Processing of metals and dielectric materials with ps-laserpulses: results, strategies, limitations and needs

Abstract

Ultra short (ps, fs) laser pulses are used, when high requirements concerning accuracy, surface roughness, heat affected zone etc. are demanded for surface structuring. Ps-laser systems that are suited to be operated in industrial environments are of great interest for many practical applications. Here results in the field of 3-d structuring (metals and transparent materials), induced processes and structuring of flexible solar cells will be presented. Beside the pulse duration, which is given by the laser system, the user has a wide variety of optimization parameters such as fluence, repetition rate and wavelength. Based on a simple model it will be shown, that there exist optimum laser parameters to achieve maximum volume ablation rates at a given average power. To take benefit of these optimum parameters and to prevent harmful effects like plasma shielding and surface melting, adapted structuring strategies, depending on the requirements, have to be used. Today's ultra short pulsed systems have average powers from a few W up to a few 10W at high repetition rates. The actual available beam guiding systems are limited and can often not fulfill the requirements needed for high throughput structuring with optimized parameters. Based on the achieved results, the needs for future beam guiding systems will be discussed.

Influence of the Pulse Duration onto the Material Removal Rate and Machining Quality for Different Types of Steel

“…Similar calculations have been done for a Gaussian shaped beam as emitted by most ultra short pulsed systems (Neuenschwander et al (2012), Neuenschwander et al (2010, Raciukaitis et al (2009)). Again a maximum removal rate per average power (ablation efficiency) is observed:…”

“…It has to be pointed out that the maximum value of the removal rate (5) is only obtained at this optimum point. A general expression for the removal rate of a Gaussian beam is also developed by Neuenschwander et al (2010) and Raciukaitis et al (2009) and reads: …”

Ultrafast-laser dicing of thin silicon wafers: strategies to improve front- and backside breaking strength

“…It should be large enough to avoid thermal heating and directed material ejections in the trench [17], but small enough to ablate a closed line when the beam is translated across the sample. Recent studies on surface ablation demonstrated that the highest ablation quality can be achieved if the ratio between the pulse distance and the focus radius is set to d p w 0 = v scan (f rep w 0 ) ≈ 1 [27,28]. This criterion could be fulfilled with the present setup at a scan speed of v scan = 1200 mm/s.…”

High-throughput and high-precision laser micromachining with ps-pulses in synchronized mode with a fast polygon line scanner

“…It can be clearly seen that there is an optimum peak fluence ϕ 0,opt with a maximum removal rate. This optimum shows the point, where the ablation process is most efficient, which is well known in the literature [1][2][3][4] and be calculated as follow:…”