This PDF file contains the front matter associated with SPIE Proceedings Volume 12401, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The Laser Megajoule facility, developed by the CEA is based on 176 Nd:glass laser beams focused on a micro-target positioned inside a 10-meter diameter spherical chamber. The facility will deliver a total energy of 1.4MJ of UV light at 0.35 μm and a maximum power of 400 TW. A specific petawatt beam, PETAL, offers a combination of a very high intensity beam, synchronized with the nanosecond beams of the LMJ. This combination allows expanding the LMJ experimental field in the High Energy Density Physics (HEDP) domain. Since September 2021, a major project milestone has been achieved with the commissioning of the half LMJ (88 beams are fully operational with 10 heating bundles of 8 beams and a specific bundle for plasma diagnostics purpose). The installation and the commissioning of new laser bundles and new plasma diagnostics around the target chamber are continuing, simultaneously to the realization of plasma experiments. Another project milestone has been achieved at the end of 2021, with a dedicated laser experiment in the facility to explore the Power-Energy Diagram.

The mitigation of transverse stimulated Brillouin scattering (SBS) via phase modulation is mandatory to avoid damage in high-energy laser systems. A novel fail-safe system that indirectly monitors the optical bandwidth applied to suppress SBS by monitoring the input, reflected, and through rf power of the SBS-suppression lithium-niobate phase modulator is demonstrated. The fail-safe system has high sensitivity and reliability provided by optimized redundant circuits for power monitoring and fail-safe decision logic. Calibration of the fail-safe’s thresholds is straightforward. The fail-safe circuitry reacts within 45 ns to stop an incorrectly modulated pulse by blocking the propagation of an electronic timing trigger.

A mid-scale (270 × 270-mm aperture) plasma-electrode Pockels cell (PEPC) has been developed for the pump laser system in FLUX (the fourth-generation laser for ultrabroadband experiments). The FLUX mid-scale PEPC is adapted from the PEPC used in the OMEGA EP beamlines (410 × 410-mm aperture), with certain dimensions scaled to reduce capacitance while maintaining key plasma characteristics. After experimental optimization of operating parameters, particularly the plasma current, <70-ns switching time with excellent (>1000:1) contrast has been demonstrated. Dependence of optical switching performance on operating conditions is explained by a plasma model.

We investigate the feasibility of a full-silica transmission metasurface exhibiting optical properties equivalent to a quarter-wave plate at the wavelength of 351 nm as an alternative to anisotropic crystals. We report the design, manufacturing process and optical characterization of full-silica quarter waveplates. We evidence the possibility to obtain a full-silica component exhibiting at 351 nm a high damage threshold and a phase retardance of λ/4 associated with a transmission efficiency higher than 95%. Such an optical component could offer a great alternative to birefringent materials for the manipulation of polarization of high-energy laser beams.

High-average-power solid-state lasers are often severely limited by thermally induced stress birefringence, leading to depolarization losses and damage issues. Depolarization losses can be mitigated by selecting appropriate polarization optics to compensate the space-variant stress birefringence distribution. While some small-aperture, low-fluence technologies are available, no solution so far can provide a combination of high fluence and large aperture with a high degree of control of the beam quality. In this work, we demonstrate the use of magnetorheological finishing (MRF) technology to carve a prescribed thickness profile in a quartz waveplate to achieve precise space-variant polarization control. An arbitrary distorted polarization distribution can be converted into a uniform linearly polarized beam using two freeform MRF crystal optics with their crystal axes offset by 45 degrees. This technology is readily scalable to high-fluence, large-aperture applications, potentially enabling new regimes of laser operation.

The National Ignition Facility (NIF) employs 192 laser beams to achieve inertial confinement fusion by irradiating a mm scale fusion target. Automatic alignment (AA) image processing algorithms are used to align 192 beams to the NIF target chamber center. Cameras placed along the beam path supply the images that are analyzed by AA algorithms to provide beam location and alignment information. NIF has the capability of using beam-specific database parameters. This allows beam line images to be processed using optimized algorithms tailored to individual beam alignment needs. For a given segment of alignment in the NIF beam path, 192 different versions of the algorithm can be run simply by changing data base parameters. This capability is vital to alignment precision in a system as complex and mature as NIF. Since optical components and devices age, laser parameters and beam alignment quality can and do change. Constant beam-by-beam monitoring of alignment performance is needed in order to mitigate any issues caused by such changes. The objective of this work is to evaluate how periodic AA algorithm beam parameter changes might better maintain alignment requirements over time in the NIF facility. We show examples from final optics assembly (FOA) and harmonic generator (THG, SHG) loops.

Stimulated rotational Raman scattering in air is a powerful parasitic process that degrades high intensity pulses propagated over significant distances. Through this inelastic scattering process, laser photons are converted to higher (Anti-Stokes) or lower (Stokes) energies, according to rotational mode transitions in the nitrogen and oxygen molecules. The full wave-mixing problem involves numerous frequencies including both Stokes and Anti- Stokes processes, multiple rotational line transitions, and multi-harmonic generation, with each generated field acting as a seed for subsequent scattering processes. Multiple numerical models of these processes were integrated into Lawrence Livermore National Laboratory’s in-house nonlinear optical chain propagation software, Virtual Beamline++. The complex spatio-temporal dynamics of single, and multi-frequency stimulated rotational Raman scattering are highlighted and discussed. General limitations of steady-state, dynamic two-level, multi-harmonic, and multi-rotational models are demonstrated and compared.

We present experimental demonstrations of the energy density storage and extraction capabilities of Tm:YLF using a table-top diode-pumped system. Here, a Tm:YLF-based oscillator, producing mJ-class pulse energies within both short (nanosecond) and long (millisecond) duration pulses, seeds a single far-field multiplexed power amplifier. The amplifier produced pulse energies up to 21.7 J in 20 ns (>1 GW peak power) using a 4-pass configuration, and 108.3 J in a long duration pulse using a 6-pass configuration. Additionally, the system was reconfigured and operated in a burst mode, amplifying a 6.8 kHz few-ms duration burst of 36 pulses up to 3.6 kW average power. An optical-to-optical efficiency of 19% was achieved during the quasi-steady-state amplification, with an individual pulse fluence over an order of magnitude lower than the saturation fluence.

The Matter in Extreme Conditions Upgrade (MEC-U) project is a major upgrade to the MEC instrument on the Linac Coherent Light Source (LCLS) X-ray free electron laser (XFEL) user facility at SLAC National Accelerator Laboratory. The MEC instrument combines the XFEL with a high-power, short-pulse laser and high energy shock driver laser to produce and study high energy density plasmas and materials found in extreme environments such as the interior of stars and fusion reactors, providing the fundamental understanding needed for applications ranging from astronomy to fusion energy. When completed, this project will significantly increase the power and repetition rate of the MEC high intensity laser system to the petawatt level at up to 10 Hz, increase the energy of the shock-driver laser to the kilojoule level, and expand the capabilities of the MEC instrument to support groundbreaking experiments enabled by the combination of high-power lasers with the world’s brightest X-ray source. Lawrence Livermore National Laboratory (LLNL) is developing a directly diode-pumped, 10 Hz repetition rate, 150 J, 150 fs, 1 PW laser system to be installed in the upgraded MEC facility. This laser system is an implementation of LLNL’s Scalable High power Advanced Radiographic Capability (SHARC) concept and is based on chirped pulse amplification in the diode-pumped, gas-cooled slab architecture developed for the Mercury and HAPLS laser systems. The conceptual design and capabilities of this laser system will be presented.

Pursuit of an academic career is often co associated with a PhD which also is a qualification for all types of jobs in industry. However, in Germany most PhD programs focus on university-based, basic, and applied research and aim to demonstrate concepts while the transfer to industry and real products is subordinate. This is where Fraunhofer comes in: our natural science and engineering PhD students participate in solving real-world problems for our industrial customers with innovative and scientific approaches while they simultaneously pursue basic research questions with an application relevance for their PhD thesis. As an example, in this paper we present a multiphysics laser diode simulation software (SEMSIS) which was developed within two industrially funded PhD projects at the Fraunhofer Institute for Laser technology ILT. In the fusion research, a vast number of high-power laser diodes are used as pump sources for the high-energy pulsed lasers in inertial confinement fusion. Improving their electro-optical efficiency and making them more robust against external optical feedback represents a crucial step towards their use in economically competitive fusion power plants. In the presented simulation software tool SEMSIS, the complex interaction of electrical, optical, thermal as well as mechanical properties and their impact on efficiency, filamentation and reliability of high-power diode lasers can be analyzed to address the previously mentioned requirements in fusion research.