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20 December 1985 Modulation Spectroscopy
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Proceedings Volume 0553, Fourier and Computerized Infrared Spectroscopy; (1985)
Event: 1985 International Conference on Fourier and Computerized Infrared Spectroscopy, 1985, Ottawa, Canada
Polarization modulation can be used to obtain infrared (IR) spectra of any sample which absorbs light of two orthogonal polarizations to different extents. Examples of applications include vibrational circular dichroism (VCD), infrared reflection-absorption spectroscopy (IRRAS), infrared linear dichroism of statically-oriented samples, and time-dependent dynamic infrared linear dichroism (DIRLD) of samples under small-amplitude oscillatory strain. Modulation spectroscopy can be performed on either Fourier transform or dispersive IR spectrometers. A photoelastic modulator (PEM) placed in a linearly-polarized beam of light can alternate the state of polarization at frequencies on the order of 50 kHz. This enables a small difference signal to be obtained in a single measurement without having to subtract or ratio two separately-measured large signals. The principles of polarization modulation are developed and examples of VCD, IRRAS, and DIRLD presented.
© (1985) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Isao Noda, A. E. Dowrey, and Curtis Marcott "Modulation Spectroscopy", Proc. SPIE 0553, Fourier and Computerized Infrared Spectroscopy, (20 December 1985);

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