Taro Sekikawa

Second-harmonic generation from a KBe(2) BO(3)F(2) crystal in the deep ultraviolet.

By use of KBe(2)BO(3)F(2) (KBBF) crystal with a size of 10 mmx10 mm x1.2 mm and a special prism-coupling technique (PCT), fourth-harmonic generation of Ti:sapphire laser systems from 200 to 179.4 nm has been achieved. Moreover, with a Ti:sapphire laser with a 50-fs pulse duration and a 1-kHz repetition rate, conversion efficiency as high as 13% from 400 to 200 nm without any surface-loss correction has also been obtained. The data show that with the PCT a KBBF crystal can produce deep-UV coherent light with measurable power output.

Generation of vacuum-ultraviolet light by an optically contacted, prism-coupled KBe2BO3F2 crystal

We have demonstrated the second harmonic of a frequency-tripled Nd:YVO4 laser with 2.5-mW quasi-cw output by using an optically contacted, prism-coupled KBe2BO3F2 crystal. We also achieved the second harmonic with a frequency-doubled single-mode Ti:sapphire laser at 172.5 nm and sum-frequency mixing with a dual-wavelength Ti:sapphire laser at 163.3 nm. These wavelengths are to our knowledge the shortest obtained by use of nonlinear crystals for second-harmonic generation and sum-frequency mixing, respectively.

Generation of subterawatt sub-10-fs blue pulses at 1-5 kHz by broadband frequency doubling.

Blue pulses with durations of 8.5 fs are generated by broadband frequency doubling of subterawatt Ti:sapphire laser systems at 1-5-kHz repetition rates. The average powers are 1.6 W at 5 kHz and 1.9 W at 1 kHz. The peak power is 0.16 TW with a duration of 12 fs at 1 kHz.

Generation and focusing of submilliwatt-average-power 50-nm pulses by the fifth harmonic of a KrF laser

We demonstrate generation and focusing of 49.7-nm pulses with an average power of 0.1 mW at 200 Hz and with a pulse energy of >1 microJ at 10 Hz by the fifth harmonic of a femtosecond KrF laser. The fifth harmonic is selected and focused with a concave Sc/Si multilayer mirror to a diameter of 2microm, resulting in a peak intensity of 0.5 TW/cm(2), which will make extreme-ultraviolet nonlinear optics feasible. A novel single-shot linear in situ method of spot-size measurement by use of self-trapped exciton luminescence is also demonstrated.

Electromodulation spectroscopy of CdS microcrystallites embedded in polymer films

CdS microcrystallites embedded in acrylonitrile-styrene copolymer films are studied by the electromodulation spectroscopy of absorption and photoluminescence(PL) to clarify the electronic structure near the absorption edge for the first time. It is elucidated that three states exist near the absorption edge. One is the lowest exciton state, another is a surface state, and the other is a D-A state. The electroabsorption spectra are explained by the quantum confined Stark shift of the lowest exciton. The electromodulation spectra are explained by assuming a surface state and a D-A state.

50-W average-power, 480-fs KrF excimer laser with gated gain amplification

We have developed a 50-W average-power KrF excimer laser with a pulse width of 480 fs by using the method of gated gain amplification at a 200-Hz repetition rate.

Generation of milliwatt narrow-bandwidth vacuum ultraviolet radiation by an all-solid-state tunable high-average-power laser system

Generation of milliwatt narrow-bandwidth vacuum ultraviolet radiation by two-photon resonant four-wave mixing in Xe at 153 nm is demonstrated. The output of extreme ultraviolet radiation was at the microwatt level at 85 nm. For this demonstration, we developed an all-solid-state tunable 5-kHz Ti:sapphire laser system that produces 0.6-ns 0.7-GHz-bandwidth pulses at an average power of 32 W at the fundamental, 12 W at the second harmonic, and 6.3 W at the third harmonic.

Auger-free luminescence excited by high-order harmonics of a femtosecond Ti : sapphire laser

We have succeeded in observing the Auger-free luminescence, which is radiative recombination of the valence-band electron with the inner-shell hole in alkali and alkaline-earth halide crystals, by using high-order harmonics of a femtosecond Ti : sapphire laser for the first time.

High-power sub-100-fs UV pulse generation from a spectrally controlled KrF laser

High-power sub-100-fs UV pulses were generated from a KrF excimer laser by spectral control and chirped-pulse amplification. The spectral width was broadened to 1.6 nm, resulting in 72-fs, nearly transform-limited pulses. The average output powers at 1 kHz were 0.6 and 1.2 W for pulse widths of 72 and 110 fs, respectively.

Sub-picosecond fluorescence spectroscopy of the M intermediate in the photocycle of bacteriorhodopsin by using up-conversion fluorometry

A fluorescence up-conversion method was applied to the measurement of the fluorescence lifetime of the M intermediate with a 13-cis retinal Schiff base. M formed under cw visible light (440–800 nm) irradiation of the purple membrane suspension of Halobacterium salinarum containing diethyl ether or guanidine hydrochloride at 24°C. An excitation source was a frequency-doubled Ti:Sapphire laser (408 nm, 240±10 fs). The 500 nm fluorescence of M was mixed with the fundamental of the laser and converted to UV for detection. The measured lifetimes (0.6 and 0.3 ps in ether and in guanidine, respectively) were shorter than those of protonated all-trans retinal Schiff bases in solution and in apoprotein.