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Laser sources which produce GHz bursts of ultrashort pulses attract a lot of attention by demonstrating superior performance in material processing. Flexibility of the laser source in a selection of parameters for custom application is highly preferable. In this work, we demonstrate a very versatile method for burst formation using the active fiber loop (AFL). It allows forming GHz bursts containing from 2 up to approximately 2200 pulses in a burst (1000 ns burst width) with identical pulse separation and any predefined intra-burst pulse repetition rate (PRR). The burst pre-shaping by the amplification conditions in the AFL and by the modulation of transmission of the acousto-optic modulator was demonstrated. Industrial-grade ultrafast laser system was able to operate in the single-pulse and GHz-burst regimes. The laser system delivered high-quality 368 fs duration (FWHM) pulses of 15.3 µJ pulse energy and 30.6 W average output power at 2 MHz PRR in the single-pulse regime. In the GHz-burst operation regime, bursts of 2.2 GHz intra-burst repetition rate were formed and amplified to more than 30 W average output power with a burst energy up to 135 µJ at a burst repetition rate of 200 kHz. The sub-picosecond duration of pulses was obtained in the GHz-burst regime at different burst widths.

In this work we present a novel method for depolarization compensation based on spatially variable wave plate. Thermally induced depolarization losses were reduced from 14.3% to 1.3% and bifocusing eliminated in a double-pass Yb:YAG amplifier.

A subpicosecond laser system featuring a fiber chirped pulse amplification-based seed laser and a double-pass end-pumped Yb:YAG crystal power amplifier was investigated. The key novelty of the system was the application of depolarization compensation using a specially designed spatially variable wave plate. To the best of our knowledge, this method was applied for the first time. The presented laser system produced pulses of 441 fs duration, 116 µJ pulse energy at 116 W average power with a beam quality of M²∼2.1, featured optical-to-optical efficiency of 32% at room temperature (T=20°C), and had residual depolarization level of 2.7%.

FemtoLux 30 is a new 30 W femtosecond industrial grade laser build to work 24/7/365 without any interruptions. Other lasers of similar optical power use water for cooling, which means additional bulky and heavy water chiller is needed which require periodical maintenance (cooling system draining and rinsing, water and particle filter replacement). Moreover, in the unfortunate event of water leakage, not only laser head but also more expensive equipment could be damaged. FemtoLux 30 uses innovative direct refrigerant cooling method that do not contain any water inside the laser head and has much higher cooling efficiency. Laser cooling equipment is integrated together with the power supply unit into a single 4U rack mounted housing with a total weight of just < 15 kg. To tailor laser for specific applications, FemtoLux 30 laser has a tunable pulse duration from < 350 fs to 1 ps and can operate in very broad AOM controlled range of pulse repetition rate from a single shot to 4 MHz. While max energy of >250 µJ, that could be achieved while operating in a burst mode, could ensure higher ablation rates for different materials. FemtoLux 30 is designed as perfect tool for display and microelectronics manufacturing, as well as for micro processing and marking of brittle materials, such as glass, sapphire or ceramics, as well as for highest quality micro processing of different metals and polymers. Innovative laser control electronics ensures easy control of FemtoLux30, thus reducing time and resources required for integrating this laser into different equipment.

In this work, a double-pass end-pumped Yb:YAG amplifier system was investigated experimentally and numerically. The amplifier was seeded by a fibre-CPA based seed laser FemtoLux 30 (Ekspla). The presented laser system produced 129 W average power and 129 μJ energy pulses at 1 MHz pulse repetition rate, with optical-to-optical efficiency of 32% at room temperature (T = 20°C). The resulting beam quality was M² ∼ 2.1 and the measured depolarization losses were to 17.9%. After the compression, 441 fs pulse duration was achieved. During the work, comprehensive amplifier modelling was performed using the code written in Matlab. The modelling results matched well the experimental data, providing the tool to predict the performance of laser systems based on ytterbium-doped isotropic crystalline, ceramic and glass laser materials prior to designing and manufacturing.

We demonstrate a method to synthesize ultra-high repetition rate bursts of ultrashort laser pulses containing any number of pulses within a burst with identical pulse separation and adjustable amplitude. The key element to synthesize the GHz bursts of ultrashort laser pulses is an active fiber loop. The method was implemented in the fiber chirped pulse amplification system to obtain 72 nJ-energy bursts of 20 pulses with a 2.65 GHz intra-burst pulse repetition rate and a 500 kHz burst repetition rate. The dispersion compensation mechanism ensured a mean pulse duration of 570 fs within the bursts.

Photopolymerization by four-beam interference lithography on a preheated SZ2080 sample was explored at different initial temperatures of the sample: 20 °C, 50 °C, 75 °C, 100 °C, 125 °C, and 150 °C, and at exposure times ranging from 0.5 s to 5 s. The average laser power selected was ∼100 mW for the 300 ps duration pulses at a 1 kHz repetition rate. The experimental results demonstrate that the higher initial temperature of the sample positively influences the crosslinking of the patterns. These findings will improve polymerization protocols for multi-beam interference lithography.

In this paper the possibility to optimize the glass dicing process by controlling the axicon-generated Bessel beam ellipticity is presented. Single-shot intra-volume modifications in soda-lime glass followed by dicing experiments of 1 mm-thick samples are performed. The Bessel beam ellipticity is essential for glass dicing process. Such beam generates intra-volume modifications with transverse crack propagation in dominant direction. Orientation of these modifications parallel to the dicing direction gives significant advantages in terms of processing speed, glass breaking force and cutting quality.

Bio-inspired surfaces are able to decrease friction with fluids and gases. The most recognizable are shark-skin-like riblet surface structures. Such bio-inspired surfaces can be formed by the laser ablation technique. In this work, bio-inspired riblet surfaces with grooves were formed using picosecond ultraviolet laser ablation on pre-heated polytetrafluoroethylene (PTFE) at various sample temperatures. The ablation of hot PTFE was found to be 30% more efficient than the conventional laser structuring at the room temperature. The friction of structured PTFE surfaces with the flowing air was investigated by using drag a measurement setup. Results show the decrease of friction force by 6% with dimensionless riblet spacing around 14–20.

The optical performance of high-resistivity silicon with a laser-ablated surface was studied in the transmission mode in the frequency range of 0.1-4.7 THz. A reciprocal relationship between the transmission brightness and the surface roughness was observed at discrete THz frequencies. The measured dispersion was reproduced by the THz wave scattering theory using an effective refractive index model. No significant differences between the samples processed either with psor ns-duration laser pulses in ambient air or in argon enriched atmosphere were found in the THz regime. It was demonstrated that the majority of optical losses of the silicon with the laser modified surface were due to the scattering of THz waves and not due to the absorption in silicon-compounds formed during the laser ablation.