2-DIMENSIONAL BEAM SMOOTHING TECHNIQUE FOR KRF LASER SYSTEMS

Broad-band random-phase (BRP) irradiation is one of the beam smoothing techniques for KrF laser drivers. We have introduced this technique i nto the KrF laser system ASHURA. By one-dimensional (1D) BRP smoothing , the speckle pattern in conventional random-phase irradiation has bee n removed. Two BRP beams were overlap-focused on the target incoherent ly. Although the obtained profile is rather smooth, some low-frequency nonuniformity remains. To improve the uniformity, a new technique for two-dimensional (2D) smoothing has been proposed. In this technique, a wedged etalon is used to get angular dispersion to the orthogonal di rection to the 1D BRP effect. The preliminary experiment has been carr ied out.