Polarization-modulation reflection-absorption spectra

The polarization modulation reflection absorption spectrum acquired using the SSD can therefore be written as... 

In PM IRRAS, the incident beam polarization is modulated between two orthogonal directions (a) perpendicular (s-polarization) and (b) parallel (p-polar-ization) to the plane of incidence of the infrared beam. At the metal surface, the electric field of the s-polarized infrared beam almost vanishes, while the electric field of the p-polarized beam is enhanced (see Fig. 9.3). Thus, the first component of the modulated signal is insensitive to the presence of the film of adsorbed molecules and can be used to obtain the background spectrum, while the other component can be utilized to obtain the spectrum of the film. Modulation between s- and p-polarizations is carried out at a high frequency (50 kHz), and the reflection absorption spectrum AR/(R) is obtained as... 

Although optical vibrational techniques are less sensitive than electron-based spectro-metric methods, these techniques are employed extensively for thin-film characterization because of the specific and characteristic vibrational spectrum shown by various functional groups and molecules present in the film. The most commonly used vibrational spectroscopic techniques are infrared (IR) and Raman spectroscopy. Because of the interference caused by absorption of IR by the underlying substrate, IR reflection-adsorption spectroscopy (IRRAS) and its polarization modulation (PM) analog, PM-IRRAS, which uses the polarization selectivity of surface adsorption, are typically employed to characterize thin films (Gregoriou and Rodman, 2006). 

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