An ultrafast light-intensity modulator, based on stimulated Raman scattering, is described. The intensity of a continuous wave laser is fully modulated at 17THz using hydrogen in a high-finesse cavity. The modulation frequency is determined by the molecular constant of the Raman medium, i.e., the Raman shift frequency. The modulation frequency can be changed in the tetrahertz range by replacing the Raman medium. Due to the accurate modulation frequency and the high beam coherence, this device is amenable to a variety of applications such as in basic science and also in advanced industrial technology.
The development of an autocorrelator, using a photomultiplier as a nonlinear optical detector, for the measurement of a quasicontinuous-wave laser beam in the milliwatt range, is described. The contribution of the two-photon absorption relative to the onephoton absorption was investigated for the Sb-Cs photocathode used in the photomultiplier by means of the Z-scan method. This autocorrelator was applied to the measurement of the intensity of a laser beam sinusoidally modulated in the tetrahertz range.
We demonstrated that 17.6-THz pulse-like intensity modulation arising from the coherent superposition of multifrequency continuous-wave emissions generated from a hydrogen-filled high-finesse cavity through a cascade stimulated Raman scattering process.
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