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Compound parabolic concentrator (CPC) targets are utilized at the National Ignition Facility Advanced Radiographic Capability (NIF-ARC) laser to enhance the acceleration of electrons and production of high energy photons, for laser durations of 10 ps and energies up to 2.4 kJ. A large enhancement of mean electron energy (>2 ×) and photon brightness (>10×) is found with CPC targets compared to flat targets. Using multiple diagnostic techniques at different spatial locations and scaling by gold activation spatial data, photon spectra are characterized for [Formula: see text] MeV. Beam width and pointing variations are given. The efficient production of MeV photons at [Formula: see text] W/cm2 with CPCs is observed, with doses of >10 rad in air at 1 m for [Formula: see text] MeV; these exceed those previously reported with laser-driven sources. Using this source, sub-mm resolution radiographs are generated through large areal density radiograph objects. These results are promising for the development of bright MeV x-ray and particle sources on Petawatt class laser systems.

The advanced radiographic capability (ARC) laser system, part of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, is a short-pulse laser capability integrated into the NIF. The ARC is designed to provide adjustable pulse lengths of ∼ 1 − 38 p s in four independent beamlets, each with energies up to 1 kJ (depending on pulse duration). A detailed model of the ARC lasers has been developed that predicts the time- and space-resolved focal spots on target for each shot. Measurements made to characterize static and dynamic wavefront characteristics of the ARC are important inputs to the code. Modeling has been validated with measurements of the time-integrated focal spot at the target chamber center (TCC) at low power, and the space-integrated pulse duration at high power, using currently available diagnostics. These simulations indicate that each of the four ARC beamlets achieves a peak intensity on target of up to a few 10 18 W / c m 2 .

The implosion efficiency in inertial confinement fusion depends on the degree of stagnated fuel compression, density uniformity, sphericity, and minimum residual kinetic energy achieved. Compton scattering-mediated 50-200 keV x-ray radiographs of indirect-drive cryogenic implosions at the National Ignition Facility capture the dynamic evolution of the fuel as it goes through peak compression, revealing low-mode 3D nonuniformities and thicker fuel with lower peak density than simulated. By differencing two radiographs taken at different times during the same implosion, we also measure the residual kinetic energy not transferred to the hot spot and quantify its impact on the implosion performance.

Relativistic electron temperatures were measured from kilojoule, subrelativistic laser-plasma interactions. Experiments show an order of magnitude higher temperatures than expected from a ponderomotive scaling, where temperatures of up to 2.2 MeV were generated using an intensity of 1×10^{18}W/cm^{2}. Two-dimensional particle-in-cell simulations suggest that electrons gain superponderomotive energies by stochastic acceleration as they sample a large area of rapidly changing laser phase. We demonstrate that such high temperatures are possible from subrelativistic intensities by using lasers with long pulse durations and large spatial scales.

ARC is a kilojoule petawatt-class laser system which generates high energy x-ray and particle sources for radiography of experiments on the National Ignition Facility. We present recent progress on laser performance measurements and system modeling.

New short-pulse kilojoule, Petawatt-class lasers, which have recently come online and are coupled to large-scale, many-beam long-pulse facilities, undoubtedly serve as very exciting tools to capture transformational science opportunities in high energy density physics. These short-pulse lasers also happen to reside in a unique laser regime: very high-energy (kilojoule), relatively long (multi-picosecond) pulse-lengths, and large (10s of micron) focal spots, where their use in driving energetic particle beams is largely unexplored. Proton acceleration via Target Normal Sheath Acceleration (TNSA) using the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility in the Lawrence Livermore National Laboratory is demonstrated for the first time, and protons of up to 18 MeV are measured using laser irradiation of >1 ps pulse-lengths and quasi-relativistic (∼1018 W/cm2) intensities. This is indicative of a super-ponderomotive electron acceleration mechanism that sustains acceleration over long (multi-picosecond) time-scales and allows for proton energies to be achieved far beyond what the well-established scalings of proton acceleration via TNSA would predict at these modest intensities. Furthermore, the characteristics of the ARC laser (large ∼100 μm diameter focal spot, flat spatial profile, multi-picosecond, relatively low prepulse) provide acceleration conditions that allow for the investigation of 1D-like particle acceleration. A high flux ∼ 50 J of laser-accelerated protons is experimentally demonstrated. A new capability in multi-picosecond particle-in-cell simulation is applied to model the data, corroborating the high proton energies and elucidating the physics of multi-picosecond particle acceleration.

The Crystal Backlighter Imager (CBI) is a quasi-monochromatic, near-normal incidence, spherically bent crystal imager developed for the National Ignition Facility (NIF), which will allow inertial confinement fusion capsule implosions to be radiographed close to stagnation. This is not possible using the standard pinhole-based area-backlighter configuration, as the self-emission from the capsule hotspot overwhelms the backlighter signal in the final stages of the implosion. The CBI mitigates the broadband self-emission from the capsule hot spot by using the extremely narrow bandwidth inherent to near-normal-incidence Bragg diffraction. Implementing a backlighter system based on near-normal reflection in the NIF chamber presents unique challenges, requiring the CBI to adopt novel engineering and operational strategies. The CBI currently operates with an 11.6 keV backlighter, making it the highest energy radiography diagnostic based on spherically bent crystals to date. For a given velocity, Doppler shift is proportional to the emitted photon energy. At 11.6 keV, the ablation velocity of the backlighter plasma results in a Doppler shift that is significant compared to the bandwidth of the instrument and the width of the atomic line, requiring that the shift be measured to high accuracy and the optics aligned accordingly to compensate. Experiments will be presented that used the CBI itself to measure the backlighter Doppler shift to an accuracy of better than 1 eV. These experiments also measured the spatial resolution of CBI radiographs at 7.0 μm, close to theoretical predictions. Finally, results will be presented from an experiment in which the CBI radiographed a capsule implosion driven by a 1 MJ NIF laser pulse, demonstrating a significant (>100) improvement in the backlighter to self-emission ratio compared to the pinhole-based area-backlighter configuration.

The advanced radiographic capability located at the National Ignition Facility (NIF) uses high intensity, short pulse lasers to create bright photon sources for diagnosing high energy density experiments. There are radiographic needs for a multi-frame time-resolved MeV gamma diagnostic for experiments on the NIF with sub-nanosecond resolution. A series of experiments demonstrated measurements of MeV x-ray spectra resolved with a time separation of a few nanoseconds through the use of gas Cherenkov detectors. A two-pulse radiographic experiment found a 30% reduction in > 2.8 MeV photon flux compared to the first frame exposure.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) uses the world’s largest and most energetic laser system to explore High-Energy-Density (HED) physics. Historically, experiments at the NIF could not radiograph an Inertial Confinement Fusion (ICF) experiment at late times due to self-emission from the capsule. The Crystal Backlighter Imager diagnostic (CBI) fielded on NIF in 2017 and has allowed radiography of ICF capsules at late times. This capability is due to the very narrow bandwidth of the imaging system, which eliminates much of the self-emission. X-rays from a backlighter source (driven by NIF beams) pass through the experiment, and the CBI uses a spherically curved crystal to reflect these x-rays at near-normal incidence (Bragg angle close to 90°) onto the detector, resulting in a very narrow bandwidth microscope. The geometry of a near-normal-incidence microscope is challenging to implement at the NIF, since the crystal must be positioned and aligned to high precision on the opposite side of the target relative to the detector. The in-chamber alignment procedure cannot take significantly longer than a simple pinhole imager, since demand for NIF shots is high and a given experiment is allotted a strict time limit. Avoiding any collision between diagnostic hardware and the target is paramount and any instrument that is placed in close proximity to a target must be able to withstand the debris produced by a 2.0 MJ NIF shot. CBI overcomes these challenges by mounting the detector and crystal on a single diagnostic instrument manipulator (DIM). The crystal is mounted on an arm that passes around the target, positioning the crystal on the opposite side of the target to the detector. This allows much of the crystal alignment to be done before the instrument is inserted into the NIF chamber, saving time. The arm that supports the crystal is mechanized so that, during insertion of the CBI, the risk of collision with the target is minimized. The CBI is designed as a robust platform that is capable of maintaining alignment tolerances of

Automated alignment for the National Ignition Facility (NIF) is accomplished using a large-scale parallel control system that directs 192 laser beams along the 300 m optical path. The beams are then focused down to a 50 μ spot in the middle of the target chamber. The entire process is completed in less than 50 min. The alignment system commands 9000 stepping motors for extremely precise adjustment of mirrors and other optics. 41 control loops per beamline perform parallel processing services running on a LINUX cluster to analyze high-resolution images of the beams and their references. This paper describes the status the NIF automatic alignment system and the challenges encountered as NIF development has transitioned from building the laser, to becoming a research project supporting a 24 h, 7 days/week laser facility. NIF is now a continuously operated system where performance monitoring is increasingly more critical for operation, maintenance, and commissioning tasks. Equipment wear and the effects of high energy neutrons from fusion experiments are issues which affect alignment efficiency and accuracy. New sensors needing automatic alignment assistance are common. System modifications to improve efficiency and accuracy are prevalent. Handling these evolving alignment and maintenance needs while minimizing the impact on NIF experiment schedule is expected to be an on-going challenge for the planned 30 year operational life of NIF.

The National Ignition Facility (NIF) is a high power laser system capable of supporting high-energy-density experimentation as a user facility for the next 30 years. In order to maximize the facility availability, preventive maintenance enhancements are being introduced into the system. An example of such an enhancement is a camera-based health monitoring system, integrated into the automated alignment system, which provides an opportunity to monitor trends in measurements such as average beam intensity, size of the beam, and pixel saturation. The monitoring system will generate alerts based on observed trends in measurements to allow scheduled pro-active maintenance before routine off-normal detection stops system operations requiring unscheduled intervention.

The Advance Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a laser system that employs up to four petawatt (PW) lasers to produce a sequence of short-pulse kilo-Joule laser pulses with controllable delays that generate X-rays to provide backlighting for high-density internal confinement fusion (ICF) capsule targets. Multi-frame, hard-X-ray radiography of imploding NIF capsules is a capability which is critical to the success of NIF's missions. ARC is designed to employ up to eight backlighters with tens-of-picosecond temporal resolution, to record the dynamics and produce an X-ray "motion picture" of the compression and ignition of cryogenic deuterium-tritium targets. ARC will generate tens-of-picosecond temporal resolution during the critical phases of ICF shots. Additionally, ARC supports a variety of other high energy density experiments including fast ignition studies on NIF. The automated alignment image analysis algorithms use digital camera sensor images to direct ARC beams onto the tens-of-microns scale metal wires. This paper describes the ARC automatic alignment sequence throughout the laser chain from pulse initiation to target with an emphasis on the image processing algorithms that generate the crucial alignment positions for ARC. The image processing descriptions and flow diagrams detail the alignment control loops throughout the ARC laser chain beginning in the ARC high-contrast front end (HCAFE), on into the ARC main laser area, and ending in the ARC target area.

The Automatic Alignment system in the National Ignition Facility is responsible for aligning 192 laser beams using camera sensor images. This paper reviews some of the image processing algorithms that generate the crucial alignment positions.

The Advance Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a laser system that employs up to four petawatt (PW) lasers to produce a sequence of short pulses that generate X-rays which backlight high-density inertial confinement fusion (ICF) targets. ARC is designed to produce multiple, sequential X-ray images by using up to eight back lighters. The images will be used to examine the compression and ignition of a cryogenic deuterium-tritium target with tens-of-picosecond temporal resolution during the critical phases of an ICF shot. Multi-frame, hard-X-ray radiography of imploding NIF capsules is a capability which is critical to the success of NIF's missions. As in the NIF system, ARC requires an optical alignment mask that can be inserted and removed as needed for precise positioning of the beam. Due to ARC’s split beam design, inserting the nominal NIF main laser alignment mask in ARC produced a partial blockage of the mask pattern. Requirements for a new mask design were needed. In this paper we describe the ARC mask requirements, the resulting mask design pattern, and the image analysis algorithms used to detect and identify the beam and reference centers required for ARC alignment.

Four of the 192 beams of the National Ignition Facility (NIF) are currently being diverted into the Advanced Radiographic Capability (ARC) system to generate a sequence of short (1-50 picoseconds) 1053 nm laser pulses. When focused onto high Z wires in vacuum, these pulses create high energy x-ray pulses capable of penetrating the dense, imploding fusion fuel plasma during ignition scale experiments. The transmitted x-rays imaged with x-ray diagnostics can create movie radiographs that are expected to provide unprecedented insight into the implosion dynamics. The resulting images will serve as a diagnostic for tuning the experimental parameters towards successful fusion reactions. Beam delays introduced into the ARC pulses via independent, free-space optical trombones create the desired x-ray image sequence, or movie. However, these beam delays cause optical distortion of various alignment fiducials viewed by alignment sensors in the NIF and ARC beamlines. This work describes how the position of circular alignment fiducials is estimated in the presence of distortion.

The Advanced Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a petawatt-class, short-pulse laser system designed to provide x-ray backlighting of NIF targets. ARC uses four NIF beamlines to produce eight beamlets to create a sequence of eight images of an imploding fuel capsule using backlighting targets and diagnostic instrumentation. ARC employs a front end that produces two pulses, chirps the pulses out to 2 ns, and then injects the pulses into the two halves of each of four NIF beamlines. These pulses are amplified by NIF pre- and main amplifiers and transported to compressor vessels located in the NIF target area. The pulses are then compressed and pointed into the NIF target chamber where they impinge upon an array of backlighters. The interaction of the ARC laser pulses and the backlighting material produces bursts of high-energy x-rays that illuminate an imploding fuel capsule. The transmitted x-rays are imaged by diagnostic instrumentation to produce a sequence of radiograph images. A key component of the success of ARC is the automatic alignment system that accomplishes the precise alignment of the beamlets to avoid damaging equipment and to ensure that the beamlets are directed onto the tens-of-microns scale backlighters. In this paper, we describe the ARC automatic alignment system, with emphasis on control loops used to align the beampaths. We also provide a detailed discussion of the alignment image processing, because it plays a critical role in providing beam centering and pointing information for the control loops.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is the first of a kind megajoule-class laser with 192 beams capable of delivering over 1.8 MJ and 500TW of 351nm light [1], [2]. It has been commissioned and operated since 2009 to support a wide range of missions including the study of inertial confinement fusion, high energy density physics, material science, and laboratory astrophysics. In order to advance our understanding, and enable short-pulse multi-frame radiographic experiments of dense cores of cold material, the generation of very hard x-rays above 50 keV is necessary. X-rays with such characteristics can be efficiently generated with high intensity laser pulses above 1017 W/cm² [3]. The Advanced Radiographic Capability (ARC) [4] which is currently being commissioned on the NIF will provide eight, 1 ps to 50 ps, adjustable pulses with up to 1.7 kJ each to create x-ray point sources enabling dynamic, multi-frame x-ray backlighting. This paper will provide an overview of the ARC system and report on the laser performance tests conducted with a stretched-pulse up to the main laser output and their comparison with the results of our laser propagation codes.

The current automation of image-based alignment of NIF high energy laser beams is providing the capability of executing multiple target shots per day. An important aspect of performing multiple shots in a day is to reduce additional time spent aligning specific beams due to perturbations in those beam images. One such alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retro-reflecting corner cubes to represent the beam center. The FOA houses the frequency conversion crystals for third harmonic generation as the beams enters the target chamber. Beam-to-beam variations and systematic beam changes over time in the FOA corner-cube images can lead to a reduction in accuracy as well as increased convergence durations for the template based centroid detector. This work presents a systematic approach of maintaining FOA corner cube centroid templates so that stable position estimation is applied thereby leading to fast convergence of alignment control loops. In the matched filtering approach, a template is designed based on most recent images taken in the last 60 days. The results show that new filter reduces the divergence of the position estimation of FOA images.

The National Ignition Facility (NIF) utilizes 192 high-energy laser beams focused with enough power and precision on a hydrogen-filled spherical, cryogenic target to potentially initiate a fusion reaction. NIF has been operational for six years and during that time, thousands of successful laser firings or shots have been executed. Critical instrument measurements and camera images are carefully recorded for each shot. The result is a massive and complex database or ‘big data’ archive that can be used to investigate the state of the laser system at any point in its history or to locate and track trends in the laser operation over time. In this study, the optical light throughput for more than 1600 NIF shots for each of the 192 main laser beams and 48 quads was measured over a three year period from January 2009 to October 2012. The purpose was to verify that the variation in the transmission of light through the optics performed within design expectations during this time period. Differences between average or integrated intensity from images recorded by the input sensor package (ISP) and by the output sensor package (OSP) in the NIF beam-line were examined. A metric is described for quantifying changes in the integrated intensity measurements. Changes in light transmission from the NIF main laser over the three year time-frame are presented.

As lithographic technology drives the minimum integrated circuit feature size toward 0.1 /spl mu/m and below, process tolerances for critical-dimension profile excursion are becoming increasingly demanding. In response, optical critical dimension metrology (OCD), an optical-wavelength light-diffraction technique, is emerging as a fast, accurate, and nondestructive sub-100-nm linewidth and profile monitor. As such, a detailed understanding of the correlation between OCD and existing metrology tools is required. Correlation between CD measurements using OCD and CD-scanning electron microscopy (SEM) techniques is investigated by measuring two types of important structures, e.g., photoresist gratings on a polysilicon gate film stack and shallow trench isolation. Intragrating CD variation is shown to account for scatter in the correlation plot. A qualitative line-profile correlation between cross-section SEM (X-SEM) and OCD is presented for photoresist gratings in a focus exposure matrix. Finally, a summary of the capability of OCD as a monitor for various processing stages is presented.

We report in situ photoluminescence and ex situ Fourier transform infrared spectra of nanoscale silicon clusters exposed to atomic hydrogen, molecular oxygen, and humidified argon. Comparisons between infrared absorption spectra of fresh and aged samples indicate that photoluminescence efficiency is correlated with a stoichiometric oxide shell and the presence of Si dangling bond passivants at the core/oxide interface. Photoluminescence quenching is demonstrated in efficiently luminescing samples upon exposure to atomic hydrogen with recovery of photoluminescence occurring upon subsequent exposure to air. The photoluminescence quenching and recovery is correlated with a partial quenching and recovery of absorption due to interfacial silane groups. The correlations between photoluminescence and infrared absorption spectra, together with the hydrogen quenching results, provide evidence that radiative recombination in these samples is associated with interfacial oxide-related defects.

The National Ignition Facility (NIF) is the world’s most energetic laser, having demonstrated in excess of 1.9MJ @351nm with Inertial Confinement Fusion pulse-shapes in July, 2012. First commissioned with 192 operational beamlines in March, 2009, NIF has since transitioned to routine operation for stockpile stewardship, inertial confinement fusion research, and basic high energy density science.

We have achieved the NIF design goals for power and energy by delivering 1.86 MJ of ultra-violet energy in a wide dynamic range (>300:1), 22.5-ns shaped ignition pulse with a peak power of 520 TW.

Automation of image-based alignment of National Ignition Facility high energy laser beams is providing the capability of executing multiple target shots per day. One important alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retroreflecting corner cubes as centering references for each beam. Beam-to-beam variations and systematic beam changes over time in the FOA corner cube images can lead to a reduction in accuracy as well as increased convergence durations for the template-based position detector. A systematic approach is described that maintains FOA corner cube templates and guarantees stable position estimation.

The requirements for beam and target alignment for successful ignition experiments on the National Ignition Facility (NIF) are stringent: the average of beams to the target must be within 25 μm. Beam and target alignment are achieved with the Target Alignment Sensor (TAS). The TAS is a precision optical device that is inserted into target chamber center to facilitate both beam and target alignment. It incorporates two camera views (upper/lower and side) mounted on each of two stage assemblies (jaws) to view and align the target. It also incorporates a large mirror on each of the two assemblies to reflect the alignment beams onto the upper/lower cameras for beam alignment. The TAS is located in the chamber using reference features by viewing it with two external telescope views. The two jaws are adjusted in elevation to match the desired beam and target alignment locations. For some shot setups, a sequence of TAS positions is required to achieve the full setup and alignment. In this paper we describe the TAS, the characterization of the TAS coordinates for beam and target alignment, and summarize pointing shots that demonstrate the accuracy of beam-target alignment.

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm(-2), which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 μm. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm(-3).

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

The automatic alignment system for the National Ignition Facility (NIF) is a large-scale parallel system that directs all 192 laser beams along the 300-m optical path to a 50-micron focus at target chamber in less than 50 minutes. The system automatically commands 9,000 stepping motors to adjust mirrors and other optics based upon images acquired from high-resolution digital cameras viewing beams at various locations. Forty-five control loops per beamline request image processing services running on a LINUX cluster to analyze these images of the beams and references, and automatically steer the beams toward the target. This paper discusses the upgrades to the NIF automatic alignment system to handle new alignment needs and evolving requirements as related to various types of experiments performed. As NIF becomes a continuously-operated system and more experiments are performed, performance monitoring is increasingly important for maintenance and commissioning work. Data, collected during operations, is analyzed for tuning of the laser and targeting maintenance work. Handling evolving alignment and maintenance needs is expected for the planned 30-year operational life of NIF.

The National Ignition Facility in Livermore, California, completed it's commissioning milestone on March 10, 2009 when it fired all 192 beams at a combined energy of 1.1 MJ at 351nm. Subsequently, a target shot series from August through December of 2009 culminated in scale ignition target design experiments up to 1.2 MJ in the National Ignition Campaign. Preparations are underway through the first half of of 2010 leading to DT ignition and gain experiments in the fall of 2010 into 2011. The top level requirement for beam pointing to target of 50μm rms is the culmination of 15 years of engineering design of a stable facility, commissioning of precision alignment, and precise shot operations controls. Key design documents which guided this project were published in the mid 1990's, driving systems designs. Precision Survey methods were used throughout construction, commissioning and operations for precision placement. Rigorous commissioning processes were used to ensure and validate placement and alignment throughout commissioning and in present day operations. Accurate and rapid system alignment during operations is accomplished by an impressive controls system to align and validate alignment readiness, assuring machine safety and productive experiments.

We report a photoluminescence study of self-assembled InAs islands subjected to in situ annealing prior to the growth of a capping layer. A distinctive double-peak feature is observed in the photoluminescence spectra of annealed samples. The power dependence of the photoluminescence spectra reveals that the double-peak emission is associated with the ground-state transition of islands in two different size branches. This observation agrees with a previous study, which demonstrated that the InAs island size distribution bifurcates during post-growth annealing. The temperature dependence of the photoluminescence intensities from samples with bimodal island size distributions illustrates that different thermal activation energies for carrier emission are associated with islands in different size branches.

We report a reflection high energy electron diffraction study of InAs self-organized quantum dots grown on GaAs (001). We observe facet reflections along the [310] and [130] azimuths, which indicate that the quantum dot shape is pyramidal with bounding facets corresponding to a family of four {136} planes. The determined structure, which possesses C2v symmetry, is quite different both from square-base pyramidal geometries which have been assumed in recent electronic structure calculations, and from previously proposed structures which have been based upon incomplete reflection high energy electron diffraction data.

As lithographic technology drives the integrated-circuit feature size towards 0.1 micron and below, overlay and alignment tolerances are becoming increasingly severe. State-of-the-art aerial imaging overlay metrology systems are limited in accuracy due to inherent limitation on tool imaging resolution and aberrations inherent to the optical system. These in effect result in measurement inaccuracy exceeding industry requirements for next generation overlay tolerances. In this paper, a spectroscopic, diffraction based, technique is proposed as an alternative solution for overlay metrology and alignment measurement in sub 0.1 micron node. With one diffraction grating on the surface overlaying a second diffraction grating on a reference layer, the spectroscopic reflection is modulated by the relative position of the two gratings. Thus, the alignment error can be extracted from broadband diffraction efficiency of measurement pads constituent to the alignment target. This novel diffraction-based overlay metrology has inherent advantages over the traditional image-based overlay metrology: the targets are less sensitive to process variations, and spectroscopic diffraction measurements are less affected by the inherent aberration of the optical system. For these reasons, a diffraction-based spectroscopic metrology has higher potential to generate overlay data that is directly related to registration errors due to alignment and not due to the process or tool aberrations. As a consequence, this technology has a higher potential to generate accurate data to correct registration errors during the lithographic process. Feasibility and accuracy of the technique is studied through a set of experiments and of rigorous simulations on grating targets with various line-width and line-to-space ratios. Correlation to aerial imaging overlay measurements is demonstrated. The results suggest the technique is capable of achieving or exceeding overlay and alignment control accuracy requirements for sub 0.1 micron design rules.

Optical critical dimension metrology (OCD), an optical-wavelength light-diffraction technique, is currently undergoing an industry-wide evaluation as a fast, accurate, and non-destructive sub-100 nm line-width monitor. The spectroscopic, zeroth-order diffraction signature obtained from a printed diffraction grating allows extraction of structural information, such as linewidth, sidewall angle, and profile characteristics. The OCD spectrometer is compact and designed for integration into etch tools and lithography tracks. Effective process monitoring requires detailed understanding of the correlation between CD-SEM and OCD measurements. Correlation between the OCD technique and CD-SEM is investigated in this paper by measuring photo-resist gratings on a polysilicon gate film stack. The scatter in the correlation plot is shown to reduce significantly when several CD-SEM measurements are averaged from a single grating. A positive offset in the correlation is observed and a mechanism is proposed to account for the discrepancy.

A spectroscopic, diffraction based technique is proposed in this paper as an alternative solution for overlay metrology in technology nodes below 90 nanometers. This novel technique extracts alignment error from broadband diffraction efficiency of specially designed diffraction targets in real-time. Feasibility of the technique is studied for a front-end process flow by measuring grating targets printed on a series of wafers which were intentionally mis-processed to introduce inter-die (grid) level programmed overlay errors. Correlation to conventional imaging overlay measurements is demonstrated. Short term and long term data sets demonstrate sub-half-nanometer in 3-sigma statistical parameters that characterize the diffraction overlay system, repeatability, reproducibility, Tool-Induced-Shift and tool-to-tool matching. The resulting total measurement uncertainty for this technique is thus demonstrated to be in the sub-nanometer range.

Summary form only given. A new microscope-based spectrometric instrument has been designed for measuring the critical dimensions of dense line and space targets on patterned silicon wafers. The repeating structure of the target behaves as a one dimensional diffraction grating. Light, focussed at normal incidence on the wafer, is diffracted symmetrically into positive and negative orders with the O/sup th/ order beam being reflected back through the objective lens. The arrangement of the optics prevents all but the O/sup th/ order beam from being collected for detection. At normal incidence, the beam is a superposition of two linearly polarized components with some phase difference, /spl Delta/. Light polarized in the direction of the grating lines is called TE polarized light, and light polarized perpendicular to the lines is called TM polarized light. Any or all of three spectra can be measured: (1) TE reflectance, (2) TM reflectance, (3) phase difference. Measurement results from both photolithography and etch applications are presented.

First results from the analysis of neutron image data collected on implosions of cryogenically layered deuterium-tritium capsules during the 2011-2012 National Ignition Campaign are reported. The data span a variety of experimental designs aimed at increasing the stagnation pressure of the central hotspot and areal density of the surrounding fuel assembly. Images of neutrons produced by deuterium–tritium fusion reactions in the hotspot are presented, as well as images of neutrons that scatter in the surrounding dense fuel assembly. The image data are compared with 1D and 2D model predictions, and consistency checked using other diagnostic data. The results indicate that the size of the fusing hotspot is consistent with the model predictions, as well as other imaging data, while the overall size of the fuel assembly, inferred from the scattered neutron images, is systematically smaller than models' prediction. Preliminary studies indicate these differences are consistent with a significant fraction (20%–25%) of the initial deuterium-tritium fuel mass outside the compact fuel assembly, due either to low mode mass asymmetry or high mode 3D mix effects at the ablator-ice interface.

The first inertial confinement fusion implosion experiments with equimolar deuterium-tritium thermonuclear fuel have been performed on the National Ignition Facility. These experiments use 0.17 mg of fuel with the potential for ignition and significant fusion yield conditions. The thermonuclear fuel has been fielded as a cryogenic layer on the inside of a spherical plastic capsule that is mounted in the center of a cylindrical gold hohlraum. Heating the hohlraum with 192 laser beams for a total laser energy of 1.6 MJ produces a soft x-ray field with 300 eV temperature. The ablation pressure produced by the radiation field compresses the initially 2.2-mm diameter capsule by a factor of 30 to a spherical dense fuel shell that surrounds a central hot-spot plasma of 50 μm diameter. While an extensive set of x-ray and neutron diagnostics has been applied to characterize hot spot formation from the x-ray emission and 14.1 MeV deuterium-tritium primary fusion neutrons, thermonuclear fuel assembly is studied by m...

The National Ignition Facility (NIF) is the world's largest optical instrument, comprising 192 37 cm square beams, each generating up to 9.6 kJ of 351 nm laser light in a 20 ns beam precisely tailored in time and spectrum. The Facility houses a massive (10 m diameter) target chamber within which the beams converge onto an ∼1 cm size target for the purpose of creating the conditions needed for deuterium/tritium nuclear fusion in a laboratory setting. A formidable challenge was building NIF to the precise requirements for beam propagation, commissioning the beam lines, and engineering systems to reliably and safely align 192 beams within the confines of a multihour shot cycle. Designing the facility to minimize drift and vibration, placing the optical components in their design locations, commissioning beam alignment, and performing precise system alignment are the key alignment accomplishments over the decade of work described herein. The design and positioning phases placed more than 3000 large (2.5 m×2 m×1 m) line-replaceable optics assemblies to within ±1 mm of design requirement. The commissioning and alignment phases validated clear apertures (no clipping) for all beam lines, and demonstrated automated laser alignment within 10 min and alignment to target chamber center within 44 min. Pointing validation system shots to flat gold-plated x-ray emitting targets showed NIF met its design requirement of ±50 μm rms beam pointing to target chamber. Finally, this paper describes the major alignment challenges faced by the NIF Project from inception to present, and how these challenges were met and solved by the NIF design and commissioning teams.