Absolute evaluation of the optical transfer function of the high aperture infrared cryogenic objective

Abstract

The field of infrared detectors is experiencing a strong movement towards smaller pixel pitches, and it is now common to see pitches close to the wavelength. This raises major problems in measuring their characteristics, especially their transfer function. The latter can be measured by optical pattern projection methods using a low F/# objective, such as the spot scan method. However, in order to obtain the quantitative transfer function measurement of detectors, the objective spatial response should be measured and deconvoluted precisely, since the size of the focused optical spot is close to the pixel pitch. Therefore, the purpose of this paper is to propose a protocol that performs an absolute measurement of a high-quality infrared objective. The main idea of the article is to link the measurement standard to a fundamental theory, the Huygens-Fresnel principle, using a particular wavefront sensor as a secondary measurement standard. This has various metrological advantages, that allow the uncertainties of the optical transfer function measurement to be controlled and evaluated. The protocol and the propagation of errors described in the article are both used to demonstrate the value of this approach.