High-efficiency electro-optic amplitude modulation with delayed coherent addition.

Amplitude modulation of laser light is required for resonant sideband extraction employed in gravitational-wave detectors. Amplitude modulation with electro-optic phase modulators is realized by interferometric phase-to-amplitude conversion. Although two outputs modulated at opposite phases to each other are obtained, usually only one of them is utilized and the other is abandoned.

Wideband and high-gain frequency stabilization of a 100-W injection-locked Nd:YAG laser for second-generation gravitational wave detectors.

Second-generation gravitational wave detectors require a highly stable laser with an output power greater than 100 W to attain their target sensitivity. We have developed a frequency stabilization system for a 100-W injection-locked Nd:YAG (yttrium aluminum garnet) laser. By placing an external wideband electro-optic modulator used as a fast-frequency actuator in the optical path of the slave output, we can circumvent a phase delay in the frequency control loop originating from the pole of an injection-locked slave cavity.

Formulation of frequency stability limited by laser intrinsic noise in feedback systems.

We investigated the influence of amplitude modulation (AM) noise and phase modulation (PM) noise of a laser source on the frequency stability in frequency stabilization systems. We estimated the frequency stability and evaluated the efficacy of a noise reduction technique (the Doppler-trend subtraction method) of a laser diode frequency stabilization system, where enhanced intensity noise arising from PM-to-AM noise conversion through a reference gas cell is reduced using the technique employed in modulation transfer spectroscopy. To evaluate the relationship between the laser's intrinsic noise and its frequency stability, we performed noise spectrum measurements and formulated frequency stability in addition to measuring Allan standard deviation.

Thermal effects in high-power CW second harmonic generation in Mg-doped stoichiometric lithium tantalate.

We investigated thermal behaviors of single-pass second-harmonic generation of continuous wave green radiation with high efficiency by quasi-phase matching in periodically poled Mg-doped stoichiometric lithium tantalate (PPMgSLT). Heat generation turned out to be directly related to the green light absorption in the material. Strong relation between an upper limit of the second harmonic power and confocal parameter was found.

Development of a wavelength-stabilized distributed bragg reflector laser diode to the Cs-D2 line for field use in accurate geophysical measurements.

We have developed a wavelength-stabilized laser diode (LD) for geophysical measurement devices, which benefit from the uniformity of laser light. Regarding this purpose, a system that has such characteristics as low power consumption, sturdiness against mechanical disturbances, and a long life with long-term frequency stability is especially required. Therefore, we adopt as the light source a distributed Bragg reflector (DBR) LD because it has various advantages concerning such properties.

100 W, single-frequency operation of an injection-locked Nd:YAG laser.

We have built a single-frequency Nd:YAG laser capable of producing an output power of 101 W by injection locking a slave laser that can emit an output power of 121 W in the free-running state to a 2-W master laser. We confirmed that the output mode was diffraction limited and linearly polarized.