Abstract
We explore a novel phase matching scheme for gas-phase rotational coherent anti-Stokes Raman spectroscopy (CARS). The scheme significantly simplifies the employment of the technique in general. Two laser beams, one broadband and one narrowband, are crossed at arbitrary angle and the generated rotational CARS signal, copropagating with the probe beam, is isolated using a polarization gating technique. The effect of phase-vector mismatch for various experimental implementations was measured experimentally and compared to calculations. The spatial resolution of the current technique is improved by more than an order of magnitude over standard gas-phase CARS experimental arrangements, providing an interaction length of less than 50 μm when desired. Both the pump and Stokes photons originate from the broadband pulse, and are therefore automatically overlapped temporally and spatially. Significantly improved signal levels are achieved because of both the ease of alignment and the higher pulse energy available to the pump and Stokes fields. We demonstrate the technique for single-laser-shot 1D rotational CARS signal generation over approximately a 1 cm field in a flame.
Highlights
Beams interacted over a large probe volume and generated large signals, but this arrangement lacked the spatial resolution needed for probing certain systems such as reacting flows
The spatial resolution of CARS measurements was improved by the development of the BOXCARS phase-matching scheme
The phase matching vector diagram for the currently reported two-beam rotational CARS scheme is shown in Fig. 1 (Left)
Summary
Beams interacted over a large probe volume and generated large signals, but this arrangement lacked the spatial resolution needed for probing certain systems such as reacting flows. The spatial resolution of CARS measurements was improved by the development of the BOXCARS phase-matching scheme.16 In BOXCARS, the three CARS beams are separated and focused down to the probe volume with small angles between the beams satisfying the phase-matching condition.
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