We report on an ytterbium-doped fiber laser (FL) pumped by an Yb:YAG thin disk laser [1]. The FL essentially acts as a brilliance converter suitable for applications requiring a diffraction limited kilowatt-class laser source. The FL can be positioned close to the application at the end of a multimode delivery fiber, which solves the length limitation of highpower single-mode delivery caused by non-linear effects in the fibers. The 11 m long fiber used in the experiments has a highly doped (1.3•1026 ions/m³) core with a diameter of 30 μm surrounded by a circular cladding with a diameter of 100 μm. The core has a N.A. of 0.06 and a V-parameter of 5.2. A commercial thin disk laser with a BPP of 4 mm•mrad is used as pump source. At the wavelength of 1030 nm, the pump light absorption is 1.4 dB/m, which is 77 times lower than the peak value at 976 nm. So far, a maximum cw output power of 925 W has been achieved at a pump power of 1203 W [2]. The output power was limited by the incomplete conduction cooling of the fiber and the temperature stability of the acrylate coating. With single pass pumping, an absolute efficiency of 77 % was achieved in good agreement with the simulation result of 81 %. Double-pass pumping will further increase the efficiency. The M² was measured to be 2.6 with the fiber coiled on a 120 mm diameter cylinder. With a fully optimized fiber, having a smaller V-number and an octagonal pump cladding, an efficiency of 85 % and a beam quality of M² < 1.5 are expected. We present the preliminary results achieved with a commercially available fiber as well as the recent results obtained with an improved active fiber as described above.

A passive few-mode multicore fiber consisting of 7 coupled cores is investigated. The fiber is compared to a largemode- area step-index fiber, with the same number of modes and a similar mode field area. Based on the 7-core fiber results a single transverse mode multicore fiber, with a mode field area of 465 μm² at 1050 nm, delivering virtually diffraction limited output beam quality is demonstrated. Stimulated Raman threshold measurements are presented and a fundamental mode high-power beam transport with more than 350 W is shown.

It is well known that thermal stress can significantly influence the properties of optical fibers. These stresses are caused by variations in the coefficient of thermal expansion (CTE) of the differently doped areas in the fiber, like the core and the cladding. On the one hand, the stress has a strong effect on the mechanical stability of fibers. On the other hand, the stress also modifies the most essential property of a fiber, the refractive index distribution, and therefore also the propagation properties. Similar to the effect of generation of birefringence in polarisation maintaining fibers, thermal stress also generates changes in the refractive index of the differently doped regions in the fiber. We report on results of non-destructive polarimetric stress measurements in ytterbium doped fiber preforms, that are codoped with aluminum as well as with phosphorus. Simple models of changes in the CTE for samples doped with multiple elements assume an additive superposition of the changes caused by each dopant. In contrast to such simple models, our investigations have shown that the induced stress cannot be explained by an additive change in the CTE of the glass material. The occurring stresses turn out to be smaller than the simple sum of the effects generated by the respective dopants. This result is also in agreement with measurements of the refractive index profile of these samples. The changes in the index are again not additive for doping with both aluminum and phosphorus.

We report an actively Q-switched Ytterbium-doped all-in-fibre laser delivering 10ns pulses with high repetition rate (from 100kHz to 1MHz). The laser operation has been validated at three different wavelengths (1040, 1050 and 1064nm). The laser can deliver up to 20Watts average power with an high beam quality (M² = 1).

We propose and study experimentally a novel passively mode-locked figure-eight fiber laser scheme based on a polarization-imbalanced Nonlinear Optical Loop Mirror (NOLM). In contrast to conventional power-imbalanced structures, the NOLM used in the proposed laser relies on a difference of nonlinear polarization rotation between the counter-propagating beams to provide switching. In this experiment, the polarization state at the NOLM input is set to linear. By controlling the polarization orientation at the NOLM input through a half-wave retarder plate, it is possible to adjust the NOLM switching power. This property of the NOLM is attractive in the frame of a figure-eight laser. Firstly, the switching power can be readily set to a value ensuring stable mode-locking operation, without having to cut into the loop and modify the NOLM length. On the other hand, we observed that stable pulsed operation is maintained over a certain range of the NOLM input polarization angle, whereas the pulse properties vary over that range. In particular, the spectral width varies from 16 to 52 nm over that range. This spectral variation is associated with a variation of the pulse temporal properties. This result can be explained by the fact that the input polarization angle allows controlling the critical power of the NOLM, which in turn affects the pulses characteristics. The proposed device thus offers a convenient way to adjust the pulses properties (in particular their spectral bandwidth and duration), simply by controlling the angle of a wave retarder, a property which is attractive for some applications.

Ordered and disordered pattern formation of solitons is experimentally investigated in the passively mode-locked doubleclad erbium-doped fiber laser. Soliton complexes of about 500 pulses are obtained which organize in different patterns analogous the states of the matter. We have identified a soliton gas, a supersonic soliton gas flow, a soliton liquid, a soliton polycrystal and a crystal of solitons.

We present both numerical models and experimental results of ultra-short pulses solid-state laser grazing-incidence amplifier modules for generation of intense picosecond pulses, in various regimes from single shot to repetition rates of GHz.

Laser operation near 1.06 μm by diode-pumped Nd:(Lu_xGd_1-x)₃Ga₅O₁₂ (Nd:LGGG, with x = 0.1) and Gd₃Al_xGa_5-xO₁₂ (GAGG, with x = 1) disordered crystals has been investigated. Cw oscillation with a slope efficiency as high as 61% and 230 mW output power was achieved with 400 mW absorbed power from a 1-W laser diode in Nd:LGGG. Under the same pumping conditions cw oscillation with a slope efficiency as high as 55% and 255 mW output power was achieved with 500 mW absorbed power in Nd:GAGG. Stable passive mode-locking with single- or multi-wavelength spectrum was obtained with a semiconductor saturable absorber mirror (SAM) and a single-prism, dispersion-compensated cavity with both the samples. Fourier-limited pulses with duration ≈ 4-9 ps and output power ≈ 40 mW were generated at three well-defined laser transitions in the range 1062-1067 nm with ND:GLGG. Two-color mode-locking regime well described by Fourier-limited synchronized pulses with duration ≈ 3.7 and 5.9 ps and output power ≈ 65 mW, with wavelength separation of 1.3 nm around 1062 nm was obtained with Nd:GAGG.

We report on a high-power, passively mode-locked, TEM₀₀ Nd:YVO₄ oscillator with adjustable pulse duration between 46 and 12ps. The laser is end-pumped by an 888nm laser diode and mode-locking is achieved with a semiconductor saturable absorber mirror (SESAM). The laser has a repetition rate of 91MHz and the M² beam quality factor is better than 1.2 at 15ps. At the optimum output coupler, it provides a maximum average output power of 45W with 32ps pulse duration. In literature, the presence of spatial hole burning (SHB) often helps to shorten the pulse length down to few picoseconds. However, SHB might be an issue for some specific application requiring e.g. low noise picosecond oscillators. In this contribution, we demonstrate that it is possible to shorten the pulse duration by lowering the intracavity losses without SHB. Pulse tunability from 46 to 12ps is achieved by changing the output coupler of the cavity while staying in the continuous-wave mode-locked regime. Pulse duration is almost linear with the output coupler transmission and increases from 12 to 32ps with average output power ranging from 15 to 45W. In this range of output power, we demonstrate the shortest pulses directly from a Nd:YVO₄ oscillator.

Semiconductor nanostructures (multiple quantum wells type) design and manufacturing are developed for ternary and quaternary A₃B₅ compounds. Characterization of SA by subpicosecond resolution pump-probe technique was made for SA samples for Yb³⁺:KY(WO₄)₂ and Nd³⁺:KGd(WO₄)₂ lasers. Recovery kinetics contains the "fast" (hundreds fs) and "slow" (hundreds ps) parts. Method of recovery time shortening based on ultra-violet laser irradiation of SA was investigated; it showed the possibility to reduce the "slow" relaxation time by an order of magnitude. Another approach based on application of nanostructured barriers between quantum wells proved also quite suitable for recovery time shortening. A special method of a reflecting interferometer for complete amplitude and phase characterization of laser mirrors was developed and tested. SA mirrors operating in Yb³⁺:KY(WO₄)₂ and Nd³⁺:KGd(WO₄)₂ lasers gave promising results for peak power and pulse duration.

We report on the realization towards a compact, pulsed XUV source for high temporal and spatial resolution pumpprobe spectroscopy. The system will be based on intracavity high harmonic generation in a Ti:sapphire oscillator. An oscillator with repetition rate of 20 MHz has been realized, which operates in the net negative (near zero) dispersion regime with intracavity pulse energy up to 280 nJ. The cavity has been extended with a secondary focus, where the high harmonic generation can take place. In the recent state, the oscillator is capable to generate XUV harmonics up to 35 eV.

A new method for obtaining high beam quality from high pulse energy optical parametric oscillators (OPOs) is demonstrated. By using different nonlinear crystals that have walk-off in orthogonal directions but are type 2 phase matched for the same interaction, the strong beam asymmetry that is common in critically type 2 phase matched OPOs is removed. Experimentally, this was demonstrated by adding BBO crystals to a type 2 phase matched KTA OPO, where the beam quality improved from M² ≈ 2 x 12 in the KTA OPO to M² ≈ 2 x 2 from the KTA-BBO OPO.

We present a study of a gain-switched end-pumped Yb-doped-fiber laser. The test laser that was mainly used in order to verify the theoretical model consist of an 8.7 m long double clad active fiber with core and inner cladding diameter of 8 μm and 130 μm respectively, and absorption of 1.5 dB/m. An important part of the system is a control unit that switches on the pumping diodes at a desired repetition rate and switches off at the moment when the first spike of the transitional effect appears in order to suppress additional oscillations. A simple rate equation model accurately predicts the main pulse parameters. It describes the population dynamics of the photons and the laser levels, including the occupation by thermal effects. Further numerical simulations show that with adequate active fiber geometry, active ion doping and sufficient pumping power, much shorter pulses in range of 50 ns and peak power of several 100W can be achieved. Such a simple system with the potential addition of a one stage active fiber amplifier can be interesting for some applications in micro-processing like scribing of solar cells, micro processing, and thin film removal.

Multi-kW beams with high brightness offer advantages in material processing applications with large distance beam propagation such as remote welding. To achieve the combination of high power and low beam parameter product, the thin disk laser concept is widely used due to its power scalability. Nevertheless, the efficient generation of several kilowatts of output power per disk at beam parameter products below ~3 mm·mrad is limited by an aspherical wavefront distortion in the disk and air turbulences in front of it. In the present paper the limiting factors are discussed and a novel method for compensation is presented. The compensating mirror consists of a silica substrate with a top-hat-shaped layer of 100 nm height to generate the desired phase-front correction and a conventional HR-coating on top. To prevent air convection in front of the thin disk crystal, the laser resonator was filled with helium. The experimental results yield a maximum output power of 3.4 kW and an optical efficiency of 49 % with a beam parameter product of ~2.6 mm•mrad (M² ~ 8) at a cooling water temperature of 30 °C.

In this work, for the first time to our knowledge, stability and noise of a thin-disk mode-locked Yb:YAG oscillator operating in both negative- (NDR) and positive-dispersion (PDR) regimes have been analyzed systematically within a broad range of oscillator parameters. It is found, that the scaling of output pulse energy from 7 μJ up to 55 μJ in the NDR requires a dispersion scaling from -0.013 ps² up to -0.31 ps² to provide the pulse stability. Simultaneously, the energy scaling from 6 μJ up to 90 μJ in the PDR requires a moderate dispersion scaling from 0.0023 ps² up to 0.011 ps². A chirped picosecond pulse in the PDR has a broader spectrum than that of a chirp-free soliton in the NDR. As a result, a chirped picosecond pulse can be compressed down to a few of hundreds of femtoseconds. A unique property of the PDR has been found to be an extremely reduced timing jitter. The numerical results agree with the analytical theory, when spectral properties of the PDR and the negative feedback induced by spectral filtering are taken into account.

A modelling and an experimental study of thermal lensing in Yb³⁺ doped sesquioxide ceramics are presented here. Wavefront measurements realised in various laser media using a Shack-Hartmann wavefront sensor enable us to study the evolution of thermal lensing versus absorbed pump power at various temperatures. A computation of thermal effects is then investigated in the framework of the finite-elements CASTEM code. At last, we propose to explain our thermal lensing measurements from simulation results.

In this paper we model and design a composite Yb:YAG/YAG hexagonal disk laser. In this edge-pumped thin disk laser configuration, the pump light incidents from disk edges and propagates through the disk along the zigzag path and repeatedly passes the gain medium, thus improve the pump uniformity and absorption efficiency. At the first we calculate the absorbed pump distribution by ray tracing method; secondly with using the fraction of the absorbed pump density as the heat source, the temperature distribution is simulated by 3D-FEM. Finally the output power is calculated by solving the quasi-three-level system rate equations. The absorption efficiency, the pump uniformity and temperature distribution are three effective parameters on the laser system operation. These parameters are investigated and optimized by this model.

Diode-pumped master oscillator fiber amplifiers (MOFA) are known as very flexible laser sources since their spectral, temporal and polarization properties are mainly determined by the seed source which can be controlled quite easily at comparatively low powers. Additionally, they exhibit several of the typical advantages of fiber-based sources such as good beam quality, high efficiency and excellent power scalability. In the last few years, polarized laser beams have shown a remarkably growing demand in material processing. In the present contribution we report on a high-power linearly polarized single-transverse-mode Yb-doped fiber amplifier seeded by a linearly polarized Yb:YAG thin disk laser with an M² of < 1.1 and a degree of linear polarization (DOLP) of 99 % at a output power of 44.5 W and an optical efficiency of 53 %. The fiber amplifier consists of a 7 m long, highly Yb-doped and polarization maintaining double-clad fiber with a core and a cladding diameter of 20 μm and 400 μm, respectively. The active fiber used for the amplifier exhibits a V-parameter of 4.9 and a cladding absorption of 3 dB/m at 976 nm. It was pumped by a fiber-coupled pump diode. With a launched pump power of 717 W, an output power of 440 W with a DOLP of about 96.5 % was extracted from the thin disk master oscillator Yb-doped fiber amplifier. An optical efficiency of 58 % and a gain of 11.7 dB were reached at a seed power of 30 W. A detailed description of our system and the latest experimental results obtained with the fiber described above as well as with other types of active fibers (e.g. non polarization-maintaining fibers) will be presented.

This paper analyzes multi-pump Raman+EDFA hybrid amplifiers with pump recycling using an improved technique that optimizes the gain and ripple of the amplifier for wavelength division multiplexing (WDM) applications. This technique is based on the equalization of Erbium's gain spectrum by adjusting the flexible gain profile of a multi-pump Raman amplification stage. The residual Raman pump recycled by the Erbiumdoped section is used to increase power pump efficiency. Multi-channel simulated gain characterization of the hybrid amplifier recycling Raman pump, in terms of global gain, ripple, and noise figure, is presented. Different configurations of the Raman stage with single, two, three and four-pump lasers are analyzed. For 8 WDM input channels with two and three-pump lasers, ripple values have presented variation from 3 to 9 dB against 4.3 to 12.6 dB obtained with the previous method, depending on the input power and number of pumps. The ripple analysis have has shown that the proper selection of pump wavelengths and powers, enables the construction of broadband hybrid Raman+EDFA amplifiers with enhanced power conversion efficiency and high and flat gains.

A quantitative study on the impact of pump-pump interaction in wide band Raman amplifiers in the S, C and L bands is reported here. For this purpose, the nonlinear coupled Raman equations are written in a novel format separating the different mechanisms which contribute to gain profile, among them, pump-pump interaction. The study is applied to a modern low loss fiber under three pump excitation. The minimum total pump power required to pump-pump interaction mechanisms is investigated for the co and couter propagating amplifier configuration. These threshold power level is significantly different for both configurations. In the co propagating configuration it is independent on the amplifier length while for the counter propagating configuration it is dependent on the amplifier length. to affect gain profile is dependent on fiber length for the counter propagation amplifier configuration while it is independent on fiber length for the co-propagating configuration. Further, a sensitivity analysis of gain flatness as a function of the central pump wavelength power is conduction for both amplifier configurations. The counter propagation configuration is less sensitive to center wavelength power level variation when compared to the co propagating configuration.

Transparent glass-ceramics containing nano-crystals were prepared by controlled heat-treatment of conventionally melt-quenched NaF-YF₃-Al₂O₃-SiO₂ oxyfluoride glass. The precipitated crystallites were composed of only cubic NaYF₄ and the average diameter was estimated as less than 10 nm from the X-ray diffraction analysis. The crystallites were so small that the transparency of the glass was kept after crystallization. NaYF4 has a crystal structure of a fluorite type that cation sites were randomly occupied by Na+ and Y3+. It is expected that the Y³⁺ sites can be substituted to other rare-earth ions which have the similar ionic radii. We have been prepared Tb³⁺ and Yb3+ co-doped glass and glass-ceramics. Green fluorescence was observed when the glass and glass-ceramics were excited by a 974 nm laser. The up-conversion intensity was enhanced by the crystallization.

Measurements of the key thermo-optical properties of Yb³⁺ in sesquioxides ceramics Y₂O₃, Sc₂O₃ and Lu₂O₃ are done at room and cryogenic temperatures. We show that laser performances are improved at low temperatures. We obtain a maximum output energy of 570 mJ, corresponding to a slope efficiency of nearly 40%, in free running regime at 1 Hz with a 10 at. % Yb:Y₂O₃ ceramic at 77 K. Temperature effects on the emitted wavelength are also investigated. Room temperature measurements, using both "laser flash" and "hot disk" methods, lead to thermal conductivity values of ytterbium doped Y₂O₃ ceramics of 6.3 W/m.K and 5.3 W/m.K respectively. We also show that the thermal expansion coefficients of a 10 at. % Yb:Y₂O₃ and a 20 at. % Yb:YAG are divided by a factor two between 293 K and 130 K.

We present results for an efficient Ho:LuLiF₄ laser in-band pumped by a cladding-pumped Tm-doped silica fiber laser. The polarized, tunable Tm-doped silica fiber-laser operates at 1938 nm, ideally suited for in-band pumping the 40 mm long weakly-doped (0.25 at.%) Ho:LuLiF₄ crystal. Using a simple laser resonator a maximum output power of 5.1 W was achieved at a wavelength of 2066 nm for 8.0 W of absorbed pump power, when using an output coupling mirror with 20% transmission, corresponding to a slope efficiency of 70%. At a higher cavity output coupling of 37%, the lasing wavelength shifted to a higher gain peak at 2053 nm, where a maximum output power of 5.4 W was obtained with a slope efficiency of 76%. Beam quality was measured to be M²~1.1 at the maximum output power for each resonator configuration. The spectroscopy, lifetime of the upper laser level, and the laser performance will be discussed in terms of future prospects for power scaling and further improvements in the laser efficiency.

Recently the importance of numerical simulations for the design of laser resonators has grown considerably. This applies in particular if the alignment of components within the resonator is crucial for its stability. In such cases a tolerance analysis is required that can be done most efficiently using numerical simulation tools. In this paper, we introduce a computer model for resonators based on components and their combination using absolute or relative positioning. We show that this approach is the basis for tolerancing and sensitivity analysis. Further we discuss the concepts of field tracing and unified optical modeling that allow the coupling of several propagation methods within one modeling task. For laser resonators this involves in particular free space propagation methods as the Fresnel integral, geometrical optics and split step beam propagation methods. The primary goal is to provide a fully vectorial simulation as accurate as required and as fast as possible. This approach covers in particular general eigenmode models and general geometries including micro-structured surfaces that can be used for additional beam control as it is shown in the examples.

A miniaturized solid state laser for marking applications has been developed featuring novel assembly strategies to reduce size, cost and assembly effort. Design and setup have been laid out with future automation of the assembly in mind. Using a high precision robot the optical components composing the laser system are directly placed on a planar substrate providing accurate positioning and alignment within a few microns. No adjustable mounts for mirrors and lenses are necessary, greatly simplifying the setup. Consisting of either a ND:YAG or a Nd:YVO₄ crystal pumped with a fiber coupled diode laser, a q-switch for pulse generation and a beam expander the entire assembly is confined in a 100ml space and delivers 4 W of continuous output power at 1.064 μm with an efficiency greater than 40%. Pulse lengths of 10-20 ns and repetition rates of up to 150 kHz have been obtained with an acousto-optic modulator. In addition, a custom designed electro-optic modulator with integrated high voltage switch has been realized. A supply unit for the entire system, including scanner and water cooling, is integrated in a 19" industrial chassis and can be operated via a graphical user interface on a standard personal computer.

We present a rod-Nd:YAG-Laser, side-pumped with eight 50W-laser diode bars at 808nm, and Q-switched with a Single Crystal Photo-Elastic Modulator at 95.1 kHz. The latter is made of a z-cut LiNbO₃-crystal, which is electrically y-excited on the mechanical resonance frequency of the x-longitudinal oscillation. With a voltage amplitude of 3 V the crystal shows a strong oscillation such that due to the photo-elastic effect a high polarization modulation is achieved, which, together with a polarizer, can be used as a simple optical switch. With this inside the laser resonator the average power is 47.8W in cw-mode and 45.5W in pulsed mode, with pulse peak powers of 4 kW and pulse widths of 100ns. This kind of operation is similar to cw-operation but offers due to the high peak powers different interaction physics with matter. The source is therefore suited for micro-welding of metals, LIDAR, rapid prototyping of plastics, marking/engraving/cutting of plastics, marking of glasses. In cases where high precision and a small heat affected zone are necessary this simple kind of pulsed operation may be advantageous, when compared to cw-operation.

The article analyses possibilities of applying a multicore active optical fiber with a hexagonal array of cores for the construction of a fiber laser. Simulations of the far-field diffraction patterns of the seven-core optical fiber have been conducted. Taking a double - clad active optical fiber operating in the fiber laser system as an example, the idea of phase-locking of the radiation generated in particular cores, and thereby the possibility of generating a supermode have been presented. Moreover, the article analyses the impact of the value of coupling between the cores on the difference in radiation phases between particular emitters during the development of the laser action in the fiber laser constructed on the basis of the optical fiber being considered. As a result of the conducted analysis a double-clad optical fiber with 7 cores doped with neodymium ions has been designed and produced and its luminescence properties have been measured.

The goal of this work was to design and investigate a gain switched, at room temperature lasing Fe:ZnSe laser. The active medium was a bulk, by Bridgman-technique grown Fe:ZnSe sample with the thickness 3.4 mm. The pumping was provided by electro-optically Q-switched Er:YAG laser with the oscillation wavelength 2.937 μm matching the local maximum of the Fe:ZnSe absorption. The Er:YAG Q-switched operation was obtained by the Brewster angle cut LiNbO₃ Pockels cell placed between the rear mirror and the laser active medium. No additional intracavity polarizers were used. The maximum pumping pulse energy and length was 15 mJ, and ~300 ns, respectively. This pulse-length is close to room-temperature measured lifetime of Fe²⁺ ions in Fe:ZnSe crystal. The pump radiation was directed into the Fe:ZnSe crystal which was placed inside the cavity formed by dichroic pumping mirror (T_HR=92% at 2.94 μm and R_HR~100% for 3.5-5.2 μm) and optimal output coupler with the reflectance R_OC=90% at 4.5 μm, radius of curvature r = -200 mm. The maximum obtained output Fe:ZnSe laser energy was 1.2 mJ, the generated output pulse duration on the wavelength 4.5 μm was 65 ns (FWHM). The output pulse profile was approximately Gaussian. The crystal showed rather high uniformity of oscillation properties throughout its volume. For the case of tuning the CaF₂ prism was implemented into the resonator. The tuning curve of generated Fe:ZnSe laser radiation covered the spectral range 3.9 - 4.7 μm.

Q-switched microchip laser emitting radiation at wavelength 1338nm was designed and constructed to obtain nanosecond laser pulses with multikilowatt peak power. This laser was based on a composite crystal which combines in one piece an active laser part (2mm long YAG crystal doped with Nd³⁺ ions 1.2 at.% Nd/Y) and a saturable absorber (0.6mm long V³⁺:YAG). The initial transmission of the V:YAG part was ~ 85%@1.34 μm. The diameter of the diffusion bounded monolith was 5 mm. The microchip resonator consists of dielectric mirrors directly deposited on the monolith surfaces. The pump mirror (HT for pump radiation @ 0.8 μm, HR for generated radiation @ 1.3 μm) was placed on the Nd:YAG part. The output coupler with reflection 90% @1.34 μm was placed on the V³⁺-doped part. To prevent a parasitic lasing at 1064 nm, the reflectivity of both this mirrors was minimized at this wavelength. The overall length of constructed microchip laser was 2.6 mm. Laser was tested under pulsed diode pumping (wavelength 808 nm, pulse length 300 μs, energy 5.1 mJ, repetition rate 25 Hz - 2 kHz). The generated pulse length was stable and it was equaled to 1.07 ± 0.02 ns. The wavelength of linearly polarized laser emission was 1338 nm. Up to the highest mean pumping power 10W, the output beam had well-defined Gaussian transversal profile with the half divergence angle not higher than 4 mrad. For the lowest pumping rep. rate, the generated pulse energy and peak power was 34 μJ and 33kW, respectively. For maximum pumping rep. rate the pulse peak power was 14kW.

A preliminary investigation of the passively Q-switched resonantly pumped Er:YAG laser system operating at wavelength 1645 nm has been performed. The output characteristics of the designed and constructed laser, i.e., the output energy, temporal profile, and spatial beam structure were registered. The Er:YAG laser crystals longitudinally pulse-pumped by Erbium glass laser radiation (repetition rate 0.5 Hz, wavelength 1535 nm) were investigated. The passive Q-switch was a Co:MALO (Co2+:MgAl2O4) crystal. To optimize the system, three Er:YAG crystals with various in Erbium/Yttrium concentration and length were studied in the free-running regime. The curved pumping mirror of linear hemispherical oscillator had a high transmittance at the pumping wavelength and maximal reflectance at the generating wavelength around 1645 nm. The output flat dielectric coupler reflectance was 90 % at 1645 nm. Out of the three Er:YAG active laser crystals, the best output characteristics in free running regime were reached for the medium with Er³⁺ concentration 0.2 at.% Er/Y and length 25 mm. For the Q-switching, three saturable absorbers Co:MALO with various length, that is various transmission, were investigated. These crystals had no anti-reflection layer and were placed between the active crystal and output mirror. The laser resonator length was 162 mm. For an incident pump energy of 131 mJ, the 1.6 mJ Q-switched single pulse energy with 58 ns pulse duration (FWHM) was obtained. The corresponding peak power was 28 kW. The spatial beam structure was close to the fundamental profile.

The study describes the efficient, acousto-optic Q-switching of the Er:YAG laser at the 1645 nm 'eye-safe' wavelength. For longitudinal pumping at the wavelength of 1532 nm, a linearly-polarized 10 W erbium fiber laser radiation was used. The investigated Er:YAG crystal was 40 mm long and its erbium concentration was 0.25 %. The active crystal was mounted in a copper heat-sink maintaining a 15°C temperature of coolant water. For giant pulse generation, the fused-silica acousto-optic modulator was inserted inside the Er:YAG laser oscillator near the output mirror of the resonator. Laser output characteristics were performed depending on the parameters of output coupler reflectance (R= 95%, 90%, 85%) and the repetition rate (from 0.1 to 10 kHz). In free running experiments almost 2.8 W of output power with 55% slope efficiency with respect to incident pump power was obtained. In Q-switching regime the high peak power generation was demonstrated. For maximum incident pump power of 7.8 W, pulse energy up to 4 mJ was generated with a pulse duration less than 40 ns at a 500-Hz repetition rate, which corresponds to nearly 110 kW of peak power. This laser source can find application as a transmitter in 'eye-safe' rangefinders, ladars etc.

In this paper we report on optimization of quasi-continuously pumped 2.4at.% Nd crystalline Nd:YAG laser in a bounce geometry passively mode-locked by semiconductor saturable absorbers consisted of 33 or 100 quantum wells in transmission mode. Depending on the laser resonator configuration, either long output trains consisted of more than 100 pulses with total energy of 170 μJ and variable pulse duration from 120 ps in the beginning to 35 ps at the end of the train, or short trains consisted of 5 pulses and the total energy of 325 μJ with 71 ps pulse duration were generated.

We review blue generation of Pr:YAlO₃ laser under flash-lamp and GaN-diode pumping at room temperature. Stimulated emission at 373.5 nm reached by intracavity frequency doubling of the near-infrared-emitting Pr:YAP laser operating at a fundamental wavelength of 747 nm in the continuous and pulsed regime is reported. With BBO crystal employed as a nonlinear medium, 12.3 mW of continuous output power at 373.5 nm has been obtained, as well as stable pulses with an output peak power of about 10 kW in the blue spectral region.

Maximum amplification and single amplified ultra-short laser pulse selected from a three stages four passes amplifiers chain will be presented. The configuration of the amplifiers chain need to be set up and aligned to avoid the inter-stages reflection. The amplified spontaneous emission pulse shape as well as the synchronization between the pumping pulse and the seed pulses train can be optimized to have maximum amplification and a single amplified pulse only. The amplification results and the detail analysis will be presented.

Two saturable absorbers, V:YAG (V³⁺:Y₃Al₅O₁₂) and V:LuAG (V³⁺:Lu₃Al₅O₁₂), were compared as a passive Q-switches for microchip laser based on Nd:YAG gain medium. The emission wavelength of this laser was in 1.3 μm spectral range. Two Q-switched monolithic microchip laser devices were prepared: Nd:YAG/V:LuAG and Nd:YAG/V:YAG. Active Nd:YAG part of both microchip lasers was the same (4mm long, 1.1 at.% Nd/Y). The thickens of saturable absorbers ensured the same initial transmission (T₀ = 85%) of the passive Q-switch part (V:LuAG was 1.1mm long, V:YAG was 0.7mm long). The gain medium and the saturable absorber were diffusion bonded to form one monolithic crystal. The diameter of both crystals was 5 mm. Laser mirrors were deposited directly onto monolith faces. The output coupler with reflection 90% for the generated wavelength was placed on the V³⁺-doped part. The pump mirror (HT@808 nm, HR@1.3 μm) was placed on opposite monolith face. Lasers were tested under longitudinal continuous diode pumping and results were compared. Both lasers generated linearly polarized radiation at wavelength 1338nm with the lasing threshold 8W. Comparing the giant pulse parameters and the laser efficiency, the better results were obtained for Nd:YAG/V:YAG microchip laser. The pulse duration (FWHM) in this case was shorter (2.16±0.04 ns) and more stable than in Nd:YAG/V:LuAG case (3.3 ± 0.5 ns). The obtained average pulse energy was slightly higher for Nd:YAG/V:LuAG microchip laser (45 μJ) than for Nd:YAG/V:YAG (41 μJ) laser. However, due to shorter pulse length higher peak power (18.5 kW) was obtained with V:YAG saturable absorber than with V:LuAG (13.7 kW).

Wavelength-tunable sources are important for applications such as fiber optics sensing, medical instrumentation, and optical communication. A tunable source design can use a Fabry-Perot (FP) cavity configuration with a tunable filter inserted into the system. In this work we experimentally demonstrated a wavelength-tunable fiber laser by the use of a PM-Er:Yb double-clad fiber placed in a FP cavity formed by two Dichroic Mirrors (DM). Our pump laser wavelength was 976 nm and the maximal output power from this laser that we can introduce to the fiber was 20 W. To get wavelength tunability we included a Diffractive Grating (DG) with 600 l/mm in our laser cavity. The zero order reflection from the DG is the output coupler and the first order diffracted beam is reflected back into the fiber using a DM. We included a half-wave plate and a polarizer in the cavity to increase the stability of the continuous wave laser operation and also to impose a linear polarization at the laser output. With this configuration we can tune the wavelength from 1535 to 1567 nm by rotating a DM at a rate of 0.02 degrees/nm. With our configuration wide tunability was possible only when we used fiber lengths between 2.5 and 3.6 m. The maximal output power was 850 mW using 3.6 m of fiber length. We believe that a Q-switched extension of this source can be used in nonlinear optics applications, such as Terahertz generation.

The properties of helical-core optical fibre made by authors from Nd³⁺/Yb³⁺-doped oxyfluoride silicate glass are presented. The construction and forming conditions of the helical-core optical fibre enabled to obtain the helix pitch from several mm and the off-set ranging from 10 μm to 200 μm. The paper also presents optimisation of Nd³⁺/Yb³⁺ ratio to enhance the emission bandwidth at 1 μm. In consequence of matching the values of the emission cross-section σ_em(Nd)and the absorption cross-section σ_abs(Yb) in the glass doped with 0.15Nd³⁺:0.45Yb³⁺ a broad (Δλ = 100nm) luminescence band in the vicinity of 1μm was obtained, which was the result of overlapping emission transitions: ²F_5/2→²F_7/2 in ytterbium and ⁴F_3/2→⁴I_11/2 in neodymium.

We propose a novel and simple technique to generate self-imaged optical bottle beam by interfering two zeroth-order Bessel beams produced from two axicons with different wedge angle. The bottle size and the bottle numbers can easily be adjusted by changing axicon's wedge angle. This technique shows much efficient in beam energy conversion compared to annular slit and much high optical damaged threshold compared to spatial light modulation. Experimental results match closely with the theoretical analysis and numerical simulation.

Extreme Light Infrastructure (ELI), the first research facility hosting an exawatt class laser will be built with a joint international effort and form an integrated infrastructure comprised at last three branches: Attosecond Science (in Szeged, Hungary) designed to make temporal investigation at the attosecond scale of electron dynamics in atoms, molecules, plasmas and solids. High Field Science will be mainly focused on producing ultra intense and ultra short sources of electons, protons and ions, coherent and high energetic X rays (in Prague, Czech Republic) as well as laserbased nuclear physics (in Magurele, Romania). The location of the fourth pillar devoted to Extreme Field Science, which will explore laser-matter interaction up to the non linear QED limit including the investigation of vacuum structure and pair creation, will be decided after 2012. The research activities will be based on an incremental development of the light sources starting from the current high intensity lasers (APOLLON, GEMINI, Vulcan and PFS) as prototypes to achieve unprecedented peak power performance, from tens of petawatt up to a fraction of exawatt (10¹⁸ W). This last step will depend on the laser technology development in the above three sites as well as in current high intensity laser facilities.

We report on generation of high-energy pulses in a highly-normal dispersion fiber laser featuring large-mode-area microstructure fibers. Passive mode-locking is achieved using high modulation depth semiconductor saturable absorber mirror (SESAM). The total cavity dispersion is varied through insertion of a low-nonlinearity passive microstructure fiber inside the cavity. We study the effect of the cavity dispersion on the mode-locking performances. A systematic experimental and numerical description of the laser operation is addressed and the impact of the spectral filtering on the laser performances is discussed.

The depolarization dynamics in a neodymium glass rod laser amplifier is studied in experiments. A method for determining the temperature distribution and the thermally induced phase distortions by the known transverse depolarization degree distribution is proposed. The experimental results obtained by this method perfectly coincide with the theoretical data even at strong radial inhomogeneity of heat release.

The radiation amplification and oscillation are obtained in an electron-beam-pumped Berdysh laser with an active volume of 10 L in the visible range from 430 to 470 nm at the broadband 4²Γ -1,2 ²Γ transition in the triatomic Kr₂F molecule of interest for amplification of ultrashort laser pulses. It is shown that, along with absorption of laser radiation in the active medium, the amplification dynamics is considerably determined by short-lived absorption induced in the amplifier windows by bremsstrahlung X-rays. For the specific pump power 0.6 ÷ 0.7MW cm^-3, the gain, corrected for nonstationary absorption, was ~10^-3 cm^-1. A scheme of aKr₂F amplifier is proposed for amplification of ultrashort pulses up to multiterawatt peak powers in the active volume ~10 L.

Taking advantage of the non-adiabatic blue-shift of high-order harmonics generated by a fixed frequency Nd:Glass laser system, we are able to report more than 50 % coverage of the XUV spectral range between 18 nm and 35 nm. The generated harmonic lines are capable of seeding Ni-like Y, Zr and Mo soft x-ray lasers and others.

The demonstration of a 7.36 nm Ni-like Sm soft x-ray laser pumped by 36 J of a Nd:glass chirped pulse amplification laser is presented. Double-pulse single-beam non-normal incidence pumping was applied for the efficient soft x-ray laser generation. Here the applied technique included a new single optic focusing geometry for large beam diameters, a single-pass grating compressor traveling-wave tuning capability and an optimized high energy laser double-pulse. This scheme has the potential for even shorter wavelength soft x-ray laser pumping.

Efficient coupling of laser energy is one of the primary concerns for devising laser based photon and charged particle sources with potential applications in a wide field of research interests. We report a two orders of magnitude efficient moderately hard x-ray (50 - 300 keV) source based on multi-walled carbon nanotubes (MWNT) irradiated by moderately intense (10¹⁵ - 10¹⁷ Wcm^-2) ultra-short laser pulses. This is also accompanied by a three orders of magnitude reduction in ion debris in comparison with conventional metallic targets making these sources operationally safe. The bremsstrahlung measurement reveals a two orders of magnitude increment in x-ray flux from MWNT. Contrary to expectation that the rise in "hot" electron temperature leads to an increment of emitted ion energies form the plasma, a monotonic reduction of ion energies with increasing laser intensity for MWNT is noticed. Angle resolved ion flux measurement reveals an extremely divergent ion emission from MWNT with an evident three orders of magnitude reduction in ion flux. Based on the scaling laws for resonance absorption, our experimental data remarkably matches with theoretical predictions based on electrostatic calculations. This confirms the localized enhancement of the laser electric field near the tip of the MWNTs yield localized hot spots in the expanding plasma sheath layer leading to a non-planar expansion. This is characterized by a decrease in ion accelerating potential as well as a divergent ion emission, as observed in experiments.

Theoretical investigation of second harmonic generation (SHG) of super intense femtosecond radiation demonstrated that temporal Intensity Contrast Ratio (ICR) of output radiation of petawatt level laser complexes can be significantly increased. The cubic polarization effects in the process give possibility of additional pulse compression. We present experimental results of SHG of radiation with average intensity 2TW/cm² in 0.6mm KDP crystal. Theoretical model of linear regime of plane wave instability in mediums with quadratic and cubic nonlinearity is developed and thoroughly discussed. Analysis of small-scale self-focusing suppression methodic is presented. The influence of surface dust to spatial noises generation in SHG process is pointed out.

Historically, an optically pumped alkali (potassium) vapor laser was the first laser proposed by A.L. Schawlow and C.H. Townes in 1958, but was not experimentally demonstrated at that time. In the next 45 years, many experiments with alkali vapors were performed that demonstrated stimulated emission, gain and amplified spontaneous emission. However, the real interest in alkali vapor lasers appeared in the last several years, when really efficient lasing in Rb and Cs vapors was demonstrated. The US Air Force Academy performed a variety of experiments on alkali lasers, including the demonstration of efficient Rb, Cs and K vapor lasers, power scaling experiments with multiple diode laser pumping sources and experiments on diode pumped alkali vapor amplifiers. As a result of this effort we have increased the alkali lasers output power to tens of watts in continuous wave operation. In this paper we present a review of the most important achievements in high power alkali lasers research and development, discuss some problems existing in this field.

In this paper we discuss laser wake field acceleration experiments made at the PEtawatt pARametric Laser (PEARL). Using free 2mm and 5 mm gas jet without preplasma we generated electron beam with energy up to 260 MeV. The charge of quasimonoenergetic beams achieved 300 pC, angular divergence 0.2 degree. The special attention is paid for diagnostics which is adapted for low repetition rate systems with low output parameters stability.

Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH₄⁺ molecule exposed with a 100 femtosecond 8 Jcm^-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH₄⁺ molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and this reduces the controlling costs.

A high-conversion-efficiency optical parametric chirped-pulse amplifier (OPCPA) with high-energy-stability is demonstrated using lithium triborate (LBO) crystals. Total conversion efficiency of 25% is realised with a net gain of greater than 10⁸. An output energy of ~180mJ at a 2-Hz repetition rate, with a stability of better than 1.5% rms is achieved. The output beam takes the spatial profile of the 20^th-power super-Gaussian pump beam, whose intensity deviates by less than 7.5% rms over the central 90%. The far-field, whose diameter is near diffraction limited, has a pointing stability of less than one-twelfth of an airy-radius. To the authors' knowledge this is the first demonstration of an all LBO OPCPA to simultaneously achieve this level of performance.

A system of differential equations describing, neglecting diffraction, the propagation of laser radiation in a medium with birefringence and cubic nonlinearity is derived. It is shown that the efficiency of depolarization compensation by means of a 90° polarization rotator or a Faraday mirror decreases with increasing B-integral (nonlinear phase incursion). Comparison of the considered method effectiveness in the case of incident linear and circular polarization showed that for the circular polarization the optimal angle of polarization rotator is different from 90° and the degree of polarization is less than for the linear one.

Laser induced breakdown of air is used to create a SW by focusing a 7 ns, 532 nm, 10 Hz Nd:YAG laser. Plasma created at the breakdown launches a compression wave into the nearest ambient air molecular layers that propagate at supersonic velocities. The propagation characteristics of SWs are studied double probe-beam deflectometry method, by two noninteracting probe beams that are parallel to each other and perpendicular to the propagation direction of the SW creating laser beam. The evolution of the laser induced SWs in air created at the focus along the direction of propagation (forward probe, FP) and in the direction opposite to the laser propagation (backward probe, BP) of the breakdown creating laser beam, are studied. The nature of the SW is estimated from the arrival time (τ) measured at different distances (Z) from the focal volume. At an input laser energy of 45 mJ, the arrival time information in the backward probe showed τ ∞ Z^2.5 behavior indicating spherical SWs and in the forward direction followed τ ∞ Z^1.6 showing planar expansion of the SWs revealing direction dependent asymmetric expansion of SWs across the focal plane. The pressure of the SWs estimated using counter pressure corrected point strong explosion theory along with the experimentally measured shock velocities are used to generate the P - U Hugoniot of shock compressed air.