Jérôme Primot

Deconvolution from wave-front sensing: a new technique for compensating turbulence-degraded images

A new technique of high-resolution imaging through atmospheric turbulence is described. As in speckle interferometry, short-exposure images are recorded, but in addition the associated wave fronts are measured by a Hartmann–Shack wave-front sensor. The wave front is used to calculate the point-spread function. The object is then estimated from the correlation of images and point-spread functions by a deconvolution process. An experimental setup is described, and the first laboratory results, which prove the capabilities of the method, are presented. A signal-to-noise-ratio calculation, permitting a first comparison with the speckle interferometry, is also presented.

Achromatic three-wave (or more) lateral shearing interferometer

A new kind of lateral shearing interferometer, called the three-wave lateral shearing interferometer, was previously described [ Appl. Opt.32, 6242 ( 1993)]. As this instrument was monochromatic and its usable light efficiency was poor, the proposed setup was well suited only for a class of wave-front sensing problems, such as optical testing, in which the source can be easily adapted. A new achromatic setup adapted to low light level applications is presented. Three replicas of the analyzed wave front are obtained by Fourier filtering of the orders diffracted by a microlens array. An important feature of these new devices is their great similarity to another class of wave-front sensors based on the Hartmann test.

Wave-front reconstruction from multidirectional phase derivatives generated by multilateral shearing interferometers.

To increase the accuracy of wave-front evaluation, we propose to exploit the natural capability of multiple lateral shearing interferometers to measure simultaneously more than two orthogonal phase derivatives. We also describe a method, based on Fourier-transform analysis, that uses this multiple information to reconstruct the wave-front under study.

Collective coherent phase combining of 64 fibers

A new architecture for active coherent beam combining of a large number of fibers is demonstrated. The approach is based on a self-referenced quadriwave shearing interferometer and active control with arrays of electro-optic ceramic modulators. Coherent phase combining of 64 independent amplified fibers is obtained. This is to our knowledge the highest reported number of combined fibers. A Strehl ratio degradation less than 2dB is achieved with a residual phase error

Theoretical description of Shack-Hartmann wave-front sensor

Abstract In this paper, we propose a complete model of Shack–Hartmann wave-front sensor, seen as a grating interferometer. A new technique for extracting the phase derivative is also proposed and the exact quantity measured is detailed.

Three-wave lateral shearing interferometer.

The three-wave lateral shearing interferometer is an interferometer specially designed for optical testing. It determines three noncollinear phase gradients from one single-fringe pattern. From these quantities, two orthogonal derivatives and the measurement error are estimated, allowing the reconstruction of the aberrated wave front. This new interferometer has several benefits; among them is that its sensitivity and dynamics can be easily adjusted to the analyzed aberrations.

Talbot experiment re-examined: demonstration of an achromatic and continuous self-imaging regime

In the original Talbot experiment, a grating made of thin slits was illuminated in polychromatic light. Reconstituting this simple experiment, we have observed that at a certain distance from the grating, achromatic lines are formed whose transverse-resolution remains unaffected over a wide propagation-distance range. To our knowledge, this phenomenon has never been reported before. A theoretical explanation of this achromatic and continuous self-imaging regime is given and experimental results are reported.

Generation of achromatic and propagation-invariant spot arrays by use of continuously self-imaging gratings

A particular class of Montgomerys self-imaging objects that we call continuously self-imaging gratings (CSIGs) is introduced. When they are illuminated by a plane wave, these objects produce a field whose intensity profile is a propagation- and wavelength-invariant biperiodic array of bright spots. The mathematical construction of these objects and their intrinsic properties are described. On a practical level, CSIGs are compact and achromatic nondiffracting array generators. We show that a good CSIG approximation can be realized by a two-level phase grating that is experimentally tested.

Experimental results from an airborne static Fourier transform imaging spectrometer

A high étendue static Fourier transform spectral imager has been developed for airborne use. This imaging spectrometer, based on a Michelson interferometer with rooftop mirrors, is compact and robust and benefits from a high collection efficiency. Experimental airborne images were acquired in the visible domain. The processing chain to convert raw images to hyperspectral data is described, and airborne spectral images are presented. These experimental results show that the spectral resolution is close to the one expected, but also that the signal to noise ratio is limited by various phenomena (jitter, elevation fluctuations, and one parasitic image). We discuss the origin of those limitations and suggest solutions to circumvent them.

Demonstration of an infrared microcamera inspired by Xenos peckii vision

We present an original and compact optical system inspired by the unusual eyes of a Strepsipteran insect called Xenos peckii. It is designed for a field of view of 30 degrees and is composed of multiple telescopes. An array of prisms of various angles is placed in front of these telescopes in order to set a different field of view for each channel. This type of camera operates in the [3-5 microm] spectral bandwidth and is entirely integrated in a Dewar in order to maximize its compactness. Experimental images are presented to validate this design.