Shigetaka Watanabe

HIGH-REPETITION-RATE HIGH-AVERAGE-POWER 300-FS KRF/TI:SAPPHIRE HYBRID LASER

We have developed a 1-kHz KrF/Ti:sapphire hybrid laser system. Average power was 7 W at 248 nm with a pulse width of 300 fs. A kilohertz Ti:sapphire regenerative amplifier at a wavelength of 745 nm is also described.

Energy distribution of photoelectrons generated from highly charged ions in a circularly polarized intense laser field

We observed the energy distribution of the photoelectrons generated from the highly charged ions in the tunneling regime by using a circularly polarized Ti:Sapphire laser (745 nm, 100 fs). The peaks for each successive charge state up to Ar3+, Kr4+, and Xe5+ were clearly resolved, and the peaks due to higher charge states were flattened in the high-energy region and deviated from those predicted by the quasistatic model. This deviation is explained by pondero-motive acceleration in the strong field gradient. In Xe, Xe8+ was generated at a peak intensity of 2.0 × 1016 W/cm2.

Ultrashort pulse generation by high-order harmonics

Summary form only given. We demonstrated for the first time the autocorrelation measurement in the extreme ultraviolet region by using the two-photon ionization of rare gases and observed 27-fs pulses at the 9th Ti:sapphire laser harmonic. The experimental setup for the autocorrelation measurement is shown. The fundamental pulses were spatially divided into two beams in a delay line before a pulse compressor.

Extreme ultraviolet emission from Xe clusters excited by high intensity lasers [for lithography]

Summary form only given. The property of EUV generation from Xe clusters irradiated with intense lasers was studied. The irradiation conditions were changed with using various laser systems. The wavelength, the pulse width, and the pump energy were widely changed. Xe cluster jet was generated with a supersonic gas jet. Typically, the average number density was measured to be 5 /spl times/ 10/sup 18/ cm/sup -3/ with the backing pressure of 7 atm. The EUV spectrum was obtained with a transmission grating spectrometer. As a result, the highest conversion efficiency can be obtained with a subpicosecond KrF laser pulse in the low density Xe cluster jet. This EUV source is thought to be a debris free source. Then it is attractive for the application to the EUV lithography. Recently, a subpicosecond KrF laser system of 50 W in average power was developed. If we use this system, 5 W EUV source can be obtained with a debris free condition.

Femtosecond measurement of high-order harmonic pulse width and electron recombination time by field ionization

Summary form only given. In recent years high-order harmonic generation has become a promising method for the production of coherent XUV or soft X-ray radiation. In this study we demonstrate a pulse width measurement of the high-order harmonic pulse using the change of the bound-free absorption by the femtosecond dynamics of field ionization. The 9th harmonic of Ti:sapphire is absorbed by neutral Kr atoms, but not absorbed by Kr/sup +/ because the photon energy of the 9th harmonic (14.1 eV) is higher than the ionization potential of neutral Kr (14.0 eV), but is lower than that of Kr/sup +/ (24.4 eV).