A particular class of Montgomery's self-imaging objects that we call continuously self-imaging gratings (CSIG's) 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, CSIG's 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.

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This paper describes a new test bench for measuring the modulation transfer function of an infrared focal plane array. The system is based on the use of a plane target made of eight gratings that projects in polychromatic light a biperiodic pattern of small and non-diffracting spots called a nondiffracting array.

A test bench has been developed at the ONERA in order to measure the spectral responses of infrared focal plane arrays. This test bench can deliver hyperspectral cartographies with rather good resolutions (better than 16 cm -1 ) on large spectral ranges (from 1,3 µm to 20 µm). The principle of this test bench will be described and experimental results obtained with a 320x240 uncooled microbolometer array will be presented. As a conclusion, the ability of uncooled microbolometer arrays to make spectral measurements will be discussed..H\ZRUGV uncooled IRFPA, microbolometer, Fourier spectrometry ,1752'8&7,21At the Office National d'Etudes et Recherches Aérospatiales (ONERA), two activities are closely linked: the conception of instruments and the performance evaluation of infrared focal plane arrays (IRFPAs). In an instrument developed for applications like imagery and/or spectrometry, the key element is the FPA whose performances have to be calibrated. As an example, in the field of multispectral imaging, high-performance FPAs are in development with large formats (640x512) and tailor-made spectral responses (see for example [1]). For the design engineer and also for the technologist, accurate spectral calibrations are necessary to extract the spectral responses of the hundred of thousand pixels. For this, a test bench for the measurement of hyperspectral cartographies has been developed in our laboratory. This test bench can deliver measurements on a large spectral range (from 1.3 µm to 20 µm) with a rather good resolution (better than 16 cm -1 ). Using this test bench, an hyperspectral study has been made on a 640x512 FPA of QWIP technology working in the long-wavelength infrared (LWIR) domain. These hyperspectral measurements contain a wealth of information that make it possible to quantify the physical phenomena of diffraction and interference involved in the pixels and to adjust rigourous models developed by the technologists [2].This test bench whose characteristics are presented in the next Section has been used to make spectral measurements on a 320x240 uncooled IRFPA of microbolometers [3]. The goal was to estimate the disparity of spectral responses across the sensor. For the technologist, this information can be related to physical parameters like the spectral absorptivity of the quarter-wave cavity as absorber which depends on the thickness of this cavity. For the design engineer, these spectral measurements give interesting information on the potential of this technology for an application of spectrometry like the field measurements of radiance and emissivity using a stationary Fourier transform spectroradiometer [4].In this paper, we present the first results from an hyperspectral study performed on a 320x240 uncooled IRFPA of microbolometers. These first results are described in Section 3. As conclusion, the potential of this technology to make spectral measurements will be discussed. 7(67 %(1&+ &+$5$&7(5,67,&6This Section presents the technique developed at the ONERA for measuring the spectral respo...