Pulse stretcher with two beamsplitting elements for excimer laser pulses.

A pulse stretcher with two beamsplitting elements and an optical ring cavity is proposed. With a two-beamsplitting-element configuration, the temporal profile of the stretched output pulse is effectively improved, and the transient peak power is significantly reduced. By optimizing the radius of curvature of the concave mirrors used in the ring cavity, the spatial profile of the stretched pulse is kept nearly unchanged. The performance of the pulse stretcher is experimentally investigated with a 193 nm excimer laser. By optimizing the splitting ratios of the two beamsplitting elements, the pulse width is extended from 15.5 ns to 46.2 ns with a stretching ratio of 2.89; the transient peak power of the stretched pulse is reduced to 27% of that of the input laser pulse; an energy transmission efficiency of 87.8% is achieved for the proposed pulse stretcher with two beamsplitting elements.