Accession Number : ADA570403


Title :   Multi-wavelength Laser Photoacoustics


Descriptive Note : Final rept. for period ending 1 Jun 2012


Corporate Author : ARMY RESEARCH LAB ADELPHI MD


Personal Author(s) : Gurton, Kristan P ; Felton, Melvin ; Tober, Richard


Full Text : http://www.dtic.mil/dtic/tr/fulltext/u2/a570403.pdf


Report Date : Sep 2012


Pagination or Media Count : 18


Abstract : An optical detection method designed to detect and identify the presence of macro-molecular gas species (e.g., organophosphate-based nerve agent simulants) at trace level concentrations is presented. The technique is based on a modified version of conventional laser photoacoustic spectroscopy (LPAS) in which optical absorption is typically measured using a single laser source. We demonstrate the ability to simultaneously measure multiple absorption related parameters that serve as a concentration independent identifier. Three continuous wave (CW) mid-infrared (MidIR) laser sources, operating at 8.68, 9.29, and 10.35 micrometers are combined and propagated axially through a specially designed flow-through photoacoustic cell. Each laser is modulated at a different frequency and the resultant acoustic signal(s) are detected and deconvolved using a PC-based 24-bit dynamic signal acquisition device. Species detection and identification is achieved by tabulating independent ratios of the acoustic response for each laser source. Quantitative absorption measured is verified using a Fourier transform infrared (FTIR) spectrometer. Results show good detection and species separation/identification at moderately low ppm concentrations.


Descriptors :   *LASER SPECTROSCOPY , *MACROMOLECULES , *OPTICAL DETECTION , ACOUSTIC SIGNALS , CHEMICAL AGENT SIMULANTS , CONTINUOUS WAVES , FOURIER TRANSFORMATION , INFRARED SPECTROMETERS , INTERMEDIATE INFRARED RADIATION , MULTISPECTRAL , NERVE AGENTS , RADIATION ABSORPTION , SPECTROSCOPY


Subject Categories : Lasers and Masers
      Optical Detection and Detectors


Distribution Statement : APPROVED FOR PUBLIC RELEASE