Publications (temp)

Machine learning approach towards laser powder bed fusion manufactured AlSi10Mg thin tubes in laser shock peening

Ondřej Stránský, Ivan Tarant, Libor Beránek, František Holešovský, Sunil Pathak, Jan Brajer, Tomáš Mocek, Ondřej Denk

2024 — Surface Engineering — DOI: —

The industry's demand for intricate geometries has spurred research into additive manufacturing (AM). Customising material properties, including surface roughness, integrity and porosity reduction, are the key industrial goals. This necessitates a holistic approach integrating AM, laser shock peening (LSP) and non-planar geometry considerations. In this study, machine learning and neural networks offer a novel way to create intricate, abstract models capable of discerning complex process relationships. Our focus is on leveraging the certain range of laser parameters (energy, spot area, overlap) to identify optimal residual stress, average surface roughness, and porosity values. Confirmatory experiments demonstrate close agreement, with an 8% discrepancy between modelled and actual residual stress values. This approach's viability is evident even with limited datasets, provided proper precautions are taken.

Highly Regular LIPSS on Thin Molybdenum Films: Optimization and Generic Criteria

Juraj Sládek, Kryštof Hlinomaz, Inam Mirza, Yoann Levy, Thibault J.-Y. Derrien, Martin Cimrman, Siva S. Nagisetty, Jan Čermák, The Ha Stuchlíková, Jiří Stuchlík, Nadezhda M. Bulgakova

2024 — Materials — DOI: —

A systematic experimental study was performed to determine laser irradiation conditions for the large-area fabrication of highly regular laser-induced periodic surface structures (HR-LIPSS) on a 220 nm thick Mo film deposited on fused silica. The LIPSS were fabricated by scanning a linearly polarized, spatially Gaussian laser beam at 1030 nm wavelength and 1.4 ps pulse duration over the sample surface at 1 kHz repetition rate. Scanning electron microscope images of the produced structures were analyzed using the criterion of the dispersion of the LIPSS orientation angle (DLOA). Favorable conditions, in terms of laser fluence and beam scanning overlaps, were identified for achieving DLOA values <10°. To gain insight into the material behavior under these irradiation conditions, a theoretical analysis of the film heating was performed, and surface plasmon polariton excitation is discussed. A possible effect of the film dewetting from the dielectric substrate is deliberated.

Fatigue Properties of Spring Steels after Advanced Processing

Radek Procházka, Adam Stehlík, Jakub Kotous, Pavel Salvetr, Tomasz Bucki, Ondřej Stránský, Sanin Zulić

2024 — Materials — DOI: —

This article deals with the effect of strain-assisted tempering (SAT) on the fatigue properties of 54SiCr6 steel used for spring steel wires in a wide variety of automotive applications, including coil springs. This steel spring wire is extremely strong, having a high elastic limit and yield point, giving the steel excellent energy accumulation and fatigue properties. This combination opens up new possibilities in helical and cylindrical coil spring design, resulting in the reduction of both size and weight. Lightweight coil springs lead to improvements in fuel consumption, stability and vehicle traction. A large plastic deformation and SAT were applied to enhance the yield point of the study material. Improvements in the static and cyclic properties of steel springs were investigated using tensile tests and 3PB fatigue tests at ambient temperature. In addition, an advanced laser shock peening (LSP) process was employed to increase the fatigue resistance of the SAT material. The results presented here show great improvements in the static and fatigue properties over commercial steel treatment. The material quality of the wires was evaluated to be insufficient for further processing with cold coiling.

Laser-assisted two-step glass wafer metallization: an experimental procedure to improve compatibility between glass and metallic films

Albin Antony, Michal Hejduk, Tomáš Hrbek, Peter Kúš, Radka Bičišťová, Petr Hauschwitz, Ladislav Cvrček

2023 — Applied Surface Science — DOI: —

We report a simple and efficient two-step experimental procedure of glass metallization using laser microstructuring at ambient conditions. An adhesive pattern was created on the glass substrate using a laser, which imposes mechanical interlocking. An adhesive Cu layer was deposited on the glass substrate by magnetron sputtering and then electroplated with a functional Cu layer. Due to the unique surface structure created on the glass using laser, we achieved a thick layer of Cu metal film with high adhesion strength, well-defined grains and grain boundaries, and low surface roughness. The total thickness of the grown film was 11.4 µm, with an average surface roughness of 1.2 µm. The magnetron-sputtered coating did not show delamination from the glass substrate at a critical load of 60 N. The proposed method of glass metallization will lead to the realization of glass-based circuit materials that can be used in high-frequency electronic devices. Also, this procedure will be an alternative to chemical-based copper plating, which involves multiple processing steps and high-cost chemicals.

Low-temperature catalyzed growth and plasmonic properties of columnar Au-SiOx nanocomposite thin films

Sergey Ya. Khmel, Sergey V. Starinskiy, Evgeniy A. Baranov, Alexandr O. Zamchiy, Alexey I. Safonov, Yuri G. Shukhov, Alexander V. Bulgakov

2023 — Interfacial Phenomena and Heat Transfer — DOI: 10.1615/InterfacPhenomHeatTransfer.2023047643 —,20d0cd627d1d008d,2370cd8f21aa0eff.html

The optical properties of noble metal nanoparticles (NPs) can be efficiently controlled by their incorporation into host matrix films. Here, we report on the fabrication of composite films of gold NPs in a silicon suboxide matrix by a novel approach using a combination of pulsed laser deposition for NP production and gas-jet, electron-beam plasma chemical vapor deposition for low-temperature (300°C) synthesis of a SiOx (x = 0.38-1.55) thin film as a matrix for the NPs. The produced nanocomposite exhibits unexpected plasmonic properties, non-monotonically dependent on the matrix thickness, due to a porous columnar matrix structure grown from the NPs with variable oxygen content along the columns. This implies that low-temperature, gold-catalyzed oxidation of silicon occurs during the structure growth. Calculations based on Mie theory show that the refractive index of the obtained SiOx matrix can be as low as 1.2 at certain film thicknesses. Mechanisms of the columnar structure formation at different deposition stages are discussed. The synthesis approach can be used for the fabrication of optical thin-film materials with controllable low refractive index.

Cryogenic laser operation of a “mixed” Yb:LuYAG garnet crystal

Sami Slimi, Venkatesan Jambunathan, Mingyan Pan, Yicheng Wang, Weidong Chen, Pavel Loiko, Rosa Maria Solé, Magdalena Aguiló, Francesc Díaz, Martin Smrž, Tomáš Mocek, Xavier Mateos

2023 — Applied Physics B: Lasers and optics — DOI: 10.1007/s00340-023-07999-9 —

We report on the continuous-wave and passively Q-switched operation of a compositionally “mixed” heavily doped 16.6 at.% Yb:(Y,Lu)3Al5O12 garnet crystal at cryogenic temperatures (100–200 K), pumped by a volume Bragg grating stabilized diode laser emitting at 969 nm. At 140 K, in the continuous-wave regime, a maximum output power of 10.65 W was achieved at ~ 1029 nm with a slope efficiency of 56% (versus the incident pump power), a laser threshold of 1.05 W and excellent beam quality. Using Cr4+:YAG as a saturable absorber, the passively Q-switched laser generated pulses with an energy/duration of 0.15 mJ/201 ns, respectively, at a repetition rate of 39.7 kHz, corresponding to a peak power of 0.39 kW.

From Localized Laser Energy Absorption to Absorption Delocalization at Volumetric Glass Modification with Gaussian and Doughnut-Shaped Pulses

Martin Zukerstein, Vladimir P. Zhukov, Yuri P. Meshcheryakov, Nadezhda M. Bulgakova

2023 — Photonics — DOI: —

Volumetric modification of transparent materials by femtosecond laser pulses is successfully used in a wide range of practical applications. The level of modification is determined by the locally absorbed energy density, which depends on numerous factors. In this work, it is shown experimentally and theoretically that, in a certain range of laser pulse energies, the peak of absorption of laser radiation for doughnut-shaped (DS) pulses is several times higher than for Gaussian ones. This fact makes the DS pulses very attractive for material modification and direct laser writing applications. Details of the interactions of laser pulses of Gaussian and doughnut shapes with fused silica obtained by numerical simulations are presented for different pulse energies and compared with the experimentally obtained data. The effect of absorbed energy delocalization with increasing laser pulse energy is demonstrated for both beam shapes, while at relatively low pulse energies, the DS beam geometry provides stronger local absorption compared to the Gaussian geometry. The implications of a DS pulse action for post-irradiation material evolution are discussed based on thermoelastoplastic modeling.

A multi-MeV alpha particle source via protonboron fusion driven by a 10-GW tabletop laser

Valeriia Istokskaia, Marco Tosca, Lorenzo Giuffrida, Jan Psikal, Filip Grepl, Vasiliki Kantarelou, Stanislav Stancek, Sabrina Di Siena, Arsenios Hadjikyriacou, Aodhan McIlvenny, Yoann Levy, Jaroslav Huynh, Martin Cimrman, Pavel Pleskunov, Daniil Nikitin, Andrei Choukourov, Fabio Belloni, Antonino Picciotto, Satyabrata Kar, Marco Borghesi, Antonio Lucianetti, Tomas Mocek, Daniele Margarone

2023 — Communications Physics — DOI: —

Nuclear fusion between protons and boron-11 nuclei has undergone a revival of interest thanks to the rapid progress in pulsed laser technology. Potential applications of such reaction range from controlled nuclear fusion to radiobiology and cancer therapy. A laser-driven fusion approach consists in the interaction of high-power, high-intensity pulses with H- and B-rich targets. We report on an experiment exploiting proton-boron fusion in CN-BN targets to obtain high-energy alpha particle beams (up to 5 MeV) using a very compact approach and a tabletop laser system with a peak power of ~10 GW, which can operate at high-repetition rate (up to 1 kHz). The secondary resonance in the cross section of proton-boron fusion (~150 keV in the center-of-mass frame) is exploited using a laser-based approach. The generated alpha particles are characterized in terms of energy, flux, and angular distribution using solid-state nuclear-track detectors, demonstrating a flux of ~105 particles per second at 10 Hz, and ~106 per second at 1 kHz. Hydrodynamic and particle-in-cell numerical simulations support our experimental findings. Potential impact of our approach on future spread of ultra-compact, multi-MeV alpha particle sources driven by moderate intensity (1016-1017 W/cm2) laser pulses is anticipated.

Double layer acceleration of ions with differently charged states in a laser induced plasma

Xiang Yao, Christof W. Schneider, Nadezhda M. Bulgakova, Alexander V. Bulgakov, Thomas Lipper

2023 — Applied Physics A — DOI: —

The electric field driven acceleration of plasma ions is an intrinsic effect in laser-induced plasma plumes and is responsible for the generation of high-energy ions. At high laser fluences (≥ 2 J/cm2), multiply charged ions are formed and affect the plume expansion dynamics. In this paper, we used kinetic energy-resolved mass spectrometry to investigate the relative abundance and kinetic energy distributions of singly- and doubly-charged ions produced by KrF-laser ablation of nine different oxide targets. The doubly charged metal ions with a lower mass-to-charge (m/z) ratio show narrow energy distributions at high average kinetic energies coinciding with the cutoff energies for the singly-charged ion distributions. The observation suggests that the recombination of higher charged ions plays a prominent role in the formation of the high-energy tail for singly-charged ions. The results are discussed in terms of component volatility and a dynamic double layer, where ions with different m/z values experience different accelerations.

Double-pass optical parametric generator pumped by Yb thin-disk laser for efficient 1.4–2.9 µm mid-IR radiation generation

Bianka Csanaková, Ondřej Novák, Lukáš Roškot, Jiří Mužík, Martin Cimrman, Jaroslav Huynh, Martin Smrž, Helena Jelínková, Tomáš Mocek

2023 — Laser Physics — DOI: DOI: 10.1088/1555-6611/acb353 —

Many different fields benefit from the usage of light sources emitting in the mid-infrared wavelength range (2–10 µ m). A rising need for precise and fast sources in the mid infrared (mid-IR) is reflected in the development of a high-power, picosecond mid-IR source capable of generation at high repetition rates. In this work, we present the optimization of an optical parametric generator, pumped by a 3 W portion of total power of the Yb:YAG thin-disk laser (1.3 ps, 90 kHz, 90 W) by comparing a single-pass and double-pass arrangement output parameters in terms of output power dependences on input power, efficiency, beam profiles, stability, and spectra. The output tunability of both arrangements spanned from 1459 nm to 2891 nm, with the upper limit being influenced by the limited transmission of the dichroic components used in the setup above 2700 nm. It was shown that the double-pass arrangement increases the output power, from 17 mW in the single-pass arrangement to 193 mW in the double-pass arrangement at 1459 nm, resulting in over ten-fold output power increase.

Laser-patterned boron-doped diamond electrodes with precise control of sp2/sp3 carbon lateral distribution

Jan Hrabovský, Michal Zelenský, Juraj Sládek, Martin Zukerstein, Jan Fischer, Karolina Schwarzová-Pecková, Andrew Taylor, Martin Veis, Soumen Mandal, Oliver Williams, Nadezhda Bulgakova

2023 — Applied Surface Science — DOI: —

A thorough study on sp3 to sp2 carbon conversion in undoped and boron-doped diamond (BDD) thin (≈ 500 nm) layers leading to the desired sp2/sp3 carbon ratio and lateral distribution, which utilizes boron atom incorporation and infrared (IR) material laser processing has been performed. Polycrystalline as-grown (AG) or chem-mechanically polished (CMP) undoped diamond/BDD layers were investigated with respect to boron content and laser wavelength (800, 1030 nm). Boron incorporation leads to an increase in IR optical absorption and reduction of required energy fluence (𝐹th ≈ 1 J cm−2 ) needed for sp3 to sp2 carbon conversion. Raman spectroscopy was performed to identify carbon conversion stages and to tailor the ideal parameters for other IR laser sources and required sp2/sp3 carbon ratio. Electrochemical parameters (𝛥𝐸p and 𝐼Ap/𝐼Cp ratio) were obtained from cyclic voltammetry measurements of outer-([Ru(NH3 )6 ] 3+/2+) and inner-([Fe(CN)6 ] 3−/4−) sphere redox markers. Values of 𝛥𝐸p and 𝐼Ap/𝐼Cp are mainly influenced after conversion of 10% of sp3 to sp2 carbon. This trend is most pronounced for the [Fe(CN)6 ] 3−/4− redox marker, by decrease or increase of these parameters on AG or CMP BDD electrodes respectively. Electrochemical findings were supported by electrochemical impedance spectroscopy where 𝑅ct keeps the same trend as 𝛥𝐸p values and double layer capacitance profoundly increases between 10 and 25% of surface conversion.

Enhancement of the spectral broadening efficiency for circular polarization states in the high absorption regime for Gaussian and doughnut-shaped beams in fused silica

Martin Zukerstein, Yoann Levy

2023 — Optics Express — DOI: —

We experimentally investigate the spectral broadening in fused silica in the multiphoton absorption regime. Under standard conditions of laser irradiation, linear polarization of laser pulses is more advantageous for supercontinuum generation. However, with high non-linear absorption, we observe more efficient spectral broadening for circular polarizations for both Gaussian and doughnut-shaped beams. The multiphoton absorption in fused silica is studied by measuring the total transmission of laser pulses and by the intensity dependence of the self-trapped exciton luminescence observation. The strong polarization dependence of multiphoton transitions fundamentally affects the broadening of the spectrum in solids.

Multi-Modal Laser-Fabricated Nanocomposites with Non-Invasive Tracking Modality and Tuned Plasmonic Properties

Yury Ryabchikov

2023 — Crystals — DOI: —

Ultrapure composite nanostructures combining semiconductor and metallic elements as a result of ultrafast laser processing are important materials for applications in fields where high chemical purity is a crucial point. Such nanocrystals have already demonstrated prospects in plasmonic biosensing by detecting different analytes like dyes and bacteria. However, the structure of the nanocomposites, as well as the control of their properties, are still very challenging due to the significant lack of research in this area. In this paper, the synthesis of silicon–gold nanoparticles was performed using various approaches such as the direct ablation of (i) a gold target immersed in a colloidal solution of silicon nanoparticles and (ii) a silicon wafer immersed in a colloidal solution of plasmonic nanoparticles. The formed nanostructures combine both plasmonic (gold) and paramagnetic (silicon) modalities observed by absorbance and electron paramagnetic resonance spectroscopies, respectively. A significant narrowing of the size distributions of both types of two-element nanocrystals as compared to single-element ones is shown to be independent of the laser fluence. The impact of the laser ablation time on the chemical stability and the concentration of nanoparticles influencing their both optical properties and electrical conductivity was studied. The obtained results are important from a fundamental point of view for a better understanding of the laser-assisted synthesis of semiconductor–metallic nanocomposites and control of their properties for further applications.

Plasmon-affected luminescent nanothermometry with multi-band SiNPs/SiNX nanocomposites

Yury Ryabchikov

2023 — Journal of Luminescence —

The design of luminescent multi-functional nanoplatforms that can be simultaneously employed for various applications is still an important research task nowadays. Nanosilicon is one of the most promising nanomaterial having unique structural and optoelectronic properties that can be used in biomedicine, optoelectronics, sensing and nanothermometry. However, its properties do not allow the creation of one luminescent multi-functional nanoplatform requiring merging of different nanomaterials. In this work, temperature-sensitive silicon-based nanocomposites with tuned multi-band emission are demonstrated. One can easily achieve the change of their single- and multi-band photoluminescence spectral position from ∼1.6 eV to ∼2.9 eV by varying the experimental parameters. Moreover, the “white” emission of silicon nitride is also observed that can be further applied for sensing or optoelectronic applications. Furthermore, the presence of silver nanoparticles leads to 80% increase of the temperature sensitivity of the photoluminescence maximum position (from ∼540 μeV/°C to ∼975 μeV/°C). The plasmonic nanostructures also considerably modify the ratiometric temperature behavior of nanocomposite emission. The shown findings suggest perspectives of silicon-based nanostructures as multi-task luminescent nanoplatforms in the fields of nanothermometry, molecule sensing, optoelectronics and biomedicine.

Porosity and Microstructure of L-PBF printed AlSi10Mg thin tubes in Laser Shock Peening

Ondřej Stránský, Sunil Pathak, Jan Kaufman, Marek Böhm, Jaromír Kopeček, Libor Beránek, František Holeškovský, Šimon Petrášek, Lucie Hlavůňková, Zbyněk Soukup

2023 — Journal of Materials Research and Technology — DOI: —

Laser powder bed fusion (L-PBF) has emerged as one of the most promising technologies for producing complex geometries that are difficult to achieve with other methods. However, its widespread adoption is hindered by issues such as deleterious microstructure, tensile residual stresses, and porous structure, mainly while working with aluminum alloys. To address these challenges, laser shock peening (LSP) offers a potential solution by mitigating the negative effects associated with aluminum L-PBF. This study investigates the impact of the important LSP parameters, namely energy, spot size, and overlap on L-PBF printed thin AlSi10Mg tubes. A total of 17 specimens were examined by varying the mentioned parameters at three levels each. The outcome of the study was evaluated in terms of residual stresses, porosity, microstructure and surface roughness. The results have shown significant improvements in residual stresses, where a maximum improvement of over 200 % was observed and a decrease in porosity by 70 %. Furthermore, the microstructure analysis revealed grain refinement and dislocation redistribution as material reactions, aligning with the observed microhardness increase. These findings demonstrate the viability of LSP as a post-processing method for demanding applications, effectively addressing the limitations of the L-PBF process.

Enhanced tribological performance and nanostructuring speed on AlTiN by beamshaping technology

T. Primus, P. Hauschwitz, T. Vitu, R. Bičišťová, P. Zeman, M. Cimrman, J. Brajer, T. Mocek, M. Smrž

2023 — Surface Engineering — DOI: —

For the first time, a dynamic beamshaping technology has been utilized for the efficient production of periodic nanostructures on top of AlTiN coating to enable dry machining without costly and environmentally hazardous cutting fluids. First, a variety of periodic nanostructures with periods in a range of 740–273 nm were produced utilizing different wavelengths. Additionally, beamshaping technology increased productivity by 4008% up to 105 cm2 min−1 by shaping the Gaussian beam into a rectangular beam of 500 × 30 µm. To simulate the application load and resulting heat production during manufacturing, friction analysis was performed at room and elevated temperature to 500°C. The analysis revealed a significant reduction in the friction coefficient – up to 27% and 19% at room temperature and 500°C, respectively. The combination of these results demonstrates that the proposed method can be scaled up for the mass production of functionalized machining tools for dry machining.

Dual-wavelength femtosecond laser-induced single-shot damage and ablation of silicon

Alexander V. Bulgakov, Juraj Sládek, Jan Hrabovský, Inam Mirza, Wladimir Marine, Nadezhda M. Bulgakova

2023 — Applied Surface Science — DOI: —

An experimental and theoretical study of laser-induced damage and ablation of silicon by two individual femtosecond pulses of different wavelengths, 1030 and 515 nm, is performed to address the physical mechanisms of dual-wavelength ablation and reveal possibilities for increasing the ablation efficiency. The produced craters and damaged areas are analyzed as a function of laser fluence and time separation between the pulses and are compared with monochromatic irradiation. The order of pulses is demonstrated to be essential in bi-color ablation with higher material removal rates when a shorter-wavelength pulse arrives first at the surface. Simulations based on the two-temperature model show that the visible pulse is profitable for the generation of the electron-hole plasma while the delayed IR pulse is efficiently absorbed in the plasma enhancing energy coupling to the target. At long delays of 30–100 ps, the dual-wavelength ablation is found to be particularly strong with formation of deep smooth craters. This is explained by the expansion of a hot liquid layer produced by the first pulse with a drastic decrease in the surface reflectivity at this timescale. The results provide insight into the processes of dual-wavelength laser ablation offering a better control of the energy deposition into material.

Faraday isolator for 100J/10Hz pulsed laser

Ondřej Slezák, David Vojna, Jan Pilař, Martin Divoký, Ondřej Denk, Martin Hanuš, Petr Navrátil, Martin Smrž, Antonio Lucianetti, Tomáš Mocek

2023 — Optica Letters — DOI: —

The authors report the first-ever demonstration of the optical isolation of a kilowatt average power pulsed laser. A Faraday isolator capable of stable protection of the laser amplifier chain delivering 100 J nanosecond laser pulses at the repetition rate of 10 Hz has been developed and successfully tested. The isolator provided an isolation ratio of 30.46 dB in the course of an hour-long testing run at full power without any noticeable decrease due to the thermal effects. This is the first-ever demonstration of a nonreciprocal optical device operated with such a powerful high-energy, high-repetition-rate laser beam, opening up the possibilities for this type of lasers to be used for a number of industrial and scientific applications.

Microstructure and surface quality of SLM printed miniature helical gear in LSPwC

Sunil Pathak, Marek Böhm, Jan Kaufman, Jaromír Kopeček, Sanin Zulić, Ondřej Stránský, Jan Brajer, Libor Beránek, Tomáš Mocek

2023 — Surface Engineering — DOI: —

The work describes the influence of underwater laser shock peening without coating (LSPwC) on selective laser melting manufactured meso-size (outside diameter ≤ 10 mm) helical gears. Five experiments were conducted using energies in the 200 mJ up to 1 J, while the spot size and overlap were kept constant as 1 mm and 90 %, respectively. Responses were measured and compared in terms of surface residual stresses, surface roughness, and microstructure of LSPwC-treated samples. Results show the development of significant compressive residual stresses in the root of the LSPwC processed helical gear, where it changes the state from tensile +45 MPa to compressive −421 MPa. Surface roughness has shown improvement, while volumetric material peak confirms the reduction by over 50%. Microstructure study was performed at the surface and by cross-section using scanning electron microscopy and electron backscatter diffraction analysis. The grain refinement and change in misorientation were observed, confirming plastic deformation.

Non-thermal regimes of laser annealing of semiconductor nanostructures: crystallization without melting

Inam Mirza, Alexander V. Bulgakov, Hanna Sopha, Sergey V. Starinskiy, Hana Turčičová, Ondřej Novák, Jiří Mužík, Martin Smrž, Vladimir A. Volodin, Tomáš Mocek, Jan M. Macak, Nadezhda M. Bulgakova

2023 — Frontiers in Nanotechnology — DOI: —

As-prepared nanostructured semiconductor materials are usually found in an amorphous form, which needs to be converted into a crystalline one for improving electronic properties and achieving enhanced application functionalities. The most utilized method is thermal annealing in a furnace, which however is time- and energy-consuming and not applicable for low-temperature melting substrates. An alternative is laser annealing, which can be carried out in a relatively short time and, additionally, offers the possibility of annealing localized areas. However, laser-annealed nanostructures are often distorted by melting, while preserving the as-prepared morphology is essential for practical applications. In this work, we analyze conditions of non-thermal ultrafast laser annealing of two kinds of nanostructures: anodic TiO2 nanotube layers and Ge/Si multilayer stacks. For both cases, regimes of crystallization have been found, which yield in preserving the initial nanomaterial morphologies without any melting signs. On these examples, ultrafast non-thermal mechanisms of structural material transformation are discussed, which can provide new opportunities for conversion of amorphous semiconductor nanomaterials into a desired crystalline form that is of high demand for existing and emerging technologies.

On the Melting Thresholds of Semiconductors under Nanosecond Pulse Laser Irradiation

Jiří Beránek, Alexander V. Bulgakov, Nadezhda M. Bulgakova

2023 — Applied Sciences — DOI: —

In this work, a unified numerical model is used to determine the melting thresholds and to investigate the early stages of melting of several crystalline semiconductors (Si, Ge, GaAs, CdTe and InP) irradiated by nanosecond laser pulses. A molten fraction approach is used for continuous transition over the melting point. The results are compared with previously published theoretical and experimental data. A survey on the thermophysical and optical properties of the selected materials has been carried out to gather the most relevant data on temperature dependent properties for the solid and liquid states of these semiconductors where such data are available. A generalization of the obtained results is established that enables evaluation of the melting thresholds for different semiconductors based on their properties and irradiation conditions (laser wavelength, pulse duration).

Ion expansion dynamics of laser induced multi-elemental plasmas

Xiang Yao, Christof W. Schneider, Nadezhda M. Bulgakova, Alexander V. Bulgakov, Thomas Lippert

2023 — Journal of Physics D: Applied Physics — DOI: 10.1088/1361-6463/acd3ff —

Ablation of multi-elemental materials by nanosecond lasers is often used to deposit oxide thin films. Understanding the ablation plume dynamics is of utmost importance to gain a detailed insight into thin film growth of materials with a complex composition. In this study, the plume expansion dynamics of several compound materials (AuCu, La0.33Ca0.67MnO3, and LiMn2O4) were characterized by measuring the angular-dependent kinetic energy (KE) distributions of ionic plasma species produced by KrF- and XeCl-excimer laser ablation in vacuum. The distributions of the lightest plume ions were found to differ fundamentally from those of other ions. The latter are similar to the energy distributions observed in single-component plumes and represent a low-energy peak and high-energy tail, while those for the lightest ions consist of at least two distinct peaks. These observations can be explained by assuming the formation of a dynamic double layer (DL) at the front of the plasma giving rise to different acceleration rates for light and heavier ions. As a consequence, heavier elements stay longer within the dynamic DL and gain larger KEs that leads to the observed ion separation. Extending these considerations into three dimensions yields an anisotropic acceleration concept for the plasma ions with high acceleration rates and longer presence within the DL normal to the target surface and lower acceleration rates and shorter time in the parallel direction.

Single-shot selective femtosecond and picosecond infrared laser crystallization of an amorphous Ge/Si multilayer stack

V.A.Volodin, Yuzhu Cheng, A.V.Bulgakov, Y.Levy, J.Beránek, S.S.Nagisetty, M.Zukerstein, A.A.Popov, N.M.Bulgakova

2023 — Optics & Laser Technology — DOI: —

Pulsed laser crystallization is an efficient annealing technique to obtain polycrystalline silicon or germanium films on non-refractory substrates. This is important for creating “flexible electronics” and can also be used to fabricate thin-film solar cells. In this work, near- and mid-infrared femtosecond and picosecond laser pulses were used to crystallize a Ge/Si multilayer stack consisting of alternating amorphous thin films of silicon and germanium. The use of infrared radiation at wavelengths of 1030 and 1500 nm with photon energies lower than the optical absorption edge in amorphous silicon allowed obtaining selective crystallization of germanium layers with a single laser shot. The phase composition of the irradiated stack was investigated by the Raman scattering technique. Several non-ablative regimes of ultrashort-pulse laser crystallization were found, from partial crystallization of germanium without intermixing the Ge/Si layers to complete intermixing of the layers with formation of GexSi1-x solid alloys. The roles of single- and two-photon absorption, thermal and non-thermal (ultrafast) melting processes, and laser-induced stresses in selective pico- and femtosecond laser annealing are discussed. It is concluded that, due to a mismatch of the thermal expansion coefficients between the adjacent stack layers, efficient explosive solid-phase crystallization of the Ge layers is possible at relatively low temperatures, well below the melting point.

Ultrafast Infrared Laser Crystallization of Amorphous Ge Films on Glass Substrates

Yuzhu Cheng, Alexander V. Bulgakov, Nadezhda M. Bulgakova, Jiří Beránek, Martin Zukerstein, Ilya A. Milekhin, Alexander A. Popov, Vladimir A. Volodin

2023 — Micromachines — DOI: —

Amorphous germanium films on nonrefractory glass substrates were annealed by ultrashort near-infrared (1030 nm, 1.4 ps) and mid-infrared (1500 nm, 70 fs) laser pulses. Crystallization of germanium irradiated at a laser energy density (fluence) range from 25 to 400 mJ/cm2 under single-shot and multishot conditions was investigated using Raman spectroscopy. The dependence of the fraction of the crystalline phase on the fluence was obtained for picosecond and femtosecond laser annealing. The regimes of almost complete crystallization of germanium films over the entire thickness were obtained (from the analysis of Raman spectra with excitation of 785 nm laser). The possibility of scanning laser processing is shown, which can be used to create films of micro- and nanocrystalline germanium on flexible substrates.

Comparative determination of atomic boron and carrier concentration in highly boron doped nano-crystalline diamond

Andrew Taylor, Petr Ashcheulov, Pavel Hubík, Zdeněk Weiss, Ladislav Klimša, Jaromír Kopeček, Jan Hrabovský, Martin Veis, Jan Lorinčík, Ivan Elantyev, Vincent Mortet

2023 — Diamond and Related Materials — DOI: —

We have compared the total boron content and hole carrier concentration values obtained from various destructive and non-destructive quantification methods in boron doped nano-crystalline diamond films prepared over a range of doping levels, using microwave plasma enhanced chemical vapour deposition. Destructive secondary-ion mass spectrometry and relatively unreported glow discharge optical emission spectrometry were complemented by non-destructive Raman, spectroscopic ellipsometry and van der Pauw Hall measurements. Measurement techniques are discussed, including details of the glow discharge optical emission spectrometry technique; use of different laser powers and wavelengths, fitting parameters for Raman spectroscopy, and improved ellipsometry modelling. Finally, measured values are compared and discussed regarding their viability for estimation of total boron and electrically active boron in doped nano-crystalline diamond layers.

Advanced micro- & nanostructuring for enhanced biocompatibility of stainless steel by multi-beam and beamshaping technology

Petr Hauschwitz, Markéta Klíčová, Senta Müllerová, Radka Bičišťová, Martin Procházka, Jan Brajer, Michal Chyla, Martin Smrž, Jiří Chvojka, Tomáš Mocek

2023 — Biomedical Materials — DOI: 10.1088/1748-605X/acd291 —

Biocompatibility is one of the key issues for implants, especially in the case of stainless steel with medium to low biocompatibility, which may lead to a lack of osseointegration and consequently to implant failure or rejection. To precisely control preferential cell growth sites and, consequently, the biocompatibility of prosthetic devices, two types of surfaces were analyzed, containing periodic nanogrooves laser induced periodic surface structure (LIPSS) and square-shaped micropillars. For the fast and efficient production of these surfaces, the unique combination of high energy ultrashort pulsed laser system with multi-beam and beamshaping technology was applied, resulting in increased productivity by 526% for micropillars and 14 570% for LIPSS compared to single beam methods. In vitro analysis revealed that micro and nanostructured surfaces provide a better environment for cell attachment and proliferation compared to untreated ones, showing an increase of up to 496% in the number of cells compared to the reference. Moreover, the combination of LIPSS and micropillars resulted in a precise cell orientation along the periodic microgroove pattern. The combination of these results demonstrates the possibility of mass production of functionalized implants with control over cell organization and growth. Thus, reducing the risk of implant failure due to low biocompatibility.

“Green” Fluorescent–Plasmonic Carbon-Based Nanocomposites with Controlled Performance for Mild Laser Hyperthermia

Yury V. Ryabchikov, Alexander Zaderko

2023 — Photonics — DOI: —

Fluorescent carbon nanodots are a promising nanomaterial for different applications in biophotonics, sensing and optical nanothermometry fields due to their strong fluorescence properties. However, their multi-modal applications are considerably limited, requiring the use of several nanoagents that could solve different tasks simultaneously. In this paper, we report the first experimental results on a facile “green” laser-based synthesis of multi-modal carbon–metallic nanocomposites with tuned optical performance. This simple approach leads to the appearance of finely controlled plasmonic properties in carbon-based nanocomposites whose spectral position is adapted by using an appropriate material. Thus, longer laser ablation provokes 29-fold increase in the absorption intensity of carbon–gold nanocomposites due to the increase in the metal content from 13% (30 s) to 53% (600 s). Despite strong plasmonic properties, the metal presence results in the quenching of the carbon nanostructures’ fluorescence (2.4-fold for C-Au NCs and 3.6-fold for C-Ag NCs for 600 s ablation time). Plasmonic nanocomposites with variable metal content reveal a ~3-fold increase in the laser-to-heat conversion efficiency of carbon nanodots matching the temperature range for mild hyperthermia applications. The findings presented demonstrate a facile approach to expanding the properties of chemically prepared semiconductor nanostructures due to the formation of novel semiconductor–metallic nanocomposites using a “green” approach. Together with the ease in control of their performance, it can considerably increase the impact of semiconductor nanomaterials in various photonic, plasmonic and biomedical applications.

Insights into Laser-Matter Interaction from Inside: Wealth of Processes, Multiplicity of Mechanisms and Possible Roadmaps for Energy Localization

Thibault J. -Y. Derrien, Yoann Levy, Nadezhda M. Bulgakova

2023 — Ultrafast Laser Nanostructuring — DOI: —

Short and ultrashort laser pulses are nowadays an integral part of up-to-date technological solutions in many areas from material micro-/nanoprocessing and synthesis of new materials to quantum computing and biomedicine. The number of laser applications in science and industries is growing precipitously with tendencies of enhancing laser processing precision and reproducibility toward creation of extremely tiny objects. Coupling more laser energy into a smaller material volume in a controllable way is one of the grand challenges, which can only be achieved through a deep understanding of a wealth of the laser-triggered transient processes at different spatiotemporal scales. The objective of this chapter is to provide a review of the main fundamental linear and nonlinear processes excited by ultrafast lasers in different kinds of materials with the aim to reveal and highlight possible mechanisms, which would enable extreme localization of energy absorption. After summarizing existing knowledge on laser-induced phenomena that includes mechanisms of laser light absorption, heat transfer peculiarities, energy thermalization at ultrafast time scales, and related hydrodynamic phenomena, an overview is given on novel insights into highly nonequilibrium processes gained in recent years via quantum and molecular dynamics simulations. The fundamental part is followed by an analysis of possible techniques and processes, which could enable extreme localization of laser energy absorption both on the surface of material samples and in the bulk. Finally, as an example of laser energy localization alternating at nanoscale, laser-induced periodic surface structures (LIPSS) are discussed. The multiplicity of the mechanisms is demonstrated via a rigorous theoretical analysis and simulations.

Picosecond pulsed laser deposition of MOS2 thin films

Jose Guadalupe Quiñones-Galvan, Inam Mirza, Jan Hrabovský, Enrique Campos-Gonzalez, Francisco de Moure-Flores, Jose Santos-Cruz, Miguel Angel Santana-Aranda, Alexander V. Bulgakov , Nadezhda M. Bulgakova

2023 — MM Science Journal — DOI: 10.17973/MMSJ.2023_06_2023003 —

MoS2 thin films were grown by the pulsed laser deposition technique using a picosecond laser at a wavelength of 1030 nm. The plasma ion mean kinetic energy and density were estimated from the time-of-flight distributions measured using a Langmuir planar probe. It has been found that the mean kinetic energy decreases with increasing the laser pulse energy. This unusual effect is explained by the difference in the volatility of the vaporized species. Samples were structurally characterized by Raman spectroscopy and grazing angle X-ray diffraction. It was found that thin films of amorphous matrices containing MoS2 nanocrystallites were grown. Optical characterization carried out by UV-vis spectroscopy yielded transmittance values above 90% in the visible spectral range and an indirect electronic transition at 1.4 eV. Chemical oxidation states for molybdenum and sulfur were analyzed by means of X-ray photoelectron emission spectroscopy, which revealed Mo-S bonding states, confirming the growth of MoS2.

Optical, magneto-optical properties and fiber-drawing ability of tellurite glasses in the TeO2–ZnO–BaO ternary system

Jan Hrabovský, Lukáš Střižík, Frédéric Désévédavy, Stana Tazlaru, Miroslav Kučera, Lukáš Nowak, Robin Kryštůfek, Jan Mistrík, Václav Dědič, Vladimír Kopecký, Grégory Gadrét, Thomas Wagner, Frédéric Smektala, Martin Veis

2023 — Journal of Non-Crystalline Solids — DOI: —

The presented work is focused on the optical and magneto-optical characterization of TeO2-ZnO-BaO (TZB) tellurite glasses. We investigated the refractive index and extinction coefficient dispersion by spectroscopic ellipsometry from ultraviolet, λ ≈ 0.193 μm, up to mid-infrared, λ ≈ 25 μm spectral region. Studied glasses exhibited large values of linear (n632 ≈ 1.91–2.09) and non-linear refractive index (n2 ≈ 1.20–2.67×10−11 esu), Verdet constant (V632 ≈ 22–33 radT−1m−1) and optical band gap energy (Eg ≈ 3.7–4.1 eV). The materials characterization revealed that BaO substitution by ZnO leads (at constant content of TeO2) to an increase in linear and nonlinear refractive index as well as Verdet constant while the optical band gap energy decreases. Fiber drawing ability of TeO2–ZnO–BaO glassy system has been demonstrated on 60TeO2–20ZnO–20BaO glass with presented mid-infrared attenuation coefficient. Specific parameters such as dispersion and single oscillator energy, Abbe number, and first-/third-order optical susceptibility are enclosed together with the values of magneto-optic anomaly derived from the calculation of measured dispersion of the refractive index.

Facile Manufacture of Oxide-Free Cu Particles Coated with Oleic Acid by Electrical Discharge Machining

Irshad Ahamad Khilji, Siti Nadiah Binti Mohd Safee, Sunil Pathak , Chaitanya Reddy Chilakamarry , Amiril Sahab Bin Abdul Sani, Venugopal Jayarama Reddy

2022 — Micromachines — DOI: —

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.

Improving functional performance characteristics of spur gears through flank modifications by non-contact advanced finishing process

Vivek Rana, Neelesh Kumar Jain, Sunil Pathak

2022 — The International Journal of Advanced Manufacturing Technology — DOI: —

This paper describes reduction in noise, vibrations, total and tooth-to-tooth, and longwave transmission errors, total and tooth-to-tooth composite errors, and radial runout of spur gears by imparting them flank modifications and their combinations by a non-contact advanced finishing process referred to as pulsed electrolytic dissolution. Eight spur gears were modified using innovatively developed 5 cathode gears and apparatus by imparting them 5 flank modifications (i.e. tip relief, root relief, end relief, profile crowning, lead crowning) individually and their 4 selected combinations. Vibrations at all rotational speeds and noise at 900 and 1200 rpm are reduced for all modified spur gears at all the values of applied loads. End relieved spur gear showed maximum reductions in noise and vibrations by 5 dBA and 3.77 m/s2 respectively for 1200 rpm speed. Reduction amount in noise and vibrations of modified gears increase with rotary speed. Lead crowned gear showed maximum reductions of 146 µm in total transmission error, 109 µm in total composite error, and 102 µm in radial runout. End relieved gear showed maximum reductions of 37 µm in tooth-to-tooth and 139 µm longwave transmission errors. Tip relieved, and tip and root relieved gear showed maximum reduction of 121 µm in tooth-to-tooth composite error. This work proves that the developed non-contact process can very effectively impart different flank modifications individually and their combinations to spur gears without any twist error. Lead crowning, end relieving, tip relieving, and tip and root relieving are main flank modifications that significantly improve functional performance characteristics of spur gears. It will result in their enhanced operating performance and service life, which will help their manufacturers and end-users.

Thermal-stress-induced birefringence management of complex laser systems by means of polarimetry

Ondřej Slezák, Magdalena Sawicka-Chyla, Martin Divoký, Jan Pilař, Martin Smrž, Tomáš Mocek

2022 — Scientific Reports — DOI: —

The novel method of the thermally-induced polarization changes driven power losses (TIPCL) analysis in the complex laser systems has been developed. The measurement has been tested on the amplifier chain of the 100 J / 10 Hz laser system ‘Bivoj’ operated at HiLASE Centre. By the usage of the measured non-uniform Mueller matrix of the amplifier chain, the optimization of the ideal input and output polarization state has been calculated numerically. The results of the optimization have been applied to the laser system, thus reducing the TIPCL from originally observed more than 33% to 7.9% for CW beam and to 9% for pulsed laser beam, respectively. To the best of our knowledge, this result represents the most efficient TIPCL suppression method for complex laser systems so far. The method also allows the definition of the ideal fully polarized non-uniform pre-compensation of input beam consequently suffering from zero TIPCL.

TOF Analysis of Ions Accelerated at High Repetition Rate from Laser-Induced Plasma

Evan Russell, Valeria Istokskaia, Lorenzo Giuffrida, Yoann Levy, Jaroslav Huynh, Martin Cimrman, Martin Srmž, Daniele Margarone

2022 — Applied Sciences — DOI: —

The generation, detection, and quantification of high-energy proton spectra that are produced from laser-target interaction methodologies is a field of increasingly growing popularity over the last 20 years. Generation methods such as target normal sheath acceleration or similar allow for collimated laminar ion beams to be produced in a compact environment through the use of short-burst terawatt lasers and are a growing field of investment. This project details the development and refinement of a python-based code to analyze time-of-flight ion spectroscopy data, with the intent to pinpoint the maximum proton energy within the incident beam to as reliable and accurate a value as possible within a feasible processing time. TOF data for 2.2 × 1016 W/cm2 intensity laser shots incident on a 2 mm Cu target that were gathered from the PERLA 1 kHz laser at the HiLASE center were used as training and testing data with the implementation of basic machine learning techniques to train these methods to the data being used. These datasets were used to ensure more widely applicable functionality, and accurate calculation to within 1% accuracy of an assumed correct value was seen to be consistently achievable for these datasets. This wider functionality indicates a high level of accuracy for previously unseen TOF datasets, regardless of signal/noise levels or dataset size, allowing for free use of the code in the wider field.

Spectral broadening and a prospect for pulse compression of Yb:YAG thin-disk laser pulses by nonlinear SHG in a BBO crystal with time predelay and tilting of the pulse fronts

Martin Duda, Ondřej Novák, Martin Cimrman, Jaroslav Huynh, Martin Smrž, Tomáš Mocek

2022 — Optics Continuum — DOI: —

Pulse compression by second harmonic generation in a type II nonlinear optical crystal controlled by a time predelay of the faster input pulse is not simple to achieve high-average-power Yb:YAG lasers with wavelength of 1030 nm. The reason is that the borate nonlinear crystals with their excellent thermal properties do not have the optimal ratio of group velocities of the interacting pulses to achieve efficient pulse compression. We have changed the effective group velocities by tilting the pulse fronts at a diffraction grating and imaging the tilted 1.7 ps pulses into the 6 and 8.5 mm thick BBO crystals. As a result, we have measured significant spectral broadening to 4.5 nm, supporting pulses as short as 100 fs, with an energy conversion efficiency in excess of 20 %. The measured data correspond well with numerical simulations. This research opens a way to extend the range of possible applications of Yb:YAG high-average-power thin-disk lasers into the fs regime.

Adaptive optics system for a short wavelength mid-IR laser based on a Shack–Hartmann wavefront sensor and analysis of thermal noise impacts

Huang Zhou, Jan Pilař, Martin Smrž, Liyuan Chen, Miroslav Čech, Tomáš Mocek

2022 — Applied Optics — DOI: —

In the article, the author team presents an adaptive optics (AO) system for a 1.94-µm laser source. The system consists of a home-made Shack–Hartmann wavefront sensor and silver-coated bimorph deformable mirror operating in a closed-loop control scheme. The wavefront sensor used an uncooled vapor phase deposition PbSe focal-plane array for the actual light sensing. An effect of thermal afterimage was found to be reducing the centroid detection precision significantly. The effect was analyzed in detail and finally has been dealt with by updating the background calibration. System stability was increased by reduction of control modes. The system functionality and stability were demonstrated by improved focal spot quality. By replacing some of the used optics, the range of the demonstrated mid-IR AOS could be extended to cover the spectral range of 1–5 µm. To the best of the authors’ knowledge, it is the first AO system built specifically for mid-IR laser wavefront correction.

Laser induced damage threshold (LIDT) of β-barium borate (BBO) and cesium lithium borate (CLBO) – Overview

Hana Turčičová, Ondřej Novák, Jiří Mužík, Denisa Štěpánková, Martin Smrž, Tomáš Mocek

2022 — Optics & Laser Technology — DOI: —

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.

Silicon surface patterning by regular stripes of laser-induced periodic surface structures

J. Sládek, Y. Levy, T.J.-Y. Derrien, Z. Bryknar, N.M. Bulgakova

2022 — Applied Surface Science — DOI: —

Laser-induced periodic surface structures (LIPSS) formation on the surface of mono-crystalline silicon is reported for a specific fabrication regime of large-area structuring. Using a femtosecond laser at 1030 nm wavelength, a particular range of fluence and beam overlap in two-dimensional scanning scheme has been identified where LIPSS-covered areas organize into stripes perpendicular to the scanning direction. The stripes, where the LIPSS appear, are regularly spaced and located in between the centers of two subsequent Gaussian pulses while the regions receiving the peak pulse fluence are free of LIPSS. The formation of the LIPSS stripes is examined by analyzing local integrated fluence, N-on-1 pulse damage geometry and thresholds of modifications. Processes at play in the generation of such stripes of LIPSS are discussed and an explanation based on interpulse feedback from amorphized areas is proposed.

Extreme laser pulse-energy measurements by means of photon momentum

Paul A. Williams, Kyle A. Rogers, Martin Divoky, Geiland Porrovecchio, Jiří Tesař, Marek Smid, John H. Lehman

2022 — Optics Express — DOI: —

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.

Investigation of the lasing performance of a crystalline-coated Yb:YAG thin-disk directly bonded onto a silicon carbide heatsink

Jan Cvrček, Martin Cimrman, David Vojna, Denisa Štěpánková, Ondřej Foršt, Martin Smrž, Ondřej Novák, Ondřej Slezák, Michal Chyla, Michal Jelínek, Tomáš Mocek

2022 — Optics Express — DOI: —

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.

10-µJ few-cycle 12-µm source based on difference-frequency generation driven by a 1-kHz mid-wave infrared OPCPA

Martin Duda, Lorenz von Grafenstein, Martin Bock, Dennis Ueberschaer, Pia Fuertjes, Lukáš Roškot, Martin Smrž, Ondřej Novák, Uwe Griebner

2022 — Optics Letters — DOI: —

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-𝜇 J pulses with sub-150-fs duration, corresponding to less than four optical cycles.

Fatigue life enhancement of additive manufactured 316l stainless steel by LSP using a DPSS laser system

Sanin Zulić, Danijela Rostohar, Jan Kaufman, Sunil Pathak, Jaromír Kopeček, Marek Böhm, Jan Brajer, Tomáš Mocek

2022 — Surface Engineering — DOI: —

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.