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Laser plasma-based particle accelerators attract great interest in fields where conventional accelerators reach limits based on size, cost or beam parameters. Despite the fact that particle in cell simulations have predicted several advantageous ion acceleration schemes, laser accelerators have not yet reached their full potential in producing simultaneous high-radiation doses at high particle energies. The most stringent limitation is the lack of a suitable high-repetition rate target that also provides a high degree of control of the plasma conditions required to access these advanced regimes. Here, we demonstrate that the interaction of petawatt-class laser pulses with a pre-formed micrometer-sized cryogenic hydrogen jet plasma overcomes these limitations enabling tailored density scans from the solid to the underdense regime. Our proof-of-concept experiment demonstrates that the near-critical plasma density profile produces proton energies of up to 80 MeV. Based on hydrodynamic and three-dimensional particle in cell simulations, transition between different acceleration schemes are shown, suggesting enhanced proton acceleration at the relativistic transparency front for the optimal case.
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Hidrógeno , Protones , Rayos Láser , Aceleradores de Partículas , AceleraciónRESUMEN
We report on the development of a pump system for ultrafast optical parametric amplifiers (uOPA) as an upgrade for the existing uOPA at the Petawatt High Energy Laser for heavy Ion eXperiments (PHELIX) and the new Petawatt ENergy-Efficient Laser for Optical Plasma Experiments (PEnELOPE). The system consists of a two-stage chirped pulse amplifier, centered around a high energy Yb:YAG regenerative amplifier that delivers 108 mJ uncompressed output energy, resulting in 92 mJ at 1030 nm after compression, pulse durations of 1.4 ps, a high beam quality of Mx/y2 = 1.02 / 1.16 and a relative energy stability of 0.35 %. A second harmonic generation (SHG) efficiency of up to 70 % is achievable and a maximum pulse energy of 43 mJ at 515 nm has been obtained, which is only limited by the damage threshold of the SHG crystal. A self-phase modulation stage makes this system a widely applicable, self-seedable pump module for uOPA without placing strong requirements on its seed oscillator.
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Due to the non-linear nature of relativistic laser induced plasma processes, the development of laser-plasma accelerators requires precise numerical modeling. Especially high intensity laser-solid interactions are sensitive to the temporal laser rising edge and the predictive capability of simulations suffers from incomplete information on the plasma state at the onset of the relativistic interaction. Experimental diagnostics utilizing ultra-fast optical backlighters can help to ease this challenge by providing temporally resolved inside into the plasma density evolution. We present the successful implementation of an off-harmonic optical probe laser setup to investigate the interaction of a high-intensity laser at [Formula: see text] peak intensity with a solid-density cylindrical cryogenic hydrogen jet target of [Formula: see text] diameter as a target test bed. The temporal synchronization of pump and probe laser, spectral filtering and spectrally resolved data of the parasitic plasma self-emission are discussed. The probing technique mitigates detector saturation by self-emission and allowed to record a temporal scan of shadowgraphy data revealing details of the target ionization and expansion dynamics that were so far not accessible for the given laser intensity. Plasma expansion speeds of up to [Formula: see text] followed by full target transparency at [Formula: see text] after the high intensity laser peak are observed. A three dimensional particle-in-cell simulation initiated with the diagnosed target pre-expansion at [Formula: see text] and post processed by ray tracing simulations supports the experimental observations and demonstrates the capability of time resolved optical diagnostics to provide quantitative input and feedback to the numerical treatment within the time frame of the relativistic laser-plasma interaction.
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We report on a compact diode-pumped, chirped pulse regenerative amplifier system with a pulse duration of 162 fs and an output pulse energy of 1 mJ before as well as 910 µJ after compression optimized for the probing of ultrafast relativistic laser-plasma processes. A chirped volume Bragg grating (CVBG) acts as a combined pulse stretcher/compressor representing a robust solution for a CPA laser system in the millijoule range. Yb3+:CaF2 is used as gain medium to support a large bandwidth of 16 nm (FWHM) when spectral gain shaping is applied. Chirped mirrors compensate for any additional dispersion introduced to the system.
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We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150 TW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20 MeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (∅ 5 µm) and planar (20 µm × 2 µm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions.
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In the search for alternative materials to replace indium-tin-oxide in transparent electrodes we have structured copper and aluminum thin films (between 5 an 40 nm) for tailoring their optical properties. Micrometer scaled holes were produced using the direct laser interference patterning (DLIP) technique. We compared the optical and electrical parameters of nanosecond and picosecond processed thin films. It was found that the optical transmittance of the structured layers was relatively increased between 25 to 125% while the electrical resistance was marginally influenced. In addition, the laser treatment enhanced the diffuse to total transmission ratio (HAZE) by values ranging from 30 to 82% (relative) as a potential advantage of µm structuring. The results also show that both of the studied metals succeed to match the target which is set by typical applications of indium thin oxide (ITO) films. Furthermore, numerical simulations are performed in order to understand the ablation process of thin film material for ps and ns pulses.
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We investigated the lasing performance of a multislab Yb:QX and Yb:YAG laser amplifiers using a facet-cooled design. Di-deuterium oxide (D2O) was used as the coolant flowing between the active slabs with the pump and laser light passing through the very low absorbing heavy-water films. A square pump profile at a maximum intensity of 40 kW/cm2 drove the amplifier with a peak fluence of 5.5 J/cm2 and a pulse duration of 6 ns. We demonstrated a maximum pulse energy of 1 J for each gain medium as well as a repetition rate of 10 Hz for Yb:YAG and 1 Hz for Yb:QX glass, thus showing the feasibility and scalability of directly water-cooled, diode-pumped, high-energy short-pulse lasers.
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We report the amplification of laser pulses at a center wavelength of 1034 nm to an energy of 16.6 J from a fully diode-pumped amplifier using Yb:CaF2 as the active medium. Pumped by a total optical power of 300 kW from high-power laser diodes, a gain factor of g=6.1 was achieved in a nine-pass amplifier configuration agreeing with numerical simulations. A measured spectral bandwidth of 10 nm full width at half-maximum promises a bandwidth-limited compression of the pulses down to a duration of 150 fs. These are, to our knowledge, the most energetic laser pulses achieved from a diode-pumped chirped-pulse amplifier so far.
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Temperature dependent absorption and emission cross-sections of 5 at% Yb(3+) doped yttrium lanthanum oxide (Yb:YLO) ceramic between 80K and 300 K are presented. In addition, we report on the first demonstration of ns pulse amplification in Yb:YLO ceramic. A pulse energy of 102 mJ was extracted from a multi-pass amplifier setup. The amplification bandwidth at room temperature confirms the potential of Yb:YLO ceramic for broad bandwidth amplification at cryogenic temperatures.
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We present a novel approach for the amplification of high peak power femtosecond laser pulses at a high repetition rate. This approach is based on an all-diode pumped burst mode laser scheme. In this scheme, pulse bursts with a total duration between 1 and 2 ms are be generated and amplified. They contain 50 to 2000 individual pulses equally spaced in time. The individual pulses have an initial duration of 350 fs and are stretched to 50 ps prior to amplification. The amplifier stage is based on Yb3+:CaF2 cooled to 100 K. In this amplifier, a total output energy in excess of 600 mJ per burst at a repetition rate of 10 Hz is demonstrated. For lower repetition rates the total output energy per burst can be scaled up to 915 mJ using a longer pump duration. This corresponds to an efficiency as high as 25% of extracted energy from absorbed pump energy. This is the highest efficiency, which has so far been demonstrated for a pulsed Yb3+:CaF2 amplifier.
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Fabrication, spectroscopic properties, and laser performance of a Yb:SiO(2) multicomponent glass have been investigated in this paper. The glass system composed of SiO(2), Al(2)O(3), and La(2)O(3) excels in terms of a high thermal stress resistance compared to other laser glasses. The laser experiments were conducted with a 3.4 mm thick and 0.9 mol. % Y(2)O(3) doped sample. A maximum slope efficiency of 51%, a maximum optical to optical efficiency of 42%, and a tuning range from 1010-1090 nm was realized. Due to the promising laser properties and a straightforward fabrication technique it may well qualify as an alternative gain medium in high-energy, ultrashort pulse laser systems.
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We report on the first demonstration of a diode-pumped, gas cooled, cryogenic multislab Yb:YAG amplifier. The performance was characterized over a temperature range from 88 to 175 K. A maximum small-signal single-pass longitudinal gain of 11.0 was measured at 88 K. When amplifying nanosecond pulses, recorded output energies were 10.1 J at 1 Hz in a four-pass extraction geometry and 6.4 J at 10 Hz in a three-pass setup, corresponding to optical to optical conversion efficiencies of 21% and 16%, respectively. To our knowledge, this represents the highest pulse energy so far obtained from a cryo-cooled Yb-laser and the highest efficiency from a multijoule diode pumped solid-state laser system.
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We present what we believe to be the first terawatt diode-pumped laser employing single-crystalline Yb:CaF(2) as the amplifying medium. A maximum pulse energy of 420 mJ at a repetition rate of 1 Hz was achieved by seeding with a stretched femtosecond pulse 2 ns in duration, preamplified to 40 mJ. After recompression, a pulse energy of 197 mJ and a duration of 192 fs were obtained, corresponding to a peak power of 1 TW. Furthermore, nanosecond pulses containing an energy of up to 905 mJ were generated without optical damage.
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A novel all-diode-pumped master oscillator power amplifier system based on Yb:YAG crystal rods has been developed. It consists of a Q-switched oscillator delivering 3 mJ, 6.4 ns pulses at a 10 Hz repetition rate and an additional four-pass amplifier, which boosts the output energy to 220 mJ, while a close to TEM(00) beam quality could be observed. Additionally a simulation of the amplification was written that allows for further scaling considerations.
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We present a novel technique to align a tiled grating in all five relevant degrees of freedom utilized in the compressor of the high-power chirped-pulse amplification laser system POLARIS at the Institute for Optics and Quantum Electronics, Jena, Germany. With this technique, alignment errors of the two gratings with respect to each other can be detected with an accuracy of 1 microrad for the rotational and 40 nm for the translational degrees of freedom. This is well sufficient to recompress 1030 nm pulses, which were stretched to 2.2 ns before amplification, to their bandwith limit of 150 fs.
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Rayos Láser , Óptica y Fotónica , Diseño de Equipo , Fotones , Factores de TiempoRESUMEN
Growth, spectroscopic properties, and laser performance of Yb:SrF(2) crystals have been investigated. In spatial multimode operation of a diode-pumped Yb:SrF(2) laser a slope efficiency of 46% was measured. 180W output power with high beam quality at a pulse duration of 1.5ms was achieved by installing a mode cleaning aperture. A maximum average output power of 270mW and a tuning range of 73nm was observed.
