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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.

Difference frequency generation in BaGa4Se7 tunable in a 6.5-8.5 μm range with a peak power of 30 MW, pulse energy of 60μJ, conversion up to 4%, and optical damage threshold of 0.08J/cm2 is presented.

Picosecond difference frequency generation in BaGa4Se7, LiGaSe2, or LiGaS2 tunable in a 5 -13 μm wavelength range with pulse energy up to 100μJ or conversion efficiency up to 4% is presented.

Reflectivity and surface topography of tempered glass were modified without any thermal damage to the surroundings by utilizing 1.7 ps ultrashort pulsed laser on its fundamental wavelength of 1030 nm. To speed up the fabrication, a dynamic beam shaping unit combined with a galvanometer scanning head was applied to divide the initial laser beam into a matrix of beamlets with adjustable beamlets number and separation distance. By tuning the laser and processing parameters, reflected intensity can be reduced up to 75% while maintaining 90% of transparency thus showing great potential for display functionalization of mobile phones or laptops.

Efficient heat management of Yb:YAG thin disk based on new highly thermally conductive crystalline coating is proved by thermal and lasing characteristics when it is used in a simple, multi-mode laser cavity under 940-nm pumping.

Shaping and compression of short laser pulses in the course of a second harmonic (2H) generation is a well verified technique in the case of Nd:glass laser radiation converted in KTP crystal cut for type II phase-matching. The laser pulse, few ps in duration, is divided into two orthogonally polarized pulses and one is delayed in respect to the other. Both of them enter the nonlinear optical crystal, in which they propagate with different group velocities. As they are approaching each other, short 2H pulse is generated at their temporal overlap. Shaping of the 2H pulse is achieved by changing the predelay and input pulse intensities. For current high power picosecond laser sources of choice, Yb:YAG lasers, borate crystals have to be used for efficient harmonic generation because of their convenient thermal properties and long lifetime. Although the requirement on group velocities is not fulfilled for the LBO and BBO crystals, numerical calculations have revealed conditions where pulse shaping and even significant pulse compression occur. Fundamental input pulse of 1.8 ps was compressed down to 0.8 ps (FWHM) by 2H generation in LBO crystal. In this work, details about the calculations and measurements of shaping of 2H picosecond Yb:YAG laser pulses in LBO and BBO crystals in dependence on input intensities and predelay will be presented. The shaped 2H pulse measurements performed by an autocorrelator agree well with the calculations, achieving almost 3-fold compression. For the most interesting cases, 2H pulses are characterized by FROG in detail.

To analyze the thermal birefringence effects in laser gain materials, knowledge of the piezooptic coefficients of the materials is required. The piezooptic coefficients of ceramic YAG were measured using the four-point bending method. To our knowledge, this is the first report of this measurement for ceramic YAG. With the measured values, the depolarization of a ceramic YAG laser was analyzed. Overall, the results agree with that of single-crystal YAG in the [111] direction. Ceramic YAG will produce a larger depolarization compared with [100]-direction YAG with an appropriate input polarization angle.

We report new observations on picosecond deep ultraviolet coherent beams generated in a CLBO as the fourth and fifth harmonics of a diode pumped high average power Yb:YAG thin disk laser operating at 77 kHz repetition rate at 1030 nm. The effects of the two-photon absorption were observed, e.g. the modification of phase matching conditions, lowering of the conversion efficiency. The fifth harmonic generation (4ω+1ω) was studied for different time delays between both pump beams and for the case of excess input power of the fundamental. The latter effect suggests a possibility of increasing DUV output at short crystals. The highest output power obtained at 257 nm was 7.6 W and 1 W at 206 nm. To our knowledge these DUV output powers rank among the highest for picosecond pulses at the repetition rate of the order of magnitude of 100 kHz.

Multi-beam micro- and nano-machining of material surfaces has been getting more important because of its great potential to increase production speed of large size laser induced periodic surface structures (LIPSS). Fast and cheap production of engineered surfaces structures can bring unique properties of surfaces like tailored wettability, friction, antibacterial properties, etc., to mass-production with consequence in, for example, energy and costs savings. However, tailoring of long-term stable interference patterns from ultrashort laser pulses requires an extremely stable laser system with nearly diffraction-limited output beams. HiLASE Centre developed such a thin-disk-based Yb:YAG sub-picosecond laser platform, PERLA, providing average output power up to 0.5 kW with 2nd and 4th harmonic generation extensions and demonstrated its potential for direct laser interference patterning (DLIP). In this paper, we focus on details of the thin-disk PERLA laser.

An overview of the latest developments of kilowatt-level diode pumped solid state lasers for advanced applications at the HiLASE Centre is presented. An overview of subcontracted and in-house-developed laser beamlines is presented. The aim of development is to build kW-class beamlines delivering picosecond pulses between 1- and 100-kHz repetition rates and high-energy nanosecond pulses at 10 Hz. The picosecond beamlines are based on Yb:YAG thin-disk amplifiers and chirped pulse amplification. The current status of the beamlines’ performance is reported. The advantages of zero-phonon line and pulsed pumping are demonstrated with respect to efficiency, thin disk temperature and beam quality. New diagnostics methods supporting the high average power lasers’ development, such as the high-resolution spectroscopy of Yb-doped materials, in situ thin disk deformation measurements, single-shot M2 measurement, realization of wavefront correction by a deformable mirror and the laser performance of a new mixed garnet ceramics, are described. The energetic, thermal and fluid-mechanical numerical modeling for the optimization of the multi-slab amplifiers is also described.

In many fields of modern physics and industrial applications high-average power pulsed diode-pumped solid-state lasers are essential. Scaling of these lasers towards higher pulse energies is often limited by the onset of thermal effects which are determined by the average power. In this paper we would like to propose a way of increasing the pulse energies by operating the PERLA B laser system in 100 Hz burst mode with 1 ms burst duration and intra-burst repetition rate of 10 kHz. The CPA-based system incorporates fiber front-end, regenerative amplifier and the multipass amplifier followed by the booster amplifier and

High-energy ps-laser pulses with excellent beam quality are required for efficient Compton X-ray source. We report on a thin-disk multipass amplifier operated in burst mode with output of 0.5 J burst energy.

In this paper, a practical model of a thin disk regenerative amplifier has been developed based on an analytical approach, in which Drew A. Copeland [1] had evaluated the loss rate of the upper state laser level due to ASE and derived the analytical expression of the effective life-time of the upper-state laser level by taking the Lorentzian stimulated emission line-shape and total internal reflection into account. By adopting the analytical expression of effective life-time in the rate equations, we have developed a less numerically intensive model for predicting and analyzing the performance of a thin disk regenerative amplifier. Thanks to the model, optimized combination of various parameters can be obtained to avoid saturation, period-doubling bifurcation or first pulse suppression prior to experiments. The effective life-time due to ASE is also analyzed against various parameters. The simulated results fit well with experimental data. By fitting more experimental results with numerical model, we can improve the parameters of the model, such as reflective factor which is used to determine the weight of boundary reflection within the influence of ASE. This practical model will be used to explore the scaling limits imposed by ASE of the thin disk regenerative amplifier being developed in HiLASE Centre.

Construction of high power nanosecond and picosecond lasers is getting important in many fields of industry and science. Hilase centre combined several hi-tech approaches in laser technology like diode pumping, disk and slab laser concept, ceramic gain media, or cryogenic cooling, and constructed nanosecond and picosecond laser platforms with unprecedented average output power and pulse energy exceeding 1000 W and 100 J, respectively.

Relations among absorption of pump beam, quantum defect and thermal load were investigated for pump wavelengths of 968 nm and near 940 nm in two independent, real-time measurement experiments complemented with thermal distribution simulation. Saturation of absorption at 969 nm pumping for non-lasing operational regime, which affects temperature rise and exists independently of the thin disk type, disk head construction, pump power and pump beam diameter is reported. Disk temperature dependence of absorption, quantum defect and disk geometry and large difference between absorption, disk temperature and o-o efficiency at both pump wavelengths are discussed.

In this work, the optimization of the second harmonic generation in an LiB3O5 crystal of the 1 kHz, 2 ps Yb:YAG laser is being investigated. Depending on the crystal thickness, an optimal intensity exists, above which the back-conversion process negatively affects the beam quality and pulse shape, while decreasing conversion efficiency. For a selected 2 mm thick frequency doubling crystal, the conversion efficiency of 80% at an optimal intensity of 120 GW cm−2 has been achieved, with output pulse duration of 1.3 ps and with beam quality of 1.4 and 1.6 in a horizontal and vertical direction, respectively, which is only slightly worse than the beam quality at a fundamental frequency.

We present a simple and fast technique for measuring laser beam parameters, including focus shift using Yaglass, a telecentric lens, and a camera. Our technique is based on imaging of visible fluorescence that represents caustic of the focused near-infrared laser beam. By processing a single camera frame, a large number of second-moment beam diameters are calculated simultaneously without any need for a traditional scan in the propagation direction. The ${{M}^2}$M2 values measured with this method and standard method are in excellent agreement. We extend this technique to measure the focus shift and focus spot size. This method is fast and allows the real-time monitoring of laser beam parameters simultaneously during the manufacturing process.

High average power picosecond Yb:YAG thin-disk lasers are being developed at Hilase. A compact 1 mJ/100 kHz and 4 mJ/100 kHz zero-phonon-line-pumped regenerative amplifiers PERLA C with a CVBG compressor provide

High average power picosecond lasers have become an import tool in many fields of science and industry. We report on progress in development of 100 kHz, 100 W picosecond Yb:YAG thin disk laser amplifier with fundamental spatial mode at the HiLASE laser center. More efficient direct pumping to an upper laser level has been employed in order to suppress thermal loading of the thin disk active medium and to increase system stability. We also carefully analyzed and described all benefits of this so called zero phonon line pumping (ZPL) for fundamental spatial mode cavity design and successfully increased extraction efficiency of the amplifier to > 28 %. A novel approach of high-power picosecond pulse compression using a space saving and easy-to-align chirped-volume Bragg grating (CVBG) with high dispersion and high net efficiency approaching 88 % allowed us to build a robust and highly compact pulse compressor. A 100 kHz train of sub-1-milijoule pulses compressed bellow 2 ps (FWHM) in almost diffraction limited Gaussian beam has been successfully generated from this highly compact (900 x 1200 mm) thin-disk-based Yb:YAG regenerative amplifier.

Even though thin-disk medium mounted on a diamond substrate is generally used for high average power operation, we found that the pulsed pumping of the Yb:YAG thin-disk mounded on a copper-tungsten heatsink could improve both optical-to-optical O-O efficiency and beam quality. We are expecting that the increase of O-O efficiency is caused by the suppression of ASE. However, the mechanism of beam quality improvement is not clear. We developed a precise measurement system of thin-disk deformations based on a Hartmann-Shack wavefront sensor. Investigating thin-disk dynamics under pulsed pumping can help to greatly improve the mode matching and allow obtaining higher output energy.

An overview of Czech national R&D project HiLASE (High average power pulsed LASEr) is presented. The HiLASE project aims at development of pulsed DPSSL for hi-tech industrial applications. HiLASE will be a user oriented facility with several laser systems with output parameters ranging from a few picosecond pulses with energy of 5 mJ to 0.5 J and repetition rate of 1-100 kHz (based on thin disk technology) to systems with 100 J output energy in nanosecond pulses with repetition rate of 10 Hz (based on multi-slab technology).

We are developing an Yb:YAG thin disk regenerative amplifier operating at 1 kHz repetition rate which should deliver output of 100 W of average power which corresponds to the pulse energy of 100 mJ. In order to achieve such high output energy, large size mode matching on a thin-disk is required to avoid optical damage but on the other hand, larger mode area is more susceptible to the influence of optical phase distortions (OPD’s) thus limits achievable pulse energy and beam quality. We developed a compact setup allowing precise measurement of the thin-disk deformations by implementation of a Hartmann-Shack wavefront sensor and a single mode probe laser diode. In comparison to the interferometric measurement methods, our approach brings a number of advantages like simplicity of alignment, compactness and robustness, at the same time keeping the high precision of measurement in a range of few nanometers.

The technology for extreme ultraviolet (EUV) lithography sources is maturing. Laser produced plasma (LPP) sources with usable power >100 W have been used in high-volume manufacturing (HVM) applications, and 250-W sources are expected to be introduced in HVM soon. However, a further increase of power and cleanness may benefit a powerful picosecond (ps) laser in the near-infrared and wavelength converted spectral region. The HiLASE Centre has been working in thin-disc laser technology and has demonstrated a 0.5-kW platform Perla-C based on a very compact Yb:YAG regenerative amplifier. 100-kHz ps operation has been achieved with a fundamental spatial mode and excellent long-term pointing and energy stability. It is reported on a thin-disc-based ps Yb:YAG solid-state laser technology platform Perla developed in the Czech Republic and the present performance of delivering >4 mJ

We are developing 100-kHz picosecond Yb:YAG thin disk regenerative amplifier with 500-W average power for medical and industrial applications. Especially in case of the next generation of semiconductor lithography, high average power solid-state laser with picosecond pulse duration as pre pulse source is a key element to realize 1-kW EUV lithography source. We compared the output characteristics of CW laser operation pumped at 940-nm and 969-nm, and measured the surface temperature of thin disk. We found that the surface temperature of thin disk pumped at 960-nm was much lower than that pumped at 940-nm. We obtained 83-W output from thin disk regenerative amplifier at the repetition rate of 100-kHz pumped at 969-nm. The measured pulse duration was 1.9-ps.

We are developing one joule energy and one picosecond pulse duration laser system at the repetition rate of 120 Hz based on Yb-doped solid-state materials. The amplified output from the thin disk regenerative amplifier is amplified by a cryogenically conduction cooled single slab amplifier. In this work, we also present a new measurement method of a gain distribution insensitive to mode matching. One of the advantages of this method is a fact that it provides real dimensions of the gain distribution. Knowledge about it allows one to find the optimum spatial mode matching to maximize the output energy.

We are developing a 100-mJ Yb:YAG thin-disk regenerative amplifier operating at 1-kHz repetition rate pumped at zero-phonon-line (968.825-nm1) and delivering 1-2 ps pulses for EUV plasma sources applicable in science and industry. Recently we achieved the output energy of nearly 50-mJ from a single laser-head cavity with good beam quality (M2

We introduce the Czech national R&D project HiLASE which focuses on strategic development of advanced high-repetition rate, diode pumped solid state laser (DPSSL) systems that may find use in research, high-tech industry and in the future European large-scale facilities such as HiPER and ELI. Within HiLASE we explore two major concepts: thin-disk and cryogenically cooled multislab amplifiers capable of delivering average output powers above 1kW level in picosecond-to-nanosecond pulsed regime. In particular, we have started a programme of technology development to demonstrate the scalability of multislab concept up to the kJ level at repetition rate of 1-10Hz. Diode pumping of solid state laser materials in general improves the stability and efficiency of solid state lasers in comparison to flash-lamp pumped laser sources. The main reason for this improvement is the fact that the rather small bandwidth emission of highly efficient semiconductor laser diodes can be perfectly matched to the absorption band of solid state laser materials. The laser is therefore pumped only with the "necessary" radiation. The laser materials under consideration for HiLASE show furthermore a small Stokes-shift between the absorption and lasing transitions. The two mentioned facts lead to a much smaller heat deposition in the active laser material in DPSSL in comparison to conventional flash-lamp pumping of active materials. The reduced heat deposition, stability and maturity of laser diodes as well as their over the years reduced prices allow nowadays to consider to work on the development of solid state pulsed laser sources entering and exceeding average power ranges in the order of 1-10kW.

We present recent progress in development of a high power picosecond 100kHz regenerative amplifier based on Yb:YAG thin-disk technology. We employed both conventional 940nm pumping and zero-phonon-line pumping (969nm) to compare the output characteristics. The amplification output under the zero-phonon-line pumping was achieved more than twice of the output under the conventional pumping. We found that the surface temperature of thin disk at 250W pumping in both wavelengths differed 120K.

We have obtained 30-mJ output at 1-kHz from Yb:YAG thin disk regenerative amplifier. By applying pulsed pumping method, we have improved the efficiency from 12% to 19%, and obtained diffraction limited beam at 24-mJ output.

We analyzed the transient response characteristics of Yb:YAG thin disk in to clarify the experimentally obtained advantages of pulsed pumping in 1-kHz repetition rate reported in ref. 2. We applied commercial 2D FEA software which can calculate transient response of thermal effects. The temperature distributions of thin disk in both the CW power of 125-W and the average power of pulsed 125-W have been calculated. Even the net heat power were same in both CW and pulsed pumping, the temperature distribution was lower in pulsed pumping which can provide higher O-O efficiency and smaller beam distortion. The time evolution of OPD in the pulsed pumping has been analyzed, too.

Development of high-power, picosecond laser sources is a desirable venture for both industry and research. Within the Hilase project, we are conducting research on both 500-mJ, 1-kHz and 5-mJ, 100-kHz picosecond laser sources based on the Yb:YAG thin-disk technology. We have developed a prototype thin-disk regenerative amplifier operating up to 10- kHz repetition rate pumped by the 940-nm fiber-coupled laser diodes. We achieved 5-mJ pulse energy at 10-kHz operation and 29.5-mJ at 1-kHz. Afterwards, we developed the high-energy regenerative amplifier operating at fixed repetition rate of 1-kHz and the pulse energy was achieved up to 40-mJ. Simultaneously, we elaborated the highrepetition rate regenerative amplifier operating at 100-kHz with pulse energy of 220-μJ. The amplified pulse was compressed with the efficiency of 88% using chirped volume Bragg grating.

The framework of the Research Program 1 (RP1) in the HiLASE[1] project is to develop both the 500-mJ at 1-kHz repetition rate and the 5-mJ at 100-kHz repetition rate laser systems with 1-2ps pulse duration based on thin disk technology for industrial, scientific, and medical applications. The front-end of our laser system contains a regenerative amplifier as the first stage of amplifier chain. We are developing the Yb:YAG thin disk regenerative amplifier with pulse energy of 120-130mJ before pulse compression at the repetition rate of 1-kHz. As the first step towards the 100-mJ class regenerative amplifier, we have developed a prototype of Yb:YAG thin disk regenerative amplifier operating in the range of 1-kHz to 10-kHz repetition rate.

We are developing one kilohertz picosecond Yb:YAG thin disk regenerative amplifier with 500-W average power for medical and industrial applications. In case of high energy pulse amplification, a large area mode matching in gain media, which is drastically degenerated by the optical phase distortion, is required to avoid optical damage. We designed in-situ thin disk deformation measurement based on the combination of a precise wavefront sensor and a single mode probe beam. In contrast to a conventional interferometric measurement, this measurement is compact, easy-to-align, and is less affected by mechanical vibrations.

We present recent progress in development of a compact regenerative laser amplifier based on the Yb:YAG thin-disk technology delivering up to 100 mJ picosecond pulses with a repetition rate of 1 kHz, designed for seeding a kW-class multipass amplifier for industrial and scientific applications. System utilizes two laser heads pumped at zero-phonon line (968.825 nm 1 ) by stabilized high-power pump diodes operated in pulsed regime. The concept is based on the CPA technique where seed pulses produced by fiber oscillator at 1030 nm are stretched and compressed by use of transmission gratings.

Design of a compact regenerative laser amplifier based on two Yb:YAG thin-disks is presented. Energy up to 100 mJ in picoseconds pulses will be delivered with a repetition rate of 1 kHz. System is designed for seeding a kW-class multipass amplifier for industrial and scientific applications. Laser heads are pumped at zero-phonon line (968.825 nm [1]) by stabilized high-power pump diodes operated in pulsed regime. Seed pulses are produced in a fiber oscillator at 1030 nm and CPA technique utilizing transmission gratings for pulse stretching and compression is applied.

A quantitative comparison of conventional absorption line (940 nm) pumping and zero phonon line (ZPL) (969 nm) pumping of a Yb:YAG thin disk laser is reported. Characteristics of an output beam profile, surface temperature, and deformation of a thin disk under the different pump wavelengths are evaluated. We found that a nonlinear phonon relaxation (NPR) of the excited state in Yb:YAG, which induces nonlinear temperature rise and large aspheric deformation, did not appear in the case of a ZPL pumped Yb:YAG thin disk. This means that the advantage of ZPL pumping is not only the reduction of quantum defect but also the suppression of NPR. The latter effect is more important for high power lasers.

We demonstrate an optimization method of beam quality and optical-to-optical (O-O) efficiency by using pulsed pumping. By changing the pulse duration and the peak intensity of pump pulse at the repetition rate of 1 kHz, the beam quality and O-O efficiency of the Yb:YAG thin-disk regenerative amplifier can be improved. We applied this method to the regenerative amplifier under the pumping wavelength of both 940 and 969 nm, and found that the method was effective in both pumping wavelengths. Although a Yb:YAG thin disk soldered on a copper tungsten heat sink, which has poor thermal properties compared with a thin disk mounted on a diamond substrate, was applied as a gain media, we obtained 45 mJ output with 19.3% O-O efficiency and nearly diffraction-limited beam.

HiLASE facility focuses on development of high average power pulsed lasers with picosecond and nanosecond laser pulses. Recently, lasers with 500 W average power with picosecond pulses and energy of 5 mJ and 1 kW average power with nanosecond pulses and energy of 100 J were reported. Current status and future plans of the HiLASE facility are presented.