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

We compare for the first time the influence of different Yb:YAG gain media on the performance of a large-area, high average–power laser system with an output energy of up to 6 J. Monocrystalline slabs grown by a new technique without central growth defect are compared with ceramics. Small signal gain, maximum output energy and thermal lensing are compared for ceramic slabs with co-sintered amplified spontaneous emission (ASE) absorber cladding, monocrystalline slab with and without optically bonded ASE absorber cladding, and surface structured monocrystalline slabs. We show that these large monocrystals with optically bonded absorber cladding have similar performance to cladded ceramics, so far the only material for high-energy Yb:YAG lasers.

We present an experimental method for optimizing the performance of an adaptive optics system, where actuator's position, shape, and number of a deformable mirror can be arbitrarily selected. A home-made photo-controlled deformable mirror (PCDM) is used to test the performances of four different actuator layouts and to simulate an arbitrary wavefront corrector. In addition to numerical simulations, the experimental setup evaluates the performances of the entire adaptive optics system, including the wavefront sensor and the control algorithm. In order to demonstrate the potential of this adaptive optics system, we have benchmarked it with a laser thermal lens simulator.

The Photo-controlled deformable mirror (PCDM) presents an interesting alternative to the conventional deformable mirror technologies as it addresses their two major bottlenecks. It offers enormous spatial resolution while keeping its complexity low due to its elegant control of the deformable surface by light projection. The PCDM prototype was a membrane type deformable mirror driven by a modified commercial mini-projector. Unique properties of PCDM allowed experimental study of actuator array disposition influence on the wavefront shaping performance of the deformable mirror. While keeping all other aspects and parameters of the experiment constant, the four actuator-array configurations were compared and resulting wavefront shaping performance assessed. Moreover, the Photo-controlled deformable mirror was numerically modelled and the experimental results were reproduced with high degree of fidelity. By using the numerical model of PCDM, a novel method to control high spatial resolution wavefront corrector was studied with promising results.

We report on the successful demonstration of the world’s first kW average power, 100 Joule-class, high-energy, nanosecond pulsed diode-pumped solid-state laser (DPSSL), DiPOLE100. Results from the first long-term test for amplification will be presented; the system was operated for 1 hour with 10 ns duration pulses at 10 Hz pulse repetition rate and an average output energy of 105 J and RMS energy stability of approximately 1%. The laser system is based on scalable cryogenic gas-cooled multi-slab ceramic Yb:YAG amplifier technology. The DiPOLE100 system comprises three major sub-systems, a spatially and temporally shaped front end, a 10 J cryo-amplifier and a 100 J cryo-amplifier. The 10 J cryo-amplifier contain four Yb:YAG ceramic gain media slabs, which are diode pumped from both sides, while a multi-pass architecture configured for seven passes enables 10 J of energy to be extracted at 10 Hz. This seeds the 100 J cryo-amplifier, which contains six Yb:YAG ceramic gain media slabs with the multi-pass configured for four passes. Our future development plans for this architecture will be introduced including closed-loop pulse shaping, increased energy, higher repetition rates and picosecond operation. This laser architecture unlocks the potential for practical applications including new sources for industrial materials processing and high intensity laser matter studies as envisioned for ELI [1], HiLASE [2], and the European XFEL [3]. Alternatively, it can be used as a pump source for higher repetition rate PW-class amplifiers, which can themselves generate high-brightness secondary radiation and ion sources leading to new remote imaging and medical applications.

The HiLASE “Bivoj” laser system developed at CLF Rutherford Appleton Laboratory in collaboration with HiLASE team as DiPOLE100 was relocated to Dolni Brezany near Prague, Czechia at the end of 2015 and fully re-commissioned at the end of 2016. In 2016, the system demonstrated average output power of 1kW generating pulses of 105 J at 10 Hz repetition rate for the first time in the world. Since then the system has been subjected to several testing campaigns in order to determine some of its key characteristics. Beam quality, wavefront quality, pointing stability, energy stability and experience with long term operation of 1 kW laser are presented. In addition, depolarization effects have been detected inside the main amplifier. Details on these results along with numerical simulations are presented.

We report on the successful demonstration of a 100J-level diode-pumped solid state laser (DPSSL) based on cryogenic gas cooled multi-slab ceramic Yb:YAG operating at 10 ns pulse duration and 10 Hz repetition rate. This result provides the first demonstration of a multi-Joule DPSSL delivering 1 kW average power and confirms the power scalability of multi-slab cryogenic gas-cooled amplifiers.

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.

We investigated wavefront aberrations in a cryogenically cooled Yb:YAG slab with a wavefront sensor using a probe beam technique under non-lasing condition. To analyze the pump-induced phase aberrations created in the crystal, the measured wavefronts were fitted with orthonormal Zernike polynomials. The Yb:YAG crystal of 2 mm thickness, 10 mm diameter, and 3 at.% doping concentration was mounted in a copper holder in a closed-loop pulse tube cryostat with cooling capacity of 12 W at 100 K. The gain medium was single-end pumped by a fiber-coupled laser diode at pumping intensity of ~6.5 kW/cm 2 with a maximum repetition rate of 100 Hz, pulse duration of 1 ms, and pump spot diameter of 2.5 mm. The time resolved measurement revealed that defocus, which was the main wavefront aberration, represents not only a thermal lensing effect but also an electronic lensing effect. The thermally induced defocus is more dominant at high repetition rate than the electronically induced defocus. We also measured wavefront aberrations of amplified beams in a cryogenically cooled Yb:YAG slab. A room temperature operated thin-disk regenerative amplifier was used as a seed laser. The seed beam was amplified in the cryogenically cooled crystal at 160 K in a double pass configuration. The wavefront measurement was conducted at semi-saturated conditions, at three different repetition rates: 10 Hz, 20 Hz and 40 Hz, and at five different pump intensities in the range between 6.5 kW/cm 2 and 14.8 kW/cm 2 . Under lasing condition, only defocus aberration were induced. Due to opposite signs of the defocus aberration of the seed beam and pumped induced in the Yb:YAG crystal, wavefront of the amplified beam had smaller PtV (Peak to Valley) and RMS values than the seed beam.

We report on the successful demonstration of a 100 J-level, diode pumped solid state laser based on cryogenic gas cooled, multi-slab ceramic Yb:YAG amplifier technology. When operated at 175 K, the system delivered a pulse energy of 107 J at a 1 Hz repetition rate and 10 ns pulse duration, pumped by 506 J of diode energy at 940 nm, corresponding to an optical-to-optical efficiency of 21%. To the best of our knowledge, this represents the highest energy obtained from a nanosecond pulsed diode pumped solid state laser. This demonstration confirms the energy scalability of the diode pumped optical laser for experiments laser architecture.

The time-resolved measurements of thermally induced wavefront aberrations in a cryogenically cooled Yb:YAG crystal are presented in dependence on temperature in the range between 250 and 130 K under non-lasing condition. A wavefront sensor was utilized to determine the wavefront aberrations. The wavefront distortions were experimentally studied for a cryogenically cooled Yb:YAG crystal in detail for the first time. The wavefront aberrations were significantly reduced at cryogenic temperatures including defocus which was the dominant aberration and which was responsible for the so-called thermal lensing effect. We found that defocus aberration is caused not only by thermally induced effects (responsible for thermal lens), but also by electronically induced change in the refractive index due to excitation of ion activators which is responsible for the electronic lensing. Nevertheless, at pumping intensity of 6.3 kW/cm2 and repetition rate of 100 Hz thermal effects were the dominant one. In addition, an improvement in the Strehl ratio along with an increase in absorbed pump energy was observed while the temperature of the gain medium was decreased. The measurements clearly show the advantages of cryogenic cooling of laser-active media for beam quality improvement.

In this paper we describe the progress of energy scaling cryogenic gas-cooled Yb:YAG amplifier technology from a 10 J, 10 Hz prototype to delivering 100 J pulses at 1 Hz. The architecture of the prototype system (DiPOLE) is presented, highlighting the key design characteristics that enable energy scaling, along with the improvements that have allowed development of a 100J-level system (DiPOLE100).

We present the workflow of the design, realization and testing of deformable mirrors suitable for high power diode pumped solid-state lasers. It starts with the study of the aberration to be corrected, and then it continues with the design of the actuators position and characteristic. In this paper, we present and compare three deformable mirrors realized for multi-J level laser facilities. We show that with the same design concept it is possible to realize deformable mirrors for other types of lasers. As an example, we report the realization of a deformable mirror for femtosecond lasers and for a CW $\text{CO}_{2}$ laser.

We report the demonstration of a cryogenic gas cooled multi-slab Yb:YAG laser, producing 10.8 J pulses at 10 Hz, and initial results from a scaled-up DPSSL designed to produce 100 J pulses.

In this paper we provide an overview of the design of DiPOLE100, a cryogenic gas-cooled DPSSL system based on Yb:YAG multi-slab amplifier technology, designed to efficiently produce 100 J pulses, between 2 and 10 ns in duration, at up to 10 Hz repetition rate. The current system is being built at the CLF for the HiLASE project and details of the front end, intermediate 10J cryo-amplifier and main 100J cryo-amplifier are presented. To date, temporal and spatial pulse shaping from the front end has been demonstrated, with 10 ns pulses of arbitrary shape (flat-top, linear ramps, and exponentials) produced with energies up to 150 mJ at 10 Hz. The pump diodes and cryogenic gas cooling system for the 10J cryo-amplifier have been fully commissioned and laser amplification testing has begun. The 100J, 940 nm pump sources have met full specification delivering pulses with 250 kW peak power and duration up to 1.2 ms at 10 Hz, corresponding to 3 kW average power each. An intensity modulation across the 78 mm square flat-top profile of < 5 % rms was measured. The 100J gain media slabs have been supplied and their optical characteristics tested. Commissioning of the 100J amplifier will commence shortly.

The effect of components of the atmosphere on photostabilized polymers and development of degradation phenomena is outlined. The processes are characteristic of heterogeneity in distribution of products of polymer degradation and stabilizer transformation or consumption. Concentration gradients of the products indicate preferential surface and near-surface changes having U-shaped characteristics and affected by the polymer material or sample thickness due to limited penetration of oxygen. Increased intensity of radiation in artificial sources induces material changes different from those resulting from natural weathering, complicating correlation between the two processes and lifetime prediction. Surface and near-surface analyses of tested samples provide a realistic insight into heterogeneity characteristic of photodegradation.

In this work, we present measurements of efficiency-optimized 940 nm diode laser bars with long resonators that are constructed with robustly passivated output facets at the Ferdinand-Braun-Institut (FBH). The measurements were performed at room temperature on a test bench developed at HiLASE Centre, as a function of operating condition. The single-diode bars generated < 1.0 kW when tested with 1 ms pulses at 1-10Hz operating frequency, corresponding to < 1 J per pulse. The maximum electrical-to-optical efficiency was < 60 %, with operating efficiency at 1 kW of < 50%, limited by the ~ 200 μΩ resistance of the bar packaging. In addition, slow axis divergence at 1 kW was below 6° FWHM and spectral width at 1 kW was below 7 nm FWHM, as needed for pumping Yb-doped solid state amplifier crystals.

A high average power cryogenically-cooled diode-pumped solid-state laser system for Hilase centre in Czech Republic is being developed by Central Laser Facility at Rutherford Appleton Laboratory, England in collaboration with Hilase team. The system will deliver pulses with energy of 100 J at 10 Hz repetition rate and will find applications in research and industry. The laser medium and other elements of the system are subject to heavy thermal loading which causes serious optical aberrations and degrade the output beam quality. To meet the stringent laser requirements of this kWclass laser, it is necessary to implement adaptive optics system, which will correct for these aberrations. During our research the sources of aberrations have been identified and analyzed. Based on this analysis, a suitable adaptive optics system was proposed. After finalizing numerical models, simulations and optimizations, the adaptive optics system was developed, characterized and installed in a cryogenically-cooled multi-slab laser system running up to 6 J and 10 Hz. The adaptive optics system consists of 6x6 actuator bimorph deformable mirror and wavefront sensor based on quadriwave lateral shearing interferometry operated in closed loop. The functionality of the system was demonstrated at full power.

Deformable mirrors have gained increasing interest in many different fields of application including laser physics, and they are becoming a universal tool for correcting optical aberrations of laser beams especially in large scale laser systems. One of the most common types of deformable mirror is a bimorph design which uses two plates of piezomaterial to which single electrodes are connected. These electrodes form the actuator array and their layout defines the resulting performance of the mirror to some extent. In the end all types of deformable mirrors currently used use an actuator array of some sort. To estimate the significance and effect of different actuator layout and shapes of actuators, an experimental study was performed. Four different commonly used actuator arrays were compared using photo-controlled deformable mirror. Using such device allows to study the effect of actuator layout separately from all other effects, since the device remains the same including all its imperfections. The experimental results are compared with numerical simulations and discussion is presented.

We report numerical and experimental results obtained with an optical setup that simulates the heating and cooling processes expected in a multi-slab high-average-power laser head. We have tested the performance of an adaptive optics system consisting of a photo-controlled deformable mirror (PCDM) and a Shack-Hartmann wavefront sensor for the effective correction of the generated wavefront aberrations. The performance of the adaptive optics system is characterized for different layouts of the actuator array and for different configurations of the heating mechanisms. The numerical results are benchmarked using a PCDM, which allowed us to experimentally compare the performances of different deformable mirrors. (C) 2014 Optical Society of America

We present the results of performance modeling of a diode-pumped solid-state HiLASE laser designed for use in inertial fusion energy power plants. The main amplifier concept is based on a He-gas-cooled multi-slab architecture similar to that employed in Mercury laser system. Our modeling quantifies the reduction of thermally induced phase aberrations and average depolarization in ${\mathrm{Yb}}^{{3+}}$ :YAG slabs by a combination of helium cryogenic cooling and properly designed (doping/width) cladding materials.

We describe the application of electron spin resonance imaging (ESRI) for measuring macroscopic diffusion coefficients of paramagnetic guests in polymeric systems. The ESRI method is based on encoding spatial information in the ESR spectra via magnetic field gradients, and on simulating the time evolution of the spectra in order to extract the diffusion coefficient, D. This paper presents one dimensional (1D) ESRI experiments planned to study (a) the dependence of the diffusion coefficients of probes on the presence of permanent crosslinks in gels, and (b) the effect of the probe site on the transport rates in self-assembled polymers. These effects were investigated, respectively, in two types of gels: chemically crosslinked (permanent) hydrogels, and reversible gels formed by self-assembly of polymeric surfactants.

A copolymer of styrene containing less than 5 mol % of chain units spin-labeled by attachment of the nitroxide via a short tether has been synthesized. ESR spectra of dilute toluene solution of the copolymer have been obtained using 9 and 250 GHz ESR. Parameters characterizing polystyrene segmental rotational diffusion in toluene solution over a broad temperature range have been determined from nonlinear least-squares fits of theoretical ESR spectra to the experimental ESR spectra. The model used was that of relatively fast internal rotation of the nitroxide about its tether, with slower polymer chain segmental motion. Together they lead to effective rotational diffusion with an anisotropic diffusion tensor. In addition, constraints in the form of an orientational potential restrict the range of angles over which this diffusion occurs relative to the polymer backbone, and the latter is assumed to reorient on an ultraslow time scale. This is referred to as a model of microscopic order but macroscopic disor...

Background At present time the number of implantations of joint replacements as well as their revisions increases. Higher demands are required on the quality and longevity of implants. The aim of this work was to determine the degree of oxidative degradation and the amount of free/residual radicals in selected ultra-high molecular weight polyethylene (UHMWPE) components of the joint replacements and demonstrate that the measured values are closely connected with quality and lifetime of the polymer components. Methods We tested both new (4 samples) and explanted (4 samples) UHMWPE polymers for total joint replacements. The samples were characterized by infrared spectroscopy (IR), electron spin resonance (ESR) and microhardness (MH) test. The IR measurements yielded the values of oxidation index and trans-vinylene index. The ESR measurements gave the free radicals concentration. Results In the group of new polyethylene components, we found oxidation index values ranging from 0.00-0.03 to 0.24. The trans-vinylene index values ranged from 0.044 to 0.080. The value of free radical concentration was zero in virgin and also in sample of Beznoska Company and non-zero in the other samples. In the group of explanted components, the measured values were associated with their history, micromechanical properties and performance in vivo. Conclusions We demonstrated that measuring of oxidative damage may help the orthopaedic surgeon in estimating the quality of UHMWPE replacement component and thus radically to avoid early joint replacement failure due to worse polyethylene quality.

In this work, we present a comparative study of high power diode stacks produced by world’s leading manufacturers such as DILAS, Jenoptik, and Quantel. The diode-laser stacks are characterized by central wavelength around 939 nm, duty cycle of 1 %, and maximum repetition rate of 10 Hz. The characterization includes peak power, electrical-to-optical efficiency, central wavelength and full width at half maximum (FWHM) as a function of diode current and cooling temperature. A cross-check of measurements performed at HiLASE-IoP and Ferdinand-Braun-Institut (FBH) shows very good agreement between the results. Our study reveals also the presence of discontinuities in the spectra of two diode stacks. We consider the results presented here a valuable tool to optimize pump sources for ultra-high average power lasers, including laser fusion facilities.

We present results for a 150 mJ, 10 Hz, ns front end system for a 100 J DPSSL. The system incorporates arbitrary temporal pulse shaping, in addition to passive and active spatial shaping of the output.

We present an adaptive optics system for active wavefront correction of the first stage amplifier of a multi-slab laser system capable of generating 100 W of average output power and transverse dimensions of 20 mm x 20 mm. The results of this experiment are compared with numerical simulations. © 2014 SPIE.

The reverse micellar phase L2 of the triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) EO13PO30EO13 (commercial name Pluronic L64), where EO is ethylene oxide and PO is propylene oxide, was studied in the ternary mixture L64/water/o-xylene and in the binary mixture L64/water, using ESR spectroscopy with nitroxide spin probes. The spin probes differed in size, structure, and polarity and belong to two main types: (a) cationic probes 4-(N,N-dimethyl-N-alkyl)ammonio)-2,2‘,6,6‘-tetramethylpiperidine-1-oxyl iodide (CATn) with n, the number of carbon atoms in the alkyl substituent, equal to 1, 4, 8, 11, and 16; (b) amphiphilic probes based on x-doxylstearic acid (xDSA) with x, the carbon atom to which the doxyl group is attached, equal to 5, 7, 10, and 16. X-band ESR spectra reflect the intercalation of the probes in the self-assembled L64 system, but different probes choose different locations in the aggregates and report on the local polarity, hydration, and degree of ord...

We present the design parameters of a diode-pumped 100J-class multi-slab Yb:YAG laser at 10 Hz scalable to the kJ regime. Results of detailed energetics and thermo-optical modeling confirm the viability of cryogenic helium-gas cooling approach to drastically reduce thermally-induced distortions in the laser slabs. In addition, a comparison of spectral measurements from laser-diode stacks and Yb:YAG crystals validates the feasibility of highly efficient diode-pumped solid-state lasers at cryogenic temperatures.

We present calculation of aberration compensation in high average power multi-slab laser by a deformable mirror. The calculations were compared with a simple experiment. For the calculations we have developed a code that works with a square-shaped piston driven push/pull deformable mirror with continuous facesheet and allows optimization of mirror parameters and actuator array geometry. We have corrected the calculated output wavefront of Hilase 10 J multi-slab laser system in MIRÓ by using several actuator array geometries. The numerical results were benchmarked on an experimental model of multi-slab chamber using a membrane deformable mirror. © 2013 SPIE.

The diffusion coefficients of small paramagnetic tracers (nitroxide spin probes) and spin-labeled poly(ethylene oxide) in hydrogels were measured at 300 K, using two-dimensional spatial-spectral ESR imaging (ESRI). The gels were prepared by copolymerization of 2-hydroxyethyl methacrylate (HEMA) and 2-(2-hydroxyethoxy)ethyl methacrylate (DEGMA), in the presence of a fixed molar concentration of glycol dimethacrylate as the cross-linker and 4,4'-azobis(4-cyanopentanoic acid) as the initiator. Variation of the amount of water in equilibrium with the gel was achieved by polymerizing different molar ratios of the monomers. Experimental concentration profiles of the diffusant were measured as a function of time, and each profile was obtained by image reconstruction, from a complete set of projections. The diffusion coefficients were determined by simulating all experimental profiles, using the Fick model of diffusion for an initially confined tracer diffusing into a finite system. The diffusion coefficients depend on the amount of water in the gels. The variation of the diffusion coefficients D with the weight fraction of the copolymer in the gel is consistent with the free volume model. The variation ofD with the molecular mass M of the diffusant scales as M -0.8 in gels containing ≥67 wt % water and as M -1.4 for the gel containing 55 wt % water. The advantages and present limitations of 2D spatial-spectral ESRI for measuring transport properties in polymers are discussed.

Blends of styrene-acrylic acid random copolymers (P(S-AA)) with poly(ethylene oxide) (PEO) have been studied. The copolymers contained up to 25 mol% AA monomers and the blends contained up to 60 wt% PEO. The presence of crystalline PEO in the blends is detected by DSC and verified by WAXS. EPR and DSC data indicate that pure polystyrene and PEO are immiscible in the temperature range 300-420K. The presence of two amorphous phases is detected for some blends based on a copolymer containing 5 mol% AA. The miscibility of the two components in the blends increases with increasing AA content of the copolymer.

Spin-labeled poly(acrylic acid) (SL-PAA) was synthesized and EPR spectra of its dilute aqueous solutions were measured at different degrees of neutralization a in the temperature range 273-353 K. The temperature dependence of parameters characterizing the segmental rotational mobility of SL-PAA and the internal rotation of the spin label relative to the polymer can were determined by simulating the line shapes of the experimental EPR spectra. The segmental rotational dynamics of SL-PAA was found to be nearly independent of its degree of neutralization. The absence of the methyl group is probably responsible for higher segmental rotational mobility of SL-PAA at all degrees of neutralization and in the entire temperature range studied, when comparing with spin-labeled poly(methacrylic acid) (SL-PMA) under the same conditions

The goal of the HiLASE project is to design and optimize parameters for 100 J/ 10 Hz Yb:YAG laser amplifiers that are scalable to the kJ regime. The HiLASE power amplifier design is based on a cryogenic, gas-cooled multi-slab concept. Simulation results of the 10 J pre-amplifier agree very well with experimental measurements. In order to fulfil the very demanding requirements, which include wall-plug efficiency > 12% and repetition rates up to 10 Hz, HiLASE and RAL teams are closely working together and developing the approach described here.

We incorrectly calculated the Strehl ratio in Table 1 in our paper published in [Appl. Opt. 53, 3255-3261 (2014)]. Here, we provide the correct values of the Strehl ratio. It should be mentioned that this does not change or affect any other results, techniques, or conclusions presented in the published paper. (C) 2014 Optical Society of America

Detailed modeling results of 100 J class laser systems with respect to the output energy, beam propagation, nonlinear phase accumu- lation, wavefront aberrations, and adaptive optics performance obtained in MIRO and MATLAB codes are presented here. The laser system is based on a cryogenically cooled Yb 3þ ∶YAG multislab amplifier with two identical amplifier heads and operates at 10 Hz repetition rate with an average power above 1 kW. © 2013 Society of Photo-Optical Instrumentation Engineers