Tetsuo Harimoto

Numerical analysis of optical parametric chirped pulse amplification with time delay

A new scheme for efficient optical parametric chirped pulse amplification is proposed by introducing a time delay between long pump and short seed pulses. Numerical results show that high conversion efficiency from the pump to seed and high gain can be achieved simultaneously, and the amplified seed pulse is stable and not sensitive to timing jitter.

Ultra-broadband optical parametric chirped-pulse amplification using an Yb:LiYF 4 chirped-pulse amplification pump laser

We demonstrate ultra-broadband optical parametric chirpedpulse amplification of 300-nm bandwidth pumped by a broadband pulse delivered from a diode-pumped, cryogenically-cooled Yb:YLF chirped- pulse amplification laser.

Far-Field Pattern Analysis for an Array Grating Compressor

A numerical analysis for far-field pattern distribution of an array grating compressor showed that alignment of segmental gratings can be achieved by adjusting only two tilted angles and the relative position distance of two segmental gratings. An alignment tolerance criterion was set up with a simple formula for an array grating with the size of meter order. For the example of an array grating with a size of 0.5 m, the angular and position tolerances are required to be 0.25 µrad and λ/13, respectively.

Spectral properties of second-harmonic generation at 800 nm in a BiB(3)O(6) crystal.

We have investigated spectral distribution and walk-off effect of second-harmonic generation in a 3-mm-long type I BiB(3)O(6) crystal. Linearly turning ability of the BiB(3)O(6) crystal is confirmed for wavelengths around 800 nm. In addition, the walk-off effect of fundamental beams is quantitatively measured by introducing a little vertical polarization component into pumping fundamental pulses. A conversion efficiency of 28% from fundamental to second harmonic is achieved at a 3.2-GW/cm(2) fundamental intensity.

Proposal for Ultrabroadband Phase-Matching Optical Parametric Chirped Pulse Amplification with a Diverged Pump Beam

We propose a novel scheme for optical parametric chirped pulse amplification with a diverged pump beam to achieve an ultrabroadband phase-matching range, in which different signal wavelengths correspond to different inclination angles of the diverged pump beam. Simulation results show that the proposed scheme amplifies a signal pulse shorter than 10 fs at a wavelength of approximately 800 nm.

Oscillating longitudinal-mode control of a microchip green laser by injection current

We describe a simple method of controlling the oscillating longitudinal mode of a diode-pumped-microchip green laser by changing injection currents to the laser diode. We observed the dependence of the oscillating longitudinal modes on the injection current and operation temperature in the microchip green laser, and demonstrated that the stable oscillating longitudinal-mode operation under the single mode, two and three modes can be achieved by only controlling injection currents from 850 to 1050 mA. The maximum output power of the microchip green laser as high as 105.5 mW was obtained under the single longitudinal-mode operation pumped by an 810 mW pumping power. The corresponding long-term power stability was better than 0.47 % for the measuring time interval of 12 hours.

A novel multipass scheme for enhancement of second harmonic generation

We present experimental evidence of enhancement of the second-harmonic generation by using a multipass non-collinear phase-matching configuration for a Q-switched nanosecond-kilohertz Nd:YVO4 laser. In comparison with the single-pass configuration, the enhancement factor of the second-harmonic laser with the two-pass configuration is up to 2.5 in a type I beta-barium borate crystal, which can be further increased by adding the third-pass through the crystal. In addition, we provide a general relationship between the phase-matching angle and tilting azimuth angles of the unconverted fundamental and second-harmonic lasers. The multipass non-collinear phase-matching configuration is capable of reducing a thermal effect due to the absorption in the crystal and effectively avoiding damages on the crystal surfaces.

Bandwidth Enhancement of Optical Parametric Chirped Pulse Amplification by Temporally Delayed Two Pump Beams

We have demonstrated ultra-broadband optical parametric chirped-pulse amplification of more than 350 nm bandwidth in the near-infrared region. We have observed a substantial enhancement (nearly 2-fold) of the parametric amplification bandwidth by using time-delayed two broadband pump pulses at degeneracy.

Evaluation of Stable Optical Parametric Amplification Involving Temporal Distribution

Numerical evaluation for stable optical parametric amplification has been carried out by involving both temporal distributions and duration differences of pump and seed pulses. It was found that there are some different optimum crystal thicknesses with respect to stable pump-to-seed energy and intensity conversions and optimal reproduction of temporal distribution, which will be practically useful in the design of a practical optical parametric chirped pulse amplification system.

Spectral and Temporal Distributions of Ultrashort Laser Pulses Diffracted by a Slit

We present numerical images for frequency-space and time-space distributions of cycle laser pulses diffracted by a slit with Fresnel-Kirchhoff diffraction formula. The wide frequency bandwidth with respect to the cycle pulse results in spectral redistribution of diffracted laser pulses and dispersion effect subsequently. Although spatial patterns still retain their asymmetry, spectral or temporal distributions lose their asymmetry gradually with increasing distance from the beam center for few-cycle pulses.