Spatial beam shaping of femtosecond pulses with an optically addressed light valve

Abstract

We propose a versatile set-up dedicated to programmable beam shaping of femtosecond pulses in a focal plane. A non-pixelated liquid-crystal light valve is used as the phase-front modulator. We demonstrate active and adaptive wavefront correction of a 4-µJ, 100-kHz amplified laser chain, where residual wavefront distorsions are decreased down to λ/15 peak-valley and λ/100 rms. The subsequent improvement for micromachining applications is investigated, and diffraction-limited holes are demonstrated on various materials. Moreover, beam patterning in the focal plane is also presented. Theoretical calculations of the required phase modulation are proposed, and experimental shapes are demonstrated, like square and circular top-hats, as well as triangle or doughnut shapes.