Athermal design of hybrid refractive/harmonic diffractive optical system for far-infrared multi-band

摘要

In order to get enough information about the target, avoid big chromatic aberration as a result of wide spectrum and the complexity of optical system and adapt different special environment temperature, a hybrid refractive/ harmonic diffractive optical system in far-infrared multi-band is described in the paper. This diffractive optical system has been designed an athermalized multi-band imaging system with harmonic diffractive element in 15-50μm spectrum, based on larger dispersion capability and particular thermal dispersive power of harmonic diffractive element. Then, at the temperature range from 0°C to 40 °C, this design can simultaneously meet with all requirements of the imaging system in five harmonic wave bands, includingl5.8-16.2μm, 18.5-20μm, 23-25μm, 30.5-33.5μm and 46-50μm. In each harmonic wave band, the magnification changes as a function of wavelength, which creates image registration error. To compensate this shortcoming, a zoom optical system is designed with three lenses by means of optical two- component method. The design results show that the hybrid refractive/harmonic diffractive optical system can realize athennalized and achromatic design, and the zoom optical system makes half image height at 3.53mm in every harmonic wave band and still realizes aberration compensation action. In the five harmonic wave bands, each optical transfer function approaches the diffraction limit at ambient temperature range of 0°C to 40 °C. Finally, the system realizes the requirements of portability, mini-type and ease for fabrication.