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A model for interpreting depth profiles of confocal Raman measurements in reflective and transmitting materials
Author(s) -
Chakraborty Subha,
Kahan Tara F.
Publication year - 2019
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.5686
Subject(s) - optics , raman spectroscopy , gaussian beam , refractive index profile , gaussian , paraxial approximation , focus (optics) , wavelength , refractive index , rayleigh scattering , materials science , confocal , excitation , beam (structure) , physics , quantum mechanics
We present a model and experimental evaluation of the depth profiles of total intensity in confocal Raman microscopy. The model assumes a Gaussian‐like beam for excitation and Raman emission to obtain a general description of the depth profile from an arbitrary sample. For samples that emit from the surface (i.e., that do not transmit light at the excitation wavelength), this model simplifies to a Lorenzian depth profile from which Rayleigh range can be extracted by the half‐width at half maxima. We extend the model to the case of transparent samples that offer significant refractive index mismatch across the surface. We show that in these cases, the axial increase of depth of focus can be approximated by two Gaussian foci, one at the paraxial focus and one at an oblique focus. This model accurately describes experimentally observed depth profiles of reflective samples and transparent samples. We further extend the analysis to the case of thin transparent films to demonstrate that the model can be used in conjunction with physical measurements to produce accurate measurements of film thickness.