Spatial Heterodyne Raman Spectrometer (SHRS) for In Situ Chemical Sensing Using Sapphire and Silica Optical Fiber Raman Probes
- Lawrence Livermore National Laboratory, Livermore, CA, USA
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, USA
A spatial heterodyne Raman spectrometer (SHRS), constructed using a modular optical cage and lens tube system, is described for use with a commercial silica and a custom single-crystal (SC) sapphire fiber Raman probe. The utility of these fiber-coupled SHRS chemical sensors is demonstrated using 532 nm laser excitation for acquiring Raman measurements of solid (sulfur) and liquid (cyclohexane) Raman standards as well as real-world, plastic-bonded explosives (PBX) comprising 1,3,5- triamino- 2,4,6- trinitrobenzene (TATB) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) energetic materials. The SHRS is a fixed grating-based dispersive interferometer equipped with an array detector. Each Raman spectrum was extracted from its corresponding fringe image (i.e., interferogram) using a Fourier transform method. Raman measurements were acquired with the SHRS Littrow wavelength set at the laser excitation wavelength over a spectral range of ∼1750 cm −1 with a spectral resolution of ∼8 cm −1 for sapphire and ∼10 cm −1 for silica fiber probes. The large aperture of the SHRS allows much larger fiber diameters to be used without degrading spectral resolution as demonstrated with the larger sapphire collection fiber diameter (330 μm) compared to the silica fiber (100 μm). Unlike the dual silica fiber Raman probe, the dual sapphire fiber Raman probe did not include filtering at the fiber probe tip nearest the sample. Even so, SC sapphire fiber probe measurements produced less background than silica fibers allowing Raman measurements as close as ∼85 cm −1 to the excitation laser. Despite the short lengths of sapphire fiber used to construct the sapphire probe, well-defined, sharp sapphire Raman bands at 420, 580, and 750 cm −1 were observed in the SHRS spectra of cyclohexane and the highly fluorescent HMX-based PBX. SHRS measurements of the latter produced low background interference in the extracted Raman spectrum because the broad band fluorescence (i.e., a direct current, or DC, component) does not contribute to the interferogram intensity (i.e., the alternating current, or AC, component). SHRS spectral resolution, throughput, and signal-to-noise ratio are also discussed along with the merits of using sapphire Raman bands as internal performance references and as internal wavelength calibration standards in Raman measurements.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF); National Aeronautics and Space administration (NASA)
- Grant/Contract Number:
- This work was performed under the auspices of the; AC52-07NA27344; CHE-1308211; OCE-1829333; NNX14AI34G; 80NSSC19K1024
- OSTI ID:
- 1630386
- Alternate ID(s):
- OSTI ID: 1903448
- Report Number(s):
- LLNL-JRNL-767250
- Journal Information:
- Applied Spectroscopy, Journal Name: Applied Spectroscopy Vol. 73 Journal Issue: 10; ISSN 0003-7028
- Publisher:
- SAGE PublicationsCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Similar Records
A versatile femtosecond stimulated Raman spectroscopy setup with tunable pulses in the visible to near infrared
Summary report of FY 1995 Raman spectroscopy technology development