This article describes the current status of the KrF development programme based on the Sprite laser system at the Rutherford Appleton Laboratory. High reliability and high shot rate have been demonstrated. Using a unique KrF-pumped Raman laser architecture, beam brightness exceeding 2×1019 Wcm-2 sterad-1 giving a focussed intensity >5 ×1017 Wcm-2 has been achieved. The development of transform-limited short-pulse oscillators is shown to be of importance in avoiding spectral broadening in air propagation of high-intensity beams. Beam smoothing of KrF beams in a multiplexed configuration has been demonstrated for the first time. The technique of echelon-free induced spatial incoherence has been shown to produce smooth intensity distributions in the far field, which remain essentially unchanged on amplification. The development of pulsed-power systems capable of exciting multikilojoule laser amplifiers for the next phase of development, the Supersprite system, is briefly discussed.

The temporal contrast is classified into two main regimes, the nanosecond-scale and the picosecond-scale contrast prior to the main pulse. The Lund terawatt laser system is shown to be improved on the nano- and picosecond-scale by a factor of 10 and 50, respectively, when it was optimized for contrast but not for energy. Calculations are also presented to emphasize the role of angular dispersion on the picosecond contrast. Finally we show a compromise between the duration and contrast of femtosecond laser pulses amplified in an optical parametric (chirped pulse) amplifier.

Frequency doubling a 140 × 110 mm 40 J sub-ps 1054 nm beam for laser matter interaction studies was investigated at the Central Laser Facility, with efficiencies greater than 60% being achieved. The conversion characteristics (efficiency, beam quality, focusability, and pulse length) for two large 157 mm diameter aperture high quality KDP crystals of thickness 2 mm and 4 mm were studied. Using a fundamental drive beam of two times diffraction limited quality, focal spots of four times the diffraction limit in the frequency doubled beam were achieved and beam degradation effects shown to be minimal.

The technique of Chirped Pulse Amplification (CPA) developed by Strickland and Mourou (1985) is now in common use on many laser systems [see, for instance, the review by Perry & Mourou (1994)] and has resulted in massive increases in focused intensities. This paper describes CPA implementation on the Vulcan laser system which has generated multi-Joule sub-picosecond pulses whilst maintaining beam quality to produce focused intensities of 5 × 1019 Wcm−2.

The properties of optical parametric amplifiers are well suited to their use as chirped pulse amplifiers in short pulse high-power systems. In addition to the possibility of very simple designs to extend to shorter pulses the limits of millijoule systems, they can be used for very high-intensity applications when used in conjunction with narrow-bandwidth high-energy lasers. Powers exceeding 10 PW and focused intensities more than 1023 W/cm2 are predicted using existing glass laser technology.

The frequency-doubling efficiency and resultant focal spot quality of a large aperture (140 × 89 mm) subpicosecond, chirped pulse amplified (CPA) 1054-nm beam for laser–matter interaction studies has been investigated using the Vulcan Nd:glass laser system (Danson et al. 1998). The effect of B-integral on the CPA beam quality was studied and is shown not to be the dominant cause of the observed frequency-doubled beam break-up. Conversion efficiency tests were carried out on small aperture KDP (type 1) crystals at a range of incident intensities up to 3 × 1011 W/cm2 giving the optimum crystal thickness for pulses in the 0.3–3 ps region. A large-aperture frequency-doubled beam was commissioned and delivered pulses of over 10 TW onto target for an electron acceleration experiment.