: A Search for Theories and Roles[END_REF]) or the toolkit governmental authorities select for policy-making [START_REF] Hood | The Tools of Government[END_REF]).

More systematic and comparative studies would be welcome that would verify whether such a co-variation do occur. Pioneering research projects undertaken, for instance, by Renate Mayntz and her associates on implementation processes in Germany have paved the way [START_REF] Marin | Policy Networks: Empirical Evidence and Theoretical Considerations[END_REF].

• What are the consequences of dissociation between power and authority? Is it true that horizontal negotiation dynamics facilitate efficiency and effectiveness much more than hierarchical authority? Do control and command processes really face dramatic difficulties to impose their schemes to peripheries that are far from being passive, as it seems to be the case for instance for issues and sectors like territorial decentralization [START_REF] Thoenig | Territorial Administration and Political Control: Decentralization in France[END_REF] or urban government (Le Galès 1998)? If this is so, what


Julien Mandon

Guy Guelachvili

Dr Nathalie Picqué
email: nathalie.picque@ppm.u-psud.fr

Frequency modulation Fourier transform spectroscopy

Keywords:

come

Improving sensitivity is presently one of the major concern of spectroscopists. This may be obtained both from the enhancement of the intrinsic signal, and from the reduction of the background noise. In this latter case, modulation has been one of the most effective approach. In particular, Frequency Modulation (FM) absorption spectroscopy [START_REF] Bjorklund | Frequency-modulation spectroscopy: a new method for measuring weak absorptions and dispersions[END_REF] has reached detection sensitivity near to the fundamental quantum noise limit, by shifting the frequency modulation of the measurements to a frequency range where the 1/f noise becomes negligible. Moreover, FM spectroscopy benefits from high-speed detection and simultaneous measurement of absorption and dispersion signals. Since Bjorklund's first demonstrations [START_REF] Bjorklund | Frequency-modulation spectroscopy: a new method for measuring weak absorptions and dispersions[END_REF][START_REF] Bjorklund | Frequency-modulation (FM) spectroscopy. Theory of lineshapes and signal-to-noise analysis[END_REF] of the efficiency of FM spectroscopy with a single-mode continuous-wave dye laser, the technique has been widely used as a tunable laser spectroscopic method in fields such as laser stabilization [START_REF] Drever | Laser phase and frequency stabilization using an optical resonator[END_REF], two-photon spectroscopy [START_REF] Zapka | Continuouswave Doppler-free two-photon frequency-modulation spectroscopy in Rb vapor[END_REF], optical heterodyne saturation spectroscopy [START_REF] Hall | Optical heterodyne saturation spectroscopy[END_REF], trace gas detection [START_REF] Maddaloni | Two-tone frequency modulation spectroscopy for ambient-air trace gas detection using a portable difference-frequency source around 3 µm[END_REF]. In most schemes, the laser wavelength is scanned across the atomic/molecular resonance to retrieve the line shape. More rarely, the modulation frequency is tuned. However in both cases, the measurements are limited to narrow spectral ranges.

This letter reports the first results in FM broadband spectroscopy. This work is motivated by our ongoing effort of implementing a new spectroscopic approach simultaneously delivering sensitivity, resolution, accuracy, broad spectral coverage and rapid acquisition. The basic idea, named FM-FTS, is to associate the advantages of FM spectroscopy and high-resolution Fourier transform spectroscopy (FTS). FTS is able to record at once extended ranges, with no spectral restriction. In particular it gives easy access to the infrared domain. In this letter, a new way of modulating the interferogram is implemented. The key concept is that a radio frequency (RF) modulation is performed. The beat signal at the output port of the Fourier transform spectrometer is modulated at constant RF, which is about 10 4 times greater than the audio frequency generally delivered by the interferometer optical conversion. Together with the advantage, over classical FTS, of measurements performed at much higher frequency, our approach benefits from the synchronous detection ability and from the simultaneous acquisition of both the absorption and the dispersion of the recorded profiles.

The experimental principle is presented in Fig. 1. The light emitted by the broadband source is first passing through the interferometer. The output beam is then phase-modulated by an electro-optic modulator (EOM) before entering the absorption cell and falling on the fast detector. The synchronous detection of the detector signal is realized by the lock-in amplifier at the EOM driver reference frequency f m . Recorded data are finally stored on the computer disk with their corresponding path difference position ∆. Their Fourier transform is the spectrum.

In more details, the electric field E at the output of the interferometer may be written as:

0 ( ) ( , ) 1 exp exp( )d c.c. (1) 2 c c c c t i i t c ω ω ω ω ⎡ ⎤ ∆ ⎛ ⎞ ∆ = + - + ⎜ ⎟ ⎢ ⎥ ⎝ ⎠ ⎣ ⎦ ∫ E E
where E 0 is the electric field amplitude of the source at ω c optical pulsation, c is the velocity of light and c.c the conjugate complex of the preceding expression in Eq. 1. The EOM effect on the beam is assumed to have a low modulation index M. As a consequence, each carrier wave of pulsation ω c , has two weak sidebands located at ± ω m = ± 2π f m . Equation [START_REF] Bjorklund | Frequency-modulation spectroscopy: a new method for measuring weak absorptions and dispersions[END_REF] becomes:

( ) { ( ) ( ) } 0 ( ) ( , ) 1 exp exp 2 M exp M exp d c.c. (2) c c c c m c m c t i i t c i t i t ω ω ω ω ω ω ω ω ⎡ ⎤ ∆ ⎛ ⎞ ∆ = + - ⎜ ⎟ ⎢ ⎥ ⎝ ⎠ ⎣ ⎦ ⎡ ⎤ ⎡ ⎤ + + - - + ⎣ ⎦ ⎣ ⎦ ∫ E E
When interacting with the gas, the carrier and the sidebands experience attenuation and phaseshift due to absorption and dispersion. Following the notations introduced in [START_REF] Bjorklund | Frequency-modulation spectroscopy: a new method for measuring weak absorptions and dispersions[END_REF], this interaction may be written as exp(-δ(ω)-i φ(ω)) where δ is the amplitude attenuation and φ is the phase shift. The following convention is adopted: δ n and φ n denotes for n = 0, ±1 the respective components at ω c and ω c ± ω m . Then Eq. 2 may be written:

( ) ( ) { ( ) ( ) ( ) ( ) } 0 0 0 1 1 1 1 ( ) ( , ) 1 exp exp exp 2 M exp exp M exp exp d c.c. (3) c c c c m c m c t i i i t c i i t i i t ω ω δ φ ω δ φ ω ω δ φ ω ω ω + + - - ⎡ ⎤ ∆ ⎛ ⎞ ∆ = + - -- ⎜ ⎟ ⎢ ⎥ ⎝ ⎠ ⎣ ⎦ ⎡ ⎤ ⎡ ⎤ + -- + - -- - + ⎣ ⎦ ⎣ ⎦ ∫ E E
The intensity I detected by the fast photodetector is proportional to :

* I( , ) ( , ) ( , ). (4) t t t ∆ ∝ ∆ ∆ E E ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 0 1 1 0 1 0 1 0 1 0 1 0 1 1 0 0 1 0 1 I( , ) exp 2 exp 2 exp 2 1 cos 2M cos exp cos exp cos 1 cos 2M sin exp sin exp sin 1 cos c m c m c t c t c t c δ δ δ ω ω δ δ φ φ δ δ φ φ ω ω δ δ φ φ δ δ φ φ ω + - + + - - - - + + ⎛ ⎡ ⎤ ∆ ⎛ ⎞ ⎡ ⎤ ∆ ∝ - + - + - + ⎜ ⎜ ⎟ ⎢ ⎥ ⎣ ⎦ ⎝ ⎠ ⎣ ⎦ ⎝ ⎡ ⎤ ∆ ⎛ ⎞ ⎡ ⎤ + -- - - -- - + ⎜ ⎟ ⎢ ⎥ ⎣ ⎦ ⎝ ⎠ ⎣ ⎦ ∆ ⎛ ⎞ ⎡ ⎤ + -- - - -- - + ⎜ ⎣ ⎦ ⎝ ⎠ ∫ ( ) ( ) ( ) ( ) ( ) ( ) 2 1 1 1 1 2 1 1 1 1 2M cos 2 exp sin 1 cos 2M sin 2 exp cos 1 cos d . ( 5
) m c m c c t c t c ω δ δ φ φ ω ω δ δ φ φ ω ω + - - + + - - + ⎡ ⎤ ⎟ ⎢ ⎥ ⎣ ⎦ ⎡ ⎤ ∆ ⎛ ⎞ ⎡ ⎤ + -- - + ⎜ ⎟ ⎢ ⎥ ⎣ ⎦ ⎝ ⎠ ⎣ ⎦ ⎞ ⎡ ⎤ ∆ ⎛ ⎞ ⎡ ⎤ + -- - + ⎟ ⎜ ⎟ ⎢ ⎥ ⎣ ⎦ ⎝ ⎠ ⎣ ⎦ ⎠
After synchronous detection at f m frequency and with the assumption that |δ 0 -δ j |<<1 and |φ 0φ j |<<1 (with j = ±1), the in-phase I cos (∆) and the in-quadrature I sin (∆) parts of the electric signal are given by ( )( )

cos 0 1 1 I ( ) M 1 cos exp 2 d . ( 6
) c c c ω δ δ δ ω - + ⎡ ⎤ ∆ ⎛ ⎞ ∆ ∝ + - - ⎜ ⎟ ⎢ ⎥ ⎝ ⎠ ⎣ ⎦ ∫ ( )( ) sin 0 1 1 0 I ( ) M 1 cos exp 2 2 d . ( 7
) c c c ω δ φ φ φ ω + - ⎡ ⎤ ∆ ⎛ ⎞ ∆ ∝ + - + - ⎜ ⎟ ⎢ ⎥ ⎝ ⎠ ⎣ ⎦ ∫
Summarizing, two interferograms are simultaneously measured, allowing to obtain broadband FM spectra. The in-phase interferogram provides spectrally resolved information on the difference of absorption experienced by each group of two sidebands. The inquadrature interferogram gives the difference between the average of the dispersions experienced by the sidebands and the dispersion undergone by each carrier.

For this first experimental demonstration, a narrow-band emission source covering 0.25 cm -1 (7.5 GHz) has been implemented as a test source. It is made of a fiber-coupled distributed feedback laser diode emitting around 1530 nm with an output power of a few mW. The current of the laser diode is modulated at about 20 Hz by a ramp generator. At each path difference step, while the interferometer is recording one interferogram sample, the laser frequency excursion is equal to 7.5 GHz, corresponding to one period of the triangular ramp. Consequently, for the interferometer, the laser diode behaves as a continuous emission source emitting over 0.25 cm -1 . The interferometer output light is phase-modulated at f m = 150 MHz by the EOM and passes through an 80-cm cell filled at 10 hPa with acetylene in natural abundance. The light is next focused on an InGaAs nanosecond infrared photodetector, which according to Eq.5 delivers a signal proportional to the intensity of the beam containing a beat signal at the RF modulation frequency. The amplified detector signal is mixed with the reference signal at f m , down to d.c., using a commercial high frequency dual-phase lock-in amplifier. The reference may be phase-shifted with respect the signal used to drive the EOM. The two channels detected in-phase and in-quadrature are measured simultaneously.

Figure 2 shows a typical in-phase interferogram of C 2 H 2 . Its shape is characteristic of an interferogram of first-derivative type line-shapes. The 3 cm period amplitude modulation is due to the beat between the two strongest acetylene lines in the explored spectral domain. Figure 3 shows the two narrow-band spectra, Fourier transform of the in-phase (absorption) and in-quadrature (dispersion) interferograms. The spectral domain extension is limited by the tuning capabilities of the diode laser, which was used as a test source. This does not restrict the generality of the present demonstration. The lines belong to the ν 1 +ν 3 and ν 1 +ν 3 +ν 5 1 -ν 5 1 overtone bands of 12 C 2 H 2 . The unapodised spectral instrumental resolution: 12.5 10 -3 cm -1 (0.375 GHz) is narrower than the Doppler width of the lines. Signal to noise ratio is of the order of 1200. The total recording time of the order of 15 minutes is due to the need of adapting the interferometer recording mode procedure to the rather low laser diode frequency excursion period.

The present validation of FM-FTS with a narrow band light source made the experience much simpler. Indeed, in wideband FTS, processing the signal of the interferogram needs special dynamic range solutions. Thanks to the only 0.25 cm -1 -wide spectrum analysed in this experiment, a sophisticate RF detection chain, presently under development, was not necessary. The design of our Connes-type interferometer allows a balanced detection of the signals recorded at the two output ports. This will be helpful to remove the part of the interferogram which is not modulated by path difference and to consequently improve the dynamic range of the measurements. Similar solutions have already been successfully practiced for time-resolved FTS [START_REF] Picqué | High-information time-resolved Fourier transform spectroscopy at work[END_REF]. In FM-FTS, they are formally even easier to implement since the signal may be band-pass filtered around the modulation radio-frequency.

In the present experimental set-up, the light should sequentially reach the equipment parts as shown in Fig. 1. Briefly, to have a broadband equivalent of FM tunable laser spectroscopy, the sidebands generated by the EOM must not be resolved by the spectrometer. Also, since each carrier and its sidebands have to experience different attenuation and phaseshift, the EOM must be placed before the cell containing the gas of interest. This matter will be discussed in more detail elsewhere.

This first FM-FTS experiment demonstrates the feasibility of coupling broadband laser sources, Fourier spectrometers and RF detection. This opens new perspectives in high sensitivity multiplex spectroscopy. FM-FTS may be coupled to a large variety of high brightness sources. This includes broadband cw lasers, supercontinua sources, mode-locked lasers as demonstrated recently [START_REF] Mandon | Frequency Comb Spectrometry with Frequency Modulation[END_REF], and Amplified Spontaneous Emission sources. Frequency nonlinear conversion may also be used when no laser source is available in the spectral range of interest.

FM-FTS may be practiced with any kind of Fourier transform spectrometers, including commercially available instruments, at the expense of reasonable modifications in the signal detection scheme. The approach is also suitable at low spectral resolution. In such case, modulation frequencies lying in the GHz domain may be used. Moreover, FM-FTS induces new practices in Fourier transform spectroscopy. The modulation frequency is very high. The optical fringes generated by the interferometer can then be scanned at a much higher frequency than what is usually practiced nowadays. Path difference variation of the order of 1 m/s, is easily affordable. It corresponds to acquisition times expressed in second when presently the most efficient existing high resolution interferometers need 1 to 10 hours to record interferograms. Additionally, due to the low étendue of the analysed laser beams in our method, miniaturized instruments may be implemented. In addition to the radio-frequency detection scheme, sensitivity may be further enhanced by using an external optical resonator, thus increasing the effective absorption length.

With FM-FTS, both the absorption and the dispersion associated with each spectral features are measured simultaneously. Despite its recognized interest for lineshape parameters retrieval, traditional dispersion spectroscopy has been poorly developed, only at low spectral resolution, mostly due to its experimental complexity. FM-FTS should represent an easy manner of getting this information over extended spectral domains, which may induce new interest to the experimental investigation of dispersion profiles.

Fig. 1 .

 1 Fig. 1. Schematic of the experimental setup.

Fig. 2 .

 2 Fig.2. Absorption interferogram using in-phase RF detection with FM-FTS. Maximum path difference is 40 cm corresponding to 12.5 10 -3 cm -1 unapodized resolution.

Fig. 3 .Fig. 1 .

 31 Fig. 3. FM-FTS dispersion and absorption spectra of the acetylene molecule at 1528.6 nm. The middle plot represents the line relative intensities taken from the HITRAN database.

Fig. 2 .

 2 Fig.2. Absorption interferogram using in-phase RF detection with FM-FTS. Maximum path difference is 40 cm corresponding to 12.5 10 -3 cm -1 unapodized resolution.

Fig. 3 .

 3 Fig. 3. FM-FTS dispersion and absorption spectra of the acetylene molecule at 1528.6 nm. The middle plot represents the line relative intensities taken from the HITRAN database.