Pulse stretcher with variable pulse length for excimer laser applications

Abstract

Excimer laser systems are often combined with pulse stretchers, e.g., in lithography and Raman spectroscopy to reduce pulse peak intensities. We developed a pulse stretcher which is suited especially for pulse length dependent applications, e.g., in material research. This pulse stretcher is based on imaging and provides identical beam profiles and divergences at different pulse lengths in combination with the possibility of switching between four pulse lengths. Therefore, beam splitters are mounted onto motorized translation stages. These features are important for the characterization and development of improved optical materials for deep-ultraviolet applications. Here, two 193 nm single tube excimer lasers (Lambda Physik: LPX 240i, Cymer: ELS 5600) were evaluated concerning their combinability with an attached pulse stretcher. The wave-front radii of the ELS 5600 are dependent on repetition rate or pulse energy and are changing during warming-up. Without adapted pulse shaping, this can cause destruction of stretcher optics due to moving foci. We found that the LPX 240i could be combined easily with a pulse stretcher using beam shaping with only one cylindrical lens. We could demonstrate that stretched 193 nm laser pulses retard aging of CaF(2) crystals.