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DSP-Based Modular Rapid and Step-Scan
1Christopher J. Manning, 2Linda H. Kidder, 3William
4Ira W. Levin, 4E. Neil Lewis
1Manning Applied Technology, 121 Sweet Avenue, Moscow, ID
Contact info is out of date
2Spectral Dimensions Inc., 3403 Olandwood Court, Suite 102,
Olney, MD 20832
3Oriel Instruments Inc., 150 Long Beach Boulevard, Stratford,
4Laboratory of Chemical Physics, National Institute of Diabetes
and Digestive and Kidney Diseases, National Institute of Health, Bethesda,
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.