Optical systems for high-power laser applications: principles and design aspects

Starting from the optical properties of laser beams, the requirements of optical systems for manipulating laser radiation in industrial applications are derived. The relevant parameters, relations to the diffraction limit and the state-of-the-art design techniques are discussed. The three important types of lasers for use in industrial materials processing operate at wavelengths ranging from the infrared (10.6 μm, CO2 laser; 1.06 μm, Nd:YAG) to the ultraviolet region (excimer lasers). Each wavelength range is associated with specific design challenges. The scarcity of suitable refractive materials for the 10 μm wavelength range and the ultraviolet below 300 nm is a major constraint. Reflective systems are used widely at the longer wavelength, but some designs suffer from coma. The 1.06 μm radiation from the Nd:YAG laser can make use of many well-developed optical means for handling visible light. Energy transport by optical fibres is commonly used. Optical systems for excimer laser applications are specific in that they image a mask onto a workpiece, and use the high photon energy and the high definition possible with the short wavelength for precision micro-machining

Finite element analysis of laser transformation hardening

The problem of determining stresses, phase compositions and temperature distributions during the transformation hardening of steel with a CO-laser beam is investigated. To model the different phases in each material point a parallel fraction model is used, in which each fraction represents one phase. The description of phase transformations is obtained by an incremental formulation of the Avrami-equation for isothermal transformation. A model is developed to describe the superheating of ferrite and pearlite. The model is demonstrated by a detailed computation of stresses, deformations and phase compositions in the case of a stationary laser flash

Laser, het onmisbare gereedschap

De toepassing van lasers in de industriele materiaalbewerking is, na de uitvinding in 1960, vrij spoedig op gang gekomen en vertoont sindsdien een stijgende lijn. Het marktaandeel van lasers voor materiaalbewerking is opgeklommen van ongeveer 20% in 1990 naar bijna 50% in 1995 van de geldswaarde van de wereldwijd verkochte lasers, bij een totale markt die door de jaren heen bij ruim 1 miljard dollar lag.\ud In dit artikel wordt een helder overzicht gegeven van verschillende soorten lasers en gebruik van laseroptiek

Zoom lens designs for use in sheet metal cutting by high power CO2-lasers

For best results and highest speed of cutting of sheet metal by high power lasers, the numerical aperture of the focussed beam must be properly matched to the material thickness. To alleviate the need for frequent changes of fixed-focal-length lenses, a zoom lens system, which allows fast and continuous adaption is desirable. Requirements include near difraction limited performance in a range of, at least, f/3 to f/8 and a back focus in excess of the focal length for lens protection against fumes and spatters. Four zoom lens diesgins for use with CO2-lasers in the 1 to 2 kW range are presented which differ in technical complexity (use of an asperic surface versus an additional lens element) and in the ranges of numerical apertures (f/2.8 to f/8 and f/2 to f/7). Only one of these has so far been built and measured, and cutting tests have shown slightly better performance at the short focal lengths over that of single (ZnSe) lenses of (optimized) meniscus shape