Thanks to the past years’ development efforts towards higher average power levels, higher repetition rates and, of course, improved robustness, ultra-short pulsed lasers have been able to enter more and more industrial 24/7-production areas. Despite some exceptions, where ultrashort-pulsed lasers with very high repetition rates are used to weld glass and other sensitive materials, the majority of industrial applications are related to material removal or the use of non-linear effects in transparent materials.
An interesting feature of ultra-short pulsed lasers in MOPA-configuration is the so-called “burst” mode. It provides pulse packages at nanosecond separation using programmable power slopes. Thus, the energy distribution of the pulses within a burst can be adjusted to the specific application task. Using burst pulses, laser-material-interaction is brought into a different regime, as subsequent pulses hit preconditioned material and plasma effects can be used effectively.
Burst pulses can help optimizing surface quality and ablation rates of engraved structures simultaneously. For laser filamentation of transparent and brittle materials, burst pulses provide filaments lengths of several millimeters.
Cold laser materials processing using ultra short pulsed lasers has become one of the most promising new technologies for high-precision cutting, ablation, drilling and marking of almost all types of material, without causing unwanted thermal damage to the part. These characteristics have opened up new application areas and materials for laser processing, allowing previously impossible features to be created and also reducing the amount of post-processing required to an absolute minimum, saving time and cost.
However, short pulse widths are only one part of thee story for industrial manufacturing processes which focus on total costs and maximum productivity and production yield. Like every other production tool, ultra-short pulse lasers have too provide high quality results with maximum reliability. Robustness and global on-site support are vital factors, as well ass easy system integration.
The laser as an industrial tool is an essential part of today’s solar cell production. Due to the on-going efforts in the solar industry, to increase the cell efficiency, more and more laser-based processes, which have been discussed and tested at lab-scale for many years, are now being implemented in mass production lines. In order to cope with throughput requirements, standard laser concepts have to be improved continuously with respect to available average power levels, repetition rates or beam profile. Some of the laser concepts, that showed high potential in the past couple of years, will be substituted by other, more economic laser types. Furthermore, requirements for
processing with less-heat affected zones fuel the development of industry-ready ultra short pulsed lasers with pulse widths even below the picosecond range. In 2011, the German Ministry of Education and Research (BMBF) had launched the program “PV-Innovation Alliance”, with the aim to support the rapid transfer of high-efficiency processes out of development departments and research institutes into solar cell production lines. Here, lasers play an important role as production tools, allowing the fast
implementation of high-performance solar cell concepts. We will report on the results achieved within the joint project FUTUREFAB, where efficiency optimization, throughput enhancement and cost reduction are the main goals. Here, the presentation will focus on laser processes like selective emitter doping and ablation of dielectric layers. An indispensable part of the efforts towards cost reduction in solar cell production is the improvement of wafer handling and throughput capabilities of the laser processing system. Therefore, the presentation will also elaborate on new developments in the design of complete production machines.
Copper vapor lasers in a MOPA-chain (MOPA, master-oscillator- power-amplifier) configuration with low divergence can be used for the high precision machining of metals and ceramics. The fundamental interaction phenomena, ablation process and possible industrial applications are presented. The following paper relates the results and experiences in the operation of a copper vapor laser MOPA chain, consisting of an oscillator and up to three amplifiers, with the triggering points for these lasers exactly variable through a master-timing-system. In principle, a low-divergent laser beam is generated (511 and 578 nm wavelengths) via an off-axis unstable resonator scheme, with precise synchronization of the amplifiers producing average powers of over 140 W. Due to the excellent beam focusability, peak power densities of some 1010W/cm2 are achievable in a 50 ns pulse duration, which provides almost material-independent precision machining at high velocities. Beginning from the principles of beam-target reciprocation, the removing and cutting of metallic as well as non-metallic materials with copper vapor lasers is described. Additionally, the potential of copper vapor lasers for industrial applications is illustrated through precision machining examples.
When high quality laser beam are combined with suitable imaging optics and manipulation systems, laser micro machining offers excellent solutions to industrial needs. In this context the presented work was performed to demonstrate the potential of the copper vapor laser for upcoming applications. Therefore, a systematic series of laser beam cutting, drilling and milling experiments were carried out using copper sheets of thickness between 0.01 mm and 0.250 mm. In a first step zero-dimensional, 1D and 2D structures were generated with depth/width ratios varying from 1:100 to 10:1 using different processing strategies. The results have been characterized in terms of the minimal geometrical deviations and processing speeds achievable.
The TEA-CO2-laser (transversely excited atmospheric pressure) is a tool for the pulsed processing of materials with peak power densities up to 1010 W/cm2 and a FWHM of 70 ns. The interaction between the laser beam, the surface of the work piece and the surrounding atmosphere as well as gas pressure and the formation of an induced plasma influences the response of the target. It was found that depending on the power density and the atmosphere the response can take two forms. (1) No target modification due to optical break through of the atmosphere and therefore shielding of the target (air pressure above 10 mbar, depending on the material). (2) Processing of materials (air pressure below 10 mbar, depending on the material) with melting of metallic surfaces (power density above 0.5 109 W/cm2), hole formation (power density of 5 109 W/cm2) and shock hardening (power density of 3.5 1010 W/cm2). All those phenomena are usually linked with the occurrence of laser supported combustion waves and laser supported detonation waves, respectively for which the mechanism is still not completely understood. The present paper shows how short time photography and spatial and temporal resolved spectroscopy can be used to better understand the various processes that occur during laser beam interaction. The spectra of titanium and aluminum are observed and correlated with the modification of the target. If the power density is high enough and the gas pressure above a material and gas composition specific threshold, the plasma radiation shows only spectral lines of the background atmosphere. If the gas pressure is below this threshold, a modification of the target surface (melting, evaporation and solid state transformation) with TEA-CO2- laser pulses is possible and the material specific spectra is observed. In some cases spatial and temporal resolved spectroscopy of a plasma allows the calculation of electron temperatures by comparison of two spectral lines.