Appl. Phys. B 105, 255–261 (2011)

The ability to temporally shape high-energy UV pulses is important for modern large-scale femtosecond X-ray sources such as X-ray free-electron lasers, where the temporal pulse profile is directly correlated with the longitudinal electron bunch density. Simulations indicate that the longitudinal flat-top intensity profile is one of the most favourable shapes for maintaining the high brilliance of an electron beam during transportation from the electron gun to the linear accelerator. However, the generation of flat-top or arbitrarily shaped high-energy pulses in the 250–300 nm range remains a challenge. Alexandre Trisorio and co-workers in Switzerland have now combined a highly efficient double-prism stretcher with an acousto-optic programmable dispersive filter applied directly in the UV spectral region to demonstrate the temporal shaping of 270 nm pulses at energies of up to 37 μJ. The technique enables the generation of highly resolved pulse shapes with flat-top, asymmetric and 'M-shaped' temporal profiles. Although the scheme is limited by two-photon absorption, it nevertheless represents a flexible and efficient method for arbitrarily shaping the phase and amplitude of high-energy picosecond UV pulses. The researchers say that their design could have important applications for free-electron lasers that demand complex temporal pulse shapes in the picosecond regime.