High resolution spectrally resolved interferometry in the mid-IR

One of the most widespread and reliable techniques for spectral phase characterization of optical elements is spectrally resolved interferometry (SRI) [1] , [2] , which utilizes a two-arm interferometer illuminated by a broadband light source and a spectrometer to record the generated spectral fringes. The investigated optical element is placed in one arm, and its spectral phase can be extracted by using Fourier-transform (FT) based methods [3] , [4] for instance, which are the most accurate, even when low dispersion values are to be determined. One detriment to this evaluation method, that it requires high spectral resolution. Considering that most of the spectrometers in the mid-infrared (MIR) region have typically a few nm spectral resolution, we propose two alternative methods for measurements in this spectral region.