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23 January 2003 Use of diffractive elements to improve IR optical systems
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Conventional optical elements have been replaced by diffractive ones in order to improve the performance of IR optical systems. Two examples are represented here.The first optical system is a MWIR scanning objective composed of air spaced doublet of CaF2 and As2S3 lenses. The combination of these materials gives an achromatic and passively athermalised optical system. It has been required to replace the As2S3 by an environmental approved material while retaining the achromatic and passively athermalised qualities. A new objective composed of ZnSe and Germanium lenses, where one of the Germanium surfaces is a diffractive one, has been designed to be also achromatic and passively athermalised. The two designs share similar optical performance. The second optical system is an objective for InSb Focal Plane Array Sensor at the MWIR spectral range. The optics includes ZnS, CaF2, Silicon and Germanium lenses. The requirement is to image a 1.06 micron laser spot on the InSb sensor. A new design composed of a front ZnS lens and 5 ZnSe lenses enables the transmittance of both the MWIR and the 1.06 micron spectral bands. Two diffractive surfaces are added to correct the chromatic aberration at the MWIR. A third diffractive surface enables focusing the 1.06 micron spot at the same plane as the MWIR image.
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Yitzhak Nevo, D. Nir, and Sylvie Wachtel "Use of diffractive elements to improve IR optical systems", Proc. SPIE 4820, Infrared Technology and Applications XXVIII, (23 January 2003);

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