Date of Award

Summer 2022

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

S. Michael Angel

Abstract

This work describes improvements to a novel instrument, the monolithic spatial heterodyne Raman spectrometer (mSHRS), which has potential to be utilized in space exploration and deep-ocean marine sensing. In previous work, the spatial heterodyne Raman spectrometer (SHRS) was demonstrated, as a small, high resolution, wide field of view spectrometer, originally developed for space applications where small size and compactness is a key consideration or where a wide field of view is advantageous, such as in remote spectroscopy. The spatial heterodyne spectrometer (SHS) was then later utilized for remote Laser-Induced Breakdown Spectroscopy (LIBS). The high throughput, high spectral resolution, and large spectral range of the SHRS were shown to not be limited by the size of the device, pointing the way to monolithic construction, the subject of this work. Several mSHRS devices were designed for Raman and LIBS spectroscopy. These fabricated for the group by a company that does custom optics. Most of the mSHRS spectrometers are compact, measuring about 3.5 x 2.5 x 2.5 cm in size and weigh about 80 g. The preliminary tests showed that the mSHRS has greatly improved the long-term stability and much improved the sensitivity over the original free-standing SHRS.

This work extends the mSHRS in three areas: remote LIBS, studies of a novel cross-dispersion mSHRS, and testing designs to further reduce the size of the mSHRS. The large field of view and large acceptance angle makes the spatial heterodyne spectrometer (SHS) spectrometer well suited for remote Raman and remote LIBS measurements. The mSHRS was recently demonstrated for remote LIBS for samples at a 4.5-meter distance, using no collection optics other than the mSHS gratings. In other work, improvements in the signal to noise ratio (SNR) for weak bands in Raman spectra were demonstrated using the mSHRS in a novel cross-dispersion mode. Like any interferometer, noise in the mSHRS is equally distributed, meaning weak bands have the same noise as strong bands. This is an issue when weak bands are measured in a spectrum that has other strong bands. The SHS interferometer offers a potential solution to this problem by taking advantage of the 2-dimensional (2D) charge coupled device (CCD) detector, using the vertical dimension to produce a low-resolution separation of the spectral bands. This is accomplished by using a prism or diffraction grating to disperse the light in the vertical direction (cross-dispersion) onto the CCD. In other work, the area of the mSHRS footprint was decreased by a factor of ~4, and the volume was decreased by a factor of ~5. The smaller mSHRS devices measure 2.2 x 2.2 x 1.3 cm in size and weigh ~17 g yet have similar spectral resolution as the larger mSHRS devices. Together, the mSHRS improvements will enable their use in new applications, including sensors for exploration of the moons of the gaseous planets, such as Europa and Enceladus, comets, and asteroids, as well as near Earth exploration in extreme environments such as the chemical measurements around deep-ocean hydrothermal vents.

Rights

© 2022, Arelis Michelle Col?n

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