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A new method for the generation of high-intensity short KrF laser pulses was developed. The method efficiently uses truncated leading-edge seed-pulse generation by stimulated Brillouin scattering and pulse-shape steepening by saturated amplification, which is mainly based on the Frantz–Nodvik solution. Short KrF pulses of 7 ps were obtained from 20 ns seed pulses without using mode-locked lasers. The experimental results agreed well with the numerical calculations.

In the Super-ASHURA KrF Laser at ETL, a main amplifier with full pumping duration (270 ns) and 12 beam lines have been completed. At present, total output energy of 2.7 kJ has been extracted from the main amplifier by double-pass amplified 12 beams (20 ns×12) with an aperture filling factor of 74%. Local intrinsic efficiency has reached 10%. In the Raman amplification which is to be used for high peak power pulse generation, multi-pass forward amplification of nanosecond Stokes pulse showed an energy conversion efficiency of 73%. Also, a multi-joule short Stokes pulse (150 ps) has been obtained from 12.5 J, and 20 ns pulse by saturated backward amplification of a self-generated Stokes pulse. To investigate the effect of irradiation smoothness, the two-dimensional profile of the target rear surface displacement has been measured by using short (

The ` Super-ASHURA ' KrF laser system is currently under development at the Electrotechnical Laboratory. An electron-beam pumped large-aperture KrF laser amplifier named ` Amp4 ' has been completed and is operational as the main amplifier. Amp4 and the currently operating ` ASHURA ' pre-amplifiers (660 J, six beams) have been combined to form the upgraded system. Laser energy extraction experiments from Amp4 have been started (2.3 kJ, 12 beams).

We have developed a useful method for power multiplication of KrF laser light, called forward Raman pulse compression. In this method, a multi-pass forward Raman amplifier is used. Adjustment of incident timing between pump and Stokes light into each path provides efficient Raman energy conversion from long KrF laser to short pulse Stokes light. Even in the case of double path configuration, output Stokes was demonstrated to grow up to 1.3 times the pump intensity. By using an intersecting multi-path of Stokes and pump light, spatial non-uniformity of the output Stokes reduced to less than 5%.

Backward Raman pulse compression of high-power KrF laser using focused geometry was investigated. This simple configuration has various advantages suitable for creating not only high-power but also high-energy Stokes pulses. An energy conversion efficiency of 27% and power gain of 30 have been achieved.

Ionization balance of l0ps KrF laser produced plasmas was investigated under various irradiation conditions. From the laser intensity dependence of relative conversion efficiencies of emissions from F-like and Ne-like Ge ions, it was found that higher ionization state was realized, when a prepulse ASE(amplified spontaneous emission) accompanying a l0ps pulse was suppressed. The absolute conversion efficiency of X-rays from 6A to 9A was also estimated.

A new technique is proposed to achieve smooth laser irradiation profiles on laser fusion targets employing the broad bandwidth of KrF lasers. In this technique, smoothing is obtained by using a spectral dispersing optical device and a random-phase plate placed in front of a focusing lens. Experimental results demonstrate that this simple optical system is effective for smooth irradiation on targets.