Diode Pumped Solid State (DPSS) Laser and Processing
Activity Description: Since the year 2000 the Chilab lab was applied to use lasers potential in micromaching. At the end of the year 2002 the lab begins to design the first Diode Pumped Solis State Laser for High Peak Power generation, in collaboration with Zaniboni Laser S.r.l. that is interested in using this laser sources for fabrication of laser marker machines. Up to now several different laser sources have been designed and tested. Besides, in the year 2005 the lab decides to generate a new Spin-Off dedicated to design and fabrication of laser for materials processing such as marking, micro-drilling, micro-cutting and micro-welding. The figure 1 shows the laser source MQL-20 (20W cw, up to 200 kHz) fabricated by Microla Optoelectronics S.r.l. (http://www.micro-la.com), the laser pulses in this case are deflected by galvo-mirrors scan head useful for marking systems and simple materials machining.
Lasers, such as Nd:YAG lasers and their harmonics are used for a variety of precision machining operations and are particularly well-suited for micromachining of polymer materials or the marking of difficult materials such as diamonds. Infra Red lasers such as CO2 and YAG tend to be used for high-speed cutting and marking metal applications, respectively. Wavelength conversion of many near infrared lasers can be accomplished by passing their light through appropriate nonlinear optical crystals like lithium niobate or beta barium borate to generate the second harmonic. The third and fourth harmonic wavelengths of lasers in the neodymium family Nd:YAG, Nd:YLF, and Nd:YVO4 are in the ultraviolet, near 355 nm and 266 nm. Wavelength conversion is a two-step process in which infrared light is converted to green wavelengths followed by conversion of green light to ultraviolet wavelengths. Since wavelength conversion requires additional optical components and conversion efficiency is typically 10 20%, ultraviolet light produced by wavelength conversion is significantly more expensive to generate than light at the fundamental wavelength. On a cost per watt basis, excimer light also is substantially more expensive than CO2 or Nd:YAG light. Consequently, industrially viable UV laser cutting applications tend to be those in which in which UV light produces a better quality of cut or allows production of finer detail.
Micro-Machining by High Peak Power LASER
Laser micro-machining is a sector with double digit annual growth rates. Laser application engineers are striving to improve quality, resolution, and reliability. They have to reduce process cost and cycle time and extent the range of materials by employing new phenomena and more sophisticated process strategies. Laser sources to support these demands have to deliver higher power at better beam quality, higher repetition rates, shorter wavelength and shorter pulse duration. The basic event is ablation of a few tens of manometers layer in the focus spot. High quality is achieved by ablation close to threshold. Here the ablation depth per laser pulse is only in the order of 1000 atom layers or few tens of nm. So, any 3D-micro-milling of material is composed of the removal of some nm-layers in the laser focus area; more the 500 000 pulses can be produced and repeat this basic process per sec. The throughput of a micromachining application is a function of ablation rate and power applied. The laser ablation rate in micromaching for a specified power can be calculated and experimentally verified. A laser micromachining system is generally comprised of a laser, a protective structure, a beam delivery system, a visible monitoring system, a motion system, and a parts handling system. Micromachining systems come in many different configurations for many different applications. In figure 2 it is shown a copper hole made in a commercial PCB.
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Partners and Projects
1. DOCUP 2.6 b (2006); Design and realization of Direct Pumped Nd:YVO4 in collaboration with MICROLA Optoelectronics S.r.l.
2. IR cw laser marking system in collaboration with ID-Tronic
3. Fiber laser welding