25 September 2014 Research on properties of an infrared imaging diffractive element
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Abstract
Novel thermovision imaging systems having high efficiency require very sophisticated optical components. This paper describes the diffractive optical elements which are designed for the wavelengths between 8 and 14 μm for the application in the FLIR cameras. In the current paper the authors present phase only diffractive elements manufactured in the etched gallium arsenide. Due to the simplicity of the manufacturing process only binary phase elements were designed and manufactured. Such solution exhibits huge chromatic aberration. Moreover, the performance of such elements is rather poor, which is caused by two factors. The first one is the limited diffraction efficiency (c.a. 40%) of binary phase structures. The second problem lies in the Fresnel losses coming from the reflection from the two surfaces (around 50%). Performance of this structures is limited and the imaging contrast is poor. However, such structures can be used for relatively cheap practical testing of the new ideas. For example this solution is sufficient for point spread function (PSF) measurements. Different diffractive elements were compared. The first one was the equivalent of the lens designed on the basis of the paraxial approximation. For the second designing process, the non-paraxial approach was used. It was due to the fact that f/# was equal to 1. For the non-paraxial designing the focal spot is smaller and better focused. Moreover, binary phase structures suffer from huge chromatic aberrations. Finally, it is presented that non-paraxially designed optical element imaging with extended depth of focus (light-sword) can suppress chromatic aberration and therefore it creates the image not only in the image plane.
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M. Rachoń, M. Rachoń, K. Węgrzyńska, K. Węgrzyńska, M. Doch, M. Doch, A. Kołodziejczyk, A. Kołodziejczyk, A. Siemion, A. Siemion, J. Suszek, J. Suszek, K. Kakarenko, K. Kakarenko, M. Sypek, M. Sypek, } "Research on properties of an infrared imaging diffractive element", Proc. SPIE 9192, Current Developments in Lens Design and Optical Engineering XV, 919219 (25 September 2014); doi: 10.1117/12.2061137; https://doi.org/10.1117/12.2061137
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