Toshimasa Kozeki

Chirped-pulse amplification of ultraviolet femtosecond pulses by use of Ce 3+ :LiCaAlF 6 as a broadband, solid-state gain medium

Chirped-pulse amplification in the ultraviolet region is demonstrated by use of a broadband Ce(3+): LiCaAlF(6) laser medium. A modified bow-tie-style four-pass amplifier pumped by 100-mJ, 266-nm pulses from a Q -switched Nd:YAG laser has a gain factor of 370 and delivers 6-mJ, 290-nm pulses. After dispersion compensation, the output pulses can be compressed to 115 fs.

Nanocluster crystals of lacunary polyoxometalates as structure-design-flexible, inorganic nonlinear materials

Lacunary polyoxometalates, large inorganic, structure-design-flexible, nanocluster crystals are found to have higher optical nonlinearity than KH2PO4 by the powder second-harmonic-generation method. Moreover, the capability of generating ultraviolet radiation down to around 300 nm is found. The basic criteria to design the high nonlinearity are also discovered by the reduction of the molecular symmetry.

High-energy, all-solid-state, ultraviolet laser power-amplifier module design and its output-energy scaling principle.

We demonstrate that a coaxially pumped, large-aperture ultraviolet power-amplifier module with solid-state tunable laser medium Ce(3+):LiCaAlF6 has 98-mJ, 290-nm, and 3-ns output pulses with a sufficient extraction efficiency of 25%. The detailed information of design parameters, including the gain-coefficient dependence on pump condition, is successfully accumulated for further energy scaling for a terawatt-class ultraviolet chirped pulse amplification laser system or a high-pulse-energy laser system.

High-Pulse-Energy Ultraviolet Ce3+:LiCaAlF6 Laser Oscillator with Newly Designed Pumping Schemes

Using a large Ce3+:LiCaAlF6 (Ce:LiCAF) crystal, 60 mJ pulses were generated directly from a quasi-coaxially pumped Ce:LiCAF laser. In addition, a new noncollinear Brewster-angle-pumping disk oscillator scheme was demonstrated for further output-energy scaling.

Direct Generation of 27-mJ, 309-nm Pulses from a Ce3+:LiLuF4 Oscillator Using a Large-Size Ce3+:LiLuF4 Crystal.

An ultraviolet solid-state Ce3+:LiLuF4 (Ce:LLF) laser which was pumped transversely by a KrF excimer laser with the repetition rate of 1 Hz produced a 27-mJ, 309-nm pulse using a large-size Ce:LLF crystal which was grown by the Czochralski (CZ) method, and the slope efficiency was approximately 17%.

Ce/sup 3+/:LiCaAlF/sub 6/ crystal for high-gain or high-peak-power amplification of ultraviolet femtosecond pulses and new potential ultraviolet gain medium: Ce/sup 3+/:LiSr/sub 0.8/Ca/sub 0.2/AlF/sub 6/

To develop high-peak-power ultrashort pulse laser systems in the ultraviolet region, a large Ce/sup 3+/:LiCaAlF/sub 6/ (Ce:LiCAF) crystal, a tunable ultraviolet laser medium with large saturation fluence and broad gain spectrum width, was grown successfully with a diameter of more than 70 mm. To demonstrate high small signal gain, a four-pass confocal amplifier with 60 dB gain and 54 /spl mu/J output energy was constructed. Chirped pulse amplification (CPA) in the ultraviolet region was demonstrated using Ce:LiCAF for higher energy extraction. A modified bow-tie-style four-pass amplifier pumped by 100-mJ 266-nm 10-Hz pulses from a Q-switched Nd:YAG laser had 370-times gain and delivered 6-mJ 290-nm pulses. After dispersion compensation, the output pulses can be compressed down to 115 fs. This is the first ultraviolet, all-solid-state high-peak-power CPA laser system using ultraviolet gain media, and this demonstration shows further scalability of the Ce:LiCAF CPA system. Additionally, a new gain medium, Ce/sup 3+/:LiSr/sub 0.8/Ca/sub 0.2/AlF/sub 6/, with longer fluorescence lifetime and sufficient gain spectrum width over 18 nm was grown to upgrade this system as a candidate for a final power amplifier gain module.

Hybrid time-resolved spectroscopic system for evaluating laser material using a table-top-sized, low-jitter, 3-MeV picosecond electron-beam source with a photocathode

Hybrid time-resolved spectroscopy of laser media comparing electron-beam excitation and optically excited cases is performed using a newly developed, table-top-sized, low-jitter, 3-MeV picosecond electron-beam source with a photocathode. The properties of an electron-beam-pumped Ce3+:LiCaAlF6 (Ce:LiCAF) ultraviolet laser medium significant differ from those of an optically pumped medium.

0.43 J, 10 Hz Fourth Harmonic Generation of Nd:YAG Laser Using Large Li2B4O7 Crystals

Using large-sized Li2B4O7 crystals, 0.43 J, 266 nm pulses are obtained from a 10 Hz Nd:YAG laser with a total conversion efficiency of 30.5%. Moreover, 4 W operation for over 15 h is demonstrated.

High-gain, reflection-double pass, Ti:sapphire continuous-wave amplifier delivering 5.77 W average power, 82 MHz repetition rate, femtosecond pulses

A confocal, reflection-double-pass, Ti:sapphire continuous-wave (cw) amplifier with a small signal gain of 4.2 has been invented. Femtosecond pulses with an 82 MHz repetition rate from a mode-locked Ti:sapphire laser are amplified to 5.77 W average power with a slightly saturated gain of 3.7 through an amplifier pumped by three cw green lasers, and the extraction efficiency reaches 10.6%.

High-energy pulse generation from solid-state ultraviolet lasers using large Ce:fluoride crystals

Abstract A large Ce3+:LiCaAlF6 (Ce:LiCAF) crystal with 15 mm diameter was grown successfully by the Czochralski method. Owing to its large size, 60 mJ, 289 nm pulses were generated directly from a quasi-coaxially pumped Ce:LiCAF laser. In addition, a new noncollinear Brewster-angle-pumping disk oscillator scheme was demonstrated for further output-energy scaling. An ultraviolet solid-state Ce3+:LiLuF4 (Ce:LLF) laser which was pumped transversely by a KrF excimer laser with the repetition rate of 1 Hz produced a 27 mJ, 309 nm pulse using a large Ce:LLF crystal which was grown by the Czochralski method, and the slope efficiency was approximately 17%.