Design principles and instrumentation for step-scan ftir
Step-scan, or step-by-step data collection in optical interferometry historically preceeded the rapid-scan method currently favored by commercial FTIR instrument manufacturers. Although rapid-scan data collection with opto-electronic sampling control has clearly been the key to the dramatic revival of FTIR, and of infrared spectroscopy in general, there are some experiments for which a return to step-scan techniques is a definite advantage. These include particularly experiments in which time resolution in the range of rapid-scan Fourier modulation periods is desirable. Step-scan FTIR differs from rapid-scan FTIR in the control of the mirror position and the timing of data collection. The rapid-scan mode involves moving the mirror continuously, and triggering data collection at evenly spaced intervals of the HeNe reference laser interference pattern. A particular advantage of rapid scanning is that minor fluctuations in the velocity of the mirror are compensated for during sampling. In contrast, with step-scan operation the mirror is stopped at, or vibrated about, each data collection point. This has the effect of uncoupling the spectral multiplexing from any temporal aspects of the experiment and makes step-scanning applicable to a wide range of dynamic spectroscopy. However, fluctuations in the mirror position are not easily compensated for and contribute to noise in the transformed spectra. The minimization of such sampling errors is the central challenge of step-scan interferometry. © 1989, SPIE.
Manning, CJ; Palmer, RA; Chao, JL
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