Spatial frequency effects of polychromatic ultrashort pulse Bessel beam arrays

摘要

Summary form only given. Thin-film micro-optical components are interesting for ultrashort-pulse beam shaping and characterization because of specific advantages (low dispersion, compactness). Arrays allow to design spatially resolving autocorrelators. Recently, we demonstrated the generation of Bessel-beams from a Ti:sapphire laser for a pulse duration >30 fs in first experiments with arrays of Gaussian-shaped micro-axicons. Theoretical predictions concerning X-pulse formation by spectral interference of conical polychromatic wavepackets in THz and optical range could be verified by detecting characteristic changes of contrast. Whereas other groups used ring-shaped absorbing slits and lenses to transform small parts of the light into an optical Bessel beam, our scheme allows to transfer more energy into the interference zone and to shape a beam matrix by using refractive micro-axicon arrays. Beside the decreasing contrast with shorter pulses, spatial frequency changes were found. Blue-shift could be excluded as responsible mechanism. As a possible explanation, travel time effects were suggested which should be array-specific and neglectable for single elements. Here we give a detailed analysis of the problem of ultrashort pulse spatial frequency effects for arrays of Gaussian-shaped elements based on angular distribution and spectral bandwidth.