Polarization-Modulation Spectrometry and its Application to Reflection-Absorption Measurements

Polarization-Modulation Spectrometry and its Application to Reflection-Absorption Measurements 

In this chapter, a sensitive method for measurement by continuous-scan Fourier-transform infrared (FT-IR) spectrometry called polarization-modulation spectrometry is introduced this is a useful method for measuring, with high signal-to-noise ratio, not only the reflection-absorption spectra of thin films adsorbed onto metal substrates but also other spectra such as vibrational circular dichroism (VCD) spectra. Polarization-modulation spectrometry is a type of double-modulation FT-IR spectrometry [1], In this chapter, descriptions of double-modulation spectrometry are given first, then polarization-modulation spectrometry is discussed, and then its application to the measurement of reflection-absorption spectra of thin films on metal substrates is discussed. 

Double-modulation FT-IR spectrometry may be considered a type of difference-spectrum measurement (see Section 6.2.3), which utilizes the Connes advantage characteristic of FT-IR spectrometry (i.e., measured wavenumbers are accurate and highly reproducible see Section 4.4.3) the infrared spectra of a sample containing a target material and a reference material are measured independently, and the spectrum of the target material is obtained by calculating the difference between the two spectra. This method is particularly 

Introduction to Experimental Infrared Spectroscopy Fundamentals and Practical Methods, First Edition. Edited by Mitsuo Tasumi and Akira Sakamoto. 

In this method, an operation is required for alternating between measuring the target sample and the reference sample at a frequency sufficiently higher than the modulation frequency inherent in an interferogram measured by an FT-IR spectrometer. By this operation, the difference spectrum and the sum spectrum can be obtained, respectively, as the alternating-current component and the direct-current component of the modulated signal. These two components can be separated by an electronic filter, and their ratio can then be calculated. 

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