Design of a catadioptric mid-wave infrared telecentric microscope with high numerical aperture and long working distance

Abstract

Infrared microscopy is widely used in the field of thermal analysis. This paper proposes a design method for a catadioptric mid-wave infrared telecentric microscope system that solves the problem of traditional microscopy systems being unable to simultaneously meet high numerical aperture, long working distance and large magnification requirements. The system is composed of a microscope objective and a tubelens. The objective uses an improved Schwarzschild structure and is connected to the tubelens through an externally located pupil. The system works in the wavelength range of 3.7 μm–4.8 μm, achieves a 0.82 numerical aperture, a 15.5 mm working distance, an 8× magnification and a 2.75 μm object-side resolution. The image size of the detector is 17um, and the MTF of the microscope system at the detector cutoff frequency is greater than 0.2, which is close to the diffraction limit. Finally, tolerance analysis and athermal analysis are conducted on the system, and the results indicate that the system possesses good manufacturability and thermal stability.