Obtaining accurate spectral response measurements of a semiconductor-based photon detector with an FTIR: Properly correcting for the pyroelectric reference detector frequency response

Pyroelectric detectors are commonly used as the reference detector when measuring a photon detector’s spectral response using a Fourier-transform infrared (FTIR) spectrometer because their fundamental spectral response is independent of wavelength. However, their photoresponse also depends on modulation frequency and, because the moving mirror in the FTIR modulates each wavelength of light at a different frequency, this introduces a frequency-dependent attenuation to measured interferograms. Depending on FTIR mirror speed, this results in significant variations of over 20% in certain regions of measured spectra. This work presents a physics-based transfer function approach to correct for this frequency-dependent attenuation and obtain accurate spectral measurements. Transfer function parameters for two different DLaTGS pyroelectric detectors are derived from spectra acquired at various FTIR mirror speeds. These functions are shown to effectively remove the frequency-dependent perturbations, aligning the spectra independent of mirror speed. Applying the correction when calculating the spectral response of a semiconductor-based infrared photon detector of interest yields an accurate spectral shape, while uncorrected spectra exhibit an unphysical increase at shorter wavelengths. This transfer function correction method provides a robust solution for accurate spectral measurements using pyroelectric detectors in FTIR spectroscopy.