Wavefront correction with a ferrofluid deformable mirror: experimental results and recent developments

We present the research status of a deformable mirror made of a magnetic liquid whose surface is actuated by a triangular array of small current carrying coils. We demonstrate that the mirror can correct a 11 microns low order aberrated wavefront to a residual RMS wavefront error 0.05 microns. Recent developments show that these deformable mirrors can reach a frequency response of several hundred hertz. A new method for linearizing the response of these mirrors is also presented.Comment: To appear in "Ground-based and Airborne Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200

Fast-recovery of the amplitude and phase of short optical pulses using a frequency-swept source based heterodyne measurement

We propose a very fast heterodyne technique to recover the amplitude and phase of short optical pulses generated, e.g., by a mode-locked laser. A linearly swept frequency source is used to scan the entire optical spectrum of the mode-locked laser in a single continuous sweep. The beat signal is recorded on a fast oscilloscope and then digitally processed allowing the simultaneous recovery of the amplitude and the phase. This measurement is fast (less than 2 μs) and requires no prior spectral information about the signal under test

A cryogenic liquid-mirror telescope on the moon to study the early universe

We have studied the feasibility and scientific potential of zenith observing liquid mirror telescopes having 20 to 100 m diameters located on the moon. They would carry out deep infrared surveys to study the distant universe and follow up discoveries made with the 6 m James Webb Space Telescope (JWST), with more detailed images and spectroscopic studies. They could detect objects 100 times fainter than JWST, observing the first, high-red shift stars in the early universe and their assembly into galaxies. We explored the scientific opportunities, key technologies and optimum location of such telescopes. We have demonstrated critical technologies. For example, the primary mirror would necessitate a high-reflectivity liquid that does not evaporate in the lunar vacuum and remains liquid at less than 100K: We have made a crucial demonstration by successfully coating an ionic liquid that has negligible vapor pressure. We also successfully experimented with a liquid mirror spinning on a superconducting bearing, as will be needed for the cryogenic, vacuum environment of the telescope. We have investigated issues related to lunar locations, concluding that locations within a few km of a pole are ideal for deep sky cover and long integration times. We have located ridges and crater rims within 0.5 degrees of the North Pole that are illuminated for at least some sun angles during lunar winter, providing power and temperature control. We also have identified potential problems, like lunar dust. Issues raised by our preliminary study demand additional in-depth analyses. These issues must be fully examined as part of a scientific debate we hope to start with the present article.Comment: 35 pages, 11 figures. To appear in Astrophysical Journal June 20 200

Wavefront correction with a ferrofluid deformable mirror: experimental results and recent developments

ABSTRACT We present the research status of a deformable mirror made of a magnetic liquid whose surface is actuated by a triangular array of small current carrying coils. We demonstrate that the mirror can correct a 11 µm low order aberrated wavefront to a residual RMS wavefront error 0.05 µm. Recent developments show that these deformable mirrors can reach a frequency response of several hundred hertz. A new method for linearizing the response of these mirrors is also presented

Dynamics of Adrenal Steroids Are Related to Variations in Th1 and Treg Populations during Mycobacterium tuberculosis Infection in HIV Positive Persons

Tuberculosis (TB) remains the most frequent cause of illness and death from an infectious agent, and its interaction with HIV has devastating effects. We determined plasma levels of dehydroepiandrosterone (DHEA), its circulating form DHEA-suphate (DHEA-s) and cortisol in different stages of M. tuberculosis infection, and explored their role on the Th1 and Treg populations during different scenarios of HIV-TB coinfection, including the immune reconstitution inflammatory syndrome (IRIS), a condition related to antiretroviral treatment. DHEA levels were diminished in HIV-TB and HIV-TB IRIS patients compared to healthy donors (HD), HIV+ individuals and HIV+ individuals with latent TB (HIV-LTB), whereas dehydroepiandrosterone sulfate (DHEA-s) levels were markedly diminished in HIV-TB IRIS individuals. HIV-TB and IRIS patients presented a cortisol/DHEA ratio significantly higher than HIV+, HIV-LTB and HD individuals. A positive correlation was observed between DHEA-s and CD4 count among HIV-TB individuals. Conversely, cortisol plasma level inversely correlated with CD4 count within HIV-TB individuals. M. tuberculosis-specific Th1 lymphocyte count was increased after culturing PBMC from HIV-TB individuals in presence of DHEA. We observed an inverse correlation between DHEA-s plasma level and Treg frequency in co-infected individuals, and CD4+FoxP3+ Treg frequency was increased in HIV-TB and IRIS patients compared to other groups. Strikingly, we observed a prominent CD4+CD25-FoxP3+ population across HIV-TB and HIV-TB IRIS patients, which frequency correlated with DHEA plasma level. Finally, DHEA treatment negatively regulated FoxP3 expression without altering Treg frequency in co-infected patients. These data suggest an enhancing role for DHEA in the immune response against M. tuberculosis during HIV-TB coinfection and IRIS

Contribution à l'étude et à la mise en oeuvre de fonction de filtrage pour les brasseurs optiques dédiés au traitement multi-longueurs d'onde

La demande croissante des réseaux optiques actuels en termes de bande passante résulte en un besoin d exploiter la capacité offerte par la fibre optique. Un des moyens indispensable pour permettre ceci est l utilisation du multiplexage en longueur d onde. Il en résulte la nécessité d utilisation de dispositifs, parmi lesquels le filtre optique, agiles en longueur d onde et transparents par rapport aux débits. C est dans ce contexte que notre travail se situe. La technologie utilisée est celle des filtres interférentiels en polarisation. Contraint par un cahier des charges particulier aux applications télécoms, le principal objectif consiste en l augmentation des performances de ce type de filtre d une part, et l association de fonctionnalités additionnelles nécessaires dans les réseaux d autre part. En utilisant le principe physique des interférences en polarisation, une structure est alors implémentée, suivant les contraintes liées aux trois paramètres majeurs du filtre que sont le contraste, la fonction d égalisation et la reconfiguration de la bande passante. Par ailleurs, les architectures des filtres optiques diffèrent selon l emplacement dans le réseau. Ainsi, si une architecture des plus simples est utilisée à la réception, au niveau des nœuds du réseau, celle-ci devient beaucoup plus complexe, s adaptant à différents degrés de nœuds, et portent le nom de multiplexeurs optiques à insertion/extraction de longueur d onde (ROADM). Un dispositif de ce type, basé sur les filtres biréfringents, est donc présenté. Une approche système est ensuite menée dans le but de mettre en évidence les avantages et les limitations de la technologie utiliséeThe growing needs, in term of bandwidth in optical networks, increase over years. To satisfy these needs, the entire bandwidth of the optical fiber has to be exploited. In this context, the wavelength division multiplexing technique is used to allow the utilization of several wavelengths and results in considerably enhanced network bit-rate. However, such networks must use specific components which have particular wavelength-capabilities. Among these components, one of the most important and critical device is the optical filter. Our work is focused on the implementation of specific optical filters, using the polarization interference filter technology. The main purpose of this work is to enhance the filter rejection ratio, and to add new functionalities such as the amplitude equalization and the bandwidth tuning functions. After satisfying optical network expectations, another point, related to the filter utilization in the network, concern the device architecture which is determined by its network-location. A simple architecture with an input and an output is needed at the reception; meanwhile, a specific one is expected at network nodes. Thus, a new kind of devices is introduced, called reconfigurable optical add/drop multiplexers (ROADM). Therefore, such a device is implemented by the birefringent filter developed in this manuscript. Then, the developed device is placed in a transmission chain, and simulation results underline its limitations, by proceeding to comparison between this structure and typical optical filters. As conclusion of this work, some solutions and perspectives are presented, and very interesting challenges are highlightedEVRY-INT (912282302) / SudocSudocFranceF

Integration of chaotic sequences uniformly distributed in a new image encryption algorithm

a new image encryption algorith

Performances of a tunable birefringent filter for high density multi-wavelength applications

International audienceWe propose the use of an alternative technology to implement the optical filters dedicated for high density multi-wavelength applications: the Polarization Interference Filters (PIFs) and particularly the Lyot filters, which constitute a very interesting solution owing to their simplicity. To reach the optical network application requirements, in term of contrast, FWHM, and equalization function, we introduce a modified Lyot filter. The proposed device is a simple N-interferometer Lyot filter placed between two mirrors, to let the light beam pass through the structure back and forth. Two other interferometers, similar to the first Lyot filter interferometer, are added at the input of the filter, before the mirror. Each interferometer is composed by a retarder (calcite birefringent plate) held between two parallel polarizers. Each retarder is associated to a Liquid Crystal Cell (LCC), dedicated to the tuning function. The adequate contrast and FWHM of optical networks are attained by let the light beam passes through the filter several time and choosing judiciously the opto-geometrical characteristics of the retarders and the LCCs, respectively. The final simulation results of the filter, in the C-band (1530-1565nm), are 79,59dB and 0,84nm for the contrast and the FWHM, respectively. The equalization function is achieved continuously by changing the central-wavelength of the two additional interferometers, for continuous values of the LCCs birefringence. The dynamic is between 0 and 57,32dB (normalized values