High Average Power Laser Systems Research Articles

Development of fiber rod based high repetition rate and average output power laser system using pre-chirp managed nonlinear amplification

Development of fiber rod based high repetition rate and average output power laser system using pre-chirp managed nonlinear amplification

Research on High Power Laser Damage Resistant Optically Addressable Spatial Light Modulator

Liquid crystal spatial light modulators (LC-SLMs) are devices that can accurately adjust the parameters of beam amplitude, phase, wavefront and polarization. However, due to the limitation of laser damage resistance of component materials, LC-SLMs still have difficulty meeting the application and development needs of a high-average power laser system. Here, we proposed an optically addressable spatial light modulator (OASLM) based on a sapphire substrate. Due to the good thermal conductivity of sapphire, the laser damage resistance of the device was greatly improved. The thermal distribution of OASLM based on the sapphire substrate and the K9 substrate is analyzed by a laser-induced temperature rise model. The experimental results also show the excellent performance of sapphire OASLM under high-power CW laser irradiation, its laser power density is increased from 10 W/cm2 to 75 W/cm2, and the working time is more than 30 min. By bonding sapphire to the other side, the laser power density can be increased to 100 W/cm2, and these are completed without active heat dissipation. This method provides a feasible path for high-average-power SLMs.

Liquid-cooled modular gas cell system for high-order harmonic generation using high average power laser systems.

We present the design and implementation of a new, modular gas target suitable for high-order harmonic generation using high average power lasers. To ensure thermal stability in this high heat load environment, we implement an appropriate liquid cooling system. The system can be used in multiple-cell configurations, allowing us to control the cell length and aperture size. The cell design was optimized with heat and flow simulations for thermal characteristics, vacuum compatibility, and generation medium properties. Finally, the cell system was experimentally validated by conducting high-order harmonic generation measurements using the 100kHz high average power HR-1 laser system at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS) facility. Such a robust, versatile, and stackable gas cell arrangement can easily be adapted to different experimental geometries in both table-top laboratory systems and user-oriented facilities, such as ELI ALPS.

YAG:Yb crystal with non-linear doping ions distribution as promising active element for high average power laser systems

The influence of optical centers concentration profiles on thermal fields under high-power end-face diode pumping is analyzed using numerical model. It is shown that non-uniform distribution profiles of optical centers concentration are very promising for high average pump power laser amplifiers. The possibility of creating concentration profiles of optical centers in gradient-activated crystals with YAG matrix with a specified distribution along the growth axis of the crystal is demonstrated. A technology of growing gradient-activated single crystal involving active mirror as active element is proposed and discussed.

Performance comparison of Yb:YAG ceramics and crystal gain material in a large-area, high-energy, high average-power diode-pumped laser.

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.

Ceramic Magneto-Optical Material

It has been more than 20 years since the 1st Nd:Y3Al5O12 (Nd:YAG) polycrystalline ceramic laser was reported, and nowadays, there are a lot of works for transparent ceramics on scintillators, phosphors, faraday rotators, and optical windows not only for laser gain media. A Faraday rotator is one of the key optics element for the isolation and birefringence compensation of laser amplifiers in high-averagepower laser systems and demands high Verdet constant, size scalability, excellent optical quality, high laser damage threshold, and a high thermal conductivity. We report the optical properties, Faraday effect and Verdet constant of ceramic TGG and TAG. Large diameter ceramic TGG (Tb3Ga5O12) have been used as Faraday devices for high-average laser systems. Advanced ceramic TAG (Tb3Al5O12) is a promising Faraday material for high-average-power lasers system.

Spatio-spectral structures in high harmonic generation driven by tightly focused high repetition rate lasers

We investigate the spatio-spectral properties of extreme ultraviolet (XUV) high harmonic radiation driven by high repetition rate femtosecond laser systems. In the spatio-spectral domain, ring-shaped structures at each harmonic order associated with long-trajectory electrons are found to form arrow-shaped structures at the cutoff. These structures are observed with two different laser systems: an optical parametric chirped-pulse amplifier system at a central wavelength of 1.55 μm and 125 kHz repetition rate, and a temporally compressed femtosecond ytterbium fiber amplifier at 1.03 μm wavelength and 100 kHz repetition rate. As recently pointed out, the observed structures are well explained by considering the space–time atomic dipole-induced phase for short and long electron trajectories in the generation plane. The tighter focusing geometry and longer wavelength associated with these emerging driving laser systems increase the ring-like divergence and spectral broadening for high harmonics. Cutoff energies and photon fluxes obtained in argon and neon are also reported. Overall, these results shed new light on the properties of XUV radiation driven by these recently developed high average power laser systems, paving the way to high photon-flux XUV beamlines.

Modeling of the performance of a cryogenic gas cooled Yb:YAG multislab amplifier with a longitudinal doping gradient concentration

A cryogenic helium gas cooled Yb:YAG multislab amplifier with a longitudinal doping gradient concentration was proposed for developing high energy, high average power laser systems. As a comparison, the performance of the gradient doped amplifier was investigated with other constant and stepped doped amplifiers in terms of energy storage capacity, heat deposition, and amplification, based on the theory of quasi-three-level laser ions, Monte Carlo, and ray-tracing approaches. Improved lasing characteristics with more homogenous distributions of gain and heat load and higher efficiency was achieved in the gradient doped multislab amplifier while lower gain medium volume was required. It is shown that at the optimum operating temperature of 200 K, the maximum output energy of 867.76 J in the gradient doped amplifier was obtained, corresponding to an optical-to-optical efficiency of 22.41%.

Design of a thin disk amplifier with extraction during pumping for high peak and average power Ti:Sa systems (EDP-TD).

Combination of the scheme of extraction during pumping (EDP) and the Thin Disk (TD) technology is presented to overcome the limitations associated with thermal cooling of crystal and transverse amplified spontaneous emission in high average power laser systems based on Ti:Sa amplifiers. The optimized design of high repetition rate 1-10 PW Ti:Sapphire EDP-TD power amplifiers are discussed, including their thermal dynamic behavior.

Efficient ASE control in cryogenic gas cooled Yb:YAG multislab amplifiers with Cr4+:YAG interlayers

A novel approach based on Cr4+:YAG interlayers to break the transmission paths of amplified spontaneous emission (ASE) in a cryogenic gas cooled Yb:YAG multislab amplifier geometry was presented for the suppression of ASE in the power scaling of high energy, high average power laser systems. The benefits of Cr4+:YAG interlayers for the overall performance of an amplifier were illustrated with respect to energy storage capacity, heat generation and amplification of the seed pulses based on the theory of quasi-three-level Yb3+ ions and Cr4+:YAG saturable absorption, the Monte Carlo and ray-tracing methods. For the amplifier with optimized Cr4+:YAG interlayers, it was found that the energy storage efficiency was increased from 39.12% to 47.38% in comparison with the amplifier without interlayers. The maximum output energy of 1119.53 J with an optical-to-optical efficiency of 28.91% in the amplifier with interlayers was obtained, while it reduced to 810.61 J with an optical-to-optical efficiency of 20.94% in the amplifier without interlayers. To our knowledge, this is the first quantitative characterization of the performance of a cryogenic gas cooled Yb:YAG multislab amplifier with Cr4+:YAG interlayers.

Advanced space power and propulsion based on lasers

One of the key components for future space exploration, manned or unmanned, is the availability of propulsion systems beyond the state of the art. The rapid development in conventional propulsion systems since the middle of the 20th century has already reached the limits of chemical propulsion technology. To enhance mission radius, shorten the transit time and also extend the lifetime of a spacecraft more efficient, but still powerful propulsion system must be developed. Apart from the propulsion system a major weight contribution arises from the required energy source. Envisioning rapid development of future high average power laser systems and especially the ICAN project we review the prospect of advanced space propulsion based on laser systems.

Energy coupling in short pulse laser solid interactions and its impact for space debris removal.

Significant advances have been made over the last decade to improve the performance, efficiency, and contrast of high peak and average power laser systems, driven by their use in a wide variety of fields, from the industrial to the scientific. As the contrast of the lasers has improved, interactions with contrasts of 1012 are now routinely undertaken. At such high contrasts, there is negligible preplasma formation and the ionized surface layer created by subpicosecond-duration pulses typically forms a highly reflective "plasma mirror" capable of reflecting between 70% and 90% of the incident energy. Although such interactions are of significant interest for applications such as harmonic source production and to enable the underlying physics to be studied, their low absorption can limit their usefulness for applications such as space debris removal.

Crystal growth and application of large size YCOB crystal for high power laser

Yttrium calcium oxyborate YCa4O(BO3)3 (YCOB) is a novel non-linear optical crystal possessing good thermal, mechanical and nonlinear optical properties. It is regards the important candidate frequency conversion material for the high-average power laser system. In this work, we described our effort to achieve the successful growth of large size YCOB single crystals, and the crystal quality of large size YCOB crystal grown by the Bridgman method. The OPCPA application of YCOB element was also introduced simply. The results confirmed that Bridgman technology can be used for the growth of large size YCOB crystal as an alternative to Czochralski method.

Compact x-ray microscope for the water window based on a high brightness laser plasma source

We present a laser plasma based x-ray microscope for the water window employing a high-average power laser system for plasma generation. At 90 W laser power a brightness of 7.4 x 10(11) photons/(s x sr x μm(2)) was measured for the nitrogen Lyα line emission at 2.478 nm. Using a multilayer condenser mirror with 0.3 % reflectivity 10(6) photons/(μm(2) x s) were obtained in the object plane. Microscopy performed at a laser power of 60 W resolves 40 nm lines with an exposure time of 60 s. The exposure time can be further reduced to 20 s by the use of new multilayer condenser optics and operating the laser at its full power of 130 W.

Experimental investigation on laser-induced surface damage threshold of Nd-doped phosphate glass

Nd-doped phosphate glass is the dominant amplifier material used in solid state high average power laser systems. Surface imperfection and subsurface damage (SSD) of the glass, resulting from the optical fabrication process, limit the increment of laser system energy output. Thus, it is important to enhance the surface damage threshold of Nd-doped phosphate glass surface. The in°uence of abrasive size, polishing powder, grinding mode, and chemical treatment on the laser-induced damage threshold (LIDT) of Nd-doped phosphate glass surface is investigated. Results show that the LIDT is affected little by different polishing powders and grinding modes. The LIDT correlates with the abrasive size, which produced different depths of SSD. A suitable acid etching treatment can remove the imperfection and the SSD for improving the LIDT of Nd-doped phosphate glass surface. The combination of several effective techniques and methods, which are low-cost and practical, should be useful to enhance the LIDT of Nd-doped phosphate glass surface.

High‐Power Solid‐State Lasers: a Laser Glass Perspective

Advances in laser glass compositions and manufacturing have enabled a new class of high‐energy/high‐power (HEHP), petawatt (PW), and high average power (HAP) laser systems that are being used for fusion energy ignition demonstration, fundamental physics research, and materials processing, respectively. The requirements for these three laser systems are different, necessitating different glasses or groups of glasses. The manufacturing technology is now mature for melting, annealing, fabricating, and finishing of laser glasses for all three applications. The laser glass properties of major importance for HEHP, PW, and HAP applications are briefly reviewed and the compositions and properties of the most widely used commercial laser glasses are summarized. Proposed advances in these three laser systems will require new glasses and new melting methods, which are briefly discussed. The challenges presented by these laser systems will likely dominate the field of laser glass development over the next several decades.

Characterization of bubble core and cloudiness in Yb3+:Sr5(PO4)3F crystals using micro-Raman spectroscopy

Ytterbium doped strontium fluoroapatite Yb3+:Sr5(PO4)3F (Yb:S-FAP) crystals have been used in high average power laser systems as gain medium. Growth induced defects associated with the crystal often affect their performance. In order to improve the crystal quality and its optical applications, it is imperative to understand the nature of these defects. In this study, we utilize micro-Raman spectroscopy to characterize two common growth-induced defects: bubble core and cloudiness. We find the bubble core consist of voids and microcrystals of Yb:S-FAP. These microcrystals have very different orientation from that of the pure crystal outside the bubble core. In contrast to a previous report, neither Sr3(PO4)2 nor Yb2O3 are observed in the bubble core regions. On the other hand, the cloudy regions are made up of the host materials blended with a structural deformation along with impurities which include CaCO3, YbPO4, SrHPO4, and Sr2P2O7 . The impurities are randomly distributed in the cloudy regions. This analysis is necessary for understanding and eliminating these growth defects in Yb:S-FAP crystals.

Large-aperture YCOB crystal growth for frequency conversion in the high average power laser system

Yttrium calcium oxyborate YCa 4O(BO 3) 3 (YCOB) is a novel non-linear optical crystal possessing good thermal, mechanical and non-linear optical properties. Large-aperture YCOB crystals with 75 mm diameter were grown for high-average power frequency conversion on the mercury laser system. The growth morphology (included facet and spiral growth), cracking and inclusions in the as-grown crystal boule were discussed as the critical problem for large-aperture YCOB crystal growth. This can be minimized through modification of the growth program, including pulling rate, separation procedure, and cooling program. High-average power frequency conversion of the mercury laser using YCOB has been demonstrated, and experimental validation of YCOB material yields 50% conversion at 10 Hz has been achieved.

Design and implementation of a TW-class high-average power laser system

We describe the design, modeling and characterization of a titanium-doped sapphire multipass, kilohertz amplifier system with output pulses of energy 4.4 mJ and duration 17 fs, giving a peak power of 0.26 TW. The thermal lensing in the second amplifier stage is virtually eliminated by cryogenic cooling of the laser crystal. Gain-narrowing and shifting of the amplified spectrum are reduced by tailoring the output spectrum of the oscillator and by using a low-loss multipass amplifier chain. Fourth-order spectral dispersion was completely eliminated by using a prism pair in addition to adjusting the stretcher and compressor grating separation and angle. We also numerically modeled the evolution of the pulse energy and spectral phase and amplitude through the amplifier system. The results of the model are in excellent agreement with measurements made using the technique of transient-grating frequency-resolved optical gating.

Frequency modulated mode locking of a diode laser pumped Nd:LiYF4 laser utilizing a KTiOPO4 phase modulator

A potassium titanyl phosphate phase modulator was used to mode lock a diode laser pumped Nd:LiYF4 laser at 270 MHz. The autocorrelation was 15 ps and the spectral bandwidth 73 GHz. The phase noise of the laser was found to be 70 fs for frequencies ≳100 Hz using a radio frequency spectrum analyzer technique. The high damage threshold and low absorption losses make this material well suited for the future development of high peak and average power laser systems. In addition, the low phase noise should be important for applications which require low timing jitter between a mode-locked laser source and an electronic reference signal.