Machining metals and silicon with GHz bursts: Surprising tremendous reduction of the specific removal rate for surface texturing applications

Bursts of 230 fs pulses with up to 25 pulses having a time spacing of 180 ps were applied to steel AISI304, copper DHP, brass and silicon in real surface texturing (milling) application by machining squares. The previously reported very high removal rates for GHz bursts could not be confirmed, on the contrary, the specific removal rate tremendously drops down to less than 10% for the metals and 25% for silicon when the number of pulses per burst is increased. This drop is fully in line with shielding effects already observed in case of MHz pulses and double pulse experiments. The increase of the number of pulses per burst directly goes with strongly increased melting effects which are assumed to additionally re-fill the already machined areas in this milling application. Calorimetric experiments show an increasing residual heat with higher number of pulses per burst. Further the removal rates of the GHz bursts directly follow the tendency of single pulses of identical duration. This fosters the hypothesis that in case of metals and silicon only melting and melt ejection lead to the high reported removal rates for GHz bursts in punching applications and that no additional "ablation cooling" effect is taking place

CIGS thin-film solar module processing: case of high-speed laser scribing

In this paper, we investigate the laser processing of the CIGS thin-film solar cells in the case of the high-speed regime. The modern ultra-short pulsed laser was used exhibiting the pulse repetition rate of 1 MHz. Two main P3 scribing approaches were investigated – ablation of the full layer stack to expose the molybdenum back-contact, and removal of the front-contact only. The scribe quality was evaluated by SEM together with EDS spectrometer followed by electrical measurements. We also modelled the electrical behavior of a device at the mini-module scale taking into account the laser-induced damage. We demonstrated, that high-speed process at high laser pulse repetition rate induced thermal damage to the cell. However, the top-contact layer lift-off processing enabled us to reach 1.7 m/s scribing speed with a minimal device degradation. Also, we demonstrated the P3 processing in the ultra-high speed regime, where the scribing speed of 50 m/s was obtained. Finally, selected laser processes were tested in the case of mini-module scribing. Overall, we conclude, that the top-contact layer lift-off processing is the only reliable solution for high-speed P3 laser scribing, which can be implemented in the future terawatt-scale photovoltaic production facilities

Photonics in Lithuania

Laser technologies are one of Lithuania’s strongest and most intensive value-added industrial sectors. Since its beginning in fundamental research nearly 60 years ago, it has grown into a fully self-sustaining ecosystem, providing optics, ultrashort pulse lasers, laser technologies and systems to the global market

Femtosecond Laser Cutting of 110–550 µm Thickness Borosilicate Glass in Ambient Air and Water

The cutting quality and strength of strips cut with femtosecond-duration pulses were investigated for different thicknesses of borosilicate glass plates. The laser pulse duration was 350 fs, and cutting was performed in two environments: ambient air and water. When cutting in water, a thin flowing layer of water was formed at the front surface of the glass plate by spraying water mist next to a laser ablation zone. The energy of pulses greatly exceeded the critical self-focusing threshold in water, creating conditions favorable for laser beam filament formation. Laser cutting parameters were individually optimized for different glass thicknesses (110–550 µm). The results revealed that laser cutting of borosilicate glass in water is favorable for thicker glass (300–550 µm) thanks to higher cutting quality, higher effective cutting speed, and characteristic strength. On the other hand, cutting ultrathin glass plates (110 µm thickness) demonstrated almost identical performance and cutting quality results in both environments. In this paper, we studied cut-edge defect widths, cut-sidewall roughness, cutting throughput, characteristic strength, and band-like damage formed at the back surface of laser-cut glass strips

Picosecond laser beam interference ablation of thin metal films on glass substrate

Interfering laser beams with the high pulse energy provide an opportunity of direct laser patterning of materials in a predetermined way. This study reports results of the laser beam interference ablation of thin metal films on the glass substrate irradiated with the picosecond laser. Gratings and grids consisting of metal wires of several hundred nanometers were produced in a chromium film. A matrix of nanodots was obtained after irradiation of a aluminum film.The period of structures caused by interference was close to 2 μmFizikos institutasFizikos katedraVytauto Didžiojo universiteta