The University of Osaka · Engineering
Professor Junji Kawanaka's research lab specializes in high-power, high-energy ultrafast laser systems, with a strong focus on cryogenic solid-state lasers and optical parametric chirped pulse amplification (OPCPA). The lab pioneers the development of diode-pumped Yb-doped laser materials—such as Yb:YLF and Yb:YAG—operating at low temperatures to achieve high efficiency, broad tuning, and exceptional beam quality. Key research directions include regenerative amplification architectures (e.g., TRAM), pulse compression techniques, and the design of next-generation petawatt-class lasers for applications in inertial fusion and fundamental physics. The lab also explores quantum collision dynamics in ultracold atomic systems, particularly in lithium traps, to understand loss mechanisms in quantum devices.
Figures are computed from collected data and may differ slightly.
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.
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).
A MOPA laser system for high pulse energy and high average power has been developed by using a cryogenic Yb:YAG. In the regenerative amplifier with our original TRAM architecture, the high pulse energies of 6.5 and 1.5 mJ were obtained at the repetition rate of 200 Hz and 1 kHz, respectively. An optical efficiency was as high as ηo-o = 9.3% with an excellent beam quality of M 2 < 1.1, which ensured that a cryogenic Yb:YAG TRAM had a high thermal strength. The following four pass power amplifier
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.
We report a measurement of the quadratic collisional loss rate coefficient \ensuremath{\beta} of a $^{7}\mathrm{Li}$ trap as a function of the trap potential in a range covering the energy of the fine-structure splitting $^{2}$${\mathit{P}}_{3/2\mathrm{\ensuremath{-}}}^{2}$${\mathit{P}}_{1/2}$. The value of \ensuremath{\beta} decreases an order of magnitude when the trap potential is increased beyond 0.24 K, and reaches the minimum value of 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensu
A 50 PW ultrahigh-peak-power laser has been conceptually designed, which is based on optical parametric chirped pulse amplification (OPCPA). A 250 J DPSSL and a flash- lamp-pumped kJ laser are adopted as new repeatable pump source. The existed LFEX-laser with more than ten kilo joules are used in the final amplifier stage and the OPCPA with the 2x2 tiled pump beams in random phase has been proposed with several ten centimeter aperture. A pulse duration of amplified pulses is set at less than 10
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