Laser beam characterization

Abstract

Many industrial applications of excimer lasers, like for example photolithography or material processing, strongly rely on the stability and the precise control of the characteristics of the emitted radiation, such as pulse energy, beam width, divergence, pointing stability etc. Therefore reliable standardized methods for the evaluation of beam parameters as well as accurate diagnostic tools for UV laser beam characterization are mandatory. Whereas the output energy and power of excimer lasers can be monitored with standard calorimetric or piezoelectric measuring tools used also for other high power lasers, recording of spatial beam profiles, or more exactly the energy density distributions, requires specific instrumentation adapted to the output characteristics of excimer lasers. Beam profiling, both in the near-field and the far-field of the radiation, is of special importance for excimer laser technology. In addition to a rapid assessment of the overall shape of a typically relatively large beam, it allows evaluation of the most important parameters and propagation characteristics. Table 7.1 gives an overview of the relevant quantities to be evaluated from the acquired energy density profiles, addressing also the respective ISO standards [1, 2, 3, 4, 5]. Thanks to the substantial improvemements achieved in recent years within the EUREKA project CHOCLAB [6], these standards can in their current version be applied successfully to excimer laser beams. This has been checked also in Round-Robin experiments by testing different measuring tools at the same laser source [7]. © 2005 Springer-Verlag Berlin Heidelberg.