An infrared interferometer with a broadband wavelength channel

•This paper analyses an infrared interferometer with a broadband wavelength channel.•π/4 phase-shifting averaging technique is raised, aiming at multi-beam interference.•Restrictions on misalignment error due to off-axis parabolic mirror are proposed.

A Fizeau infrared interferometer designed and built with a broadband wavelength channel ranging from mid-wave infrared to long-wave infrared is described. The exchange of working wavelengths from 4.41 μm to 10.6 μm is provided because the elements making up the optical paths are reflectors or beam splitters, together with the relay lenses and imaging lens for chromatic aberrations correction, which also realize the reimaging technique to permit the high cold stop efficiency. An elaborate dual-triangle optical path design is applied to share one detector for both alignment and view. On the premise of online calibration of the piezoelectric transducer, π/4 phase-shifting averaging technique is applied for compensation of ripple error introduced by multi-beam interference due to high reflectivity of infrared test optics, with simulative and experimental validation. Besides, considering the small field of view of the off-axis parabolic mirror as the beam collimator, the restrictions of misalignment indicated by carrier fringes are given through model of ray tracing, which guarantees the performance of the infrared interferometer with accuracy better than PV 0.05λ and rms 0.01λ.