Bernhard Henrich

Fast micromachining using picosecond lasers

Laser micromachining is mostly based, so far, on Q-switched laser sources. Their nanosecond pulse width often limits the accuracy and quality of laser processes by thermally initiated effects. Precision micromachining benefits from ultra short laser pulses. Up to now mostly amplified fs lasers with low repetition rates were used, with the result of low processing speed. New diode pumped solid-state picosecond lasers can also meet the demands of precise micro-machining. Their pulse duration of about 10 picoseconds provide the optimum performance e.g. for metal processing. These lasers also provide high average powers and much higher repetition rates of more then 100 kHz to maximize throughput. New potentials of picosecond lasers for the processing of different materials with high precision and increased speed will be discussed.

Generation of tailored picosecond-pulse-trains for micro-machining

Novel solid-state picosecond lasers provide a strong benefit for high precision micro-machining. Pulse repetition rates as high as > 500 kHz with pulse energies of > 4 μJ enable fast machining with the precision of low fluence ablation. In addition, new potentials for these lasers are given by advanced modulators with digital timing control that allow the user to generate sequences or groups of pulses: E.g. a sequence of two pulses can be generated and repeated up to 300 kHz. The amplitude of these two pulses can be adjusted independently and the delay is selectable in 20 ns steps. This kind of pulse-strategies with picosecond lasers can support higher ablation rates, similar to the machining results that were demonstrated with double ns-pulses, recently. In another application, groups of > 20 pulses were repeated with > 50 kHz for ultra-precise machining. The distribution of the energy yields a few hundred nJ per pulse and results in an ablation depth per pulse in the range of several nm. Therefore the ablation depth formed by a group can be digitally controlled by the number of pulses in group. Samples for high quality drilling, cutting and structuring of several materials will be presented and the new potentials of this kind of picosecond laser processing with improved precision and speed will be discussed.

Improved picosecond laser radiation for micromachining

Picosecond laser pulses are used to micro-machine virtually any material with highest precision and minimal thermal impact. Best quality has been demonstrated at low fluence removal near ablation threshold with pulse energies of a few µJ. Economical throughput is achieved by very high pulse repetition rates of more than 500kHz. Picosecond laser systems broke into the industrial market more than 2 years ago. However, picosecond laser micro-machining is not yet a mature technology because wide and practical experience of micro-machining with picosecond pulses is limited thus far. In order to achieve outstanding quality and maximum throughput in laser micro-machining with picosecond lasers the proper selection of laser parameters is important and the proper process parameters are also critical.This article reports experimental results related to the influence of pulse trains for ablation efficiency and quality and shows examples of micro-machining using different laser wavelengths. An outlook for developments in these areas is presented.Picosecond laser pulses are used to micro-machine virtually any material with highest precision and minimal thermal impact. Best quality has been demonstrated at low fluence removal near ablation threshold with pulse energies of a few µJ. Economical throughput is achieved by very high pulse repetition rates of more than 500kHz. Picosecond laser systems broke into the industrial market more than 2 years ago. However, picosecond laser micro-machining is not yet a mature technology because wide and practical experience of micro-machining with picosecond pulses is limited thus far. In order to achieve outstanding quality and maximum throughput in laser micro-machining with picosecond lasers the proper selection of laser parameters is important and the proper process parameters are also critical.This article reports experimental results related to the influence of pulse trains for ablation efficiency and quality and shows examples of micro-machining using different laser wavelengths. An outlook for development...

High power Nd:YVO/sub 4/-regenerative laser amplifier with 100 kHz repetition-rate

This article deals with a high power, high repetition-rate picosecond regenerative amplifier based on Nd:YVO/sub 4/. Using novel electro-optic modulators (EOM), the system generates average powers well above 10 Watt at repetition-rates up to 100 kHz. The combination of good beam quality, high power and high repetition rate qualifies this laser system as a valuable tool for micro-machining. In particular, metallic materials like steel can be processed with a high speed of operation.

Powerful red and blue laser radiation generated by frequency doubling and tripling the output of a mode locked 1342 nm Nd:YVO/sub 4/-laser in pp-KTP

Summary from only given. We report on the generation of powerful picosecond laser pulses in the red (671 nm) and blue (447 nm) spectral range by second and third harmonic generation of a mode-locked Nd:YVO/sub 4/-laser operating at 1342 nm. The nonlinear crystals used for both the second and third harmonic are periodically poled quasi-phase-matched KTP-crystals (pp-KTP).

High rep rate picosecond laser materials processing

Novel solid-state picosecond lasers open new vistas for the industrial application of precise micro-machining. These directly diode-pumped sources provide high efficiency and high average power from a robust set up with good beam quality. Pulse repetition rates of several hundreds of kHz enable a maximized throughput. The pulse duration of about 10 picoseconds has been proved as an optimum for the processing of many materials, e.g. metals. Random access to the pulses via TTL-triggering enables the user to synchronize the repetition rate to external processes and to run bursts, sequences and groups of pulses. Examples for high quality drilling, cutting and structuring of several materials will be presented and the new potentials of picosecond laser processing with the required precision and speed will be discussed.Novel solid-state picosecond lasers open new vistas for the industrial application of precise micro-machining. These directly diode-pumped sources provide high efficiency and high average power from a robust set up with good beam quality. Pulse repetition rates of several hundreds of kHz enable a maximized throughput. The pulse duration of about 10 picoseconds has been proved as an optimum for the processing of many materials, e.g. metals. Random access to the pulses via TTL-triggering enables the user to synchronize the repetition rate to external processes and to run bursts, sequences and groups of pulses. Examples for high quality drilling, cutting and structuring of several materials will be presented and the new potentials of picosecond laser processing with the required precision and speed will be discussed.

High average power 80 MHz repetition rate additive pulse mode-locked femtosecond Yb:YAG laser

Summary form only given. In this paper we report on an additive-pulse-mode-locked Yb:YAG laser which generates high average power fs-laser pulses with a repetition rate of 80 MHz. For pumping we use a fiber coupled diode laser which emits 20 W of 940 nm light out of a fiber with 200 /spl mu/m core diameter. The pump light is focused into a Yb:YAG rod to a spot size of 200 /spl mu/m. To improve the homogeneity of the pump light distribution inside the laser crystal, the transmitted pump-light is reflected back into the crystal.