Norihito Saito

An Efficient Method for Quasi-Continuous-Wave Generation at 589 nm by Sum-Frequency Mixing in Periodically Poled KTP

Quasi-continuous-wave generation at 589 nm in periodically poled KTP was achieved by sum-frequency mixing of synchronized mode-locked pulses emitted at 1064 and 1319 nm from two mode-locked Nd:YAG lasers. As acousto-optic mode lockers operated by the same frequency were used for mode locking, pulse trains were well synchronized with phase control of the radio frequency. The maximum output power at 589 nm was 260 mW mixing 1.9 W at 1064 nm and 0.88 W at 1319 nm. Conversion efficiency was reached to 14%, even for single-pass pumping using 5-mm-long periodically poled KTP.

All-solid-state rapidly tunable coherent 6-10 μm light source for lidar environmental sensing

We report on an all-solid-state rapidly tunable pulsed coherent 6-10 μm light source achieved in an optical parametric oscillator (OPO) pumped with an electronically tuned Cr:ZnSe laser and its application to lidar remote sensing for environmental detection. We designed a lidar system using the 6-10 μm light source and a telescope with a primary mirror of 50 cm and a high-efficient HgCdTe detector. The lidar system would be a valuable system in the measurement of chemical agents in the 100-300 m.

1 W 589 nm Coherent Light-Source Achieved by Quasi-Intracavity Sum-Frequency Generation

We proposed a novel configuration for efficient generation of coherent 589-nm light by sum-frequency generation mixing 1064 and 1319 nm emitted from two continuous-wave Nd:YAG lasers. A 5-mm-long periodically-poled KTiOPO4 was used as a nonlinear optical crystal and it was set in the 1064-nm-Nd:YAG laser. Output beam oscillated from the 1319-nm-Nd:YAG laser was superimposed on a propergation axis of 1064-nm beam stored in the 1064-nm laser using a beam combiner from outside of the laser.?Output power of sum frequency reached to 1 W and it was ten times higher than that by extracavity sum-frequency generation using the same appatatus.

Influence of Cerium Concentration on Transmittance and Surface Damage Threshold in Ce-doped KTP

Optical transmittance and surface damage threshold of cerium-doped (2, 9, and 33 ppm) KTP crystals were investigated with dependence on cerium concentration and polarization directions with respect to the fundamental crystal axes. Although transmittance from ultra-violet to mid-infrared region was gradually decreased with increase of cerium concentration, even transmittance at 532 nm in 33 ppm cerium-doped KTP, which showed the lowest transmittance, was 7 % higher than that of undoped KTP reported in Ref.[6]. On the other hand, surface damage threshold at 1064 nm was raised with increase of cerium concentration and the maximum damage threshold was measured to be 8 GW/cm2 using 33-ppm cerium-doped KTP, when b-axis polarized beam was input to surface of the crystal. The threshold was a factor of 2.4 larger compared with that of undoped KTP.

Photoisomerization of azobenzene derivative combined liposome suing a two-photon UV-Blue pulsed laser

Azobenzene-based photo devices have attracted ongoing interest for applications in controlled drug release since the first report by Kano et al. in the early 1980s.[1, 2] However, the poor penetration of UV light which is necessary for chemical structure change of azobenzene limits the in vivo application of azobenzene. In this study, a broadly tunable pulsed laser with a tuning range from the UV to blue region was developed and used for conformational change of the azobenzene derivative.

Coupled thermo-optical modeling of high power operation of Tm, Ho:YLF solid-state lasers

Integrated computational model for operation of co-doped Tm,Ho solid-state lasers is developed coupling (i) 8-level rate equations with (ii) TEM00 laser beam distribution, and (iii) complex heat dissipation model. Simulations done for Q-switched ≈0.1 J giant pulse generation by Tm,Ho:YLF laser show that ≈43 % of the 780 nm light diode side-pumped energy is directly transformed into the heat inside the crystal, whereas ≈45 % is the spontaneously emitted radiation from 3F4, 5I7 , 3H4 and 3H5 levels. In water-cooled operation this radiation is absorbed inside the thermal boundary layer where the heat transfer is dominated by heat conduction. In high-power operation the resulting temperature increase is shown to lead to (i) significant decrease in giant pulse energy and (ii) thermal lensing.

Rapidly-tunable mid-infrared coherent light source with difference frequency generation

We have demonstrated broadly tunable mid-infrared generation from 5 mum to12 mum by difference frequency generation pumped with an electronically-tuned-Ti:sapphire laser. Rapid- and random-access of wavelength is realized in the mid-infrared region.

Development of all-solid-state coherent 589 nm light source: toward the realization of sodium lidar and laser guide star adaptive optics

We report an all-solid-state coherent 589 nm light source in single-pass sum-frequency generation (SFG) with actively mode-locked Nd:YAG lasers for the realization of sodium lidar and laser guide star adaptive optics. The Nd:YAG lasers are constructed as a LD-side-pumped configuration and are operated at 1064 and 1319 nm for 589 nm light generation in SFG. Output powers of 16.5 and 5.3 W at 1064 and 1319 nm are obtained with two pumping chambers. Each chamber consisted of three 80-W-LD arrays. Single transverse mode TEM00; M2 ~1.1 is achieved with adjustment of cavity length considering thermal lens effect with increase of input LD power. The cavity length is set to approximately 1 m. Accordingly the mode-locked lasers are operated at a repetition rate of approximately 150 MHz. Synchronization of two pulse trains at 1064 and 1319 nm is accomplished by control of phase difference between two radio frequencies input in acousto-optic mode-lockers. Then temporal delay is controlled with a resolution of 37 ps/degree. Pump beams are mixed in periodically poled stoichiometric lithium tantalate (PPSLT) without an antireflection coating. The effective aperture and length of the crystal are 0.5 × 2 mm2 and 15 mm. When input intensity is set at 5.6 MW/cm , an average output power of 4.6 W is obtained at 589.159 nm. Precise tuning to the sodium D2 line is accomplished by thermal control of etalons set in the Nd:YAG lasers. The output power at 589.159 nm is stably maintained within ±1.2% for 8 hours.

High Power Yellow Light Generation for Laser Guide Star

6.3 W coherent yellow light generation at 589.159 nm was achieved by the sum frequency generation of two mode-locked lasers with wavelengths of 1064nm and 1319 nm for the laser guide star of the astronomical telescope.

Efficient sum-frequency generation with quasi-intracavity configuration

Quasi-intracavity sum-frequency-generation was demonstrated. Output power at 589 nm reached to 1 W mixing 1064 and 1319 nm of cw Nd:YAG lasers. The output power was ten times higher than that by extracavity sum-frequency-generation.