Publikace

This book covers the fundamentals of different laser-based manufacturing and processing, namely laser shock peening, laser micromachining, laser cleaning, cladding, remelting, laser honing, and other several aspects of lasers. The book discusses the general laser interaction with different materials. The application of laser-based post-processing of additive manufacturing and repair engineering is reported. It also provides the reader with mechanism of lasers in manufacturing and recent developments in tools, technologies, controls, and operations.

A large amount of material is machined by electrical discharge machining (EDM) and the machined debris is flushed away as waste. The present study aims to establish EDM as a top-down method which can effectively machine hard-to-cut materials while the by-product, i.e., metal debris, can be utilized as micro/nano particles. In the present work, titanium-alloy grade 5 was machined using a die-sink EDM and the debris was collected from the dielectric fluid with a multistage filtration system. The collected debris was cleaned and the particles were characterized. Particles were examined by scanning electron microscopy, x-ray diffraction, and energy-dispersive x-rays to determine size, shape, and chemical crystal structure. The average size of the formed particles was 5.14 µm and they were spherical. A fractal analysis was performed on the SEM images to deepen the study of the formed particles.

Extreme lasers capable of short, high-energy pulses are probing the frontiers of science and advancing practical technology. The utility of such lasers increases with their average power delivery, which enables faster data acquisition, higher flux of laser-driven particle and radiation sources and more efficient material processing. However, the same extreme energies and electric field strengths of these lasers are currently preventing their direct and high accuracy measurement for these experimental applications. To overcome this limitation, we use the momentum of the laser pulses as a measurement proxy for their energy. When light reflects from an ideal mirror, its momentum is transferred to the mirror, but its energy is reflected. We demonstrate here a force-sensing mirror configuration to measure laser pulse energies up to 100 J/pulse (10 ns duration, 10 Hz repetition rate) from a kilowatt-level average power multi-slab laser operated at the HiLASE facility of the Czech Academy of Sciences. We combine a radiation-pressure power meter with a charge integrator photodiode to form what we refer to as a Radiation Pressure Energy Meter. To our knowledge, this is the first demonstration of a high-accuracy, non-absorbing, SI traceable primary standard measurement of both single and average pulse energies of a 1-kW-average-power pulsed laser source. With this, we demonstrate a practical method for in-situ calibration of the traditional thermal instruments (pyroelectric detectors) currently used for indirect measurements of energy and power of such extreme lasers.

Additive manufacturing (AM) has brought enormous benefits to mankind and has already shown its usefulness in a variety of cutting edge fields. Metallic additive manufacturing, which fosters the development of smart technologies and production systems, is one of the essential pillars of Industry 4.0. Additionally, AM is a vital facilitator of the circular economy, aiming to reduce use of resources while increasing commercial prospects. As a result, less material will be used, and physical inventory will be minimised.

Particle synthesis has seen significant advances in current trends. However, the synthesis of metal particles without oxidation is a challenge for researchers. The current study presents a straightforward, convenient, and convincing approach for manufacturing copper (Cu) particles free of surface oxide. The die-sink Electrical Discharge Machine (EDM) of copper alloys with oleic acid resulted in the formation of Cu particles with diameters between 10 to 20 µm. X-ray diffraction (XRD) was used for particle examination after cleaning and sonication with distilled water. Cu particles with oleic acid coating retained a Cu phase without oxidation after synthesis. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to determine the size and morphology of generated particles. Fourier transforms infrared (FT-IR) analysis revealed the oleic acid-coated Cu surface bonded with an oxygen atom. Also, the agglomeration and change of size involving Cu particles with increasing voltages in the pulse supply in EDM were reported.

We report on high-energy, few-cycle pulse generation in the long-wave infrared spectral region via difference-frequency generation (DFG) in GaSe and AgGaSe2 nonlinear crystals. The DFG is driven by the signal at 3.5 µm and idler at 5 µm of a high-power mid-wave infrared optical parametric chirped pulse amplification (OPCPA) system operating at a 1-kHz repetition rate. The DFG pulses contain up to 17 µJ of energy and cover a spectrum from 8.5 µm to 14.5 µm. They are generated with a conversion efficiency of 2.1 %. Compression results in 10.2-? J pulses with sub-150-fs duration, corresponding to less than four optical cycles.

This paper investigates the post-processing of additively manufactured stainless steel (SS) 304 L samples through laser shock peening (LSP). Four samples, differently processed, (i) as-built (AB); (ii) as-built + annealed; (iii) as-built + polished; and (iv) as-built + annealed + polished, were used to study the effect of LSP at pre-identified parameters to understand the mechanism and behavior of processing different conditions. In addition, compressive residual stresses and surface morphology were considered as a response to measure the effects of LSP on processed samples. The results have shown significant improvements in compressive residual stresses where the values have changed from initial tensile to compressive (−1170 MPa) and remain compressive up to the depth of 1 mm in most cases. The results of this research help better understand the LSP mechanism in the post-processing of AM Parts.

Under controlled laboratory conditions, lasers represent a source of energy with well-defined parameters suitable for mimicking phenomena such as ablation, disintegration, and plasma formation processes that take place during the hypervelocity atmospheric entry of meteoroids. Furthermore, lasers have also been proposed for employment in future space exploration and planetary defense in a wide range of potential applications. This highlights the importance of an experimental investigation of lasers’ interaction with real samples of interplanetary matter: meteorite specimens. We summarize the results of numerous meteorite laser ablation experiments performed by several laser sources—a femtosecond Ti:Sapphire laser, the multislab ceramic Yb:YAG Bivoj laser, and the iodine laser known as PALS (Prague Asterix Laser System). The differences in the ablation spots’ morphology and their dependence on the laser parameters are examined via optical microscopy, scanning electron microscopy, and profilometry in the context of the meteorite properties and the physical characteristics of laser-induced plasma.

Present work aims to study the fatigue life behaviour of additively manufactured (AM) stainless steel 316L in a laser shock peening (LSP) process. The fatigue behaviour of as-built samples and LSPeened sample were studied on the AM samples. A new diode-pumped laser system was utilized as an instrument to perform LSP operations. LSP operation was performed under two different sacrificial layers of different materials i.e. vinyl tape and aluminium tape. The other essential LSP parameters, namely energy, pulse width, spot size, overlap, and number of layers were kept constant based on the previous experimental findings. The characterization was done for analyzing the residual stresses using a hole drilling process, and a 4-point bending machine. A considerable improvement in compressive residual stress and fatigue life was observed in the LSPeened samples. Such improvements in residual stresses and fatigue life may pave a road to establishing diode-pumped lasers for LSP applications.

Complete reference on laser materials processing. Covers special application of laser-based post-processing of additive manufacturing and repair engineering. Presents recent developments in tools, technologies, controls, and operations.

We investigated the use of crystalline coatings as the highly reflective coating of an Yb:YAG thin disk directly bonded onto a silicon carbide heatsink. Compared to commonly used ion-beam-sputtered coatings, it possesses lower optical losses and higher thermal conductivity, resulting in better heat management and laser outputs. We pumped the disk up to 1.15 kW at 969 nm and reached 665 W of average output power, and disk temperature of 107 °C with a highly multi-modal V-cavity. These promising results were reached with this novel design despite the adoption of a cheap silicon carbide substrate having more than 3 times lower thermal conductivity compared to frequently used CVD diamond.

Published data of laser induced damage thresholds (LIDT) of nonlinear BBO and CLBO crystals, which are used for the generation of deep-ultraviolet radiation, are collected and plotted against laser pulse duration. The LIDT measurement techniques are briefly described and their relevance relative to the intended application of the crystal is discussed. The intrinsic and extrinsic factors affecting the evolution of the LIDT are reported. Our own experience with the LIDT of BBO and CLBO crystals in the fifth harmonic generation (FiHG) process is presented. Lowering of the LIDT for crystals with antireflection coatings is treated.

Nonlinear photoionization of dielectrics and semiconductors is widely treated in the framework of the Keldysh theory whose validity is limited to photon energies that are small compared to the band gap and relatively low laser intensities. The time-dependent density functional theory (TDDFT) simulations, which are free of these limitations, enable one to gain insight into nonequilibrium dynamics of the electronic structure. Here we apply TDDFT to investigate the photoionization of silicon crystal by ultrashort laser pulses in a wide range of laser wavelengths and intensities and compare the results with predictions of the Keldysh theory. Photoionization rates derived from the simulations considerably exceed the data obtained with the Keldysh theory within the validity range of the latter. Possible reasons for the discrepancy are discussed and we provide fundamental data on the photoionization rates beyond the limits of the Keldysh theory. By investigating the features of the Stark shift as a function of photon energy and laser field strength, a manifestation of the transient Wannier-Stark ladder states is revealed, which become blurred with increasing laser field strength. Finally, it is shown that the TDDFT simulations can potentially provide reliable data on the electron damping time that is of high importance for large-scale modeling.