Schematic sketch of the FSRS scheme (for details see text).
(a) Schematic experimental setup. ND: Neutral density filter, Pol : Polarizer, QWP : Quarter-wave plate, HWP: Half-wave plate, DM: Dichroic mirror, MO: Microscope objective, Spec: Spectrometer. (b) Schematic sketch of the II-FSRS scheme. (c) The inset shows the polarization orientations of the pump and probe pulse components in the sample (for details see text).
Measured spontaneous Raman scattering spectrum of acetonitrile.
FSRS measurement of acetonitrile: reference spectrum (cyan-dashed curve) and the SRS modulated spectrum (blue curve) showing a small dip at 2921 cm−1. The difference (red curve) corresponds to an inverted Raman intensity spectrum.
FRIKES measurement of acetonitrile: reference spectrum (cyan-dashed curve) and the SRS modulated spectrum (blue curve) showing a strong peak on top of a broad background signal. The difference (red curve) corresponds to a Raman intensity spectrum.
(a) Incident probe pulse spectrum (blue curve) and transmitted reference spectrum behind Pol3 (red curve) in the II-FSRS setup on a logarithmic scale. (b) Retardation error, normalized to a retardation of λ/4, of the experimental system calculated from (a) according to Eq. (9) .
Measured and calculated II-FSRS spectra at pump pulse polarization angle of (a) 0° (≡180°), (b) 90°, (c) 45°, and (d) 135°.
Comparison of the different spectroscopy methods. The FSRS, FRIKES, and II-FSRS spectra were obtained with the same pulse parameters, only with different polarization orientations, as indicated by the arrows. The retrieved nonlinear susceptibility χ(3) is shown in the plot below, together with the independently measured spontaneous Raman spectrum for comparison.
Waveplate and polarizer orientations (in degrees, with respect to x axis) for the different schemes, * = not inserted, RL: Raman loss, RG: Raman gain, DL: dispersive lineshape.
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