A wide-band dual-field optical system working at 1-5μm is designed. The freeform off-axis three-mirror optical structure is adopted for the narrow field design with adding a plane mirror to fold the optical path. The focal length is 600mm, the f-number is 6, and the field of view is 2.34°×2.34°. The wide field is designed with a lens group, where the focal length is 17.3mm, the f-number is 2, and the diagonal field of view is 30°. In terms of arrangement, a hole is dug in the center of the primary mirror of the off-axis three-mirror system as the clear aperture of the lens group, so as to realize simultaneous imaging of the same target through both optical paths.
The design of the Diffractive/Refractive optical system needs to strictly control the ghost image. It is proposed to divide the ghost caused by the strong light source and the field of view. For the ghost image caused by strong light sources in the field of view, in order to reduce the computational amount, the optical surface that can produce serious ghost is selected by Code V, the optical system is modeled in ASAP and gives appropriate refraction and diffraction properties to the optical working surface, and the light source with different incident angles is set to light trace to obtain the location and energy information of the ghost image. For ghosts caused by a strong light source outside the field of view, the scanning light source is directly set up for light tracing, and the transmission path of the ghost image is extracted according to the ghost location and intensity information of the focal surface to provide reference for the subsequent ghost suppression.
KEYWORDS: Infrared radiation, Signal to noise ratio, Infrared imaging, Sensors, Ray tracing, Code v, Reflection, Black bodies, Interference (communication), Monte Carlo methods
Narcissus of cooled infrared system should be controlled strictly. So, accurate and rapid analysis of narcissus is very important. Deriving the SNR of narcissus based on the definition of noise equivalent power. Using simulation software CodeV and ASAP analyses the narcissus. Screen out the optical surface whose narcissus is serious in CodeV. Then build the model of the system in ASAP and add reasonable surface properties, get the result of size and average irradiance of the image narcissus spot by real ray tracing. Calculate the SNR of narcissus by putting the value of average irradiance into front formulation. On this basis, the simulation analysis and experimental test about the Narcissus of an infrared lens were performed. The experimental result is consistent with the simulation analysis.
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