Comprehensive ablation study of near-IR femtosecond laser action on the titanium-based alloy Ti6Al4V: morphological effects and surface structures at low and high fluences

The surface of a titanium-based alloy Ti6Al4V was subjected to modifications by a near-IR femtosecond Ti:Sapphire laser, emitting at 775 nm pulses of 200 fs duration, in single-pulse and multi-pulse regimes, with up to 400 accumulated pulses, and pulse energies ranging from 2.5 to 250 $$\upmu $$ μ J. The whole range of induced effects is presented, from gentle ablation and pattern occurrence to substantial crater formation. Very observable laser-induced parallel periodic surface structures are reported, appearing both within the damage spot area, with low fluences, and at the peripheries of the craters, with higher fluences—but also on crater walls, and inside the crater structures. Damage threshold fluences $$({F}_{\mathrm{th}})$$ ( F th ) and the incubation factor $$(\zeta )$$ ( ζ ) were also determined. Graphic abstract

Actively Q-switched Nd:YLF laser emitting at 908 nm

An actively Q-switched quasi-three-level Nd:YLF laser emitting at 908 nm, for the first time to our knowledge, was demonstrated. A RTP double-crystal scheme was used to realize electro-optical Q-switcher, and a L-shaped cavity structure was designed to suppress parasitic oscillation at 1047 nm. An 806 nm laser diode was used as the pump source with about 480 μs pulse width. With 46.4 mJ pump pulse energy input at repetition rate of 100 Hz, maximum output pulse energies of 0.84 mJ and 0.73 mJ were obtained with output transmissions of 6.5% and 11%, respectively. The corresponding peak pulse powers were up to 14.3 kW and 12.1 kW, and the output pulse widths were 58.6 ns and 60.3 ns. The central laser wavelengths were both at 908.3 nm with spectral bandwidth of over 0.7 nm.

High-power ultrafast fiber lasers for materials processing

State-of-the-art fiber-laser systems can deliver femtosecond pulses at average powers beyond the kilowatt level and multi-mJ pulse energies by employing advanced large-mode-area fiber designs, chirped-pulse amplification, and the coherent combination of parallel fiber amplifiers. By using sophisticated coherent phase control, one or even several output ports can be modulated at virtually arbitrary power levels and switching speeds. In addition, an all-fiber setup for GHz-burst generation is described allowing to access an even wider range of laser parameters. The combination of all these approaches together with the robustness, efficiency, and excellent beam quality inherent to fiber-laser technology has the potential to strongly improve existing materials-processing applications.

Modification of Aerosol Gold Nanoparticles by Nanosecond Pulsed-Periodic Laser Radiation

This study investigates the processes of interaction of nanosecond pulsed-periodic laser radiation with the flow of aerosol agglomerates of gold nanoparticles synthesized in a spark discharge. Nanoparticles in a gas flow are spatially separated nano-objects whose interaction with each other and with the walls of an experimental cell was insignificant. Therefore, the energy absorbed by nanoparticles was used only for their own heating with further shape and size modification and on heat transfer to the surrounding gas. In the research, we used laser radiation with wavelengths of 527 and 1053 nm at pulse energies up to 900 µJ and pulse repetition rates up to 500 Hz. The dynamics of changes in the nanoparticles size during their sintering process depending on the laser pulses energy is characterized by an S-shaped shrinkage curve. Complete sintering of the initial agglomerates with their transformation into spherical nanoparticles is achieved by a series of impacting laser pulses. The result of nanoparticles’ laser modification is largely determined by the pulse energy and the efficiency of the nanoparticles’ radiation absorption.

Frequency-Mixing Lasing Mode at European XFEL

We demonstrate generation of X-ray Free-Electron Laser (XFEL) pulses in frequency mixing mode at the SASE3 line of the European XFEL. The majority of the SASE3 FEL segments are tuned at two frequencies ω1 and ω2 following an alternate pattern. Leveraging on non-linearities generated through longitudinal dispersion in the system, we obtain electron bunching at a frequency difference ωFM=ω2−ω1. FEL amplification at ωFM follows in a few last radiator segments. We report on the generation of frequency mixing at photon energies between 500 eV and 1100 eV with pulse energies, depending on the length of the radiator, in the mJ level. This method allows generating low photon energies in cases where the FEL runs at high electron energy and the target photon energy cannot be reached in the main undulator, with the simple addition of a short, custom-made afterburner.

Analytical model for the depth progress of percussion drilling with ultrashort laser pulses

A simplified analytical model is presented that predicts the depth progress during and the final hole depth obtained by laser percussion drilling in metals with ultrashort laser pulses. The model is based on the assumption that drilled microholes exhibit a conical shape and that the absorbed fluence linearly increases with the depth of the hole. The depth progress is calculated recursively based on the depth changes induced by the successive pulses. The experimental validation confirms the model and its assumptions for percussion drilling in stainless steel with picosecond pulses and different pulse energies.

Thrust Measurements on the High Efficient and Reliable Vacuum Arc Thruster (HERVAT)

In this work, thrust measurements of the high efficient and reliable vacuum arc thruster (HERVAT) are performed for different pulse energies. The thruster system includes a thruster head together with a newly developed pulse processing unit (PPU). The complete system (HERVAT + PPU) is able to perform more than 1 × 107 pulses. Moreover, the influence of an integrated active magnetic nozzle is investigated. As a result, the thrust to power ratio, the average thrust level and the impulse bit for each configuration are measured and calculated. For the thrust measurements, a highly sensitive horizontal thrust balance with an active force actuator is used and operated in the thrust compensation mode. The investigated system is able to achieve levels from 5 to 40 μN and thrust to power ratios from 1 to 2 μN/W. The experimental results are compared to the data available in literature.