Coherent Raman scattering in a low-pressure gas

A nonlinear optical process in which phase-related light fields drive molecular vibrations in a dilute gas and generate coherent radiation shifted by vibrational frequencies.

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Stimulated Raman scattering: A nonlinear optical process in which intense light drives Raman transitions and amplifies frequency-shifted radiation. The gas process is a coherent, phase-sensitive realization of stimulated Raman scattering.
Raman scattering: Inelastic scattering of light in which photons exchange energy with molecular or material excitations. The coherent gas process builds on Raman energy shifts but adds phase-correlated emission.
Coherent anti-Stokes Raman spectroscopy: A nonlinear spectroscopy that generates anti-Stokes light through coherent Raman interactions. It uses the gas-phase process to detect vibrational signatures with directional emission.
Spontaneous Raman scattering: Raman scattering in which individual scattering events occur without a driving coherent Raman field. Unlike coherent emission, its scattered photons are not phase-aligned across molecules.
Raman coherence: A phase-correlated superposition of molecular states connected by a Raman transition. The driving fields create this molecular coherence, which radiates collectively.
Stokes shift: A decrease in photon frequency when energy is transferred to an excitation during scattering or emission. Vibrational excitation commonly produces the lower-frequency Raman component.
Raman laser: A laser that converts pump light to new frequencies through stimulated Raman scattering in a gain medium. A low-pressure gas can serve as the Raman-active medium for wavelength conversion.
Hyper-Raman scattering: A nonlinear scattering process in which a molecule interacts with two incident photons and emits one shifted photon. It is a distinct higher-order Raman process, not ordinary vibrational coherence driven by two fields.
Four-wave mixing: A third-order nonlinear optical process in which three optical fields generate a fourth field. The Raman-shifted output can be described as four-wave mixing mediated by vibration.
Anti-Stokes shift: An increase in photon frequency when a photon gains energy from an existing excitation. The driven molecular vibration can return energy to light at the higher-frequency sideband.