Next Generation Raman: Developing A Monolithic Spatial Heterodyne Spectrometer For Multi-Scale Chemical Mapping In Marine Environments

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The goal of this project is to develop a radically new type of instrument, a monolithic Raman spectrometer, designed to generate chemical images of solids liquids and/or gases in ocean environments at all depths. The instrument uses a technique called Raman Spectroscopy, where light scattered off of a sample at composition specific wavelengths (colors) is collected in a 2-dimensional (2D) image (picture) to produce a chemical map of the sampling area. In this project the key technological advancement is the new type of Raman instrument, called a Monolithic Spatial Heterodyne Raman Spectrometer (MSHRS). Although great progress has been made in the development of instrument platforms and sampling systems necessary to support Raman spectroscopy for oceanographic applications, advances in Raman spectrometer technology have not kept pace for use in these environments. The value of Raman measurements, balanced by the effort and cost of deploying current instruments, justifies the development of a new type of Raman spectrometer that is suitable for extreme environments like the deep ocean. The MSHRS being developed in this project overcomes some major limitations with existing systems for operation in the oceans such as instrument size and weight, power requirement, ruggedness (no moving parts), and sensitivity. The MSHRS technology being developed will allow deployment of instrument platforms and sampling systems necessary to support Raman spectroscopy for a broad range of oceanographic applications. This will support Raman measurements on minerals, opaque solids, and in water for important chemical species such as methane, carbon dioxide (CO2), sulfate, and sulfides in environments to depths up to 3.6 km, where the pressure is 360 times higher than at the surface. The MSHRS will generate chemical maps to show the 1D and 2D spatial distribution of these and other chemicals, even in complex mixtures typical of natural environments. The value of Raman measurements, balanced by the effort and cost of deploying current instruments, justifies the development of this new type of Raman spectrometer. The proposed MSHRS alone will be a major advance over "off the shelf" spectrometers currently used in marine Raman applications, reducing the size while increasing robustness and sensitivity over conventional designs. And, when combined with small diode lasers and the latest imaging detectors, the instrument can be truly miniaturized with no loss of performance. The MSHRS is potentially small enough to be deployed on autonomous swimming and drifting platforms (called gliders, Argo floats) or manipulator arms on remotely operated vehicles (ROVs). This work will support the development of a new Raman capability that will facilitate a wide range of new applications as well as basic chemical measurements in marine systems and will fuel transformative oceanographic research. While the focus of the proposed work is the study of process dynamics for oceanographic applications; the technology has much wider applicability. In addition to support of basic and applied research, industrial applications using the new capability for on-line analysis and process evaluation are likely. The investigators have a long history of mentoring students from underrepresented groups and the two students supported by this project are current female graduate students. These students will also benefit by collaborating with scientists at Lawrence Livermore National Laboratory and will gain a National Lab perspective on homeland security and defense applications. The Spatial Heterodyne Raman Spectrometer (SHRS), recently described by Angels group (the project principal investigator, PI), is a radically different design, offering tremendous advantages over conventional dispersive Raman systems, including 10 to 100 times larger acceptance angle and subsequently a much larger field of view, 100 to 10,000 higher light throughput for extended sources, very high spectral resolution and a wide spectral range. The SHRS design also allows for the spectrometer to be extremely small because the spectral resolution is not a strong function of device size. In the proposed work we will take the SHRS to the next level by developing a Monolithic SHRS (MSHRS) where the spectrometer optical components are a single piece of fused silica. This will provide a robust Raman spectrometer, immune to shock and vibrations, with increased sensitivity at a size and weight orders of magnitude smaller than current oceanographic Raman instruments. The MSHRS will be evaluated in terms of resolution, spectral range, throughput and robustness to vibration. Raman system figures of merit (e.g., resolution, sensitivity, light throughput, etc.) will be determined using solid, liquid, solutions and gases. In model applications we will evaluate the MSHRS for monitoring reaction dynamics in model oxic/anoxic mixing systems characteristic of a range of oceanographic environments. As a measure of the stability and precision of the MSHRS we will also evaluate its use for measuring selected isotope ratios for species relevant to the fundamental ocean.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.