Academic literature on the topic 'Oscillateur classique'

The 2000s have been a lively decade for cities. The Worldwatch Institute estimated that 2007 was the first year in human history that more people worldwide lived in cities than the countryside. Globalisation and new digital media technologies have generated the seemingly paradoxical outcome that spatial location came to be more rather than less important, as combinations of firms, industries, cultural activities and creative talents have increasingly clustered around a select node of what have been termed “creative cities,” that are in turn highly networked into global circuits of economic capital, political power and entertainment media. Intellectually, the period has seen what the UCLA geographer Ed Soja refers to as the spatial turn in social theory, where “whatever your interests may be, they can be significantly advanced by adopting a critical spatial perspective” (2). This is related to the dynamic properties of socially constructed space itself, or what Soja terms “the powerful forces that arise from socially produced spaces such as urban agglomerations and cohesive regional economies,” with the result that “what can be called the stimulus of socio-spatial agglomeration is today being assertively described as the primary cause of economic development, technological innovation, and cultural creativity” (14). The demand for social justice in cities has, in recent years, taken the form of “Right to the City” movements. The “Right to the City” movement draws upon the long tradition of radical urbanism in which the Paris Commune of 1871 features prominently, and which has both its Marxist and anarchist variants, as well as the geographer Henri Lefebvre’s (1991) arguments that capitalism was fundamentally driven by the production of space, and that the citizens of a city possessed fundamental rights by virtue of being in a city, meaning that political struggle in capitalist societies would take an increasingly urban form. Manifestations of contemporary “Right to the City” movements have been seen in the development of a World Charter for the Right to the City, Right to the City alliances among progressive urban planners as well as urban activists, forums that bring together artists, architects, activists and urban geographers, and a variety of essays on the subject by radical geographers including David Harvey, whose work I wish to focus upon here. In his 2008 essay "The Right to the City," Harvey presents a manifesto for 21st century radical politics that asserts that the struggle for collective control over cities marks the nodal point of anti-capitalist movements today. It draws together a range of strands of arguments recognizable to those familiar with Harvey’s work, including Marxist political economy, the critique of neoliberalism, the growth of social inequality in the U.S. in particular, and concerns about the rise of speculative finance capital and its broader socio-economic consequences. My interest in Harvey’s manifesto here arises not so much from his prognosis for urban radicalism, but from how he understands the suburban in relation to this urban class struggle. It is an important point to consider because, in many parts of the world, growing urbanisation is in fact growing suburbanisation. This is the case for U.S. cities (Cox), and it is also apparent in Australian cities, with the rise in particular of outer suburban Master Planned Communities as a feature of the “New Prosperity” Australia has been experiencing since the mid 1990s (Flew; Infrastructure Australia). What we find in Harvey’s essay is that the suburban is clearly sub-urban, or an inferior form of city living. Suburbs are variously identified by Harvey as being:Sites for the expenditure of surplus capital, as a safety valve for overheated finance capitalism (Harvey 27);Places where working class militancy is pacified through the promotion of mortgage debt, which turns suburbanites into political conservatives primarily concerned with maintaining their property values;Places where “the neoliberal ethic of intense possessive individualism, and its cognate of political withdrawal from collective forms of action” are actively promoted through the proliferation of shopping malls, multiplexes, franchise stores and fast-food outlets, leading to “pacification by cappuccino” (32);Places where women are actively oppressed, so that “leading feminists … [would] proclaim the suburb as the locus of all their primary discontents” (28);A source of anti-capitalist struggle, as “the soulless qualities of suburban living … played a critical role in the dramatic events of 1968 in the US [as] discontented white middle-class students went into a phase of revolt, sought alliances with marginalized groups claiming civil rights and rallied against American imperialism” (28).Given these negative associations, one could hardly imagine citizens demanding the right to the suburb, in the same way as Harvey projects the right to the city as a rallying cry for a more democratic social order. Instead, from an Australian perspective, one is reminded of the critiques of suburbia that have been a staple of radical theory from the turn of the 20th century to the present day (Collis et. al.). Demanding the “right to the suburb” would appear here as an inherently contradictory demand, that could only be desired by those who the Australian radical psychoanalytic theorist Douglas Kirsner described as living an alienated existence where:Watching television, cleaning the car, unnecessary housework and spectator sports are instances of general life-patterns in our society: by adopting these patterns the individual submits to a uniform life fashioned from outside, a pseudo-life in which the question of individual self-realisation does not even figure. People live conditioned, unconscious lives, reproducing the values of the system as a whole (Kirsner 23). The problem with this tradition of radical critique, which is perhaps reflective of the estrangement of a section of the Australian critical intelligentsia more generally, is that most Australians live in suburbs, and indeed seem (not surprisingly!) to like living in them. Indeed, each successive wave of migration to Australia has been marked by families seeking a home in the suburbs, regardless of the housing conditions of the place they came from: the demand among Singaporeans for large houses in Perth, or what has been termed “Singaperth,” is one of many manifestations of this desire (Lee). Australian suburban development has therefore been characterized by a recurring tension between the desire of large sections of the population to own their own home (the fabled quarter-acre block) in the suburbs, and the condemnation of suburban life from an assortment of intellectuals, political radicals and cultural critics. This was the point succinctly made by the economist and urban planner Hugh Stretton in his 1970 book Ideas for Australian Cities, where he observed that “Most Australians choose to live in suburbs, in reach of city centres and also of beaches or countryside. Many writers condemn this choice, and with especial anger or gloom they condemn the suburbs” (Stretton 7). Sue Turnbull has observed that “suburbia has come to constitute a cultural fault-line in Australia over the last 100 years” (19), while Ian Craven has described suburbia as “a term of contention and a focus for fundamentally conflicting beliefs” in the Australian national imaginary “whose connotations continue to oscillate between dream and suburban nightmare” (48). The tensions between celebration and critique of suburban life play themselves out routinely in the Australian media, from the sun-lit suburbanism of Australia’s longest running television serial dramas, Neighbours and Home and Away, to the pointed observational critiques found in Australian comedy from Barry Humphries to Kath and Kim, to the dark visions of films such as The Boys and Animal Kingdom (Craven; Turnbull). Much as we may feel that the diagnosis of suburban life as a kind of neurotic condition had gone the way of the concept album or the tie-dye shirt, newspaper feature writers such as Catherine Deveny, writing in The Age, have offered the following as a description of the Chadstone shopping centre in Melbourne’s eastern suburbChadstone is a metastasised tumour of offensive proportions that's easy to find. You simply follow the line of dead-eyed wage slaves attracted to this cynical, hermetically sealed weatherless biosphere by the promise a new phone will fix their punctured soul and homewares and jumbo caramel mugachinos will fill their gaping cavern of disappointment … No one looks happy. Everyone looks anaesthetised. A day spent at Chadstone made me understand why they call these shopping centres complexes. Complex as in a psychological problem that's difficult to analyse, understand or solve. (Deveny) Suburbanism has been actively promoted throughout Australia’s history since European settlement. Graeme Davison has observed that “Australia’s founders anticipated a sprawl of homes and gardens rather than a clumping of terraces and alleys,” and quotes Governor Arthur Phillip’s instructions to the first urban developers of the Sydney Cove colony in 1790 that streets shall be “laid out in such a manner as to afford free circulation of air, and where the houses are built … the land will be granted with a clause that will prevent more than one house being built on the allotment” (Davison 43). Louise Johnson (2006) argued that the main features of 20th century Australian suburbanisation were very much in place by the 1920s, particularly land-based capitalism and the bucolic ideal of home as a retreat from the dirt, dangers and density of the city. At the same time, anti-suburbanism has been a significant influence in Australian public thought. Alan Gilbert (1988) drew attention to the argument that Australia’s suburbs combined the worst elements of the city and country, with the absence of both the grounded community associated with small towns, and the mental stimuli and personal freedom associated with the city. Australian suburbs have been associated with spiritual emptiness, the promotion of an ersatz, one-dimensional consumer culture, the embourgeoisment of the working-class, and more generally criticised for being “too pleasant, too trivial, too domestic and far too insulated from … ‘real’ life” (Gilbert 41). There is also an extensive feminist literature critiquing suburbanization, seeing it as promoting the alienation of women and the unequal sexual division of labour (Game and Pringle). More recently, critiques of suburbanization have focused on the large outer-suburban homes developed on new housing estates—colloquially known as McMansions—that are seen as being environmentally unsustainable and emblematic of middle-class over-consumption. Clive Hamilton and Richard Denniss’s Affluenza (2005) is a locus classicus of this type of argument, and organizations such as the Australia Institute—which Hamilton and Denniss have both headed—have regularly published papers making such arguments. Can the Suburbs Make You Creative?In such a context, championing the Australian suburb can feel somewhat like being an advocate for Dan Brown novels, David Williamson plays, Will Ferrell comedies, or TV shows such as Two and a Half Men. While it may put you on the side of majority opinion, you can certainly hear the critical axe grinding and possibly aimed at your head, not least because of the association of such cultural forms with mass popular culture, or the pseudo-life of an alienated existence. The art of a program such as Kath and Kim is that, as Sue Turnbull so astutely notes, it walks both sides of the street, both laughing with and laughing at Australian suburban culture, with its celebrity gossip magazines, gourmet butcher shops, McManisons and sales at Officeworks. Gina Riley and Jane Turner’s inspirations for the show can be seen with the presence of such suburban icons as Shane Warne, Kylie Minogue and Barry Humphries as guests on the program. Others are less nuanced in their satire. The website Things Bogans Like relentlessly pillories those who live in McMansions, wear Ed Hardy t-shirts and watch early evening current affairs television, making much of the lack of self-awareness of those who would simultaneously acquire Buddhist statues for their homes and take budget holidays in Bali and Phuket while denouncing immigration and multiculturalism. It also jokes about the propensity of “bogans” to loudly proclaim that those who question their views on such matters are demonstrating “political correctness gone mad,” appealing to the intellectual and moral authority of writers such as the Melbourne Herald-Sun columnist Andrew Bolt. There is also the “company you keep” question. Critics of over-consuming middle-class suburbia such as Clive Hamilton are strongly associated with the Greens, whose political stocks have been soaring in Australia’s inner cities, where the majority of Australia’s cultural and intellectual critics live and work. By contrast, the Liberal party under John Howard and now Tony Abbott has taken strongly to what could be termed suburban realism over the 1990s and 2000s. Examples of suburban realism during the Howard years included the former Member for Lindsay Jackie Kelly proclaiming that the voters of her electorate were not concerned with funding for their local university (University of Western Sydney) as the electorate was “pram city” and “no one in my electorate goes to uni” (Gibson and Brennan-Horley), and the former Minister for Immigration and Citizenship, Garry Hardgrave, holding citizenship ceremonies at Bunnings hardware stores, so that allegiance to the Australian nation could co-exist with a sausage sizzle (Gleeson). Academically, a focus on the suburbs is at odds with Richard Florida’s highly influential creative class thesis, which stresses inner urban cultural amenity and “buzz” as the drivers of a creative economy. Unfortunately, it is also at odds with many of Florida’s critics, who champion inner city activism as the antidote to the ersatz culture of “hipsterisation” that they associate with Florida (Peck; Slater). A championing of suburban life and culture is associated with writers such as Joel Kotkin and the New Geography group, who also tend to be suspicious of claims made about the creative industries and the creative economy. It is worth noting, however, that there has been a rich vein of work on Australian suburbs among cultural geographers, that has got past urban/suburban binaries and considered the extent to which critiques of suburban Australia are filtered through pre-existing discursive categories rather than empirical research findings (Dowling and Mee; McGuirk and Dowling; Davies (this volume). I have been part of a team engaged in a three-year study of creative industries workers in outer suburban areas, known as the Creative Suburbia project.[i] The project sought to understand how those working in creative industries who lived and worked in the outer suburbs maintained networks, interacted with clients and their peers, and made a success of their creative occupations: it focused on six suburbs in the cities of Brisbane (Redcliffe, Springfield, Forest Lake) and Melbourne (Frankston, Dandenong, Caroline Springs). It was premised upon what has been an inescapable empirical fact: however much talk there is about the “return to the city,” the fastest rates of population growth are in the outer suburbs of Australia’s major cities (Infrastructure Australia), and this is as true for those working in creative industries occupations as it is for those in virtually all other industry and occupational sectors (Flew; Gibson and Brennan-Horley; Davies). While there is a much rehearsed imagined geography of the creative industries that points to creative talents clustering in dense, highly agglomerated inner city precincts, incubating their unique networks of trust and sociality through random encounters in the city, it is actually at odds with the reality of where people in these sectors choose to live and work, which is as often as not in the suburbs, where the citizenry are as likely to meet in their cars at traffic intersections than walking in city boulevards.There is of course a “yes, but” response that one could have to such empirical findings, which is to accept that the creative workforce is more suburbanised than is commonly acknowledged, but to attribute this to people being driven out of the inner city by high house prices and rents, which may or may not be by-products of a Richard Florida-style strategy to attract the creative class. In other words, people live in the outer suburbs because they are driven out of the inner city. From our interviews with 130 people across these six suburban locations, the unequivocal finding was that this was not the case. While a fair number of our respondents had indeed moved from the inner city, just as many would—if given the choice—move even further away from the city towards a more rural setting as they would move closer to it. While there are clearly differences between suburbs, with creative people in Redcliffe being generally happier than those in Springfield, for example, it was quite clear that for many of these people a suburban location helped them in their creative practice, in ways that included: the aesthetic qualities of the location; the availability of “headspace” arising from having more time to devote to creative work rather than other activities such as travelling and meeting people; less pressure to conform to a stereotyped image of how one should look and act; financial savings from having access to lower-cost locations; and time saved by less commuting between locations.These creative workers generally did not see having access to the “buzz” associated with the inner city as being essential for pursuing work in their creative field, and they were just as likely to establish hardware stores and shopping centres as networking hubs as they were cafes and bars. While being located in the suburbs was disadvantageous in terms of access to markets and clients, but this was often seen in terms of a trade-off for better quality of life. Indeed, contrary to the presumptions of those such as Clive Hamilton and Catherine Deveny, they could draw creative inspiration from creative locations themselves, without feeling subjected to “pacification by cappuccino.” The bigger problem was that so many of the professional associations they dealt with would hold events in the inner city in the late afternoon or early evening, presuming people living close by and/or not having domestic or family responsibilities at such times. The role played by suburban locales such as hardware stores as sites for professional networking and as elements of creative industries value chains has also been documented in studies undertaken of Darwin as a creative city in Australia’s tropical north (Brennan-Horley and Gibson; Brennan-Horley et al.). Such a revised sequence in the cultural geography of the creative industries has potentially great implications for how urban cultural policy is being approached. The assumption that the creative industries are best developed in cities by investing heavily in inner urban cultural amenity runs the risk of simply bypassing those areas where the bulk of the nation’s artists, musicians, filmmakers and other cultural workers actually are, which is in the suburbs. Moreover, by further concentrating resources among already culturally rich sections of the urban population, such policies run the risk of further accentuating spatial inequalities in the cultural realm, and achieving the opposite of what is sought by those seeking spatial justice or the right to the city. An interest in broadband infrastructure or suburban university campuses is certainly far more prosaic than a battle for control of the nation’s cultural institutions or guerilla actions to reclaim the city’s streets. Indeed, it may suggest aspirations no higher than those displayed by Kath and Kim or by the characters of Barry Humphries’ satirical comedy. But however modest or utilitarian a focus on developing cultural resources in Australian suburbs may seem, it is in fact the most effective way of enabling the forms of spatial justice in the cultural sphere that many progressive people seek. ReferencesBrennan-Horley, Chris, and Chris Gibson. “Where Is Creativity in the City? Integrating Qualitative and GIS Methods.” Environment and Planning A 41.11 (2009): 2595–614. Brennan-Horley, Chris, Susan Luckman, Chris Gibson, and J. Willoughby-Smith. “GIS, Ethnography and Cultural Research: Putting Maps Back into Ethnographic Mapping.” The Information Society: An International Journal 26.2 (2010): 92–103.Collis, Christy, Emma Felton, and Phil Graham. “Beyond the Inner City: Real and Imagined Places in Creative Place Policy and Practice.” The Information Society: An International Journal 26.2 (2010): 104–12.Cox, Wendell. “The Still Elusive ‘Return to the City’.” New Geography 28 February 2011. < http://www.newgeography.com/content/002070-the-still-elusive-return-city >.Craven, Ian. “Cinema, Postcolonialism and Australian Suburbia.” Australian Studies 1995: 45-69. Davies, Alan. “Are the Suburbs Dormitories?” The Melbourne Urbanist 21 Sep. 2010. < http://melbourneurbanist.wordpress.com/2010/09/21/are-the-suburbs-dormitories/ >.Davison, Graeme. "Australia: The First Suburban Nation?” Journal of Urban History 22.1 (1995): 40-75. Deveny, Catherine. “No One Out Alive.” The Age 29 Oct. 2009. < http://www.smh.com.au/opinion/society-and-culture/no-one-gets-out-alive-20091020-h6yh.html >.Dowling, Robyn, and K. Mee. “Tales of the City: Western Sydney at the End of the Millennium.” Sydney: The Emergence of World City. Ed. John Connell. Melbourne: Oxford UP, 2000. 244–72.Flew, Terry. “Economic Prosperity, Suburbanization and the Creative Workforce: Findings from Australian Suburban Communities.” Spaces and Flows: Journal of Urban and Extra-Urban Studies 1.1 (2011, forthcoming).Game, Ann, and Rosemary Pringle. “Sexuality and the Suburban Dream.” Australian and New Zealand Journal of Sociology 15.2 (1979): 4–15.Gibson, Chris, and Chris Brennan-Horley. “Goodbye Pram City: Beyond Inner/Outer Zone Binaries in Creative City Research.” Urban Policy and Research 24.4 (2006): 455–71. Gilbert, A. “The Roots of Australian Anti-Suburbanism.” Australian Cultural History. Ed. S. I. Goldberg and F. B. Smith. Cambridge: Cambridge UP, 1988. 33–39. Gleeson, Brendan. Australian Heartlands: Making Space for Hope in the Suburbs. Sydney: Allen & Unwin, 2006.Hamilton, Clive, and Richard Denniss. Affluenza. Sydney: Allen & Unwin, 2005.Harvey, David. “The Right to the City.” New Left Review 53 (2008): 23–40.Infrastructure Australia. State of Australian Cities 2010. Infrastructure Australia Major Cities Unit. Canberra: Commonwealth of Australia. 2010.Johnson, Lesley. “Style Wars: Revolution in the Suburbs?” Australian Geographer 37.2 (2006): 259–77. Kirsner, Douglas. “Domination and the Flight from Being.” Australian Capitalism: Towards a Socialist Critique. Eds. J. Playford and D. Kirsner. Melbourne: Penguin, 1972. 9–31.Kotkin, Joel. “Urban Legends.” Foreign Policy 181 (2010): 128–34. Lee, Terence. “The Singaporean Creative Suburb of Perth: Rethinking Cultural Globalization.” Globalization and Its Counter-Forces in South-East Asia. Ed. T. Chong. Singapore: Institute for Southeast Asian Studies, 2008. 359–78. Lefebvre, Henri. The Production of Space. Trans. Donald Nicholson-Smith. Oxford: Blackwell, 1991.McGuirk, P., and Robyn Dowling. “Understanding Master-Planned Estates in Australian Cities: A Framework for Research.” Urban Policy and Research 25.1 (2007): 21–38Peck, Jamie. “Struggling with the Creative Class.” International Journal of Urban and Regional Research 29.4 (2005): 740–70. Slater, Tom. “The Eviction of Critical Perspectives from Gentrification Research.” International Journal of Urban and Regional Research 30.4 (2006): 737–57. Soja, Ed. Seeking Spatial Justice. Minneapolis: U of Minnesota P, 2010.Stretton, Hugh. Ideas for Australian Cities. Melbourne: Penguin, 1970.Turnbull, Sue. “Mapping the Vast Suburban Tundra: Australian Comedy from Dame Edna to Kath and Kim.” International Journal of Cultural Studies 11.1 (2008): 15–32.

La spectroscopie de dichroïsme circulaire (CD) est une des techniques fondamentales en biologie structurale qui permet la détermination du contenu en structures secondaires d'une protéine. Le rayonnement synchrotron a considérablement augmenté l’utilité de la méthode, car il permet de travailler avec une gamme spectrale étendue et à meilleure intensité. Le développement de modèles permettant d’établir une relation entre la structure d’une protéine et son spectre CD d’une manière efficace n’a pourtant pas suivi l’évolution technique et l’analyse de spectres CD de protéines entières reste un défi sur le plan théorique. Dans ce contexte, nous avons développé un modèle "minimaliste" pour la spectroscopie CD des protéines, où chaque atome C-alpha de la chaîne principale porte un oscillateur de Lorentz classique, i.e. une charge mobile qui est tenue par un potentiel quadratique. Les oscillateurs sont couplés par un potentiel coulombien et leurs déplacements suivent les tangentes locales respectives de la courbe spatiale décrite par les atomes C-alpha. Le système d'oscillateurs est couplé à une onde électromagnétique plane décrivant la source de lumière et le phénomène d'absorption est modélisé par des forces de friction. Nous montrons que le modèle reproduit correctement le phénomène CD d'une chaîne polypeptidique hélicoïdale et en particulier son signe en fonction de l'orientation de la chaîne. Comme première application, nous présentons l'ajustement du modèle au spectre CD d'un polypeptide composé de 15 résidus qui se plie sous forme d'une hélice alpha. La transférabilité de ces paramètres est ensuite évaluée pour la myoglobine, une protéine de 153 résidus contenant 8 hélices alpha
Circular dichroism (CD) spectroscopy is one of the fundamental techniques in structural biology that allows us to investigate the secondary structure of proteins. Synchrotron radiation has considerably increased the usefulness of the method because it allows to work with a wider range of spectrum and much greater signal-to-noise ratios. The development of a theoretical model to establish a relationship between the structure of a protein and its CD spectra in an efficient manner proved to be a complex task. The calculation of the CD spectra of large molecules, such as protein, remains a challenge, due to the size and flexibility of the molecules. In this context, we have developed a “minimal” model to explain the CD spectroscopy of proteins, which associates each C-alpha position on the protein backbone with a classical Lorentz oscillator i.e. a mobile charge attaches to a corresponding atom by a quadratic potential. The coupling between charges is through the Coulomb potential and their displacements follow the direction of the respective local tangents to the Calpha space curve. This system is coupled to a planar electromagnetic wave describing the light source and the absorption phenomenon is modeled by frictional forces. We show that the model correctly reproduces the CD phenomenon of a helical polypeptide chain and in particular its sign depending on the orientation of the chain. At first, we have fitted a model to CD spectra of a polypeptide chain of 15 residues folded into alpha helix. The transferability of these parameters is then evaluated with myoglobin, a protein of 153 residues containing eight alpha helices

Nous étudions en détail les effets de polarisation dans les mélanges paramétriques à trois ondes en cavité. Nous nous intéressons tout d'abord à l'étude théorique de l'Oscillateur Paramétrique Optique (OPO) de type II dans lequel nous insérons une lame biréfringente. En type II signal et complémentaire sont polarisés orthogonalement et nous montrons que le couplage induit par la lame créée une zone d'accrochage où l'OPO fonctionne à dégénérescence de fréquence. Après avoir caractérisé de manière approfondie les propriétés classiques de ce système, nous étudions l'intrication quantique des faisceaux jumeaux et relions les résultats obtenus à différents critères d'information quantique. Nous faisons également l'étude expérimentale et théorique d'un système de régénération tout-optique basé sur la génération vectorielle de seconde harmonique à reconversion paramétrique de type II avec une double cavité et étudions la faisabilité d'un tel système dans des conditions télécom.

Calcul des intégrales radiales à l'approximation quasi classique (JWKB) des fonctions d'onde radiales, complétée par une description en termes de trajectoires elliptiques de l'électron optique. Obtention d'expressions analytiques de ces intégrales dont on simplifie le calcul à l'aide d'une méthode basée sur le développement limite d'une fonction bien adaptée à des calculs par interpolation ou extrapolation : elles s'expriment toutes en termes de deux fonctions fondamentales qui ne dépendent que de la différence entre deux nombres quantiques principaux effectifs des états initial et final. Déduction de forces d'oscillateur et probabilités de transition aussi précises que celles obtenues par quantique.

On étudie l'oscillateur non linéaire a un degré de liberté, qualifié d'anharmonique et monomial car son hamiltonien peut s'exprimer comme celui d'un oscillateur harmonique perturbe par un monome de degré alpha, entier strictement supérieur a deux. On considère seulement les solutions périodiques.

Cette thèse est consacrée à l'étude théorique et expérimentale de différents niveaux de corrélations quantiques en variables continues, mettant en jeu une ou deux quadratures. Dans cet objectif, un oscillateur paramétrique optique de type II, où signal et complémentaire sont émis suivant des polarisations orthogonales, a été développé. Une lame biréfringente introduite à l'intérieur de la cavité induit un couplage des deux modes et permet un fonctionnement dégénéré en fréquence.

Un protocole original de préparation conditionnelle d'un état non-classique, de distribution statistique sub-Poissonienne, a été étudié théoriquement et mis en oeuvre expérimentalement. Il repose sur les corrélations d'intensité des faisceaux émis au-dessus du seuil en l'absence de lame. Une compression de 9.5 dB du bruit sur la différence d'intensité a été obtenue.

En présence de la lame, les faisceaux émis sont dégénérés en fréquence et en principe intriqués. La dégénérescence a permis la première mesure des anti-corrélations de phase au-dessus du seuil. Malgré un excès de bruit qui reste à expliquer, ce résultat ouvre une voie intéressante pour la génération directe d'états intriqués intenses. L'oscillateur paramétrique optique, avec ou sans lame, peut également fonctionner au-dessous du seuil et générer des faisceaux fortement intriqués. L'intrication obtenue, stable pendant plusieurs heures, est la plus forte observée à ce jour et elle est préservée jusqu'à des fréquences de bruit très basses. En présence de la lame, les propriétés quantiques originales du système sont également détaillées et une opération passive, réalisée à l'aide de lames biréfringentes, est mise en évidence pour optimiser l'intrication. L'action d'opérations passives sur un état à deux modes est discutée théoriquement.

Les microlasers developpes au leti, dont le mode de fabrication collective autorise une production de masse a tres faible cout, ont ete utilises pour pomper un opo miniature. Ces microlasers, fabriques a partir d'un substrat de yag:nd sur lequel est depose un absorbant saturable yag:cr#4#+ par epitaxie en phase liquide, emettent a la longueur d'onde 1. 064 m des impulsions de quelques j et de largeurs de l'ordre de la nanoseconde, a des taux de repetition de plusieurs dizaines de khz. Ils sont pompes avec des diodes laser standards de puissance 1 w. La principale difficulte pour pomper un opo avec un microlaser est d'atteindre son seuil d'oscillation. Le calcul de ce seuil montre que les faibles energies delivrees par les microlasers ne nous permettraient pas de pomper un opo en configuration extracavite. Afin de nous familiariser avec le concept de l'opo, nous avons tout de meme realise un opo base sur la conversion parametrique 1. 064 m 1. 572 m + 3. 293 m dans un cristal de ktp, pompe avec un laser delivrant des impulsions de plusieurs mj. Bien que les experiences menees avec la volonte d'abaisser le seuil d'oscillation de l'opo aient donne de bons resultats, les plus bas seuils mesures (200 j) restent bien superieurs aux energies delivrees par les microlasers (inferieures a 10 j). Nous avons alors developpe un micro-opo intracavite. Afin d'atteindre le seuil d'oscillation, l'opo est place a l'interieur de la cavite laser. Le micro-opo ainsi realise fonctionne a la longueur d'onde 1. 572 m. Il genere des impulsions de plusieurs j et de largeurs de l'ordre de la dizaine de nanoseconde, a des taux de repetition pouvant etre superieurs a 10 khz. En notre connaissance, il s'agit du premier micro-opo qui ait ete realiser en utilisant un microlaser impulsionnel pompe par une diode laser de puissance 1 w. Afin d'optimiser les performances du micro-opo intracavite, nous avons developpe un programme de calcul pour simuler son fonctionnement.

Cette thèse étudie l'amplification
d'une image par un processus paramétrique. Réaliser cette
amplification de manière continue nécessite de placer le milieu
paramétrique dans une cavité optique. En théorie, cette
amplification est sans bruit, et permet de générer des états
non-classiques du champ.

On étudie tout d'abord classiquement la propagation d'une image
dans un système paraxial, puis les cavités dégénérées
transversalement. On en déduit un formalisme permettant de décrire
la transmission d'une image à travers une cavité paraxiale
quelconque. Ce formalisme est illustré par l'étude théorique et
expérimentale de la transmission d'une image à travers une cavité
particulière : la cavité hémi-confocale. Une partie théorique
s'intéresse ensuite aux spécificités de l'amplification d'image.
L'amplificateur paramétrique en cavité sous le seuil
d'oscillation, connu pour générer du vide comprimé, peut également
amplifier un faible signal injecté. On montre l'apparition de
bruit supplémentaire sur le signal amplifié, spécifique à
l'amplification, dû au couplage au bruit de la pompe. On étudie
ensuite du point de vue quantique le comportement multimode
transverse d'un amplificateur paramétrique optique en cavité
hémi-confocale.

Enfin, une partie expérimentale étudie le comportement d'un
oscillateur paramétrique optique confocal au dessus du seuil et on
prouve qu'il produit des faisceaux non-classiques multimodes
transverses. On montre ensuite qu'il est possible d'amplifier de
manière sensible à la phase un signal dans cette même cavité sous
le seuil d'oscillation. Dans une seconde expérience en
configuration de double cavité hémi-confocale, plus stable, on
réalise la première amplification paramétrique multimode d'une
image en cavité.

Cette these de doctorat concerne la conception de nouveaux oscillateurs parametriques optiques (opo) avec comme objectif l'amelioration des proprietes spatiales et spectrales des faisceaux generes par rapport aux dispositifs actuels. L'originalite de ces dispositifs repose sur l'utilisation de cristaux non lineaires de geometrie cylindrique. Une methode originale d'usinage en cylindres de mono-cristaux orientes a ete developpee : les cristaux ainsi usines presentent des caracteristiques de cylindricite et de poli sur la tranche compatibles avec leur utilisation dans un dispositif resonant. Les geometries de cavite permettant un couplage optimum entre les ondes dans l'opo sont definies en prenant en compte les specificites liees a l'insertion intra-cavite d'un cristal non lineaire cylindrique : ces dispositifs imposent un controle rigoureux de la focalisation du rayonnement incident. Cette etape a permis la realisation d'un opo en regime impulsionnel pompe a 1064nm en quasi-accord de phase dans un cristal de ppktp cylindrique, permettant une accordabilite continue du signal sur une plage spectrale de 523nm. De meme, l'accordabilite angulaire d'un opo en accord de phase de type i dans un cristal de ktp a ete demontree sur 31,5\, ce qui correspond a environ 3 fois la gamme angulaire exploitable avec un cristal parallelepipedique. Une methode originale pour la caracterisation de faisceaux gaussiens a ete appliquee a la mesure du facteur de qualite (m 2) du faisceau signal emis par cet opo. Ces mesures ont conduit au developpement d'un modele simple qui definit les geometries de cavite permettant d'obtenir un affinement spatial de l'onde resonante dans la cavite de l'opo. L'application de ce modele a debouche sur la realisation d'un opo accordable en accord de phase emettant un faisceau signal dont le facteur de qualite m 2 est inferieur a 1,5 sur toute la plage angulaire consideree.

Ce mémoire de thèse est consacré à l'étude théorique et expérimentale d'oscillateurs paramétriques optiques (OPO) multimodes dans deux régimes: l'optique des images et l'optique des impulsions. On rappelle les outils utilisés habituellement pour décrire et manipuler les états non-classiques de la lumière, en insistant sur l'importance du concept de mode du champ dans sa description quantique, qu'il soit transverse ou longitudinal. On rappelle ensuite les techniques de manipulation des modes transverse (images) et des modes longitudinaux (impulsions) au niveau théorique et expérimental. L'accent est mis sur le rapprochement de ces deux domaines où l'on peut facilement identifier un grand nombre de variables similaires. Un modèle général des OPO multimodes est développé, s'appuyant sur un traitement multimode de la conversion paramétrique dans un cristal non-linéaire d'ordre deux. Ce modèle conduit à des états non-classiques multimodes, intéressants pour l'information quantique, et peut être appliqué aux cas d'un OPO dans une cavité dégénérée pour les modes transverses, et d'un OPO pompé en modes synchrones (SPOPO). Tous ces développements théoriques s'orientent vers plusieurs expériences d'optique multimode décrites dans ce manuscrit. La première est une étude de la transmission et le doublage de fréquence d'images dans une cavité auto-imageante. Deux expériences d'imagerie quantique sont ensuite décrites: l'une conduit à une réduction de bruit multimode dans un OPO au dessus du seuil et la seconde utilise un OPO dans une cavité auto-imageante et permet la production et la caractérisation d'un état trimode sous le seuil de l'OPO. Enfin, on décrit la mise en place expérimentale d'un SPOPO qui conduit à des premiers résultats de réduction de bruit sur un peigne de fréquence.