Abstract

Spectrally and temporally resolved characterization of wavefronts of ultrashort pulses is important for the optimization of lasers and components, detecting laser-matter interaction (carrier generation, thermal lensing, self phase modulation), or decoding information. Time-integrated, spectrally resolved wavefront analysis requires tunable or multiple filters or dispersive elements. It was shown [1] that spectrally integrated wavefronts of few-cycle pulses were fairly identical to those reconstructed from discrete spectral sampling. However, the technique suffers from distortions by filters, is not single-shot capable and inapplicable for extracting temporal information. The approach of wavefront autocorrelation [2] combines wavefront division in sub-apertures (Shack-Hartmann sensor, SHS) with nonlinear autocorrelation. By replacing the microlenses of a SHS by microaxicons which generate stable, tilt-tolerant, extended focal zones, improved performance is obtained. A further method extends the wavefront division to frequency resolved optical gating (shackled FROG [3]). Here, we present another essential extension of SHS-based pulse diagnostics. By programming variable axicons into liquid-crystal-on-silicon spatial light modulators (LCoS-SLMs) of stable pulse transfer [4], a more flexible, robust analysis of ultrafast wavepackets is enabled at the same time. Experiments were performed with a Ti:sapphire oscillator (Venteon, pulse duration < 6 fs, spectral bandwidth > 200 nm, repetition rate 80 MHz). A phase-only, reflective LCoS-SLM (2 Megapixels, HoloEye) was used as adaptive array generator. Phase profiles were programmed via gray value maps. The phase transfer was studied with an LX-SPIDER (APE). For extreme off-axis illumination it was shown that parasitic spot deformations can be compensated (Fig. 1). Positions, size, shape and density of sub-beams can be adapted to changing situations while keeping temporal distortions minimal. By encoding geometry, spectral signature or phase, individual spots are better recognized (Fig. 2).

© 2011 Optical Society of America