Multibeam second-harmonic generation by spatiotemporal shaping of femtosecond pulses

We present a technique for efficient generation of the second-harmonic signal at several points of a nonlinear crystal simultaneously. Multispot operation is performed by using a diffractive optical element that splits the near-infrared light of a mode-locked Ti:sapphire laser into an arbitrary array of beams that are transformed into an array of foci at the nonlinear crystal. We show that, for pulse temporal durations under 100 fs, spatiotemporal shaping of the pulse is mandatory to overcome chromatic dispersion effects that spread both in space and time the foci showing a reduced peak intensity that prevents nonlinear phenomena. We experimentally demonstrate arbitrary irradiance patterns for the second-harmonic signal consisting of more than 100 spots with a multipass amplifier delivering 28 fs, 0.8 mJ pulses at 1 kHz repetition rate.This work was supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) and FEDER through the projects FIS2010-15746, FIS2009-09522, and SAUUL (CSD2007-00013) and the Fundació Caixa Castelló (P1-1B2010-26). The authors are grateful to the Serveis Centrals d’Intrumentació Científica of the Universitat Jaume I and the Centro de Láseres Pulsados, Salamanca. We are indebted to Professor Jürgen Jahns for providing us with the diffractive lenses