Many materials e.g. diamond or silicon do not show sufficient absorption at one micron, the fundamental wavelength of Nd-based solid-state laser sources. Frequency conversion to the second and fourth harmonic allows the efficient processing of these materials. High beam quality is another important property for micro material processing with lasers. It facilitates small focus diameters and due to high Rayleigh length even at strong focusing drilling of holes with high aspect ratio. Together with high average output powers it allows fast processes with high quality. At least flexible pulse peak power and repetition rate is necessary to optimize the process. Two laser systems which fulfill these requirements are investigated. A pulse pumped Nd:YAP system which delivers an average output power of 124 W at the second harmonic and a Nd:YAG with an average output power up to 50 W in the second harmonic. Due to its active Q-switch the pulse peak power of this system is variable in a wide range. Efficient laser processing of different ceramics with these laser system are presented.
We report on the micro structuring of fused silica (a-SiO2) and calcium fluoride (CaF2) with a conventional KrF excimer laser (248 nm) by utilization of the effects in the laser-induced plasma-assisted ablation (LIPAA). Mask projection of the UV light is realized onto the rear (instead of the front) side of the UV transparent samples. The plasma generated from a metal target located behind the rear surface of the VUV window effectively assists in the ablation. In the case of fused silica, we obtain high-quality complex micro structures with structure depths even above 500 μm in aspect ratios of 1:5 and better. The ablation rate in fused silica can reach a level as high as 1 μm per pulse with this novel method, demonstrating a remarkable efficiency. While the ablation rate observed for CaF2 remains at 50 nm per pulse, the up to 100 μm deep micro structures demonstrate an excellent quality without signs of severe cracking or stress outside the mask projected area. This technique permits high-quality micro fabrication of bio-medical, electronic and opto-electronic devices based on oxides and fluorides by use of a conventional UV laser.
To meet the industry's demand for reducing machine cycle lengths concerning laser-drilling a laser was developed at the LMTB-laboratories that emits high-power peak-pulses at excellent beam-quality. In co-operation with Technical University of Berlin (TU Berlin) a Nd:YAG Master-Oscillator Power-Amplifier (MOPA) laser system is undergoing permanent enhancements aiming at shorter pulse duration, higher fluence and improved long-term stability. Presently, the output power of the oscillator (10W@1064nm) with a beam-quality of M2=1.3 is amplified to more than 100W@1064nm with M2=2.3 and a single pulse energy up to 800 mJ. The pulse duration can be varied between 31 and 230ns. On account of the excellent beam quality, frequency conversion was carried out down to 266nm. The MOPA-System was used for laser micro scribing and drilling experiments into metals and ceramics where the influence of the beam quality on the geometrical shape of the hole is investigated and compared with applications conducted with similar laser systems. Additionally means in optimizing the drilling process such as burr-minimizing and melt-reduction were introduced. Furthermore, experiments using tapered drilling technique are undertaken. A maximum aspect ratio of 1:180 in sapphire was obtained. We achieved high ablation rates and precise structures in Al2O3 (ceramic and sapphire), AlN, ZrO2, Ni-base alloy, platinum, tungsten and many more materials. Further improvement of the system was undertaken by means of multimode fibers as phase conjugate mirrors (PCM) using the effect of stimulated brillouin scattering (SBS).
To meet the industry's demand for reducing machine cycle lengths concerning laser-drilling a Nd:YAG Master-Oscillator Power-Amplifier (MOPA)-system was developed at the LMTB-laboratories that emits high-power peak-pulses at excellent beam-quality. Presently, the output power of the oscillator (10W@1064nm) with a beam-quality of M2 = 1.3 is amplified to 95W@1064 nm with M2=2.3 and a single pulse energy up to 500 mJ. The pulse duration can be varied between 26 and 230 ns. On account of the excellent beam quality, frequency conversion resulted in 49W@532nm and 4.8@266nm. The MOPA-System is used for laser micro drilling experiments into metals and ceramics where the influence of the beam quality on the geometrical shape of the hole is investigated and compared with applications conducted with similar laser systems. Additionally means in optimizing the drilling process such as burr-minimizing and melt-reduction were introduced. Furthermore, experiments using tapered drilling technique are undertaken. A maximum aspect ratio of 1:200 in stainless steel was obtained.
Ceramic and crystalline wafer substrates are widely used in microelectronics. The individual choice is based on their thermal, optical and mechanical properties. For a variety of applications high quality laser micro processing of these materials, i.e. the generation of blind and through holes, grooves and even complex three dimensional micro structures, is gaining in importance. The department of applied laser technologies of the LMTB GmbH has conducted extensive studies on the versatility of q-switch Nd:YAG laser systems for the micro structuring of ceramic and crystalline wafer substrates that differ strongly in their optical and mechanical properties, such as Al2O3, AlN, sapphire, Si and SiC. This paper discusses the laser material micro machining results in respect to the laser parameters used to optimize the micro processing quality and speed for the different materials.
To meet the industry's demand for reducing machine cycle lengths concerning laser-drilling a Nd:YAG Master-Oscillator Power-Amplifier (MOPA)-system was developed at the LMTB-laboratories that emits high-power peak-pulses at excellent beam-quality. Presently, the output power of the oscillator (10W@1064nm) with a beam-quality of M2=1.3 is amplified to 95W@1064nm with M2=2.3 and a single pulse energy up to 500mJ. The pulse duration can be varied between 26 and 230ns. On account of the excellent beam quality, frequency conversion resulted in 49W@532nm and 4.8@266nm. The MOPA-System is used for laser micro drilling experiments into metals and ceramics where the influence of the beam quality on the geometrical shape of the hole is investigated and compared with applications conducted with similar laser systems. Additionally means in optimizing the drilling process such as burr-minimizing and melt-reduction were introduced. Furthermore, experiments using tapered drilling technique are undertaken. A maximum aspect ratio of 1:200 in stainless steel was obtained.
High beam quality is one of the most important properties for micro material processing with lasers. It facilitates slight focus diameters and due to high Raleigh length even at strong focusing drilling of holes with high aspect ratio. Together with high average output powers it allows fast processes with high quality. Another important point is the wavelength of the laser radiation. Many materials e.g. diamond or silicon show no sufficient absorption at fundamental wavelength of Nd based solid-state laser sources. Frequency conversation to the second and fourth harmonic allows the efficient processing of these materials. At least flexible pulse peak power and repetition rate is necessary to optimize the process. Three laser systems which fulfill these requirements are investigated. A pulsed pumped Nd:YAG System which delivers an average output power of 315 W with M2 = 2.6 at the fudamental wavelength and 124 W at the second harmonic. Another pulsed pumped System based on Nd:YAG with an average output power up to 125 W with M2 = 2.2 at the fundamental wavelength, 49.5 W at the second harmonic and 4.75 W at 266 nm. Due to its active Q-switch the pulse peak power of this system is variable in a wide range. Furthermore, a continuously pumped amplifier arrangement with nearly diffraction limited output of 120 W average power has been achieved at 10 kHz repetition rate.
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