Enhanced step mode FTIR position control

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Montana State University - Bozeman, College of Engineering


This thesis presents a modification to a typical Fourier transform infrared (FTIR) spectrometer to achieve finer spatial sampling and increased frequency range for step-scan experiments with little modification to the existing hardware. Commercially available step-scan FTIR spectrometers currently have the ability to measure spectra up to 15798 cm_1, which is limited by a HeNe reference laser used for controlling the mirror's position. The proposed technique involves using a digital signal processor (DSP) to measure the HeNe reference signal and estimate the mirror position. The DSP then outputs a new synthetic signal that is used by the spectrometer to control the mirror to finer steps, allowing it to measure spectrums up to 47394 cm_1. Enhanced closed-loop mirror position data is presented to show the quality of the DSP estimate along with spectrograms taken of an erbium crystal to show the overall spectral improvements. To validate the erbium crystal enhanced step-scan spectrogram, a continuous scan experiment is given for comparison. The results demonstrate previously unattainable step-scan performance.




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