High-Speed High-Resolution Gas-Phase Raman Spectroscopy

Abstract

A new Raman spectrometer has been developed that can produce a complete high-resolution gas-phase vibrational spectrum during the time period of a single laser pulse. Conventional gas-phase Raman spectroscopy uses a single narrow-band laser to produce signals that are weak, requiring relatively long collection times. This spectrometer uses a degenerate OPO as a broad-band source that covers a continuous range of >3000 cm(-1). When a beam from this broad-band source is added to a narrow-band laser beam, the intensity of the Raman signal is amplified by the nonlinear optical effect. The resulting instrument can generate spectra with high-spectral (<1 cm(-1)), spatial (<0.05 mm2), and temporal resolution (<1 s).

Gas Chromatography−Multiplex Coherent Raman Spectroscopy

“…Recent results also provide promising evidence of the high selectivity of this technique. In a previous paper, all but two of the major Raman peaks were spectroscopically resolved when a mixture of eight randomly chosen species was analyzed with the multiplex coherent Raman spectrometer. The same paper also shows FT-IR spectra from the same gaseous mixtures; in these spectra, the resolution for MCR is roughly 1 order of magnitude better than that for FT-IR.…”

“…The spectrometer has been described in more detail elsewhere . An injection-seeded Nd:YAG laser (Spectraphysics GCR-230) produces a beam of light with a repetition rate of 10 Hz and a wavelength of 532 nm that is used to pump a hydrogen-filled Raman shifter.…”

“…Since broadband dye lasers have a bandwidth that is roughly 1 order of magnitude smaller than that needed to cover the entire vibrational spectrum (>3000 cm -1 ), the resulting vibrational spectra have not been complete. Recently, a broadband degenerate OPO has been developed that produces light over a sufficiently broad range to permit the generation of the entire vibrational spectrum in as few as one laser pulse . Particularly attractive about the resulting spectrometer was its ability to fully resolve narrow peaks (2−3 cm -1 fwhm) from a mixture of several species.…”

High Speed Nonlinear Interferometric Vibrational Analysis of Lipids by Spectral Decomposition

“…Classical CARS used picosecond narrow bandwidth lasers for both the pump and Stokes pulses,1 producing good spectral resolution but requiring spectral scanning to cover the spectrum. In 2002, Chen and coworkers,2 Xie and coworkers3, and Muller and coworkers4 reported multiplex CARS (mCARS), which uses a broadband Stokes pulse so CARS spectra can be dispersed onto a detector array, parallelizing data collection. In 2004, Saykally and coworkers5 replaced the narrowband pump pulse by a chirped broadband pulse, maintaining high resolution while simplifying pulse generation to a single fs laser source.…”

Multimodal Characterization of Materials and Decontamination Processes for Chemical Warfare Protection

“…Raman spectroscopy is an inelastic scattering technique that can be used as a probe to study solids, liquids, and gases. 133 Inelastic scattering is a two-photon process that involves the annihilation and the creation of a photon. 134 A Raman signal arises due to changes in the polarizability of a bond during molecular vibration.…”