Spatially Offset Raman Spectroscopy for Depth Resolved Propellant Analysis

Physical Sciences Inc. (PSI) will develop a compact, spatially offset Raman sensor for non-contact, depth resolved measurements of solid rocket motor propellant. The Raman sensor, currently under development at PSI, will use a high throughput spatial heterodyne interferometric spectrometer (SHS). The SHS is 104 more sensitive to Raman photons than a conventional diffraction grating based slit-spectrometer operating with the same spectral resolution. The current Raman design will be modified to include a digital micromirror device (DMD) in order to collect spatially offset Raman signal (SORS) at varying penetration depths within a material. This system will utilize a commercial 785 nm laser, as well as a borescope to increase the sensorÆs standoff distance. This will allow for the borescope to be inserted through the nozzle of the motor and interrogate the propellant, avoiding surface contaminants and removing the need for sample preparation prior to measurements. The Phase I effort will focus on functional testing of the SORS breadboard. In parallel, the Phase I will design a prototype mechanical borescope, in order to better inform the final design for a Phase II prototype.