WAVEFRONT PRESERVING LASER BEAM SHAPER

摘要

An optical arrangement for laser beam shaping comprises a polarisation transforming optical element and polarisation analysing optical element which contribute together to spatially variable power losses and create a predetermined transmission pattern, defined by a distribution TXY. The polarisation transforming optical element is fabricated from a transparent and optically isotropic material such as fused silica, by inscribing at least one in-volume anisotropic layer of self-assembled sub-wavelength nanogratings using the ultrafast laser direct writing technique. At all transverse coordinates of the anisotropic layer or layers, constant phase retardation between orthogonal polarisation components is ensured. A space-variant polarisation control and the predetermined transmission distribution TXY are created by varying orientations of the nanogratings being inscribed. This invention can be employed in high power laser systems to form a beam profile of a desired shape. The overall power conversion efficiency of the whole beam shaping system when converting a Gaussian beam into a flat-top beam is not lower than 50%.