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A 253 J with 26 ns at 0.2 Hz laser performance was demonstrated using a LD pumped cryogenically cooled Yb:YAG ceramics laser amplifier. A high energy storage of 344 J was achieved with a stored energy density of 0.58 J/cm3 using a 1 kJ output multidirectional-pumping system. High energy-extraction efficiency of 56.5% was achieved with high energy fluence of 4.63 J /cm2. To the best of our knowledge, this is the highest output energy obtained with a repetitive nanosecond pulse by LD pumped solid-state laser. This paper presented a design of 1 kJ amplifier based on experimentally proven numerical data.

A 11.5 J at 40 ns output has been obtained from a diode-pumped cryo-cooled Yb:YAG ceramics active-mirror laser amplifier system. The system consists of two amplifier heads which has four Yb:YAG ceramic disks and two pump LD modules. The Yb:YAG ceramics are cooled by conventional cryostat from rear side and are pumped by LD modules from front-side. A pump pulse is delivered to Yb:YAG ceramics coaxially with a seed pulse to reduce damage risk at a dielectric coating of Yb:YAG ceramics due to simplified coating design. To realize this system design, a LD module has been developed to keep a rectangle pattern with side length of around 37 mm among imaging depth of about 10cm at working distance of about 410 mm. As an experimental result of two pass amplification, a 11.5 J pulse energy was obtained with input energy of 1.0 J and total pump energy of 90.2 J. Then, an optical-to-optical conversion efficiency was 11.6% and an extraction efficiency was estimated to be 42%. In our knowledge, this is the highest output energy with nano second pulse duration in cryo-cooled Yb:YAG active-mirror laser amplification scheme. A repetition rate of 0.05 Hz depends on a limitation of a repetition rate of the seed pulse. A dependence of small-signal-gain on pumping repetition rate of the active-mirror laser head was experimentally evaluated. From the experimental result, we have estimated a feasible repetition rate of over 5 Hz. A 10 Hz operation will be demonstrated to reduce a thermal resistance between Yb:YAG ceramics and cryostat. Finally, this laser amplifier system is installed to a 100-J class laser system as preamplifier.

A 100 J class diode-pumped solid-state laser system has been developed as a platform for acceleration of laser processing application. A 117 J output of pulse energy has been demonstrated with the main amplifier.

We demonstrated 117-J laser output in a nanosecond regime with a diode-pumped Yb:YAG ceramic laser amplifier. The repetition rate was 0.05 Hz, and the pulse duration was around 40 ns. 5-J input energy was amplified by two cryogenically cooled Yb:YAG ceramic laser heads. Six Yb:YAG ceramic disks in each laser head were cooled by cryogenic helium gas with a temperature of 175 K. The output energy of the first and second laser heads was about 28 and 117 J.

We report a directly modulated laser diode system capable of generating picosecond-pulse bursts and nanosecond pulses simultaneously. A generated pulse shape can be arbitrary controlled with a temporal resolution of 1 ns and wavelength of 1064 nm. A two-stage Nd:YVO4 amplifier boosts the pulse energy to hundreds of microjoules to process JIS 304 stainless steel. Characterization of processed holes irradiated by different pulse durations and shapes reveals that the ablation efficiencies with the nanosecond pulses are two times higher than those with the picosecond-pulse bursts. A clear hole with a taper angle of 1.5° is realized by the picosecond-pulse bursts with a 10-ns pulse interval. The combination of pulses with large differences in timescales offers an efficient production line with a single laser system.

A 64J at 10 ns output was demonstrated by diode-pumped cryogenically cooled Yb:YAG ceramic laser amplifier. An extraction efficiency was evaluated 43.3% at stored energy of 148J with small-signal-gain of 20.4.

A compact 40kW at 10Hz output LD module has been developed for cryogenically cooled Yb:YAG ceramics active-mirror laser amplifiers for 10J at 10Hz output laser system. Pumping intensity is 2.5kW/cm2 and footprint of the LD module is 18cm × 77cm.

Ultrafast optical response has been investigated using fs laser system on a perovskite-type cobalt oxide, Pr0.5Ca0.5CoO3 which undergoes the insulator-metal transition at 89 K. After the photo-irradiation at 30 K, the reflectivity shows a sudden increase. The ultrafast reflectance changes are quantitatively reproduced by the numerical calculation considering the linear combination of the dielectric functions of the initial insulating and the final metallic state, indicating ultrafast phase transition on the time scale of femtosecond.

A new 5-O-membered crown ether spin-labelled with a triphenylmethyl group was prepared. The intramolecular unpaired π-electron delocalization was investigated by ENDOR. The ENDOR of the crown methylene group adjacent to the aromatic ring revealed non-equivalence in the magnitude of the proton hyperfine splittings. Based on the temperature-dependent ENDOR line separation, the activation energy of the conformational change of the methylene protons was estimated. Upon metal chelation into the crown ring the dissociation of the dimer to the monomer radical was greatly affected, and an increase in the activation energy of the vibrating methylene protons was detected.