Nonplanar, crossed-beam phase matching has been employed to obtain pure rotational coherent anti-Stokes Raman spectroscopy (CARS) [and coherent Stokes Raman spectroscopy (CSRS)] spectra to within a few wavenumbers of the incident pump frequency. Using this approach, the rotational CARS (and CSRS) radiation is spatially separated from the pump and Stokes beams; therefore small Raman shifts can be observed with a single monochromator.

Folded BOXCARS for rotational Raman studies.

A novel technique for the generation of single-pulse rotational CARS spectra is presented and demonstrated flows and flames. The technique is based on a multiple four-color interaction, where the rotational in gas with two photons of different frequencies from a broadband dye laser, and by coupling to a energies are excited photon from a frequency-doubled Nd:YAG laser a rotational CARS photon is created. An interesting third feature of the technique is the possibility of simultaneously generating both a rotational and vibrational using a double-folded BOXCARS arrangement. This technique is demonstrated on N2 CARS spectrum molecules.

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Rotational Cars Generation Through A Multiple Four-color Interaction

Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15 000 spatially correlated rotational CARS spectra in N2 and air over a 2D field of 40 mm2.

Communication: Two-dimensional gas-phase coherent anti-Stokes Raman spectroscopy (2D-CARS): Simultaneous planar imaging and multiplex spectroscopy in a single laser shot

Hybrid fs/ps rotational CARS temperature and oxygen measurements in the product gases of canonical flat flames

Pure rotational coherent anti-Stokes Raman spectroscopy is applied for quantitative gas-phase temperature measurements in the vaporizing spray of an automotive fuel injector. Interferences from elastically scattered stray light are greatly reduced by use of a polarization technique and spectral filtering in a double monochromator. The applicability of this technique to probing low-temperature sprays is successfully demonstrated.

Gas-phase temperature measurement in the vaporizing spray of a gasoline direct-injection injector by use of pure rotational coherent anti-Stokes Raman scattering.

THE techniques of coherent Raman spectroscopy are revolutionising the applications and scope of Raman spectroscopy. Particularly important aspects are: very high resolution spectroscopy (the Doppler width being proportional to the Raman shift of the band under study); nanosecond (and sub-nanosecond) spectroscopy, where the resolution obtained may be limited by the Fourier transform of the experimental time scale; discrimination against luminescence from the sample (whether laser induced or not). We discuss here coherent anti-Stokes Raman spectroscopy (CARS) at low frequency shifts.

I. R. Beattie

Papers

Low frequency coherent anti-Stokes Raman spectroscopy of air