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Continuous internal response calibration for FT-IR spectrometry

Calibration of Fourier transform infrared (FT-IR) spectrometer response is crucial to quantitative spectroradiometric measurements. The use of light emitting diodes (LEDs) as probes of detector channel response is further demonstrated. Detector channel response functions significantly impact spectrometer performance. LED modulation bandwidths, some extending well into the megaHertz (MHz) range, are more than fast enough for characterization of FT-IR detector channel responses. A variety of optical probe signals can be generated using LEDs driven by waveform generators, lock-in amplifiers or digital signal processors. Accurate determination of the phase and gain responses of both the IR signal and laser reference channels is straightforward. With appropriate modulation of the IR LEDs, channel response is measurable on a scan-by-scan basis, perhaps even to the point of accurately determining detector saturation in real time.