Alain Kattnig

Demonstration of image-zooming capability for diffractive axicons

Diffractive axicons are optical components producing achromatic nondiffracting beams. They thus produce a focal line rather than a focal point for classical lenses. This gives the interesting property of a long focal depth. We show that this property can be used to design a simple imaging system with a linear variable zoom by using and translating a diffractive axicon as the only optical component.

Relevance of continuously self-imaging gratings for noise robust imagery

We have designed miniaturized, simple, and robust cameras composed of a single diffractive optical element (DOE) that generates a continuously self-imaging (CSI) beam. Two different DOEs are explored: the J0 Bessel transmittance, characterized by a continuous optical transfer function (OTF) and the CSI grating (CSIG), characterized by a sparse OTF. In this Letter, we will analyze the properties of both DOEs in terms of radiometric performances. We will demonstrate that the noise robustness is enhanced for a CSIG, thanks to the sparsity of its OTF. A camera using this DOE has been made and experimental images are presented to illustrate the noise robustness.

Model of the second-order statistic of the radiance field of natural scenes, adapted to system conceiving

An optimal imaging system must fulfill its specifications without an expensive and undue quality. However the translation of high-level human requirements into low-level system demands is not easy. As human specifications deal only with objects or scenes to be sen, the knowledge of these objects and its properties relevant to the information transfer through the imaging system is critical. As many imaging system quality criteria are based on the knowledge of second order statistical properties of scenes or objects to be imaged, the goal of this paper is to show that it is possible to extract these properties from high-level mission requirements.

Absorbing metasurface created by diffractionless disordered arrays of nanoantennas

We study disordered arrays of metal-insulator-metal nanoantenna in order to create a diffractionless metasurface able to absorb light in the 3–5 μm spectral range. This study is conducted with angle-resolved reflectivity measurements obtained with a Fourier transform infrared spectrometer. A first design is based on a perturbation of a periodic arrangement, leading to a significant reduction of the radiative losses. Then, a random assembly of nanoantennas is built following a Poisson-disk distribution of given density, in order to obtain a nearly perfect cluttered assembly with optical properties of a homogeneous material.

Image formation by use of continuously self-imaging gratings and diffractive axicons

When illuminated by a plane wave, continuously self-imaging gratings (CSIGs) produce a field whose intensity profile is a propagation- and wavelength-invariant biperiodic array of bright spots. In the case of an extended and incoherent source, we show that CSIGs produce multiple images of the source. The fundamental properties of these gratings will be derived. In particular, methods to assess the image quality in angle of CSIGs will be introduced. It turns out that this new type of pinhole-array camera works on the same principle as diffractive axicons, which are known to produce wavelength-invariant nondiffracting beams. The formalism developed for CSIGs will be also extended to axicons. CSIGs and axicons both produce focal lines and can be robust in field, in compensation of a trade-off with the resolution. They also offer interesting properties in terms of compactness, achromaticity and long depth of focus for imaging systems. However, compared to classical imaging systems, they produce degraded images and an image processing is necessary to restore these images. Experimental images obtained with these components in the visible and infrared spectral ranges will be presented.

SYSIPHE: focus on SIELETERS, the medium and longwave infrared spectral imaging instrument

Sysiphe is an airborne hyperspectral imaging system, result of a cooperation between France (Onera and DGA) and Norway (NEO and FFI). It is a unique system by its spatial sampling -0.5m with a 500m swath at a ground height of 2000m- combined with its wide spectral coverage -from 0.4μm to 11.5μm in the atmospheric transmission bands. Its infrared component, named Sieleters, consists in two high étendue imaging static Fourier transform spectrometers, one for the midwave infrared and one for the longwave infrared. These two imaging spectrometers have very close design, since both are made of a Michelson interferometer, a refractive imaging system, and a large IRFPA (1016x440 pixels). Moreover, both are cryogenic and mounted on their own stabilization platform which allows at once to actively control and independently measure the line of sigh. These data are useful to reconstruct and to georeference the spectral image from the raw interferometric images. Sysiphe first flight occurred in September, 2013.

A telescope design and performance analysis tool: the mission-quality criterion

We present a quality criterion for telescopes based on the fulfillment of observation needs as defined by a client. It is intended for the pre-conception and broad control level. The criterion is built from the fidelity measure by limiting the spatial scales taken into account to the scales useful to the proper imaging of the detail of interest. By construction this mono-dimensional criterion allows trade-off between spatial and radiometric resolution. The comparison of different design strategies is also possible, for example between undersampled large aperture telescopes and well sampled smaller telescopes. It can also be used to predict the usefulness of each available telescope for a given observational purpose. Being global, the criterion requires only high-level specifications, thus allowing the client to exercise a greater degree of control over the instrument definition. We present here a pre-calibration of the mission quality criteria enabling to give an absolute quality value for the telescope and to determine whether the observation mission is fulfilled. A comparison of test-case telescopes is then made by varying several design parameters.

Mission-driven evaluation of imaging system quality

Image-quality criteria are usually intended to achieve the best possible image at a given sampling rate, which is ill-suited to applications where the detection of well-defined geometric and radiometric properties of scenes or objects are paramount. The quality criterion developed here for designing observation systems is based on properties of the objects to be viewed. It is thus an object-oriented imaging quality criterion rather than an image-oriented one. We also propose to go beyond optimization and calibrate a numerical scale that can be used to rate the quality of the service delivered by any observation system.

SYSIPHE, airborne hyperspectral system: Focus on the SIELETERS thermal hyperspectral imaging instrument

The SYSIPHE system is the state of the art airborne hyperspectral imaging system developed in European cooperation. With a unique wide spectral range and a fine spatial resolution, its aim is to validate and quantify the information potential of hyperspectral imaging in military, security and environment applications. The first section of the paper recalls the architecture of the project. The second one describes the SIELETERS sensors, their implementation onboard the platform and the data processing chain. The last section gives illustrations on the work in progress.

Sieleters, an airbone Imaging Static Fourier Transform Spectrometer: design and preliminary laboratory results

Sieleters is an airborne hyperspectral imager, composed of two cryogenic instruments (MWIR and LWIR), both based on a static interferometer. Its first flight is expected for June, 2013. We present design details and preliminary laboratory results.