The problem of optimizing the parameters of a laser pulse compressor consisting of four identical diffraction gratings is solved analytically. The goal of optimization is to obtain maximum pulse power, completely excluding both beam clipping on gratings and the appearance of spurious diffraction orders. The analysis is carried out in a general form for an out-of-plane compressor. Two particular “plane” cases attractive from a practical point of view are analyzed in more detail: a standard Treacy compressor (TC) and a compressor with an angle of incidence equal to the Littrow angle (LC). It is shown that in both cases the LC is superior to the TC. Specifically, for 160-cm diffraction gratings, optimal LC design enables 107 PW for XCELS and 111 PW for SEL-100 PW, while optimal TC design enables 86 PW for both projects.

To overcome Yb laser, kilowatt-level 1535 nm fiber laser is utilized to in-band pump an Er:Yb co-doped fiber (EYDF) amplifier. An output power of 301 W narrow-linewidth EYDF amplifier operating at 1585 nm, with 3 dB bandwidth of 150 pm and M²<1.4, is experimentally demonstrated. To the best of our knowledge, it is the highest output power in L band narrow-linewidth fiber amplifiers with good beam quality. Theoretically, a new ion transition behavior among energy levels for in-band pumping EYDF is uncovered, and a spatial-mode-resolved nonlinearity-assisted theoretical model is developed to understand its internal dynamics. Numerical simulations reveal that the reduction in optical efficiency is significantly related to excited-state absorption (ESA). ESA has a nonlinear hindering effect on power scaling. It can drastically lower the pump absorption and slope efficiency with increasing pump power for in-band pumped EYDF amplifiers. Meanwhile, to improve power to kilowatt level via in-band pumping, optimized approaches are proposed.

A colliding microjet liquid sheet target system was developed, and tested for pairs of round nozzles of 10, 11, and 18µm in diameter. The sheet’s position stability was found to be better than a few micrometers. Upon interaction with 50mJ laser pulses, the 18µm jet has a resonance amplitude of 16µm at a repetition rate of 33Hz, while towards 100Hz it converges to 10µm for all nozzles. A white-light interferometric system was developed to measure the liquid sheet thickness in the target chamber both in air and in vacuum, with a measurement range of 185nm – 1µm and an accuracy of ±3%. The overall shape and 3D shape of the sheet follow the Hasson-Peck model in air. In vacuum versus air, the sheet gradually loses 10% of its thickness, so the thinnest sheet achieved was below 200nm at a vacuum level of 10-4mbar, and remained stable for several hours of operation.

The high-energy/high-intensity laser facility PHELIX of the GSI Helmholtzzentrum f ̈ur Schwerionenforschung in Darmstadt, Germany, has been in operation since 2008. Here, we review the current system performance, which is the result of continuous development and further improvement. Through its versatile frontend architecture, PHELIX can be operated in both long and short pulse modes, corresponding to ns pulses with up to 1 kJ pulse energy and sub-ps, 200 J pulses, respectively. In the short-pulse mode, the excellent temporal contrast and the control over the wavefront make PHELIX an ideal driver for secondary sources of high-energy ions, neutrons, electrons, and X-rays. The long-pulse mode is mainly used for plasma heating, which can then be probed by the heavy-ion beam of the linear accelerator of GSI. In addition, PHELIX can now be used to generate X-rays for studying exotic states of matter created by heavy-ion heating using the ion beam of the heavy-ion synchrotron of GSI.

Dr. Jie Zhang, a distinguished physicist, has made significant contributions in the fields of high-energy density physics and inertial confinement fusion. Because of these, he was elected academician of the Chinese Academy of Sciences in 2003, academician of the German National Academy of Sciences in 2007, Fellow of the Academy of Sciences for the Developing World (TWAS) in 2008, foreign member of the Royal Academy of Engineering in the United Kingdom in 2011, and foreign associate of the National Academy of Sciences in the United States in 2012. In 2015, he was awarded the prestigious Edward Teller Medal, the most important international award in inertial confinement fusion and high-energy density physics. In 2021, he was awarded the Future Science Prize in Physical Sciences.

The intensity attenuation of a high-power laser is a frequent task in the measurements of optical science. Laser intensity can be attenuated by inserting an optical element, such as a partial reflector, polarizer, or absorption filter. These devices are, however, not always easily applicable, especially in the case of ultra-high power lasers, because they can alter the characteristics of a laser beam or get easily damaged. In this study, we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator (RPA), a device with randomly distributed pinholes, without changing beam properties. With this device a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its characteristics. Additionally, it was confirmed that the temporal profile of a laser pulse, including the spectral phase, was preserved. Consequently, the RPA possesses significant potential for a wide range of applications.

We report the first high-repetition rate generation and simultaneous characterization of nanosecond-scale return currents of kA-magnitude issued by the polarization of a target irradiated with a PW-class high-repetition-rate Ti:Sa laser system at relativistic intensities. We present experimental results obtained with the VEGA-3 laser at intensities from 5e18-1.3e20Wcm-2. A non-invasive inductive return-current monitor is adopted to measure the derivative of return-currents on the order of kA/ns and analysis methodology is developed to derive return-currents. We compare the current for copper, aluminium and Kapton targets at different laser energies. The data shows the stable production of current peaks and clear prospects for the tailoring of the pulse shape, promising for future applications in high energy density science, e.g. electromagnetic interference stress tests, high-voltage pulse response measurements, and charged particle beam lensing. We compare the target discharge of the order of hundreds of nC with theoretical predictions and a good agreement is found.

A multi-shot target assembly and automatic alignment procedure for laser-plasma proton acceleration at high-repetition-rate are introduced. The assembly is based on a multi-target rotating wheel capable of hosting >5000 targets, mounted on a three-dimensional motorised stage to allow rapid replenishment and alignment of the target material between laser irradiations. The automatic alignment procedure consists of a detailed mapping of the impact positions at the target surface prior to the irradiation that ensures stable operation of the target, which alongside the purpose-built design of the target wheel, enable the operation at rates up to 10Hz. Stable and continuous laser-driven proton acceleration at 10 Hz is demonstrated, with observed cut-off energy stability about 15%.

Based on the paraxial wave equation, this study extends the theory of small-scale self-focusing (SSSF) from coherent beams to spatially partially coherent beams (PCBs) and derives a general theoretical equation that reveals the underlying physics of the reduction in the B-integral of spatially PCBs. From the analysis of the simulations, the formula for the modulational instability (MI) gain coefficient of the SSSF of spatially PCBs is obtained by introducing a decrease factor into the formula of the modulational instability (MI) gain coefficient of the SSSF of coherent beams. This decrease can be equated to a drop in the injected light intensity or an increase in the critical power. According to this formula, the reference value of the coherence of spatially PCBs is given, offering guidance to overcome the output power limitation of the high-power laser driver due to SSSF.

Tight focusing with very small f-numbers is necessary to achieve highest at-focus irradiances. However, tight focusing imposes strong demands on precise target positioning in-focus to achieve the highest on-target irradiance. We describe several near-infrared, visible, ultraviolet, soft and hard X-ray diagnostics employed in the ~10²² W/cm² laser-plasma experiment. We used ~10 J total energy femtosecond laser pulses focused into a ~1.3-µm focal spot on 5–20 µm thick stainless-steel targets. We discuss the applicability of these diagnostics to determine the best in-focus target position with ~5 µm accuracy (i. e., around ½ of the short Rayleigh length) and show that several diagnostics (especially, 3ω reflection and on-axis hard X-rays) can ensure this accuracy. We demonstrated target positioning within several µm from the focus, ensuring over 80% of the ideal peak laser intensity on-target. Our approach is relatively fast and does not rely on coincidence of low-power and high-power focal planes.