M. Watanabe

Optical generation of millimeter-wave signals up to 330 GHz by means of cascadingly phase locking three semiconductor lasers

We developed a technique for the optical generation of high-purity millimeter-wave signals by synthesizing the outputs from three cascadingly phase-locked semiconductor lasers. A semiconductor optical amplifier was used to generate four-wave mixing (FWM) signals from the three laser fields. One of the degenerating FWM pairs was used to construct an optical phase-locked loop (OPLL), which ensured that the frequency separations of the three lasers were kept at a ratio of 1 : 2. Using a commercially available p-i-n photodetector, we also developed a conventional OPLL capable of operating at frequencies up to 110 GHz. By combining these techniques, we generated high-purity millimeter-wave optical-beat signals at frequencies up to 330.566 GHz.

Generation of quasi-continuous-wave vacuum-ultraviolet coherent light by fourth-harmonic of a Ti:sapphire laser with KBBF crystal

We report the generation of quasi-continuous-wave vacuum-ultraviolet (VUV) coherent light based on a Ti:sapphire laser with two successive frequency doubling stages. In the first stage, UV light at 399 nm with power of 1.1 W was obtained by exploiting an enhanced cavity. With a KBBF crystal as nonlinear material, quasi-continuous-wave VUV coherent light with power of about 25 mW at 199.5 nm and 4.7 mW at 193.5 nm were achieved through a single-pass SHG configuration, respectively, in the second stage.

Continuous-wave sum-frequency generation near 194 nm with a collinear double enhancement cavity

Abstract A double resonant cavity for sum-frequency generation has been successfully operated; it accomodates a walk-off-compensated configuration of β-BaB 2 O 4 crystals with collinear circulation of the fundamental beams. Continuous-wave 194 nm coherent radiation has been obtained with an output power of 31 μW.

Tunable 397-nm light source for spectroscopy obtained by frequency doubling of a diode laser.

Continuous-wave radiation of 1.8 mW at 397 nm was generated by frequency doubling a 100-mW GaAlAs diode laser in a lithium iodate crystal placed in an external enhancement cavity. The radiation had a narrow linewidth and a continuous frequency-scanning range of 6 GHz. The UV radiation obtained was applied to laser cooling of calcium ions stored in a rf trap.

Generation of continuous-wave coherent radiation tunable down to 190.8nm in ?-BaB2O4

Continuous-wave coherent radiation tunable in the wavelength range 190.8–196.1 nm has been generated by sum-frequency generation in β-BaB2O4. The fundamental beams were supplied by a Ti:Al2O3 laser and a frequency-doubled argon-ion laser.

Harmonic synchronization of Fourier-synthesized optical pulses to an external optical clock

The fifth-harmonic synchronization of Fourier-synthesized 40-GHz optical pulses to a slower 8-GHz mode-locked optical pulse train was demonstrated by means of an advanced optical phase-locked-loop technique. For the Fourier synthesis, three continuous-wave semiconductor lasers were phase locked to generate the 40-GHz optical pulses, where an optical single-sideband modulator was used to obtain arbitrary waveforms. For the synchronization, a modified clock-recovery technique based on optical four-wave mixing was developed, where the timing-error signal was fed back to one of the Fourier-component lasers in order to minimize the timing jitter with respect to the optical clock. Synchronization with an estimated root-mean-square timing jitter of 0.43 ps was, thus, achieved.

Terahertz-Photomixing Efficiency of a Photoconductive Antenna Embedded in a Three-Dimensional Photonic Crystal

We report on generation of coherent terahertz radiation by photomixing with a photoconductive antenna placed in a three-dimensional photonic crystal cavity. We observed efficiency peaks around the frequencies near the photonic bandedges and at the planar defect modes. The efficiency peaks observed near the photonic bandedges are associated with the increase of the optical mode density at the bandedge. The relatively low efficiency at the planar defect mode frequencies are explained by the mode diffusion in the lateral direction of the defect layer.

Laser cooling of a single Ca+ ion: Observation of quantum jumps

This paper describes trapping and laser cooling of a Ca+ ion in an rf quadrupole ion trap. A single Ca+ ion is laser cooled to below 130 mK and quantum jumps are observed by exciting the ion into the metastable D5/2 state via the P3/2 state. The lifetime of the metastable D5/2 state is estimated from the distribution of the dark periods of the quantum-jump signal. Collision-induced jumps between the metastable D3/2 state and the D5/2 state in a background gas are also directly observed.

Saturation spectroscopy of potassium for frequency stabilization of violet diode lasers

We observed saturated absorption spectra of potassium at 404.8 nm with a frequency-stabilized violet diode laser. A diffraction grating in the Littrow configuration was used to get a single-mode output, and simultaneous resonant optical feedback from a confocal Fabry–Perot cavity was employed to stabilize the laser frequency. The observed short-term frequency fluctuations are 300 kHz for 1 s, and the upper limit on the instantaneous linewidth is 1.5 MHz. The optically locked laser can be continuously scanned over 4 GHz. The observed typical linewidth of the potassium transition is 3.6 MHz with a signal-to-noise ratio of 17. The transition is suitable for stabilizing frequency of violet diode lasers to a sub-MHz level.

Classical and quantum properties of optical parametric amplifier/deamplifier

Abstract The classical gain and the variances of coupled, signal and idler modes of output from continuous nondegenerate optical parametric amplifier are theoretically analyzed under parametric amplification and deamplification conditions. The correlation between the signal and idler modes is also discussed. The results provide design references for nonclassical light generation systems.