An overview is given of the applications of short and ultrashort lasers in material processing. Shorter pulses reduce heat-affected damage of the material and opens new ways for nanometer accuracy. Even forty years after the development of the laser there is a lot of effort in developing new and better performing lasers. The driving force is higher accuracy at reasonable cost, which is realised by compact systems delivering short laser pulses of high beam quality. Another trend is the shift towards shorter wavelengths, which are better absorbed by the material and which allows smaller feature sizes to be produced. Examples of new products, which became possible by this technique, are given. The trends in miniaturization as predicted by Moore and Taniguchi are expected to continue over the next decade too thanks to short and ultrashort laser machining techniques. After the age of steam and the age of electricity we have entered the age of photons now Keywords: Micro-machining, Laser, Ablation 101, (Figure 2.3) has simulated the interaction and ablation behaviour of aluminium, copper and silicon at 266 nm wavelength. The optical penetration depth was 7, 12 and 5 nm respectively. The applied power density was in the range of 5 to 50.109 W/cm2. It was found that the material evaporates as small particles (0.3-10 nm), most of them smaller than 1 nm. The average velocity of

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Variety and complex interaction of physical processes during laser cutting is a critical characteristic of the laser cutting of metals. Small spatial and temporal scales complicate significantly the experimental investigations of the multi-phase fluid flow in the conditions of laser cutting of metals. In these conditions, the surface formed during the cutting is an indicator determining the melt flow character. The quantitative parameter reflecting the peculiarities of the multi-phase fluid flow, is normally the roughness of the forming surface, and the minimal roughness is the criterion of the qualitative flow [1-2]. The purpose of this work is to perform the experimental comparative investigation of the thermophysical pattern of the multi-phase melt flow in the conditions of the laser cutting of metals with the laser wavelength of 10.6 μm and 1.07 μm. During the laser cutting, the local material melting and melt removal by an assistant gas jet take place. Cutting of low-carbon steel sheets is usually carried out in an oxygen jet (oxygen-assisted laser cutting). In this case, the exothermic reaction of iron oxidation is an additive energy source. The power balance for the oxygen-assisted laser cutting and the cutting with a chemically inert gas is written respectively as: AW + W ox = W m + W cond (1) AW = W m + W cond (2) where A is the absorption coefficient; W is the laser power; W ox is the power released at the exothermic reaction; W m is the power consumed for melting; and W cond is the power lost from the cut region due to thermal conductivity. In [2, 3] the authors calculated the energy losses from the thermal conductivity in the laser cutting conditions W cond = λ m t ∆T f(Pe), where f(Pe) is the dimensionless function of the Peclet number Pe = (V b ρ m С m) / λ m , ΔT=T*-T 0 = 2000 0 С [4], λ m is the metal thermal conductivity, С m is the metal heat capacity, ρ m is the metal density, t is the steel sheet thickness, and b is the cut width. Passing to dimensionless variables, we have the general expression for the energy balance: Q + Q ox Pe [1 + L m / (C m ΔT)] + f(Pe), where the following designations are used: dimensionless laser power Q = A W ⁄ (λ m t ΔT),

Using the model of a cylinder-type heat source, the power loss owing to heat conduction in laser cutting and welding of metals is calculated analytically. The case of laser cutting is described by taking into account the influence of the generated cutting kerf using numerical calculations. Both the analytical and the numerical solution for the power loss deposited into the material are well described by approximative formulae. The theoretically predicted power loss into the cut workpiece is confirmed by measurements of the temperature rise within the metal sheet in laser cutting experiments.

This study presents a novel numerical model for laser ablation and laser damage in glass including beam propagation and nonlinear absorption of multiple incident ultrashort laser pulses. The laser ablation and damage in the glass cutting process with a picosecond pulsed laser was studied. The numerical results were in good agreement with our experimental observations, thereby revealing the damage mechanism induced by laser ablation. Beam propagation effects such as interference, diffraction and refraction, play a major role in the evolution of the crater structure and the damage region. There are three different damage regions, a thin layer and two different kinds of spikes. Moreover, the electronic damage mechanism was verified and distinguished from heat modification using the experimental results with different pulse spatial overlaps.

Direct applications of High Power Diode Lasers (HPDLs) like hardening, heat conduction welding of metals and joining of polymers have already been demonstrated also in the industrial environment. Relatively low intensities in the range of 10(exp 3) Wcm(exp -2) are sufficient for these applications. While the commercial HPDL systems are built on the basis of diode laser bars with 40 W output power, in the meantime a record cw-output power of 267 W per bar has been demonstrated. The achievable higher output power per bar will lead to enhanced applicability of HPDLs and thus to a further steep increase of their industrial use. Improved packaging technology, multiplexing the emission of single bars and coherent coupling as well as promising new diode laser structures like Z-shaped broad area emitters are discussed. In this report emphasis is laid on the potential applicability of commercial HPDLs for metal working with elevated intensities up to 10(exp 5) Wcm(exp -2), like oxygen cutting and the worldwide first deep penetration HPDL-weld up to a sheet thickness of 6 mm in stainless steel. These results have been predicted by proper theoretical modeling. Strong reduction of phase space dimension takes place in convective-diffusive type Free Boundary Problems typical for thermal processing. This property makes possible to construct approximate finite dimensional dynamical systems being solvable with controlled error. Numerical solutions of the full problem are used to investigate the quality of the approximate model. Observable quantities of the technical processes like signals from monitoring devices are part of the solution and solutions to the inverse problem are given

High peak power lasers have been used for years for ablating matter. The most relevant application of this process is laser marking. Marking meets the demands of applications although the quality of ablation has potential to be further improved. However, the qualitative results of the ablation process especially for highly efficient removal of matter in the liquid phase like drilling have not met the standards of alternative processes - the latter is only the case in niches. On the other hand, the ablation by ultrafast lasers in the pulse regime of ps or below, which might meet the quality demands in terms of geometric precision, was too slow for economically feasible application because of the lack of average power. In fact, both process domains have been developed substantially and thus lead to a technological level which make them ready for industrial innovations. In a series of three articles on laser drilling - from fundamentals to application technology - the resu lts of more than a decade of research and development are summarized with the purpose of displaying the bright application future of this laser process. This present part I deals with fundamentals, modeling, and simulation of laser drilling. Part II covers processing techniques, whereas part III is dedicated to systems and application technology. Fundamentals, modeling, and simulation: Theoretical analysis of the process from fs- to s-pulses involves three inputs: numerical simulation, relevant analytic modeling, and as an important input for understanding, process analysis. The reduction of the models guided by experimental input leads to descriptions and knowledge of the process, which allows for strategic improvement of the applicability. As a consequence, process strategies can be derived, meeting the challenges of the application related to shape and accuracy of the surface free of recast as well as the economical demand for high speed processing. The domains of "cold ablation," "hot ablation," and "melt expulsion" are differentiated. Especially, the formation of recast up to closure of the drill is quantified. Tailoring the process parameters toward the individual application according to the know-how reached by the state of the art modeling and simulation leads to sound innovations and shorter innovation cycles

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