Junji Kawanaka

30-mJ, diode-pumped, chirped-pulse Yb:YLF regenerative amplifier

A diode-pumped chirped-pulse regenerative amplifier with a cooled Yb:YLF crystal has been developed. The output pulse energy is 30 mJ at 20-Hz repetition rate. A high effective extraction efficiency of 68% is obtained, which is attributed to reduced saturation fluence at low temperature and to a high effective pulse energy fluence during regenerative amplification. After pulse compression by use of a parallel grating pair, 18-mJ pulse energy and 795-fs pulse duration are obtained.

Quantum-Defect-Limited Operation of Diode-Pumped Yb:YAG Laser at Low Temperature

We have demonstrated a quantum-defect-limited operation in a diode-pumped Yb:YAG oscillator at low temperature. The highest slope efficiency of 90% at the crystal temperature of 70 K was obtained, which was close to the quantum efficiency of 91.2%. An optical-to-optical efficiency and a laser gain were 74% and 8 cm-1, respectively at a low pump intensity of 2.3 kW/cm2.

Observation of vacuum-ultraviolet Kr(2)* laser oscillation pumped by a compact discharge device.

We have demonstrated vacuum-ultraviolet (VUV) Kr(2) * laser oscillation as a result of the realization of a stable self-sustained discharge of high-pressure Kr by use of a compact discharge device. Glow discharge was obtained with as much as 10 atm of pure Kr. The VUV emission intensity centered at 147.8 nm abruptly increased when the charging voltage exceeded a certain value. In addition to this threshold behavior, considerable spectral narrowing (4.0?0.4 nm) was observed when the charging voltage increased. The maximum output energy at 148 nm was 150muJ . The gain coefficient was estimated to be 1.1% cm (-1) .

Tunable Continuous-Wave Yb:YLF Laser Operation with a Diode-Pumped Chirped-Pulse Amplification System.

We have demonstrated a diode-pumped Yb:LiYF(4) (Yb:YLF) laser oscillator for the first time to our knowledge. A wide tuning range of 25 nm and a high slope efficiency of 50% were obtained at a high laser-diode pump intensity of 100 kW/cm(2). Emission and absorption spectra of the Yb:YLF crystal at 8 K represent a wide laser gain width of 38 nm, indicating efficient laser operation similar to that of a four-level laser system with a reduced saturation fluence of 11 J/cm(2).

Improved high-field laser characteristics of a diode-pumped Yb:LiYF4 crystal at low temperature.

We have demonstrated a diode-pumped Yb:LiYF4 laser oscillator at liquid nitrogen temperature in free-running mode. The obtained laser gain was 21 cm-1, which was 15 times as high as that at room temperature. The effective tuning range was broadened to 35 nm due to absorption spectral narrowing.

Discharge-pumped vacuum ultraviolet Kr2* laser

We have realized a stable self-sustained discharge of high-pressure rare gases (Ar and Kr) using a compact discharge device. The glow discharge was obtained up to 10 atm of pure Kr. The vacuum ultraviolet emission intensity centered at 148 nm abruptly increased when the charging voltage exceeded a certain value. This threshold behavior indicates the onset of the stimulated emission at the wavelength. In addition to this threshold behavior, a considerable spectral narrowing was observed when the charging voltage exceeded the threshold value. The deconvoluted spectral width was 0.5 nm (FWFIM), which was much narrower than that of 4 nm (FWHM) at the charging voltage below the threshold. This significant spectral narrowing also strongly indicates the onset of the stimulated emission at 148 nm.

Quantum-defect-limited operation of diode-pumped Yb:YAG laser at low temperature

A high slope efficiency of 90.3% was obtained in a diode-pumped Yb:YAG oscillator at 70 K. An optical-to-optical efficiency of 74% was also high at a low pump intensity of 2.3 kW/cm2.

Oscillation characteristics of a discharge-pumped VUV Kr excimer laser

We have used a pair of newly constructed electrodes to improve the discharge stability and electrical input power. The electrode shape was designed so that the discharge width became narrower, which lead to the increase of the input power density by 22%. As a result, the maximum output energy increased from 150 to 200 μJ at 147.8 nm. The pulse duration of 250 ns (FWHM) became shorter compared to the previous result (400 ns). This long pulse operation indicated the laser oscillation in an afterglow mode. The laser beam shape was circular with a beam divergence of 2.5 mrad. Because of the long pulse duration, this beam shape reflected on a cavity mode (multi-mode) as a result of the optical feedback. A small signal gain coefficient increased almost linearly with the increase of the discharge voltage. The maximum gain coefficient at 147.8 nm was 3.5%cm-1 at 31 kV.

0.2 J, 100 Hz Cryogenic Laser by Using Yb:YAG Crystal

A diode-pumped MOPA laser system with 0.2-J pulse energy and 100-Hz repetition rate has been demonstrated with liquid-nitrogen-cooled Yb:YAG crystals. The slope efficiency was as high as 30% in the four-pass main amplifier.

Milli-Joules, Kilo-Hertz Regenerative Amplifier Using Total-Reflection Active-Mirror with Cryogenic Yb:YAG

A regenerative amplifier by using total-reflection active-mirror with a cryogenic YAG/Yb:YAG composite ceramics has been demonstrated up to kHz repetition rate. A 6.5-mJ pulse energy and a 9.3% optical efficiency were obtained at 200-Hz.