The invention relates to two modified Petzval infrared two-band detecting optical system which is infrared two-band monolayer harmony diffraction optical system and the infrared two-band double harmony diffraction optical system. The monolayer includes the refractor and the refraction/harmony diffraction mixed lens; the double harmony diffraction optical system includes the refractor and the double refraction/harmony diffraction mixed lens. The infrared two-band monolayer harmony diffraction optical system is to lead the harmony diffraction lens into the infrared single-range Petzval objective lens system to reach the dual spectrum detection of middle-infrared 3.4-4.2 mum and thermal infrared 8-11 mum. The infrared two-band double harmony diffraction optical system can improve the diffraction efficient by the double harmony diffraction element. So the diffraction efficient can reach to above 90% in the invention, the image surface contrast has been improved, so it provides a new device for the infrared system. |