A COMPARISON BETWEEN FOURIER TRANSFORM SPECTROSCOPY AND CONVENTIONAL SCANNING TECHNIQUES.
Tomas B. Hirschfeld, Peter R. Griffiths · The Knowledge Bank (The Ohio State University) · 1969
Recent advances in Fourier Transform Spectroscopy have brought this technique into direct competition with scanning spectrophotometers over the $3-1000 \\mu$ infrared range. These advances stem mainly from the combination of a small built-in digital computer for direct spectrum display and closed loop operation and a laser beam referenced interferometer of high resolution $(0.5 cm^{-1})$ and large aperture $(2 1/2^{\\prime})$. With this instrument $2.8-20 \\mu$ double-beam spectra can be obtained in 30 sec to 5 min at constant resolutions of $2 cm^{-1}$ to $0.5 cm^{-1}$. The instrument has been used to study very small (100 nanogram) or very opaque (blank cell transmission $<1%$) samples, and an interchange for work out to $1000 \\mu$ is available. Various features of this instrument are radical new departures from existing instrumentation. All control knobs are absent, the desired spectral parameters being typed into the system, after which the computer attends to all necessary instrument settings. The double beam uses a digital electronic ratio system, eliminating the difficulties of optical null or analogrationing. Stray light is nonobservable and polarization effects are barely visible, while frequncy accuracy to 0.1 $cm^{-1}$ is maintained by the laser calibration interferometer. A pyroelectric detector assures high speed, and a feedback regulated source provides stability. The absence of long optical levers reduces cell wedging and scattering effects. The built in computer provides a very powerful data handling capability. Signal averaging, automatic scale expansion, and baseline corrections for single beam work if desired are all available. Future instruments will include deconvolution of slit width, peak integration, peak printout, and reflectance calculation software.