Trace Explosives UV Raman Detection Enhancements
Abstract
Over the last six years we have been pioneering the field of UV resonance Raman spectroscopy (UVRR) as a trace detection methodology, for the standoff detection of explosives. Our work has developed novel deep UV lasers for the 200-250 nm Raman excitation region, h,as fabricated deep UV highly sensitive standoff UVRR spectrometers, and, has improved UVRR measurement methodologies. Our work to da,te has demonstrated < 1 microgm/cm2 detection limits for explosives such as PETN on Aluminum substrates, for example. Our work here,has dramatically increased the sensitivity of UVRR by helping develop a revolutionary continuously wavelength tunable CW deep UV las,er excitation source, and by designing a Rayleigh rejection filter that can operate in the deep UV to minimize stray light between 2,24 to 250 nm.This revolutionary deep UV laser source was codeveloped by Spectra-Physics Lasers, a leading American Laser Company and, Sirah Lasertechnik, a highly innovative German laser company. This laser will generate continuously wavelength tunable light throug,hout the visible and UV. It will, most importantly be able to generate >20 mW of deep UV light between 206 and 235 nm.Crucially, the, laser output will be CW such that it will enable the first tunable, CW UVRR spectrometer that can minimize nonlinear optical respon,ses. This will maximize UVRR S/N, such that it maximizes UVRR sensitivity to trace explosives.This revolutionary CW ring laser (~$35,0 K) was funded by an ONR DURIP grant designed to enable the construction of this revolutionary standoff UVRR spectrometer.As part o,f our development of more efficient UVRR spectrometers we also designed novel approaches to fabricate Rayleigh rejection photonic cr,ystals that operate deep in the UV. We worked with Semrock Optics and succeeded in fabricating Rayleigh rejection filters that funct,ion at wavelengths as low as 224 nm. This is the shortest wavelength yet obtained by utilizing the present dielectric thin film depo,sition technology, which does not presently function below 224 nm due to material deep UV absorption. As discussed below, we have es,tablished collaborations with dielectric film deposition optical companies who have calculated that novel dielectric films fabricate,d by using CaF2 should perform well at deep UV wavelengths between 206 to 230 nm. We intend to collaborate with these companies to p,ioneer deep UV Rayleigh rejection filters. These filters will revolutionize deep UVRR spectral measurements because they dramaticall,y decrease UVRR spectrometer stray light and because they simplify UV Raman spectrograph design. The spectral advances here will ena,ble detection of ultra-low concentrations of explosives which will increase ONR personnel safety and Naval operation capabilities.Ap,proved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 08, 2022
- Source ID
- N000142212414
Entities
People
- Sanford A Asher
Organizations
- Office of Naval Research
- United States Navy
- University of Pittsburgh