Phase-Matched Raman-Resonant Four-Wave Mixing in a Dispersion-Compensated High-Finesse Optical Cavity

A highly efficient intracavity four-wave mixing in a Raman-active medium pumped by a continuous-wave laser is first demonstrated. Managing the intracavity dispersion to satisfy the phase matching in a high-finesse cavity substantially enhances the anti-Stokes emission. This process is observed in a region far beyond small signal approximation, indicating the generation of phase-locked sidebands arising from molecular modulation. This points to a novel approach of an optical modulator and mode-locked laser operating at a frequency of more than 10 THz.

Figure 1

(a) Energy diagram of Raman-resonant FWM. $\Omega$: Raman shift frequency. (b) Simplified illustration of a relation between longitudinal modes of a high-finesse cavity and intracavity fields related to the FWM interaction.

Figure 2

The power ratio of the anti-Stokes and Stokes emissions ($P_{\mathrm{AS}}/P_{\mathrm{S}}$) as a function of the partial pressure of hydrogen (the lower abscissa axis). The corresponding frequency shift of $\Delta \Omega$ is shown in the upper abscissa axis. The partial pressure of xenon gas was 0.14 MPa.

Figure 3

The measured spectra of the output beams under different pressures of the intracavity medium. AS1: first anti-Stokes emission, $P$: pump emission, S1: first Stokes emission, and S2: second Stokes emission. The inset in (b) shows a beam profile of the anti-Stokes emission.

Figure 4

Intensities of each emission as a function of the total output power. $P$: pump laser, S1: first Stokes emission, S2: second Stokes emission, and AS1: first anti-Stokes emission.