Jan Pilar

100 J-level nanosecond pulsed diode pumped solid state laser

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.

Design of high-energy-class cryogenically cooled Yb3+∶YAG multislab laser system with low wavefront distortion

Abstract. Detailed modeling results of 100 J class laser systems with respect to the output energy, beam propagation, nonlinear phase accumulation, wavefront aberrations, and adaptive optics performance obtained in MIRÓ and MATLAB codes are presented here. The laser system is based on a cryogenically cooled Yb3+∶YAG multislab amplifier with two identical amplifier heads and operates at 10 Hz repetition rate with an average power above 1 kW.

Design and optimization of an adaptive optics system for a high-average-power multi-slab laser (HiLASE)

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.

DiPOLE100: A 100 J, 10 Hz DPSSL using cryogenic gas cooled Yb:YAG multi slab amplifier technology

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.

HiLASE cryogenically-cooled diode-pumped laser prototype for inertial fusion energy

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.

Quantification of structural changes of UHMWPE components in total joint replacements

BackgroundAt 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.MethodsWe 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.ResultsIn 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.ConclusionsWe 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.

Scalable cryogenic gas cooled multi-slab 10 J and 100 J, 10 Hz DPSSL system

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.

Simulation of performance of wavefront correction using deformable mirror in high-average-power laser systems

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.

Permanent and reversible gels: Transport of guests and guest-host interactions

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.

Characterization of diode-laser stacks for high-energy-class solid state lasers

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.