Ellipsometric Raman Spectroscopy

Abstract

We introduce a new experimental technique referred to as ellipsometric Raman spectroscopy (ERS) to quantify the Raman optical activity (ROA) where ellipsometry is combined with Raman spectroscopy. The Stokes parameters were determined for Raman scattered light using Fourier decomposition in measurements with achromatic optical components in a nine-point method. We tested the methodology with ultrapure water, a well-known chiral alcohol, and a chiral polymer, and we show that ERS allows for studying not only the vicinities of chiral carbons but also molecular species coupled to form chiral structures. Furthermore, in ERS, isotropic and anisotropic scattering contribute equally, thus making it possible to analyze the low-wavenumber region in samples such as the chiral polymer studied here, for which the ROA signal probably arises mainly from isotropic scattering.

Achromatic Ellipsometry: Theory and Applications

“…In 1946, the Nobel laureate Subrahmanyan Chandrasekhar formulated the equations for radioactive transfer of partially polarized light [12], which was only possible due to Stokes' work. In addition to Stokes theory, new material developments for achromatic optical elements made possible the measuring of all polarization states as a function of wavelengths (optical spectrum), i.e., the necessary observables to enlighten the materials structure [2,13,14,17,18].…”

“…It allows the characterization of several states of light polarization using one equation [14,18] and can result in forms interpreted as linearly and circularly polarized light. Beyond that, from the concept of polarization ellipse, it is possible to understand Stokes' description to identify all states of light polarization, including partially polarized beams [12].…”

“…In this matrix formalism, the effects on the light polarization from any beam due to optical components can be mathematically represented also by matrix, in this case, the Muller matrix [12,14]. Concerning the fixed optical components, the analysis method via Fourier series employs a quarter-wave plate and a fixed linear polarizer, as can be seen in Figure 2.…”

“…In addition, it is possible to obtain full information regarding molecular organization [2,12], anisotropy [10], and asymmetry [13] factors in photoluminescent materials. All these studies and several applications in diverse materials lead to the development of a new method for Raman Optical Activity studies, named ellipsometric Raman spectroscopy (ERS) [14,15]. In this new methodology, Basilio et al [14] have been shown that EE combined with the Stokes theory can also be applied, not only for emitted but also for the scattered light.…”

“…All these studies and several applications in diverse materials lead to the development of a new method for Raman Optical Activity studies, named ellipsometric Raman spectroscopy (ERS) [14,15]. In this new methodology, Basilio et al [14] have been shown that EE combined with the Stokes theory can also be applied, not only for emitted but also for the scattered light. From this experiment, one can obtain meaningful information about materials optical activity even for easily photodegradable ones (both biological and polymeric) due to the limited exposition to exciting light.…”