Optical Technologies for Inertial Fusion Energy

The physics principles of laboratory-scale inertial confinement fusion (ICF) have been recently demonstrated in implosion experiments at the National Ignition Facility (NIF), a ~2 megajoule, 192 beam UV laser at the Lawrence Livermore National Laboratory. The demonstration of thermonuclear ignition in deuterium-tritium fuel on NIF represents the climax of a 60-year-old quest in fusion research. Turning laser-driven ICF into an energy source relies on the expectations that the results from single shot experiments can be replicated at much higher repetition rates of about 10 shots per second to produce high average power at relatively low cost. This requires the development of new laser technologies, mass production of suitable targets, accurate injection and tracking systems and new materials for the reactor chamber components and final optics. Ultra broadband, deep UV light and beam zooming are laser advances that can dramatically improve the laser energy coupling to the target thereby reducing the laser energy and power requirements. An overview of the current state of laser fusion research and prospects for providing economically viable energy with high availability will be provided.

Marvel Fusion is developing compact high average power Petawatt laser system to drive nanostructured fusion fuel. Such system enable ultrafast deposition of energy into a target. Emphasis is placed on development of highly efficient driver and excellent contrast.

In this presentation, we will navigate the journey from cutting-edge research to practical, scalable solutions, paving the way for the future of clean, commercial fusion energy. Our focus will include bridging the laser technology gap to fusion power plants through a strategic facility roadmap designed to systematically mitigate critical target physics and technology risks for direct drive IFE. This approach supports transitioning from mature flash-lamp scientific laser systems to innovative diode-pumped kJ industrial laser systems. We will introduce Focused Energy's digital twin or IFE power plant model, used for optimizing the laser architecture and system performance. Key considerations are the choice between second or third harmonic light, and the level of spectral bandwidth to stabilize laser-plasma instabilities. Additionally, we will emphasize the critical role of industrialization, volume production and robust manufacturing supply chain in improving quality, reliability, and cost-effectiveness of laser drivers on the path to fusion commercialization. Finally, we will report on our progress on early non-IFE commercial applications, such as laser-driven radiation sources.

Blue Laser Fusion is commercializing a laser fusion technology capable of achieving the world’s first clean, on-demand, renewable energy generation. BLF’s IFE innovations enable a novel high efficiency 10 MJ laser coupled to a high gain, low cost, solid fuel target to achieve commercial fusion. We present recent progress, in collaboration with Caltech as well as Osaka University in Japan, on the modular pulsed laser system, including performance of pulsed laser energy storage in a large-scale optical enhancement cavity (OEC), injected with a multi-kilowatt coherent beam combined fiber amplified laser system. An optical enhancement cavity is a Fabry Perot cavity that is designed to store large amounts of energy within the 2-mirror cavity by carefully timing the round-trip time of the intracavity laser pulse with the following injected laser, resulting in phase matching and stacking of the laser pulse. Through the combination of multiple OECs and input lasers, the architecture can deliver broad spectral width, appropriate polarization, high spatial beam quality, precise temporal tuning optimized for direct drive IFE for a high gain, solid fuel target.

The National Ignition Facility achieved scientific breakeven in December 2022. While this was a major accomplishment, many challenges remain in making Inertial Fusion Energy (IFE) a reality. In particular, reliable commercial IFE will require a laser system that is much more efficient, lower cost, and higher energy, with superior spatio-temporal control of laser radiation. To accomplish this, Xcimer Energy is combining 𝜒3 nonlinear optical (NLO) gas amplifiers with high-energy excimer amplifiers in a highly flexible architecture that can affordably scale to tens of megajoules of laser energy on-target with an efficiency of 5% to 7%, with the ability to deliver energy to-target from a very small solid angle (<10e-3 sr). This will provide a practical path to rapidly demonstrate and commercialize IFE by allowing the use of simpler fusion targets that can achieve high gain robustly, and allowing repetition rates for electrical power production of under 1 Hz which relaxes requirements throughout the plant. Furthermore, this laser architecture enables the well-studied HYLIFE reactor concept utilizing thick liquid FLiBe molten salt flows to protect the first structural wall, allowing a 30-year lifetime from existing low-activation steel and eliminating the need to develop and qualify new first-wall materials. Xcimer Energy has raised funds from leading clean-tech venture firms, and is beginning construction of the “Phoenix” prototype laser facility in Denver, Colorado. Phoenix will be a kilojoule-scale testbed for low-pressure gas NLO (Brillouin and Raman) amplifier development, and will be online in early 2026. Xcimer is currently recruiting for scientific and engineering positions including nonlinear optical physics, low density plasma chemistry and kinetics, plasma physics, pulsed-power, optics, and laser & fusion engineering.

The National Ignition Facility (NIF) has demonstrated fusion with energy gain, an ‘existential’ step on the path to enabling commercial fusion energy. NIF uses 1990s laser technology with less than 1% electrical efficiency and only firing every few hours, far from ~15% efficiency and ~15Hz needed for commercial energy applications Methods and technologies to meet these technical and economic requirements will be presented.

The Argon Fluoride (ArF) laser is very attractive for achieving the performance needed for inertial-fusion power plants. The combination of short wavelength (193 nm) and broad bandwidth capability (10 THz FWHM) would provide the best laser-target interaction for direct-drive implosions. This includes highest hydrodynamic efficiency and resistance to laser plasma instabilities. Simulations conducted by scientists at the Naval Research Laboratory indicate the gains (>100) needed for a laser-fusion power plant can be achieved with less than 1 MJ of laser energy. [1] We will present our designs for a high-energy (30 kJ) high-repetition-rate (10 Hz) ArF beamline and its application to a direct-drive laser-fusion pilot power plant. [2] This work builds on the extensive electron-beam pumped high-energy excimer laser research conducted at the U.S. Naval Research Laboratory. [1] The importance of laser wavelength for driving inertial confinement fusion targets. II. Target design, A. J. Schmitt and S. P. Obenschain, Phys. Plasmas 30, 012702 (2023) [2] Direct Drive Laser Fusion Facility and Pilot Plant, M.W. McGeoch and S.P. Obenschain, J Fusion Energy, 43, 23 (2024).

Acousto-optics consists of launching acoustic waves in a medium to modulate its refractive index and create a tunable optical grating. Here, we will present the theoretical basis of a new scheme to generate acousto-optics in a gas, where the acoustic waves are initiated by the localized absorption (and thus gas heating) of spatially-modulated UV light. Our theoretical and numerical analysis encompasses the physical chemistry of UV absorption by ozone and subsequent chemical reactions, the hydrodynamics of the waves launched by the heat deposition and the diffraction properties of the resulting optical elements. Our model shows good agreement with experiments and suggests future directions for the applications of these optical elements, like for the final optics of inertial fusion energy facilities. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and funded by the LDRD Program at LLNL under Project Tracking Code No. 24-ERD-001.

As Inertial Fusion Energy (IFE) begins to transition from science fiction to becoming a reality, some complex physics need to be solved along the way. Plasma mirrors are an excellent application of material ablation and the optical effects of fluids. These optical elements are used in ultra-fast / high energy Peta-Watt laser systems. Most systems of this nature consist of a pilot beam and an on-target beam. The plasma mirror is a bit of a misnomer as it is typically a piece of fused silica, the lower energy pilot beam passes through the glass following one optical path to a detector. The high energy beam vaporizes the top layer of the glass creating a plasma, this plasma is highly reflective to the beam thereby sending the high energy beam along a second optical path to the target chamber. Modeling requires an understanding of the optical properties of the beam, the material properties of the optical element, the fluid properties of vaporization and then ionization of a material, the movement of the newly formed plasma and the optical effects the newly formed state of matter have on the beam. This research seeks to accurately model these effects with a multi-physics simulation.

The final optics in a laser-driven inertial fusion energy (IFE) plant must withstand intense radiation from the target during continuous operation. Manufacturing optics that are resilient to these harsh conditions is a significant challenge. To tackle this problem, we can create optics in gases. Interfering ultraviolet lasers are used to induce density modulations in an ozone-oxygen mixture, allowing it to act as a volume diffraction grating. These transient optics are intrinsically debris-resistant and feature significantly higher damage thresholds than conventional optics, making them suitable for the extreme environment near inertial confinement fusion (ICF) targets. In this study, we created an ozone grating using the 4th harmonic of an Nd:YAG laser. We demonstrated the efficient diffraction of a probe beam by the structured gas and investigated several key properties of the system. Our experimental findings match a theoretical model for gas gratings and suggest optimal parameters for their effective use. This work was partially supported by NNSA Grant DE-NA0004130, NSF Grant PHY-2308641, and the Lawrence Livermore National Laboratory LDRD program (24-ERD-001).

High-energy laser systems envisioned as future IFE laser drivers will use hundreds to thousands of 10 cm (and above) aperture optical components for amplifying, filtering, carrying, sometimes compressing and/or frequency-converting, and focusing laser beams. These optical components will need to combine low losses with high wavefront quality and high damage resistance over millions of shots. Current ICF laser drivers and UHI laser systems have taken advantage of diffraction gratings either in transmission or in reflection bringing the technology to the required performance. We will show the strong potential of silica-based metasurfaces for manipulating high-energy laser beams and will outline some potential applications of these new structures for future IFE laser drivers.

Future inertial fusion energy plants depend on the successful development of the “final turning mirror” which must exhibit high-performance and survivability under multi-giga shot laser irradiation while being directly exposed to the byproducts of the fusion reaction. Here we investigate the potential of a paradigm shifting approach: the use of gallium alloy liquid metal mirrors. These alloys are liquid near room temperature, exhibit reflectance similar to aluminum, and are able to self-heal. A series of characterization and damage testing experiments were conducted, ultimately indicating favorable performance under exposure to 355 nm, 6 ns laser pulses including testing in a vacuum environment. Laser damage in air is associated with the formation of gallium oxide which is mitigated in a vacuum environment. Our results highlight the potential of liquid metal gallium alloys to serve as robust and long-lasting turning mirrors in future power plants.

Lithium Borate (LBO) crystals have become essential for frequency conversion in the laser industry, boasting one of the largest commercial markets among non-linear crystals. There is a need in a growth method producing large boules of high-quality material at a competitive price. Traditional growth methods have posed challenges such as lengthy growth times of several months per boule and issues with crystal quality including flux inclusions, striations. We have developed a novel rapid growth process for large LBO boules suitable for mass production. Building upon the Top-Seeded Solution Growth (TSSG) method, our process achieves unparalleled growth rates, exceeding those reported in literature by 10 times. We have demonstrated growth rates up to 10 mm/day, reducing the growth cycle for a typical 2-3 kg LBO boule from several months to just a couple of weeks. Crucially, our accelerated growth conditions have not compromised crystal quality. As-grown boules exhibit superior morphology and higher optical quality compared to conventionally grown crystals. They are entirely free from striations and inclusions also demonstrating record low optical absorption of ~ 0.5 ppm/cm at 1064 nm.

UV generation using Lithium Triborate (LBO) crystals with robust broadband anti-reflection (AR) surface structuring is required for Inertial Fusion Energy (IFE). Unique challenges and discoveries from recent efforts to apply sub-wavelength structuring on optical surfaces as a replacement for thin films, especially in the ultraviolet (UV), are explored. Our coupling of crystal growth, fabrication, AR surface development, and system integration to solve all the practical challenges, will bring ARSS on LBOs to public and private markets sooner.

Since the groundbreaking achievement of ignition and self-sustaining fuel burn at the U.S. National Ignition Facility (NIF), the field of fusion, specifically laser inertial fusion energy (IFE), has rapidly accelerated and transformed. Numerous countries are investing more heavily or initiating new fusion programs, with significant collaborative efforts from international research institutions and the private sector accelerating the path to practical fusion energy. The implications for the photonics market include an increased demand for lasers, optics, optical materials, diagnostics, and other key technologies, creating new opportunities for photonics companies and shifting market dynamics. Future challenges and strategies for achieving higher energy yields and commercial viability are outlined, emphasizing the critical role of photonics in enabling the next generation of fusion energy solutions.

The interaction of light and matter can create bonding structural and morphological changes in nano/micro-scale from the surfaces of diverse materials, sometimes even deep within them. This feature has been utilized in laser processing to produce new value for both science and industry. Recent advances in high-power, ultrashort pulsed laser and fast beam delivery technologies are rapidly expanding the possibilities of laser processing. At the same time, the number of parameters to be controlled has become enormous, which is why we have introduced Data Science. In this talk, we will discuss new data-driven laser processing utilizing high-speed data acquisition and AI data optimization for higher throughput and quality. We also aim for this technology to contribute to sustainable manufacturing and society in the future.

Optical frequency combs have revolutionized time and frequency metrology by providing rulers in frequency space that measure large optical frequency differences and/or straightforwardly link microwave and optical frequencies. One of the most successful uses of frequency combs beyond their original purpose has been dual-comb interferometry. An interferometer can be formed using two frequency combs of slightly different line spacing. Dual-comb interferometers without moving parts have no geometric limitations to resolution, therefore miniaturized devices using integrated optics can be envisioned. Dual-comb interferometers outperform state-of-the-art devices in an increasing number of fields including spectroscopy and holography, offering unique features such as direct frequency measurements, accuracy, precision, and speed.

Today, approximately 12,000 satellites orbit Earth. By 2030, estimates show numbers above 60,000. Today, we service spacecraft when absolutely necessary. By 2030’s, in-space services will be routine; refueling, repair, relocation, assembly, and manufacturing. Advances are underway to realizing this future, enabling a sustainable version will require photonics technologies.

The recent demonstration of ignition and target gain more than 1 in inertial confinement fusion (ICF) experiments at the National Ignition Facility has spurred great interest in both public and private sectors of inertial fusion energy (IFE). Although such remarkable progress in ICF provides a critical step in basic ignition physic validation, a substantial amount of work remains to demonstrate not only that implosion physics can meet the high-gain requirements for IFE (when a ratio of neutron yield to incident laser energy ~100), but also that target and laser technology can be developed to efficiently drive these implosions. The high-gain requirements also necessitates a high laser–energy coupling fraction to the target, which implies that various coupling loss mechanisms due to laser–plasma instabilities (LPIs) are mitigated. Recent advances in laser technology have demonstrated the promise of broadband lasers for LPI mitigation. This talk will discuss requirements for laser drivers that are consistent with current understanding of implosion physics and mass production target technology.

The architecture and technology of the master oscillator power amplifier (MOPA) that comprise a beamline of the multi-beam fusion lasers such as NIF that have recently demonstrated fusion scientific gain greater than one, that have evolved over the more than 50 years of research in Inertial Confinement fusion (ICF). The majority of ICF lasers worldwide such as NIF, the Omega laser at the University of Rochester, Laser Megajoule in France and SGIII in China are frequency tripled Nd doped phosphate glass systems. This presentation will summarize the advances that have been made in propagation including non-linear effects, multi-pass architectures and precision pulse shaping that has led to the recent achievement on NIF. While the focus of the presentation will be solid state lasers, the architecture and system strategies for excimer lasers that are also viable candidates for future IFE systems will also be discussed.

The design and construction of the National Ignition Facility (NIF) laser system rests on more than four decades of optical materials R&D and advanced manufacturing development. This approach and the associated wealth of information provides a template for assessing different Inertial Fusion Energy (IFE) laser-driver designs. The historical development of the NIF gain media (Nd-doped phosphate laser glass) is used to illustrate common challenges that IFE will need to be overcome to select and produce gain material at the scale and volume needed.

Review the history of the development of the growth of large crystals of KDP and KD*P over the last 50 years to enable large aperture Pockels cells and frequency conversion optics to support lasers for inertial confinement fusion. Review current state of the art, and what will be required to continue advances.

In the mid to late 1970s there was considerable debate as to which laser technology should be pursued—glass lasers (1-µm wavelength) or CO2 lasers (10 µm). Based on target physics considerations, theorists were advocating for shorter wavelengths. The physics understanding was confirmed by exciting results from the group at Ecole Polytechnique, who observed close to 100% target absorption with just a few joules of fourth-harmonic energy. These results motivated the leadership at LLE to plan similar experiments at the third harmonic with a few more joules. This presentation covers a small time period from 1979 to 1980 during which highly efficient third-harmonic generation (THG) became understood theoretically and demonstrated experimentally, leading to the worldwide adoption of THG with glass lasers for fusion research. This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number DE-NA0004144.

For high energy chirped pulse amplification laser systems, the laser damage of optical components after the compression stage, in particular diffraction gratings and mirrors for beam transport, remains one of the main limitations to the maximal output energy of lasers. We will provide an overview of historical pulse compression gratings for ultrafast, recent advancements, and challenges going forward. Acknowledgements: This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.

The front end of the National Ignition Facility (NIF) known as the Injection Laser System (ILS) has a 30-year history of development and phased upgrades. It continues to be modernized in support of enhanced NIF performance, reliability, and sustainability. This talk will provide an overview of the ILS subsystems and their design features developed to meet demanding specification challenges. Critical upgrades will be reviewed including the High-Fidelity Pulse Shaping system, wavelength/bandwidth control, FM-AM measurement/mitigation, and the first-generation Programmable Spatial Shaping system. Future upgrades planned or in progress will be discussed including the second-generation Programmable Spatial Shaping system, Diode-Pumped Multi-Pass Amplifier, and prospects for higher speed pulse shaping and bandwidth control.

Electra is a repetitively pulsed, electron beam pumped excimer laser at the Naval Research Laboratory that is developing the technologies that can meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. The technologies developed on Electra are designed to be directly scalable to a full size fusion power plant beam line. Recently, the electron beam diodes of the Electra facility have been modified to a reduced aperture to increase the power deposition rate for efficient argon fluoride at 193 nm operations. Electra has achieved over 700 J in KrF (248 nm) operation per shot and 200 J per shot in ArF operation. Gain measurements at 193 nm indicate higher wall-plug efficiency for ArF (10%) than KrF (7%). The native emission of argon fluoride bandwidth exceeds 10 THz which is broader than the krypton fluoride bandwidth.

The talk covers the development of inertial fusion energy (IFE) drivers at Lawrence Livermore National Laboratory from the first system specifically designed to meet requirements of IFE drivers. The Mercury Laser Project goals were to develop key technologies within an architecture that could be scalable to multi-kilojoule applications including 10Hz repetition rate with high efficiency and reliability. In 2006 the Mercury system achieved the significant milestone of operation continuously for several hours at 60J and 10Hz. Armed with this knowledge along with technological improvements, a full-scale beam line was conceptually designed to meet powerplant requirements. This system used modest extensions of existing laser technology to ensure near term feasibility and showed predicted performance that meets or exceeds the baseline design point: 2.2-MJ pulse energy produced by 384-beamlines at 16-Hz, with 18% wall-plug efficiency. High reliability and maintainability are achieved by implementing compact line-replaceable laser units to maintain system availability.

The simulation of power laser chains using dedicated models and codes in the nanosecond range (LMJ, NIF) or sub-picosecond range (PETAL, APOLLON) makes it possible to predict the performance of these laser facilities from commissioning to the energy ramp-up phases, but also to simulate new laser architectures. We present the various applications of the models and codes used to simulate power laser chains.

We report on the development of a high repetition rate Nd:glass laser head to be integrated in kJ lasers, of particular interest for inertial confinement fusion research. The interest of this module is its cooling architecture, giving the capacity to operate at 0,1Hz repetition rate under flashlamp pumping, and in the future at 10Hz under diode-pumping.

In the context of new research to develop a laser driver for Inertial Fusion Energy, efforts are underway to overcome thermal limitations and increase the repetition rate of high-power laser facilities. Thus, with the same standard of laser performance, the development of high-thermal conductivity solid-state laser media at 1053 nm has become crucial. Bonding an optically inactive heatsink crystal to the gain medium has proven to be efficient to reduce the heat generated during pumping. Our past work highlighted material and geometrical considerations for thermal effects reduction in a diode-side-pumped bonded laser rod composed of a single gain layer. We have developed a numerical model to perform a parametric study discussed thereafter. Here, we suggest an optimization by examining the thickness and the number of gain layers within the bonded geometry. Both material combination and gain medium distribution of the samples are discussed using simulations and experiments.

There are many studies on laser-induced damage threshold of laser optics that will be used in Inertial Fusion Energy plants, however, little is known about how neutron irradiation will affect these properties. In this study, we perform neutron irradiation experiments on fused silica optics and study how the neutron dosage affects their optical properties and damage thresholds. Neutron production via thick target deuteron breakup has been carried out at the Lawrence Berkeley National Lab’s 88-Inch cyclotron and used in the irradiation of REBCO semiconductor tape. The altered properties of the REBCO strips confirmed a varying flux of neutron dosage and provided a model for how neutron irradiation of fused silica will be carried out. Using an array of optical characterization methods and neutron irradiation at the cyclotron, we show how optical performance is altered by neutron dosage in the aim that this information can be used toward damage mitigation of optics in IFE plants.

Frequency conversion of optical pulses produced by solid-state lasers and parametric amplification of broadband optical pulses are made possible at high energy by the manufacturing of high-quality, large-aperture nonlinear crystals. Phase matching of the interacting waves is required for efficient interactions, and in the common case of critical phase matching, this requires precise control of the interaction geometry and crystal alignment. A diagnostic suitable for accurately resolving the transverse variations in phase-matching conditions has been developed for large-scale crystals. Results pertaining to deuterated dihydrogen phosphate (DKDP) and other crystals will be presented.

Direct-drive laser-fusion targets can often include thin films deposited on the plastic ablator shell to provide various functions. An experimental system involving synchronized femtosecond and picosecond lasers of different wavelengths is employed to initiate and characterize dynamics of coated and uncoated polystyrene planar targets irradiated by conditions similar to a “picket” prepulse from a direct-drive pulse shape. Ultrafast imaging of the resulting blowoff plasma expansion and shock-wave propagation is used to compare the impact of different coating configurations. The subsequent damage crater morphologies are also analyzed as evidence of the dynamics of the solid-to-liquid interface expansion. These results may help future efforts to develop laser drivers and target designs that make laser fusion economically viable.

Laser technologies have played a pivotal role in advancing science. Ultrafast lasers focused to ultra-high intensities (> 10^21 W/cm^2) make it possible to generate high density plasmas at which produce intense sources of x-rays rays and drive fusion reactions, and to accelerate electrons to GeV energies in a few tens of centimeters . Simultaneous advances in laser and target technologies were key to demonstrate laser driven fusion with net energy gain at the Lawrence Livermore National Laboratory National Ignition Facility in Dec. 2022. In large part, advances in laser technologies rely on advances in materials. In this talk I will describe basic laser architectures that are being developed as drivers for laser fusion. In particular I will emphasize the role of dielectric coatings which are ubiquitous in high power laser systems and will layout the opportunities that exist to advance these materials to the next level. I will provide a glimpse of parallel efforts in materials’ studies which are fundamental to support and advance laser fusion. Work supported by the U.S. Department of Energy, Fusion Energy Sciences, under Award No. DE-SC0024882: IFE-STAR.

Optical coatings used in transport optics should withstand exposure of the order of ten years and 10^10 pulses. In such long operation, it might be impossible to avoid contamination and optical coating material laser damage. This necessitates the development of materials that not only provide high-damage-initiation threshold and long-term stability of damage-initiation sites, but also avoid damage growth. In this work, we explore two high-index coating materials incorporated in high-reflector multilayer dielectric mirror coatings fabricated with different deposition methods. Under nanosecond pulses at a 351-nm wavelength, we found a systematic difference in the damage-growth thresholds. This indicates that the difference arises from the material properties after exposure to laser damage and the ensuing interaction (such as absorptivity) with the laser pulses. The results highlight that the choice of coating material is critical for reliable long-term operation of ultraviolet beam-transport optics.

We present an investigation of damage of multilayer mirror at the high intensity and wavelength around 920 nm and 1064 nm. The optics is produced by MF and RF magnetron- sputtering methods. We compare MF and RF magnetron sputtering on HfO2 and SiO2. As result of our research, we were able to produce mirror with HfO2/SiO2 with RF and MF magnetron sputtering. We have tried different technique, and different designs. The best results for 20fs @ 920 nm are 0.9 J/cm2 for quarter wave stack.