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Spatial Heterodyne Raman Spectroscopy for Planetary Surface Exploration.

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Title:Spatial Heterodyne Raman Spectroscopy for Planetary Surface Exploration.
Authors:Egan, Miles J.
Contributors:Chemistry (department)
Keywords:spatial heterodyne spectrometer
Raman spectroscopy
Fourier transform
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Date Issued:May 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:Raman scattering is a phenomenon characterized by the inelastic scattering of light by a
molecule that has a normal mode of vibration capable of producing an instantaneous
induced dipole moment when radiation is incident upon said molecule. The activity of
vibrational modes in the Raman spectrum can be predicted via group theory by first
identifying all the symmetry elements of a molecule or mineral, classifying said molecule
into a point or space group, followed by removal of superfluous degrees of freedom and
finally disambiguation of the vibrational degrees of freedom into irreducible
representations. A vibrational mode is active in the Raman (IR) spectrum if the vibrational
mode, as represented by an irreducible representation, contains a change in polarizability
(change in dipole moment).
In recent years, advancements in the speed, sensitivity and size of excitation sources,
spectrographs and detectors has allowed the application of Raman spectroscopy to
transition from delicate laboratory instruments to rugged in-situ spectrometers. The
advancement in Raman instrumentation has simultaneously expanded the potential
applications of Raman spectroscopy, which now ranges from pharmaceutical drug quality
control to explosives detection to geological analysis on planetary surfaces. One of the most
promising innovations in the field of Raman spectroscopy is the development of the spatial
heterodyne Raman spectrometer (SHRS). SHRS is a variant of a Michelson interferometer
in which the mirrors of a Michelson are replaced with two stationary diffraction gratings.
When light enters SHRS, it is reflected off the diffraction gratings at frequency dependent
angles that in turn produce crossed wavefronts in space that can be imaged by a plane
array detector. The crossed wavefronts, which represent a superposition of interference
fringes, are converted to a Raman spectrum upon Fourier transformation.
This thesis is divided into four parts. In Chapter 1, the historical evolution of the theory
and instrumentation of Raman spectroscopy is covered in detail. In Chapters 2 and 3, SHRS
is used to measure the Raman spectra of materials of importance to planetary science
exploration at standoff distances. Finally, in Chapter 4, the author takes account of the
lessons learned from the preceding chapters and recommends some future work.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2017.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Chemistry

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