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Generation of harmonic frequencies effectively broadens the spectral region of a laser system and thus extends its application potential. In our case the fundamental beam of 1030 nm wavelength is produced by PERLA C system at the HiLASE laser centre in Dolni Brezany, Czechia. The system is Yb:YAG thin-disk based operating at a repetition frequency of 50-100 kHz and delivers pulses of 1-2 ps duration [1] , [2] . The second harmonic (2H, 515 nm) and third harmonic (3H, 343 nm) are generated in an LBO(2H) crystal and an LBO(3H) crystal, respectively. Both crystals were cascaded with a dual waveplate inbetween them, so that the phase matching in the LBO(3H) could be of Type I providing a higher effective nonlinear coefficient than of Type II (0.69 pm/V compared to -0.45 pm/V). The fourth harmonic (4H, 257.5 nm) is generated as a second harmonic of 515 nm in a CLBO(4H) crystal. The fifth harmonic (5H, 206 nm) is produced in SFG process of 4H+1H in a CLBO(5H) crystal, where the 1H beam is the residual beam after the second harmonic [3] . A good conversion in all the nonlinear processes is conditioned by high quality crystals, excellent fundamental beam and proper pulse temporal overlap in sum frequency processes. The output powers achieved in all the harmonics confirm high standard of our harmonics generation system as well as the top quality of our fundamental beam. At present we have at a disposal a 200 W fundamental beam with 1 ps pulses, 90 W in the second harmonic, and 38 W in the third one. Our best result in the FHG was 20 W at 257.5 nm, however, up to now our users prefer lower DUV outputs, see the figure below. It presents the output power time progression of the harmonics generated from a fundamental beam of about 60 W. The second harmonic was used e.g. for green optical transmission tests of optical fibres based on phosphate glasses [4] . A unique application of the fourth harmonic was a crystallization of amorphous TiO2 nanotube layers via laser annealing [5] . The fifth harmonic is used at present e.g. for irradiation of different chemical compounds with the aim of their photolysis and subsequent analysis of the constituents. All harmonics are offered for user experiments related to laser matter interaction.

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.

Deep ultraviolet radiation of solid-state near-infrared (∼ 1 pm) lasers is often generated as the second harmonic of the frequency doubled beam, i.e. the wavelength of ∼260 nm, and as the sum harmonic frequency, the wavelength of ∼200 nm. For these processes usually BBO and CLBO crystals are used. The big advantage in the fourth harmonic generation of the BBO crystal is its high nonlinear coefficient (1.69 pm/V), however, its walk-off angle (84.5 mrad) is quite big and limits the exploitable length of the crystal. The nonlinear coefficient of the CLBO crystal is half of that for BBO (0.83 pm/V), but the walk-off is small (28.8 mrad). Unpleasant with the CLBO is its hygroscopicity, which has to be compensated by keeping the crystal at higher temperature, 150 °C recommended [1]. Nevertheless, the elevated temperature is beneficial for lowering the nonlinear absorption which proceeds as two photon absorption [2]. Regarding the nonlinear absorption, both crystals do not differ much. Our study concerns the CLBO crystals as converters into the deep ultraviolet (DUV) range.

We report on the generation of picosecond pulses at 515 nm and deep ultraviolet pulses at 257 nm and 206 nm. They are generated as second, fourth and fifth harmonic frequencies of the high power diode-pumped Yb:YAG thin-disk laser at the fundamental wavelength of 1030 nm. The laser at the fundamental wavelength is based on a chirped-pulse amplification of oscillator pulses in two-stage regenerative amplifier based on thin-disks as active media. The diode pumping at the zero phonon line is used. The pulses are produced at ~100 kHz repetition frequency, 2-10 ps pulse duration and ≤2 mJ pulse energy. The fundamental beam is doubled in an LBO crystal at an efficiency of 42%. Subsequently the fourth harmonic frequency (257 nm) is produced by frequency doubling of the second harmonic frequency in a CLBO crystal. The unconverted part of the fundamental beam after SHG is used with the fourth harmonic beam as 1ω+4ω frequency sum in a further CLBO crystal for the fifth harmonic frequency (206 nm) generation. Two issues are important in the efficient optical conversion: nonlinear absorption given mainly by two-photon absorption (TPA) and proper timing of interacting pulses. In our simulations we take into account TPA and study the consequences of different timing of 1ω- and 4ω-pulses on the CLBO when generating the 5th harmonic. It was found that 1.4 ps delay of the 1ω-pulse after the 4ω-pulse is necessary to get the highest 5ω-output. Also the 5ω-pulse duration is affected by the timing.

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.

A design for generation of two ultra-high power laser beams, 130 TW and 1.4 PW, using a chain of optical parametric chirped pulse amplifiers, first pumped by a 10 Hz frequency doubled Nd:YAG laser, and later by the frequency tripled single-shot kilojoule level iodine laser Prague Asterix Laser System is presented. Expected enhancement of the parameters in the upgrade, besides the output power, are up to 1022 W/cm2 from 1016 W/cm2 in target intensity, and about 20 fs from 0.5 ns in pulse duration. Owing to the limited dimensions of the Prague Asterix Laser System building, the lay-out of the new equipment had to use only the left-over space in the laser hall.

We report on the generation of picosecond deep ultraviolet pulses at 257.5 nm and 206 nm produced as the fourth and fifth harmonic frequencies of the diode-pumped Yb:YAG thin-disk laser at the fundamental wavelength of 1030 nm. We present a proposal for a picosecond pulse mid-IR source tunable between 2 and 3 μm. The laser at the fundamental wavelength is based on a chirped-pulse amplification of pulses of a sub-ps laser oscillator in a regenerative amplifier with a thin-disk active medium. The diode pumping at the zero phonon line is used. The output beam is close to the fundamental spatial mode and the pulses are characterized by a 100 kHz repetition frequency, less than 4 ps pulse duration and ≤1 mJ pulse energy. The fundamental beam is split and the main part is first frequency doubled in an LBO crystal. Subsequently the fourth harmonic frequency (257.5 nm) is produced by frequency doubling of the second harmonic frequency in BBO/CLBO crystals. The remaining part of the fundamental beam is summed with the fourth harmonic beam in the 1ω+4ω quantum reaction in a further CLBO crystal for the fifth harmonic frequency (206 nm) production. The design for the generation of the mid-IR wavelengths is based on the optical parametric generation and amplification. The first stage contains a temperature tuned PPLN, the following amplification stages are based on KTA crystals tuned by angle. Picosecond output pulses tunable between 2 and 3 μm at an average power of 10 W are proposed.

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

A two-stage optical parametric amplifier driven by a frequency-tripled beam from the high-energy iodine laser system SOFIA was built. This single-shot Optical Parametric Chirped Pulse-Amplification facility (OPCPA) and the system synchronizing the pump and signal pulses are described in detail. The chirped seed pulse of a Ti:sapphire oscillator running at the central wavelength of 800 nm is amplified in the two-stage (LBO and KDP) optical parametric amplifier over 108 times. The amplified spectral bandwidth of 68 nm corresponds to the pulse duration of 14 fs when a transform-limited pulse is assumed. This implies a compressed pulse of TW power. Systematic gain measurements reveal a good match with the theoretical predictions. Signal and idler beam fluence profiles are presented. The suitability of the iodine photo-dissociation laser as a pump source for the OPCPA technique is thus proved for the first time experimentally. A distinctive feature of the iodine laser is its very narrow gain bandwidth (

The hybrid iodine photodissociation laser SOFIA has been constructed. The pulse feeding the amplifier chain is the idler wave of an optical parametric oscillator (OPO) tuned to the atomic iodine transition at 1315 nm. This solid-state oscillator enables ps-synchronization to other laser systems. A homemade automatic stabilization of the OPO idler wave as to wavelength and pointing ensures long-term stable operation of the whole system. The active medium of the SOFIA amplifiers is a mixture of C3F7I and He. The SOFIA pulses are frequency-tripled in two KD*P crystals and then serve as the driver in a two-stage optical parametric amplification scheme in which chirped broadband Ti:sapphire laser pulses are amplified (OPCPA).

Mid-IR wavelength range offers variety of interesting applications. Down-conversion in the optical parametric devices is promising to generate high average power mid-IR beam due to inherently low thermal load of the nonlinear crystals if a powerful and high quality pump beam is available. We developed 100 kHz pump laser of 100-W level average power. The stretched pulses of Yb-fiber laser oscillator at 1030 nm wavelength are injected into the regenerative amplifier with an Yb:YAG thin-disk. Diode pumping at zero phonon line at wavelength of 969 nm significantly reduces its thermal load and increases conversion efficiency and stability. We obtained the beam with power of 80 W and 2 ps compressed pulsewidth. We are developing a watt level mid-IR picosecond light source pumped by a beam of the thin disk regenerative amplifier. Part of the beam pumps PPLN, which is seeded by a continuous wave laser diode at 1.94 μm to decrease the generation threshold and determine the amplified spectrum. The 3 W pumping gave output of 30 mW, which is by up to two orders higher compared to unseeded operation. The gain of about 107 was achieved in the PPLN in the temporal window of the pump pulse. The spectrum and beam of the generated idler pulses in the mid-IR was measured. We obtained an amplified signal from the second stage with the KTP crystal. We expect watt level mid-IR output for initial 50-W pumping. The generation of longer wavelengths is discussed.

We report on the generation of 100 kHz 0.1mJ-level deep ultraviolet pulses based on frequency-quadrupled (257.5 nm) beam of a diode pumped Yb:YAG thin disk laser at the HiLASE Centre. The 100-kHz beamline used for the generation of the harmonic frequencies is operated at an average output power of 100 W level and 2 picosecond duration of pulses. The amplification of the oscillator beam is performed in a regenerative amplifier where the thin disk serves as an active mirror. The CPA technique is used for achieving high average output power of the whole system. The outcoming laser beam at 1030 nm wavelength is frequency-doubled in an LBO crystal and then frequency-quadrupled in BBO crystal, conversion efficiencies being 40% and 19%, resp. The basic characteristics of the harmonics generation in both crystals are given.

This paper reports on properties of a plasma formed by sequential action of two laser beams on a flat target, simulating the conditions of shock-ignited inertial confinement fusion target exposure. The experiments were performed using planar targets consisting of a massive copper (Cu) plate coated with a thin plastic (CH) layer, which was irradiated by the 1ω PALS laser beam (λ = 1.315 μm) at the energy of 250 J. The intensity of the fixed-energy laser beam was scaled by varying the focal spot radius. To imitate shock ignition conditions, the lower-intensity auxiliary 1ω beam created CH-pre-plasma which was irradiated by the main beam with a delay of 1.2 ns, thus generating a shock wave in the massive part of the target. To study the parameters of the plasma treated by the two-beam irradiation of the targets, a set of various diagnostics was applied, namely: (i) Two-channel polaro-interferometric system irradiated by the femtosecond laser (~40 fs), (ii) spectroscopic measurements in the X-ray range, (iii) two-dimensional (2D)-resolved imaging of the Kαline emission from Cu, (iv) measurements of the ion emission by means of ion collectors, and (v) measurements of the volume of craters produced in a massive target providing information on the efficiency of the laser energy transfer to the shock wave. The 2D numerical simulations have been used to support the interpretation of experimental data. The general conclusion is that the fraction of the main laser beam energy deposited into the massive copper at two-beam irradiation decreases in comparison with the case of pre-plasma. The reason is that the pre-formed and expanding plasma deteriorates the efficiency of the energy transfer from the main laser pulse to a solid part of the targets by means of the fast electrons and the wave of an electron thermal conductivity.

We report on the generation of the second (515 nm) and fourth (257.5 nm) harmonics from a 100 kHz diode-pumped solid-state laser operating at a wavelength of 1030 nm which uses one Yb:YAG thin disk in the regenerative amplifier and delivers 60 W of the average output power in pulses of 4 ps duration. Thirty-five W in green light and 6 W in deep ultraviolet (DUV) were achieved. The sensitivity of the second harmonic generation efficiency toward the lithium triborate crystal temperature is demonstrated in experiment. The overall conversion efficiency from NIR to DUV of 10% was achieved. The β-barium borate and cesium lithium borate crystals were used as green to DUV convertors and compared regarding the efficiency and spectral bandwidths. The achieved output power is unique for DUV picosecond pulses.

Amplification of femtosecond pulses using an ultra-narrowband gaseous pulse laser was demonstrated for the first time. A single-shot sub-nanosecond iodine photodissociation laser with a bandwidth of 20 pm was used as a driver in an allstage OPCPA. An externally triggerable OPO tuned to laser line of 1315.24 nm was used in the front end of the iodine laser. Frequency tripled beam at 438 nm was used to pump parametric amplifiers, LBO and KDP crystals. The signal pulses from a Ti:sapphire laser at the central wavelength of 800 nm with a bandwidth of 70 nm (FWHM) were stretched from 12.5 fs to 250 ps and amplified by a factor of 2×10 8 . The amplified pulses of typical bandwidth of 50 nm were compressed down to 27 fs. The output power of 0.5 TW was achieved. An optimized amplifier chain and addition of a third nonlinear crystal would enable to generate femtosecond pulses of several terawatts. The broadband pulses at 800 nm central wavelength were amplified in the KDP crystal for the first time, due to the suitable wavelength of the pump pulses. Availability of large aperture KDP crystals promises the generation of petawatt beam at kJ iodine laser facilities.

A high-quality phase conjugation of the stimulated Brillouin scattering has been achieved even in a highly transient regime, as proved by the mask restoration in the backscattered signal. A special two-lens system of laser beam insertion into a scattering medium was used. A reliable onset of the phase conjugation has been reached using a splitted part of the oscillator Q-switched pulse as a prepulse in the Brillouin cell. Results with and without the prepulse are compared. A possibility of the creation of the phase conjugated mirrors even in high-power gaseous lasers with short pulses is thus proved.

The laser laboratory SOFIA (Solid-State Oscillator Followed by Iodine Amplifiers) started its operation in 2003 as a test facility the laser system PALS (Prague Asterix Laser System). The basic SOFIA project now is the realization of the OPCPA (Optical Parametric Chirped Pulse Amplification) method where the iodine photodissociation laser system serves as a pump. This unique method of the amplification of ultrashort pulses presents a big challenge for the iodine lasers which have a narrow gain bandwidth (/spl sim/0.02 nm) and therefore the classical methods of the pulse shortening are not applicable. The main advantage of the gas laser system as a pump for the parametric amplification of ultrashort pulses is a high spatial homogeneity of the pumping beam and a suitable temporal profile. The SOFIA laser system has been built up as a hybrid laser where the oscillator beam is produced in a solid- state optical parametric oscillator (MOPO-HF pumped by the third harmonics of Nd:YAG laser) tuned to 1315 nm (the iodine spectral line) and subsequently amplified in two gaseous iodine amplifiers.

In this paper we build a new smaller iodine laser SOFIA and we also aim to develop the optical parametric chirped pulse amplification (OPCPA) method in laboratory of solid-state oscillator followed by iodine amplifiers and prepare its fast implementation at PALS(Prague Asterix Laser System).

For what we believe to be the first time, mask restoration in a backscattered signal in a highly non-steady-state regime of stimulated Brillouin scattering was attained. A special two-lens system of laser beam insertion into a scattering medium was used. Results are compared with those of ordinary one-lens focusing.

In this paper we present and discuss the results of our experiments concerning the study of stimulated Brillouin scattering (SBS) at the laser Perun which have been performed since the last workshop (Bechyne 1992).

In ultrashort pulse amplification a narrowband gas pump pulse laser has been used for the first time. An all-stage optical parametric chirped pulse amplifier (OPCPA) was driven by a single-shot iodine photodissociation laser. For the first time a broadband amplification was achieved in potassium dihydrogen phosphate crystal at 800 nm seeding. Ti:sapphire laser pulses stretched from 12.5 fs to 250 ps were amplified and compressed to 27 fs at a 0.5 TW output power. The results suggest using narrowband high power gas lasers as OPCPA drivers to generate petawatt beams.

The results achieved in a highly non-steady-state regime of stimulated Brillouin scattering with an iodine laser beam are presented. The input energy dependencies of beam divergence and reflected energy were obtained in one-lens and two-lens systems of beam insertion. In both cases the correction of the optical distortion of a launched beam wave front is attainable only for input energies lower than twice that of the threshold.

Prague Asterix Laser System (PALS) installed in the user type laboratory is described. This kJ class, subnanosecond, 3 TW near infrared system is a par t of EU cooperation network of laser user facilities Lasernet and about 1/5 of its capacity is offered under the scheme of so called transnational access to European users. Various physical programmes run on this system are briefly outlined. The proposed u pgrades have mostly in view an enhancement of utility of the system with respect to the access scheme. The most ambitious among them are extensions (i) into the very short wavelength domain by implementing an x -ray laser (ii) into the femtosecond region by using a parallel Optical Parametric Chirped Pulse Amplification (OPCPA) chain.

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.

Compression of ps pulses by frequency up-conversion in nonlinear optical crystal cut for type II phase matching is a well established method, if one desires intense, sub-ps up-converted pulses. For efficient compression of 1 μm light, time predelay must be introduced between the ordinary and extraordinary input pulses and group velocity of generated second harmonic pulses νSH g must be in between the group velocities of fundamental pulses νFH g,o and νFH g,e [1]. This requirement is satisfied for example in (D)KDP crystal and Nd:glass laser pulses, where νSH g equals to the average of νFH g,o and νFH g,e For high repetition rate, high power Yb:YAG lasers, e.g. [2], crystals from KDP family are not suitable and borate crystals with better thermal properties have to be used.

Picosecond, high average power laser is critical in the HVM EUV source technology. 100kHz, mJ, laser is realized by thin disc laser architecture for LPP, and > MHz laser is discussed for 10kW level EUV FEL.

In the last fifteen years stimulated Raman backscattering (SRBS) in plasma has been intensively elaborated as a promising tool on the way towards high intense lasers. There are several advantages of this technique in comparison to the world-wide used the CPA-Chirped Pulse Amplification technique for a laser amplification. We present the principle of the SRBS technique, the best results so far obtained in theory and experiment, and a possible SRBS project at the PALS Research Centre in Prague.

The development of kW-class diode-pumped picosecond laser sources emitting at various wavelengths started at the HiLASE Center four years ago. A 500-W Perla C thin-disk laser with a diffraction limited beam and repetition rate of 50–100 kHz, a frequency conversion to mid-infrared (mid-IR), and second to fifth harmonic frequencies was demonstrated. We present an updated review on the progress in the development of compact picosecond and femtosecond high average power radiation sources covering the ultraviolet (UV) to mid-IR spectral range at the HiLASE Center. We also report on thin-disk manufacturing by atomic diffusion bonding, which is a crucial technology for future high-power laser development.