We report on the micro structuring of fused silica (a-SiO 2 ) and calcium fluoride (CaF 2 ) 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 CaF 2 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 Nd:YAG MasterOscillator Power-Amplifier (MOPA)-system was developed at the LMTB-laboratories that emits high-power peakpulses 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.
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