Christopher J. Stolz

Battelle Memorial Institute · Lawrence Livermore National Laboratory

The design and status of the diode-pumped 10 Hz, 150 J, 150 fs, 1 PW laser system under development for the Matter in Extreme Conditions Upgrade (MEC-U) project will be presented.

The nodular defect shape and the laser incidence angle have a dramatic impact on the spatial distribution of light intensification within the nodule as well as how the laser light is drained from the defect. Nodular defect geometries unique to ion beam sputtering, ion-assisted deposition, and electron-beam (e-beam) deposition, respectively, are mod...

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a...

Nodular defect shape and laser incidence angle has a dramatic impact on the spatial distribution of light intensification as well as how the laser light is drained from the defect.

Laser-induced damage in coating materials with a high index of refraction, such as hafnia, limits the performance of high power and high energy laser systems. Understanding the underlying physics responsible for laser damage holds the key for developing damage-resistant optical films. Previous studies have reported a substantial difference in laser...

Laser-induced damage threshold of transparent conductors, such as Indium Tin Oxide (ITO), is limited by their high optical absorption due to free carriers. However, the effective absorption of a transparent conductor thin film can be reduced by an order of magnitude, without changing the electrical characteristics of the film, when placed in a low...

High intensity and high energy laser facilities place increasing demands on optical components, requiring large surface area optics with exacting specifications. Petawatt lasers are high energy, short-pulse laser systems generally based on chirped-pulse amplification, where an initial low energy short pulse is stretched, amplified, and then recompr...

Electric field enhancement due to nodular defects within quarter-wave optical thickness multilayer mirrors is impacted by the inclusion diameter, inclusion depth, inclusion composition, nodular shape, multilayer angular bandwidth, multilayer coating materials, number of layers, angle of incidence, and polarization. In this modeling study, the elect...

Hafnia is a high refractive index material used in the manufacturing of dielectric coatings for next generation lasers. The formation of defects during deposition is the major barrier to realizing high laser-damage resistant coatings for future high energy density laser applications. Understanding the precursors responsible for laser-induced damage...

Optimum material selection for high fluence interference coatings is wavelength dependent (increased bandgap with decreased wavelength) whereas the deposition process depends on pulse length (increased densification with decreased pulse length).

The thin film damage competition series at the Boulder Damage Symposium provides an opportunity to observe general trends in laser damage behavior between different coating types (high reflector, antireflector, polarizer, and Fabry-Perot filter), wavelength ranges (193 to 1064 nm), and pulse length ranges (40 fs to 18 ns). Additionally, the impact...

Large laser systems that deliver optical pulses with peak powers exceeding one Petawatt (PW) have been constructed at dozens of research facilities worldwide and have fostered research in High-Energy-Density (HED) Science, High-Field and nonlinear physics [1]. Furthermore, the high intensities exceeding 10¹⁸W/cm² allow for efficiently driving secon...

The HAPLS laser system has been commissioned to its first integrated performance milestone, delivering laser pulses with 16J sub-30fs duration at a 3⅓Hz repetition rate. This first all-diode-pumped petawatt-class laser offers the average powers required for secondary source applications.

Lawrence Livermore National Laboratory (LLNL) and Colorado State University (CSU) have co-developed a planarization process to smooth nodular defects. This process consists of individually depositing then etching tens of nanometers of SiO2 with a ratio of 2:1, respectively. Previous work shows incorporating the angular dependent ion surface etching...

The response of a potential candidate protective capping layer (SiO2 or Al2O3) to laser exposure of 1ω (1053 nm) to high-reflector silica-hafnia multilayer coatings in the presence of variously shaped Ti particles is investigated by combining laser damage testing and numerical modeling. Each sample is exposed to a single oblique angle (45 deg) lase...

We describe a damage testing system and its use in investigating laser-induced optical damage initiated by both intrinsic and extrinsic precursors on multilayer dielectric coatings suitable for use in high-energy, large-aperture petawatt-class lasers. We employ small-area damage test methodologies to evaluate the intrinsic damage resistance of vari...

The possibility of imploding small capsules to produce mini-fusion explosions was explored soon after the first thermonuclear explosions in the early 1950s. Various technologies have been pursued to achieve the focused power and energy required for laboratory-scale fusion. Each technology has its own challenges. For example, electron and ion beams...

The laser resistance of a transparent conductive layer such as ITO is increased by placement into the low electric field region of a Fabry-Perot multilayer filter.

Investigation of large-aperture laser damage at oblique incidence shows that the damage induced by laser contaminants on HR multilayer coatings depends on the thickness and thermal-mechanical properties of the protective capping materials

We report an investigation on the response to laser exposure of a protective capping layer of 1ω (1053 nm) high-reflector mirror coatings, in the presence of differently shaped Ti particles. We consider two candidate capping layer materials, namely SiO2 and Al2O3. They are coated over multiple silica-hafnia multilayer coatings. Each sample is expos...

We investigate the optical damage performance of multi-layer dielectric (MLD) coatings suitable for use in high energy, large-aperture petawatt-class lasers. We employ small-area damage test methodologies to evaluate the damage resistance of various coatings as a function of deposition methods and coating materials under simulated use conditions. I...

Broadband low dispersion mirrors are fluence-limiting and pulse-shape-limiting components in short pulse lasers. To better understand the current technology state of broadband low dispersion mirrors, a laser damage competition was held at the 2015 Laser Damage Conference. Participants were asked to submit mirrors that met a minimum reflection of 99...

High dielectric constant multilayer coatings are commonly used on high-reflection mirrors for high-peak-power laser systems because of their high laser-damage resistance. However, surface contaminants often lead to damage upon laser exposure, thus limiting the mirror’s lifetime and performance. One plausible approach to improve the overall mirror r...

Multilayer interference optical mirror coatings are traditionally fluence-limited by nodular inclusions. Planarization of these defects modifies the geometrically and interference-induced light intensification to increase the laser resistance of mirror coatings. Previous studies using engineered defects on the substrate or buried in the middle of t...

We present techniques for measuring the damage performance of a variety of optical components with ps laser pulses, introduce a novel beam diagnostic technique, and explore the sensitivity of damage resistance to laser spot size for the case of high-reflectivity, multilayer dielectric (MLD) mirrors.

Planarizing or smoothing over nodular defects in multilayer mirrors can be accomplished by a discrete deposit-and-etch process that exploits the angle-dependent etching rate of optical materials. Typically, nodular defects limit the fluence on mirrors irradiated at 1064 nm with 10 ns pulse lengths due to geometrically- and interference-induced ligh...

Narrow-bandwidth Fabry-Perot transmission filters are used in telecommunications, fiber lasers1, and for diode pumped alkali lasers (DPAL)2. Because of their interference properties, extremely high standing-wave electric fields occur at peak transmission. For this study, the filters met a minimum transmission of 90% and were spectrally centered wit...

Substrate defect planarization has been shown to increase the laser resistance of 1053 nm mirror coatings to greater than 100 J / cm 2 , an increase of 20-fold, when tested with 10 ns laser pulses. Substrate surface particles that are overcoated with optical interference mirror coatings become nodular defects, which behave as microlenses intensifyi...

Multilayer mirrors are fluence-limited by nodular defects. Such defects originate from the deposition source, inadequate cleaning, transport, pump down, heating, shedding from rotating hardware, etc. These overcoated inclusions behave as micro-lenses resulting in light intensification within the multilayer structure. To minimize the impact of these...

Anti-reflecting (AR) surface relief nano-textures have been integrated with fused silica diffraction gratings to demonstrate the potential of stable diffractive 3ω beam samplers with increased energy to target at the National Ignition Facility (NIF). TelAztec’s AR texturing process was used to etch Random-type AR (RAR) microstructures in sub-scale...

Planarizing nodular defects with angle-dependent ion etching and uniform deposition increased the 1064 nm laser resistance of optical interference mirror coatings by greater than 20×.

The velocity of particles ejected from electron beam evaporated source materials is measured for both hafnia and silica coatings.

Optical instruments and laser systems are often fluence-limited by multilayer thin films deposited on the optical surfaces. When comparing publications within the laser damage literature, there can be confusing and conflicting laser damage results. This is due to differences in testing protocols between research groups studying very different appli...

Brewster angle plate polarizing beamsplitters play a critical role in splitting and combining beams within high power laser systems. A laser damage competition of polarizer beamsplitter coatings creates the opportunity to survey the current laser resistance these coatings within private industry, governmental institutions, and universities by a dir...

The National Ignition Facility (NIF), the world's largest and most energetic laser system, is now operational at Lawrence Livermore National Laboratory. The NIF will enable exploration of scientific problems in national strategic security, basic science and fusion energy. One of the early NIF goals centres on achieving laboratory-scale thermonuclea...

The heating dynamics of CO{sub 2}-laser heated micron-sized particles were determined for temperatures <3500 K measured using infrared imaging. A coupled mass and energy conservation model is derived to predict single particle temperatures and sizes, which were compared with data from particles deposited on non-absorbing substrates to assess the re...

We present the results of performance modeling of diode-pumped solid state laser beamlines designed for use in Laser Inertial Fusion Energy (LIFE) power plants. Our modeling quantifies the efficiency increases that can be obtained by increasing peak diode power and reducing pump-pulse duration, to reduce decay losses. At the same efficiency, beamli...

Excimer lasers are a critical technology for the $400 billion annual market of manufactured integrated circuits. Other uses of excimer lasers include medical applications such as laser eye surgery and micro-machining industrial applications. Ultraviolet laser mirrors are used for beam steering, therefore high reliability is desired for such commerc...

Growing laser damage sites on multilayer high-reflector coatings can limit mirror performance. One of the strategies to improve laser damage resistance is to replace the growing damage sites with predesigned benign mitigation structures. By mitigating the weakest site on the optic, the large-aperture mirror will have a laser resistance comparable t...

Femtosecond laser machining is used to create mitigation pits to stabilize nanosecond laser-induced damage in multilayer dielectric mirror coatings on BK7 substrates. In this paper, we characterize features and the artifacts associated with mitigation pits and further investigate the impact of pulse energy and pulse duration on pit quality and dama...

This Applied Optics feature issue is dedicated to the eleventh topical meeting on Optical Interference Coatings held on 6-11 June 2010 in Tucson, Arizona, USA. This topical conference is held in a three year rotation with conferences in Europe and Asia and is a premier opportunity to discuss advances in research and development within the field of...

A system of customized spatial light modulators has been installed onto the front end of the laser system at the National Ignition Facility (NIF). The devices are capable of shaping the beam profile at a low-fluence relay plane upstream of the amplifier chain. Their primary function is to introduce "blocker" obscurations at programmed locations wit...

Substrate scratches can limit the laser resistance of multilayer mirror coatings on high-peak-power laser systems. To date, the mechanism by which substrate surface defects affect the performance of coating layers under high power laser irradiation is not well defined. In this study, we combine experimental approaches with theoretical simulations t...

UV antireflection coatings are a challenging coating for high power laser applications as exemplified by the use of uncoated Brewster's windows in laser cavities. In order to understand the current laser resistance of UV AR coatings in the industrial and university sectors, a double blind laser damage competition was performed. The coatings have a...

Customized spatial light modulators have been designed and fabricated for use as precision beam shaping devices in fusion class laser systems. By inserting this device in a low-fluence relay plane upstream of the amplifier chain, "blocker" obscurations can be programmed into the beam profile to shadow small isolated flaws on downstream optical comp...

We are converting a quad of NIF beamlines into eight, short-pulse (1–50 ps), petawatt-class beams for advanced radiography and fast ignition experiments. This paper describes progress toward completing this project.

IntroductionProduction of Nd:phosphate Laser Glass and KDP Frequency-Conversion CrystalsYb : S-FAP CrystalsYCOB CrystalsAdvanced Material Concepts for Power-Plant DesignsSummaryReferences

Femtosecond laser machining is optimized to stabilize nanosecond induced-laser damage and to double the power handling capability of multilayer mirror coatings. Higher per-pulse energy of the machining laser degrades the feature edge quality.

Computer simulations using finite difference time domain of conical pits show that electric field intensification within multilayer high reflector coatings is minimized when the incident and cone angle are matched.

Removal of laser-induced damage sites provides a possible mitigation pathway to improve damage resistance of coated multilayer dielectric mirrors. In an effort to determine the optimal mitigation geometry which will not generate secondary damage precursors, the electric field distribution within the coating layers for a variety of mitigation shapes...

Replacing growing damage sites with benign, laser damage resistant features in multilayer dielectric films may enable large mirrors to be operated at significantly higher fluences. Laser damage resistant features have been created in high reflecting coatings on glass substrates using femtosecond laser machining. These prototype features have been d...

In order to determine the current status of thin film laser resistance within the private, academic, and government sectors, a damage competition was started at the 2008 Boulder Damage Symposium. This damage competition allows a direct comparison of the current state of the art of high laser resistance coatings since they are tested using the same...

A laser damage competition was held at the 2008 Boulder Damage Symposium in order to determine the current status of thin film laser resistance within the private, academic, and government sectors. This damage competition allows a direct comparison of the current state-of-the-art of high laser resistance coatings since they are all tested using the...

The 1600 mirrors required for the National Ignition Facility (NIF) are now coated with the last optics currently being installed. The combined surface area of the NIF mirrors is almost 450 square meters, roughly 3.4 times greater than the surface area of the two Keck primary mirrors. Additionally, the power handling specification of NIF mirrors is...

Electric-field modeling provides insight into the laser damage resistance potential of nodular defects. The laser-induced damage threshold for high-reflector coatings is 13x lower at the third harmonic (351 nm) than at the first harmonic (1053 nm) wavelength. Linear and multiphoton absorption increases with decreasing wavelength, leading to a lower...

The Optical Society of America's Topical Meeting on Optical Interference Coatings convenes every three years to survey and capture advancements in the broad area of optical coatings. This meeting serves as a focal point for global technical interchange in the field of optical interference coatings. It includes papers on research, development, and a...

The National Ignition Facility (NIF), a 192-beam fusion laser, is presently under construction at the Lawrence Livermore National Laboratory with an expected completion in 2008. The facility contains 7,456 meter-scale optics for amplification, beam steering, vacuum barriers, focusing, polarization rotation, and wavelength conversion. A multiphase p...

Previous work concluded that plasma scalds on laser-conditioned multilayer dielectric mirror coatings are a stable, benign damage morphology. Recent large-aperture measurements indicate that plasma scalds may lead to fratricide of down-stream optics by increasing beam contrast. This paper describes the results of measurements performed to examine t...

This volume contains papers presented at the 35th Annual Symposium on Optical Materials for High-Power Lasers, held at the National Institute of Standards and Technology in Boulder, Colorado, 22-24 September 2003. The symposium was attended by 125 participants from China, India, Russia, France, Germany, Japan, the United States, and the United King...

The Mercury laser uses ytterbium-doped strontium fluorapatite (Yb:S-FAP) crystals as the gain medium with a nominal clear aperture of 4 x 6 cm. Recent damage test data have indicated the existence of bulk precursors in Yb:S-FAP that initiate damage starting at approximately 10 J/cm2 at 9 ns under 1064 nm irradiation. In this paper, we report on pre...

We present the status of plans to commission a short-pulse, quad of beams on the National Ignition Facility (NIF), capable of generating > 10 kJ of energy in 10 ps. These beams will initially provide an advanced radiographic capability (ARC) to generate brilliant, x-ray back-lighters for diagnosing fuel density and symmetry during ignition experime...

We report on the operation of the Mercury laser with fourteen 4 $\times$ 6 cm$^{2}$ Yb:S-FAP amplifier slabs pumped by eight 100 kW peak power diode arrays. The system was continuously run at 55 J and 10 Hz for several hours, (2$\times$10$^{5}$ cumulative shots) with over 80% of the energy in a 6 times diffraction limited spot at 1.047 $\mu $m. Imp...

The initiation of laser damage within optical coatings can be better understood by electric-field modeling of coating defects. The result of this modeling shows that light intensification as large as 24x can occur owing to these coating defects. Light intensification tends to increase with inclusion diameter. Defects irradiated over a range of inci...

The Mercury laser operated continuously for several hours at 55J and 10Hz with fourteen 4x6cm2 Yb:S-FAP amplifier slabs pumped by eight 100kW diode arrays. Average power frequency conversion employing YCOB yielded 50% conversion efficiency.

This volume contains papers presented at the 37th Annual Symposium on Optical Materials for High-Power Lasers that was held at the National Institute of Standards and Technology in Boulder, Colorado, 19-21 September 2005. The symposium was cosponsored by Lawrence Livermore National Laboratory (USA), and the Pacific Northwest National Laboratory (US...

In operational laser systems, it is often difficult to keep optical components completely free of foreign material. We have investigated the performance of high damage threshold 1.053 mum high reflectors in the presence of surface contaminants. We have looked at the impact of stainless steel, aluminum, Azurlite(R), dust, cotton fibers and polyester...

The laser damage test for qualifying a coating run of anti-reflection coated optics consists of scanning a pulsed 1064 nm laser to illuminate approximately 2400 sites over a 1 cm x 1 cm area on a test sample. Scans are repeated at 3 J/cm2 increments until the fluence specification for the optic is reached. In the past, initiation of 1 or more damag...

Antireflection (AR) coatings typically damage at the interface between the substrate and coating. Therefore the substrate finishing technology can have an impact on the laser resistance of the coating. For this study, AR coatings were deposited on Yb:S-FAP [Yb3+:Sr5(PO4)3F] crystals that received a final polish by both conventional pitch lap finish...

Laser resistant coatings are needed for beam steering (mirrors), pulse switching (polarizers), and high transport efficiency on environmental barriers (windows / lenses) on large laser systems. A range of defects limit the exposure fluence of these coatings. By understanding the origin and damage mechanisms for these defects, the deposition process...

The Mercury laser project is part of a national inertial fusion energy program in which four driver technologies are being considered including solid-state lasers, krypton fluoride gas lasers, Z-Pinch and heavy ions. Mercury's operational goals of 100 J, 10 Hz, 10% efficiency in a 5 times diffraction limited spot will demonstrate the critical techn...

Operation of the Mercury laser with two amplifiers has yielded 30 Joules at 1 Hz and 12 Joules at 10 Hz with over 8x10⁴ shots on the system. Static distortions in the Yb:S-FAP amplifiers were corrected by a magneto-rheological finishing technique.