Atmospheric Turbulence Compensation with Laser Phase Shifting Interferometry

Laser guide stars with adaptive optics allow astronomical image correction in the absence of a natural guide star. Single guide star systems with a star created in the earth's sodium layer can be used to correct the wavefront in the near infrared spectral regime for 8-m class telescopes. For possible future telescopes of larger sizes, or for correction at shorter wavelengths, the use of a single guide star is ultimately limited by focal anisoplanatism that arises from the finite height of the guide star. To overcome this limitation we propose to overlap coherently pulsed laser beams that are expanded over the full aperture of the telescope, traveling upwards along the same path which light from the astronomical object travels downwards. Imaging the scattered light from the resultant interference pattern with a camera gated to a certain height above the telescope, and using phase shifting interferometry we have found a method to retrieve the local wavefront gradients. By sensing the backscattered light from two different heights, one can fully remove the cone effect, which can otherwise be a serious handicap to the use of laser guide stars at shorter wavelengths or on larger telescopes. Using two laser beams multiconjugate correction is possible, resulting in larger corrected fields. With a proper choice of laser, wavefront correction could be expanded to the visible regime and, due to the lack of a cone effect, the method is applicable to any size of telescope. Finally the position of the laser spot could be imaged from the side of the main telescope against a bright background star to retrieve tip-tilt information, which would greatly improve the sky coverage of the system.Comment: 11 pages, 10 figure

Holographic Imaging of Crowded Fields: High Angular Resolution Imaging with Excellent Quality at Very Low Cost

We present a method for speckle holography that is optimised for crowded fields. Its two key features are an iterativ improvement of the instantaneous Point Spread Functions (PSFs) extracted from each speckle frame and the (optional) simultaneous use of multiple reference stars. In this way, high signal-to-noise and accuracy can be achieved on the PSF for each short exposure, which results in sensitive, high-Strehl re- constructed images. We have tested our method with different instruments, on a range of targets, and from the N- to the I-band. In terms of PSF cosmetics, stability and Strehl ratio, holographic imaging can be equal, and even superior, to the capabilities of currently available Adaptive Optics (AO) systems, particularly at short near-infrared to optical wavelengths. It outperforms lucky imaging because it makes use of the entire PSF and reduces the need for frame selection, thus leading to higher Strehl and improved sensitivity. Image reconstruction a posteriori, the possibility to use multiple reference stars and the fact that these reference stars can be rather faint means that holographic imaging offers a simple way to image large, dense stellar fields near the diffraction limit of large telescopes, similar to, but much less technologically demanding than, the capabilities of a multi-conjugate adaptive optics system. The method can be used with a large range of already existing imaging instruments and can also be combined with AO imaging when the corrected PSF is unstable.Comment: Accepted for publication in MNRAS on 15 Nov 201

Validazione di Piani di Disaster Recovery mediante Simulatore

Contribution published online at: http://www.mimos.it/nuovo/contenuto_view.asp?check=10

UV-induced expression of key component of the tanning process, the POMC and MC1R genes, is dependent on the p-38-activated upstream stimulating factor-1 (USF-1).

Protection against UV-mediated DNA damage and the onset of oncogenesis is afforded by the tanning response in which UV irradiation triggers melanocytes to increase production of melanin that is then transferred to keratinocytes. A key component of the tanning process is the UV-mediated induction of the pro-opiomelanocortin (POMC) and MC1R genes encoding the alpha-melanocyte-stimulating hormone and its receptor, respectively, which play a crucial role in pigmentation by regulating the intracellular levels of cAMP. How these genes are regulated in response to UV irradiation is not known. Here we have shown that UV-induced activation of the POMC and MC1R promoters is mediated by p38 stress-activated kinase signaling to the transcription factor, upstream stimulating factor-1 (USF-1). Importantly, melanocytes derived from USF-1 -/- mice exhibit a defective UV response and fail to activate POMC and MC1R expression in response to UV irradiation. The results define USF-1 as a critical UV-responsive activator of genes implicated in protection from solar radiation

Overview of alternative infrared detectors and focal plane arrays for LWIR applications

For a variety of scientific, space and defence applications, there is an increasing demand for long-wavelength infrared (LWIR) detector focal plane arrays and compact infrared instruments. In the first part, we present an overview of alternative detectors to standard mercury cadmium telluride photodiodes for LWIR detection, such as the HgCdTe avalanche photodiode, the quantum-well infrared photo-detectors, the superlattice detectors and the carbone nanotubes-based bolometers. In the second part, we focus on new concepts developed to meet the requirement of miniaturization of infrared instruments. Original IRFPA-based micro-optical assemblies have been achieved, demonstrating several optical functions such as imagery, spectral filtering, spectrometry and wavefront sensing

Multi-Lateral Shearing Interferometry: Principle and Application to X-Ray Phase Imaging

International audienc

Study of the MTF of a MWIR T2SL focal plane array in IDDCA configuration

International audienceType-II InAs/GaSb superlattice (T2SL) has recently matured into a commercially available technology addressing both MWIR and LWIR spectral domains. As the prerequisites such as Quantum Efficiency (QE) and dark current were met, more advanced figures of merits related to the ElectroOptic (EO) system as a whole can now be studied to position this technology. In this paper, we focus on modulation transfer function (MTF) measurements. Knowing the MTF of a detector is indeed of primary importance for the EO system designers, since spatial filtering affects the system range. We realized MTF measurements on a 320 × 256 MWIR T2SL FPA provided by IRnova, using a Continuously Self Imaging Grating (CSIG). The advantage of this experimental configuration is that no high performance projection optics is required thanks to the self-imaging property (known as Talbot effect) to project a pattern with known spatial frequencies on the photodetector. Besides, the pattern being propagation invariant, alignment is easier and the bench does not require exact knowledge of the focal plane distance to operate, opening measurement in Integrated Detector Dewar Cooler Assembly (IDDCA) configuration. Extracted from measurements, the pixel size is 26 µm for a pitch of 30 µm