High-damage-threshold beam shaping using binary phase plates.

An approach to near-field beam shaping using a pixellated binary phase plate is presented. Continuous spatial-intensity modulation without phase modulation is obtained in an image plane of the phase plate after far-field Fourier filtering. The phase plate is a substrate with etched pixels introducing a pi-phase shift at the use wavelength. The pixel distribution is designed with a modified error-diffusion algorithm. Because of the absence of absorption from the metal layer of conventional shapers, the damage threshold of a phase shaper is mostly limited by the damage threshold of the substrate. A damage threshold of the order of 40 J/cm(2) is demonstrated in the nanosecond regime.