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Deep Ultra Violet Standoff Raman Sensor

SHS Raman

PSI is developing a high optical throughput Raman sensor that operates in the deep ultraviolet (DUV) for the detection of explosive residues on surfaces from a standoff of 1 meter.

The sensor is based on a solid-state DUV excitation source coupled with a Spatial Heterodyne Spectrometer (SHS) receiver. The sensor measures Raman signals across a ~830–2680 cm-1 spectral range from a 2.6 cm2 interrogation area from a 1 m standoff in a single snapshot with a 17 cm-1 spectral resolution. Acquired spectra are processed through an on-board deep learning spectral correlation algorithm that provides real-time target identification. The prototype provides end-to-end identification capability with an on-board automated detection algorithm that generates target identifications in real-time. Measurements with explosives/simulants have demonstrated the system’s ability to measure Raman spectra and identify targets in 1 s up to 2 min (bulk solids: ≤1s; particulate residues at ~1500 ug/cm2): ≤ 30s; residues at 600 ug/cm2: ≤2 minutes).

Photograph of the assembled DUV Raman sensor

Key Features

PSI’s Compact, no-moving parts DUV Spatial Heterodyne Spectrometer (SHS): Orders of magnitude higher throughput than grating spectrometers with equivalent spectral resolution.
Solid-state UV laser: Leverages n4 Raman cross section scaling, coupled with minimal to no fluorescence and a solar blind spectral range.
PSI’s Automated chemical target recognition (ACTR) algorithm module. PSI’s UV Raman sensor utilizes a bistatic receiver and transmitter design. The receiver is a high throughput SHS, developed by PSI, that is set to Littrow at ~750 cm-1 Raman shift (267.2 nm). The transmitter utilizes a 262 nm Neodymium-doped yttrium lithium fluoride (Nd:YLF) laser (CystaLaser) that can generate up to 30 mW of time-averaged power. The output of the laser transmitter illuminates a 2.25 cm diameter spot (i.e. 400 mm2) at a target placed 1 meter from the sensor head. The SHS collects Raman scattered photons from a ground sample distance (GSD) that is overlapped with the transmitter’s excitation spot. The SHS utilizes a commercially available electron multiplying charge coupled device (EMCCD) and diffraction gratings. A single board computer (SBC) is used to execute system control, data processing and an automated chemical target recognition (ACTR) algorithm. Automated chemical target detection is achieved using a deep learning spectral correlation algorithm. The sensor head is equipped with a range finder and context camera that allows positioning of the target to be interrogated within the field of view of the receiver and position the sensor at the required 1 m standoff. The sensor head weighs 40.5 lbs. and occupies 1 cu. ft. The EMCCD is the primary size driver of the overall sensor head footprint. The system utilizes a power supply module (PSM) that contains a liquid cooling module (LCM), the associated coolant distribution components, a custom power distribution board, the SBC and other required electronics for system control. The PSM weighs 35 lbs. and weighs 0.76 cu. ft.

Benefit to Warfighter/Customer

PSI’s solid-state DUV Raman technology provides the defense community, first responders, and law enforcement with improved chemical, biological, and explosive detection capabilities. The system enables non-contact, standoff surface detection and identification of explosive residues from unmanned ground vehicles and areal systems. The system addresses key performance limitations of current Raman technology by improving sensitivity, enlarging the interrogated area per second, and increasing the standoff range. Additional applications include identification of narcotics or other dangerous substances by forensic personnel in the field, as well as identification and validation of raw materials in pharmaceutical drug manufacturing.