Monitoring and shaping of excimer laser beam profiles

Abstract
The special requirements and possibilities of laser spatial intensity profiling in the UV spectral range are discussed in this paper, along with a description of a high resolution beam monitoring system. Especially developed for excimer lasers, this device allows real-time acquisition of beam profiles with various cross-sections from about 100 mm down to 100 micrometers . The acquired intensity distributions can be comprehensively analyzed, e.g., with respect to homogeneity, energy density, and energy fraction above a given threshold. In addition, we report on experiments with a highly integrating and high efficiency beam homogenizer consisting of crossed cylindrical lenses. It can be used to generate flat-top intensity distributions for nearly any type of input profile, also Gaussian. In combination with the laser beam monitor a high precision adjustment of the employed optics can be performed. The remaining non-uniformity of the obtained beam profile is in the range of 1%, allowing a variety of applications in material processing, medicine and spectroscopy, which strongly require a laterally constant energy density.