<title>Monitoring and shaping of excimer laser beam profiles</title>

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 100mm down to 1OOim. 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.

Planar Laser-Induced Fluorescence of H20 to Study the Influence of Residual Gases on Cycle-to-Cycle Variations in SI Engines

“…Downloaded by [Northeastern University] at 14:19 03 January 2015 Distribution measurements will also be seriously affected by camera noise and beam profile variations. Camera noise could be reduced by careful low pass filtering, and beam profile variations could in principle be reduced by normalizing each image with a simultaneously recorded laser profile, or by using homogenizing optics to create a stable profile which is effectively decoupled from the lateral fluctuations of the laser beam (Mann et al, 1993). Finally, temperature variations could bias the measurements.…”

Numerical modeling of spatial coherence using the elementary function method

“…Because of the shape and intensity profile of the raw excimer beam, these transformations cannot be made using the simple optical systems used for lasers with well-behaved Gaussian beams. The most popular technique is beam integration, or beam folding, that consists of mixing fractions of the input beam to smooth out the intensity spikes [26][27][28][29][30]. This device implicitly assumes spatial incoherence of the mixed beams.…”

Diffraktive Phasenelemente für partiell-kohärente UV-Laserstrahlung

“…Die inhomogene Intensitätsverteilung, die hohe Divergenz und die geringe Fokussierbarkeit (geringe räumliche Kohärenz) der Excimer-Laserstrahlung muß den jeweiligen Anforderungen angepaßt werden. Die Erzeugung von homogenen Profilen mit rechteckigen Strahlquerschnitten kann mit Multifacettenelementen [14] refraktiv [41] oder diffraktiv [43] realisiert werden. Die Formung von Excimer-Laserstrahlung mit Diffraktiven Phasenelementen zur effizienten Mikromaterialbearbeitung konnte erfolgreich für ringförmige Foki [5], [52], Spot-Arrays [27] oder Sechsecke [52] demonstriert werden.…”