Differential absorption Mueller matrix spectroscopy and the infrared detection of crystalline organics

Abstract

The complete 16-element Mueller matrices for backscattering from amino acids, sugars, and other enantiomorphic compounds pressed into wafer form were measured at infrared wavelengths. For each compound a pair of CO(2) laser lines was selected from the 9.1-11.6-mum region such that one line excited an absorption band in the compound, whereas the other did not. It was observed that at least some of the matrix elements differed significantly depending on which of the two wavelengths was used in the measurement. We propose that a neural network pattern recognition system can be trained to detect the presence of specific compounds based on multiwavelength backscatter Mueller matrix measurements.

10.1007/s10786-008-2020-6

“…Let us analyze the informative output signal of the photodetector in the regime of spectropolarimeter operation with two polarization modulators using the conventional approach [8,9,12]. The initial state of polarization of the laser beam corresponds to the Stokes vector defined as Transformation of the initial Stokes vector by the entire optical system is described as a sequential product of this vector and the Mueller matrices of the corresponding elements of this system.…”

“…M [1] M [2] M [3] M [4] M [5] M [6] M [7] M [8] M [9] M [10] M [11] M [12] a constant factor). It should be noted that, owing to the small capacitance of modulators (<25 pF) and low frequency of the control signals, the output transformers operate virtually in an idle mode.…”

“…Polarimeters (ellipsometers) intended for the measurement of elements of the Mueller matrix employ polarization modulators (converters) representing combinations of phase plates (quarter-or half-wave plates) [2,3] or phase modulators (e.g., electro-optical modulators [4][5][6], including those based on liquid crystals [7] and elasto-optical [8][9][10] and magneto-optical [11] media). It is expedient to perform spectropolarimetric measurements using phase modulators, which allow exact adjustment of the phase shift (phase modulation depth) at every wavelength and exhibit a higher operation speed compared to that of the polarization converters based on rotary phase plates.…”

“…Carrieri et al [9] reported on the development of a middle-IR spectropolarimeter intended for the identification of organic compounds using the backscattering matrix; the instrument was based on a CO 2 laser, two elasto-optical polarization modulators, and a sophisticated electronic analog measuring system for multichannel lock-in detection and determination of the matrix elements. Carrieri et al [9] reported on the development of a middle-IR spectropolarimeter intended for the identification of organic compounds using the backscattering matrix; the instrument was based on a CO 2 laser, two elasto-optical polarization modulators, and a sophisticated electronic analog measuring system for multichannel lock-in detection and determination of the matrix elements.…”