ABSOLUTE DETECTOR CALIBRATION APPLIED TO NONLINEARITY ERROR-CORRECTION IN FT-IR MEASUREMENTS

A method for correcting the effects of detector nonlinearity in Fourie r transform infrared (FT-IR) spectrometers has been developed, The met hod incorporates directly measured results, No adjustable parameters a re used. The absolute responsivity of two HgCdTe (MCT) detector/preamp lifier systems as a function of incident photon flux was calibrated ag ainst a transfer-standard Ge detector with a diode laser source at 1.3 2 mu m With the use of the MCT detector, preliminary measurements were made on an FT-IR spectrometer in both the near- and mid-infrared spec tral regions, The measured nonlinear interferograms were corrected by using the detector response curve and the measured de output of the pr eamplifier. Ln the resultant spectra, the nonzero values in the spectr al region below the detector cutoff frequency mere significantly reduc ed when the corrected interferograms were used, The transmittance spec tra of a Si wafer and a neutral-density filter mere measured with an M CT detector and a deuterated triglycine sulfate (DTGS) detector, Error s in transmittance caused hy detector nonlinearity were greatly reduce d with the use of the correction method.