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A modular commercial FT-IR spectrometer has been modified for step-scan operation by the addition of a digital signal processor (DSP) and a high dynamic range analog-to-digital converter (ADC).  The system consists of one DP accessory  card residing in PC bus, one interface card in the optical bench, and an optional breakout box where signals may be conveniently accessed for experimental interface.  The simplicity of the hardware components is compensated by translating system complexity into the DSP and PC software.  While the execution speed of software algorithms is invariably slower than dedicated hardware,  the continuing exponential increase in computing speed has made this an acceptable tradeoff.  Virtually the entire functionality of the spectrometer is encoded in software.

The performance of the system compares favorably with theoretical predictions.  The outstanding performance of the ADC and DSP are essential to this excellent performance.  New developments in DSP are described which allow very rapid and accurate correction for the effects of velocity and position errors, further improving performance.  This novel system is suitable for a variety of measurements including spectral imaging and time-resolved spectroscopy over a wide range of time-scales.  Other traditional step-scan measurements such as photoacoustic spectrometry and sample modulation measurements, as well as conventional rapid-scan FT-IR spectrometry, are also supported.  Results are shown for a variety of measurements including open beam spectra and 100% lines in both step-scan and rapid-scan operation.  Results obtained in spectral imaging application are shown.  Polymer stretching and photoacoustic application are discussed.