Skaidrių terpių tūrinis modifikavimas bei apdirbimas sukeliant medžiagos įtrūkius įvairios erdvinės sandaros lazerių pluoštais

In this thesis, the investigation of laser glass processing methods, based on material cracking, is presented. Two methods were investigated – intra-volume modification and mechanical separation, and bottom-up processing. It was demonstrated that glass scribing can be enhanced by inducing directional transverse cracks using axicon-generated asymmetrical Bessel-like laser beams. Experimental and theoretical research showed that such beams can be generated via aberration-control or angular spectrum modulation of the axicon-generated beam. In this work, the influence of the axicon shape and its rotation around the axis, perpendicular to the beam propagation axis, was investigated. Variously shaped amplitude and phase masks were investigated and compared. Laser-fabricated axicons were investigated as an alternative to traditional elements. High material removal efficiency over 100 µm3/µJ was demonstrated using the second method and nanosecond laser pulses or GHz bursts of picosecond pulses with the overall burst duration in the nanosecond scale. Technologies for cutting long contours, fabrication of chamfers and gas nozzles for laser-plasma accelerators were developed. Developed laser processing methods were thoroughly compared to traditional by evaluating the quality and flexural strength of cut samples

Glass cutting using a bessel-gaussian beam generated by a conical lens

The goal of this work was to investigate the in-volume modification of glass combined with a mechanical cleaving process for glass cutting using picosecond Bessel-Gaussian beams. Experiments were carried out using the fundamental harmonic of diode-pumped solid-state lasers with pulse duration of 10 ps and 300 ps. The Bessel-Gaussian beam was generated by focusing the Gaussian beam with a conical lens together with a 4F optical system. The conical lens, generated intensity distribution, in-volume modifications of glass were investigated and glass cutting experiments were carried out during this research. It was found that due to manufacturing tolerances the investigated conical lens shape deviated from an ideal cone and had an oblate tip and an ellipse-shaped cross-section. The intensity pattern, generated by such lens, was nonsymmetrical and modulated along the propagation axis. The central core diameter depended on the distance from the axicon tip. Also, as the beam propagation distance increased, the intensity pattern was gradually spread into several maxima. Such beam distribution affected the formation of cracks in the bulk of glass, which tended to orientate along the major axis of an ellipse-shaped central core of the beam. The maximum length of cracks was 183 μm when 2 mJ laser pulses with duration of 300 ps were applied. Cracks size depended linearly on the pulse energy on the logarithmic scale. It was demonstrated that the direction of cracks orientation can be adjusted by rotating an axicon. Laser induced in-volume modifications combined with a cleaving process could be applied for thick glass cutting. Cutting of straight contours was demonstrated by single pass technique using a Bessel-Gaussian beam and 300 ps laser pulses. Maximum cutting speed of 1 mm-thick soda-lime glass sheets was 240 mm/s when 2 mJ laser pulses were applied. Cutting quality depended on the pulse energy and scanning speed. Minimal sidewall surface roughness was 1.6 μm when the pulse energy was 0.6 mJ, scanning speed 10 mm/s. It was concluded that the optimal cutting speed with the lowest roughness depends linearly on the pulse energy

High-density gas capillaries for Betatron X-ray sources of laser-accelerated electrons

P. 64Recent developments of high-repetition-rate multi-Terawatt few-cycle femtosecond 1030 nm OPCPA system delivering 40-75 mJ 7-20 fs pulses at 1 kHz rate [1], the interest in using betatron hard X-ray sources driven by laser-accelerated electrons for the spectroscopic absorption measurement of the Warm Dense Matter [2] raise the requirement of manufacturing and characterization of high-density gas targets of micrometric dimensions. [...]Fizikos katedraFizinių ir technologijos mokslų centrasFizinių ir technologijos mokslų centras, VilniusVytauto Didžiojo universiteta

High-density gas capillary nozzles manufactured by hybrid 3D laser machining technique from fused silica

Funding: Research Council of Lithuania (S-MIP-17-79)In this report, an efficient hybrid laser technique, nanosecond laser rear-side processing and femtosecond laser-assisted selective etching (FLSE) for the manufacturing of high-density gas capillary targets, is demonstrated. Cylindrical capillary nozzles for laser betatron X-ray sources were numerically simulated, manufactured from fused silica by 3D laser inscription and characterized using interferometry and gas density reconstruction. The dependence of gas concentration profiles on the wall roughness of cylindrical channels is presentedFizikos katedraFizinių ir technologijos mokslų centras, VilniusVytauto Didžiojo universiteta

Impact of the wall roughness on the quality of micrometric nozzles manufactured from fused silica by different laser processing techniques

In this report, the impact of the wall roughness of the cylindrical micronozzles with the diameter of 50 μm, 100 μm and 200 μm on the concentration profiles of the gas targets for laser plasma wakefield acceleration was investigated. Micronozzles were manufactured using three different laser processing techniques – nanosecond laser rear-side (RS) machining with and without the subsequent etching in the potassium hydroxide (KOH) solution and hybrid laser machining technique – the combination of nanosecond laser rear-side machining and femtosecond laser-assisted selective etching (FLSE). Processing efficiency, accuracy and the wall roughness of micronozzles, fabricated by these techniques, are compared, and the best application areas are defined. Finally, the numerical simulation results of the gas concentration profiles are compared with experimental data with the satisfactory agreementFizikos katedraFizinių ir technologijos mokslų centrasFizinių ir technologijos mokslų centras, VilniusVytauto Didžiojo universiteta

Laser wakefield accelerated electron beams and betatron radiation from multijet gas targets

Laser Plasma Wakefield Accelerated (LWFA) electron beams and efficiency of betatron X-ray sources is studied using laser micromachined supersonic gas jet nozzle arrays. Separate sections of the target are used for the injection, acceleration and enhancement of electron oscillation. In this report, we present the results of LWFA and X-ray generation using dynamic gas density grid built by shock-waves of colliding jets. The experiment was done with the 40 TW, 35 fs laser at the Lund Laser Centre. Electron energies of 30–150 MeV and 1.0 × 108–5.5 × 108 photons per shot of betatron radiation have been measured. The implementation of the betatron source with separate regions of LWFA and plasma density grid raised the efficiency of X-ray generation and increased the number of photons per shot by a factor of 2–3 relative to a single-jet gas target source

Carrier-envelope phase controlled dynamics of relativistic electron beams in a laser-wakefield accelerator

International audienceIn laser-wakefield acceleration, an ultra-intense laser pulse is focused into an underdense plasma to accelerate electrons to relativistic velocities. In most cases, the pulses consist of multiple optical cycles and the interaction is well described in the framework of the ponderomotive force where only the envelope of the laser has to be considered. But when using single-cycle pulses, the ponderomotive approximation breaks down, and the actual waveform of the laser has to be taken into account. In this paper, we use nearsingle-cycle laser pulses to drive a laser-wakefield accelerator. We observe variations of the electron beam pointing on the order of 10 mrad in the polarization direction, as well as 30% variations of the beam charge, locked to the value of the controlled laser carrier-envelope phase, in both nitrogen and helium plasma. Those findings are explained through particle-in-cell simulations indicating that low-emittance, ultrashort electron bunches are periodically injected off-axis by the transversally oscillating bubble associated with the slipping carrier-envelope phase