The Dynamic Compression Sector laser: A 100-J UV laser for dynamic compression research

With applications in astrophysics, inertial confinement fusion (ICF), and material processing, high-energy-density (HED) physics is an important area of active research to study materials at high pressures and temperatures. More recently, facilities designed to prepare matter in these states with laser irradiation have been established, each with their own unique driver. The Matter in Extreme Conditions (MEC) instrument¹ at the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory utilizes a pair of beams from a frequency-doubled Nd:glass system to deliver tens of joules of 527-nm light to a uniformly illuminated target and can be fired on a 7-min shot cycle. The spot size is controlled with phase plates and is variable, as is the duration of the pulse, which can range from 2 to 200 ns. An additional joule-level femtosecond beam centered around 800 nm is available as well. Another unique system known as DiPOLE100² is currently in use at the HiLASE facility in the Czech Republic. This diode-pumped solid state laser utilizes a ceramic gain medium, and is capable of both a high energy of 100 J and a repetition rate of 10 Hz, which it achieves with state-of-the-art cryogenic cooling techniques. This laser operates at 1030 nm and delivers 10-ns pulses on target with a near-diffraction–limited focus.³ 

The Dynamic Compression Sector (DCS) is a Washington State University (WSU)-operated user facility located at the Advanced Photon Source (APS) at Argonne National Laboratory. DCS is a unique facility dedicated to the study of time-dependent phenomena (structural changes, deformation, and chemical reactions) in condensed matter under extreme dynamic compression. With a suite of shock-compression drivers in combination with the high-energy x-rays available at the APS, DCS experiments entail time-resolved measurements of material response at pressures ranging from ∼5 to 350 GPa with nanosecond resolution. The newest shock station at the DCS facility⁴ features a one-of-a-kind 100-J, frequency-tripled Nd:glass laser codeveloped by the Laboratory for Laser Energetics (LLE) and Logos Technologies. This laser utilizes a number of pulse-shaping and beam-smoothing technologies developed in the field of inertial confinement fusion and adapted to suit the DCS research needs.

Until recently, shock waves at the DCS were generated through impact loading⁵ carried out using gas and powder guns and a two-stage gas gun that launches projectiles at materials of interest. With surfaces polished to optical quality, a spatially uniform shock wave can be generated. The magnitude of the shock wave is determined by the projectile velocity and is highly repeatable, with a temporal jitter of ∼150 ns. With the impact facilities at DCS, typically 5 to 10 experiments can be conducted in a day.

With laser-induced dynamic compression, the shock-generation mechanism is ablation.^6,7 The material of study is coated with an ablator, which absorbs laser energy, and is heated on a nanosecond time scale. The ablated material, which can be solid, liquid, gaseous, or plasma, is ejected from the surface. The recoil force associated with this ejection is the source of pressure that propagates through the ablator into the sample. This process allows one to study dynamic compression on shorter (nanosecond) time scales and higher shock pressures (>300 GPa) than those achieved through impact.

With the above considerations in mind, the DCS laser (shown in Fig. 1) was designed and constructed to produce 100-J, 351-nm pulses of variable shapes with durations between 5 and 20 ns. The laser can be fired once every 20 min and is capable of delivering this energy on target within a 500-μm super-Gaussian spot, with interchangeable optics to enable spot sizes of 250 and 1000 μm. The beam within this spot has been measured to have an rms variation in intensity of ±8.7% across this super-Gaussian profile.

The description of the DCS laser is organized as follows: Sec. II, on laser design, discusses necessary requirements on a shock-driving laser and covers a suite of technologies and techniques employed to achieve the specifications listed above. These include a number of aspects of design that are commonplace in larger-scale glass lasers designed for ICF. A brief overview of important concepts such as smoothing by spectral dispersion (SSD),^8–10 distributed polarization rotators (DPRs),^11,12 and distributed phase plates (DPPs)¹³ is provided to orient the reader prior to a detailed description of its components. Section III follows the beam path of the laser from the fiber front end through all stages of amplification, covering specific relevant aspects of performance. Section IV covers all beam conditioning, frequency conversion, and diagnostics following amplification. Since many of the final optics are mounted within the target chamber, a brief description of the chamber’s function, along with the beam path through it, is provided as well. A description of the user interface is covered in Sec. V.

Efficiently achieving a uniform shock wave through ablation places a number of requirements on the driving laser. One of the more obvious requirements is a spatially uniform beam profile. Contrast high enough to keep prepulse intensity below the ablator damage threshold is also important to avoid preheating and ionization of the sample before delivery of the shock-driving impulse. With significant energy requirements, it is necessary to ensure efficient absorption through any plasma that may be generated at the ablator’s surface.¹⁴ This can be achieved with shorter ultraviolet (UV) wavelengths, which have a greater penetration depth. To generate various shock temporal profiles, it is necessary to control the temporal profile of the delivered impulse. For this reason, a laser system with flexibility in pulse shape is required.

Since many of the requirements for the shock-generating beam are similar to those imposed by laser-fusion experiments, the DCS laser has been designed after larger-scale glass lasers often constructed for ICF research, such as OMEGA and the National Ignition Facility (NIF).^15–18 As such, it utilizes a number of technologies and techniques developed for these glass lasers, such as SSD, a DPR, and a DPP. While the basics of design and use of these tools remain the same, the scale of the DCS laser allows for a modified implementation to better suit the specific requirements of the facility. The most significant difference between the DCS laser and larger lasers of its kind is that it utilizes a single beam. For this reason, the system is more flexible in terms of where certain stages of a given beam-conditioning technology are implemented.

Having a flat beam profile on target is of utmost importance for generating a uniform shock wave.¹⁹ In general, this is not easily accomplished with the beams that are produced from most large-scale glass amplifying systems without additional conditioning since they are designed with a more flattopped and sharp-edged intensity profile in the near field for efficient energy extraction. As is often the case in ICF-scale glass lasers, the desired far-field profile in the DCS laser is achieved with the use of a DPP. The DPP is a diffractive optical element that imprints a specific phase profile on a beam in the near field in order to achieve a particular intensity profile in the far field. In the case of the DCS laser, the primary DPP design, in conjunction with the 1-m final focusing lens, produces a 500-μm super-Gaussian focal spot in the far field.

Because this far-field pattern is produced through interference, a side effect to generating such a profile with a DPP is that the pattern contains large intensity variations often referred to as “speckle.” For this reason, two additional techniques are utilized to smooth the beam’s far-field profile. The first technique is SSD. It is a technique that can be employed in a number of ways, but in all cases, it involves a combination of frequency modulation and angular dispersion provided by gratings. The idea is that a broadened spectrum, when dispersed by a grating, will be spread out in the far field, smearing out intensity variations. While greater dispersion will result in a higher degree of smoothing, it also elongates the beam along the same direction, distorting the focal-spot profile. Ultimately, SSD design parameters for this laser were chosen by the DCS Collaborative Access Team based on predictions from models.

Since SSD smoothes the beam along only one direction, another back-end optic, the DPR, is utilized to introduce an additional degree of smoothing along the other. The DPR is a birefringent wedged optic that deflects two beams in slightly different directions, each with an orthogonal polarization. With the appropriate choice of wedge angle, the end result in the far field is a pair of overlapped beams that are slightly offset and do not interfere. This results in a decrease in rms intensity variation by a factor of $2$⁠. The optic itself is constructed from KDP and is cut such that its wedge vertex is at 45° with respect to two crystallographic axes. In this way, the desired output can be produced with an input polarization either parallel or perpendicular to its wedge axis.

The schematic in Fig. 2 illustrates how the above technologies work together to create the desired output of a smooth, evenly illuminated super-Gaussian spot in the far field. A beam (already frequency modulated) passes through a pair of gratings to induce smoothing along one axis. Both doubling and tripling of the light take place directly after the gratings. The DPR is oriented to deflect the beam in a direction perpendicular to the SSD direction, and because of its birefringence, it deflects two separate beams, increasing smoothness along that direction. The combination of a final focusing lens and DPP is what results in the desired super-Gaussian beam profile on target.

Figure 3 schematically shows the overall design of the DCS laser. It resides in a 30-ft × 15-ft room adjacent to the x-ray hutch containing the target chamber and spans two optical tables. The amplifier portion consists of a fiber-based front end, which shapes and applies SSD modulation, followed by three separate stages of amplification. The first two stages lie on the first table and consist of a regenerative amplifier and a four-pass rod amplifier, which achieve ∼2 J in the infrared (IR). The final stage of amplification takes place in a disk amplifier, which lies between the tables. After six passes through this amplifier, the pulse energy is ∼200 J. The second table contains SSD gratings, frequency-conversion crystals, and a suite of diagnostics. Frequency conversion results in a final output of 100 J in the UV. The remaining back-end optics, such as the DPP and DPR, are located within a vertical transport column near the target chamber and are described in Sec. IV.

The front end of the DCS laser is a fiber-based system, which consists of a number of rack-mounted units that sit apart from the free-space stages of amplification. It provides the main amplifier chain with a high-repetition-rate source of shaped seed pulses along with the frequency modulation (FM) necessary to facilitate SSD. The laser begins with a 40-mW, 1053-nm continuous-wave (cw) source (Koheras ADJUSTIK) from which pulses are carved by a Mach–Zehnder LiNbO₃ modulator (EOspace) capable of >35-dB extinction. The repetition rate is 329 Hz, which is derived from dividing down the external APS storage ring clock of 352 MHz. The modulator is driven by the amplified output of an arbitrary waveform generator (AWG) that has a resolution of 125 ps. The AWG is capable of producing arbitrary pulse shapes that can be uploaded through the laser’s integrated software, but it is typically run using one of four preprogrammed pulse shapes defined by DCS, ranging in duration from 5 to 17 ns. These pulse shapes, measured at the output of the laser, shown in Fig. 4, have been demonstrated to vary by less than ±10% of the design amplitude from shot to shot.

The pulse shape out of the final disk amplifier bears little resemblance to that of the front end. This is primarily due to a phenomenon commonly referred to as “square pulse distortion” and occurs in systems with high gain saturation. When this is the case, the leading edge of a pulse sees more gain than the trailing end, and the pulse develops a temporal asymmetry.²⁰ With many stages of amplification in the DCS laser, this effect is quite significant, and pulses leaving the front end must be heavily precompensated in order to achieve the desired final shape. Figure 5 shows the contrasting shapes of the AWG input and the UV output of the laser. While this distortion can be modeled to a certain extent, in practice, achieving a particular specified shape in the UV requires small iterative corrections to the AWG input.

After shaping, the light passes through a chain of fiber amplifiers before entering a modulation chassis, which provides the multifrequency modulation necessary for SSD.²¹ Modulation frequencies at 21.3, 23.4, and 32.5 GHz result in a spectrum broadened to roughly 4 Å. An acousto-optic modulator (AOM) provides an additional 50 dB of contrast over a 20-ns window before the light is delivered to the regenerative amplifier on the first table via a polarizing fiber. The pulse energy at the output of the front end is at a nanojoule level.

The regenerative amplifier is the first stage of amplification on the first laser table. Its design is similar to those used at the NIF. The amplifying medium is a 5-mm-diam, 120-mm-long diode-pumped Nd:glass (Schott APG-1) rod. While YLF is a common choice for a gain medium at 1053 nm, glass is used in this application because its gain spectrum is broad enough to cover the SSD spectrum. With a 3.75-m-long cavity, it can support pulses up to 20 ns long. Since stability is essential in a system of this size in a user facility, the laser is kept in an enclosure, separated from all diagnostic cameras, and fired at a low repetition rate to avoid thermal instabilities.

The beam path through the regen is shown in Fig. 6. Light from the front end is injected through a pair of Faraday isolators. The cavity is electro-optically shuttered at a rate of 2.7 Hz, during which it is held in the cavity for roughly 30 round trips, and is switched out with an energy of ∼20 mJ. Its output energy is stable to <1% rms.

One potential problem with amplifying the SSD spectrum in such a highly saturating amplifier is the effect of the gain profile. Although the SSD bandwidth is small compared to that of the laser glass, a small slope in the gain is enough to result in an asymmetric FM spectrum, which effectively modulates the amplitude of the pulse. This effect is mitigated with the inclusion of an intracavity birefringent filter. The slope of the filter’s transmission profile can be adjusted with tilt, and it is tuned to flatten the output spectrum.

The next stage of amplification is a four-pass rod amplifier. The amplifying medium is a 1-in.-diam flash-lamp–pumped Nd:glass rod. The small-signal gain in the rod can be as high as 8 when flash lamps are fired at 2.2 kV. In practice, lamps are fired at voltages between 1.8 and 2 kV, depending on pulse shape, in order to achieve the desired output energy of ∼2 J.

Before this stage of amplification, the output of the regen is expanded to overfill an apodizer, which, when combined with the gain profile of the remaining stages of amplification, is designed to result in a flattop super-Gaussian profile at the output of the entire laser. This profile provides the uniform illumination that is necessary for the DPP to properly function downstream. The apodizer itself is a binary pixelated beam shaper,²² which imprints a 1-cm-diam super-Gaussian profile with a parabolic shape onto the beam. The parabolic shaping, along with the intensity distribution of the Gaussian beam illuminating the apodizer, serves to precompensate for the effects of gain nonuniformities in both the rod and disk amplifiers. The plane in which the apodizer lies serves as a primary image plane for all subsequent image relays.

Pulses transmitted through the apodizer have an energy of ∼5 mJ. This light passes through an isolator and a relay that images the apodizer to the midpoint of the four-pass path through the amplifier. This path is achieved through the passive polarization switching geometry shown in Fig. 7. Here, a quarter-wave plate results in a rotation of polarization upon two passes, which allows a thin-film polarizer and 0° mirror to fold the path back onto itself. Working with this geometry, it is possible to form a cavity between the end mirror and the folding mirror, which can result in parasitic lasing. This is avoided with a slight intentional misalignment of the end mirror that is compensated for with the folding mirror. The adjustment introduces a small degree of walk-off per pass, which has little effect on the intended pass but introduces enough loss on multiple passes to inhibit self-lasing.

Upon exiting the rod amplifier, the pulse energy is ∼2 J. The beam is then expanded to 20 mm and injected into the disk amplifier. This final stage of amplification consists of four 15-cm Nd:glass (Hoya LH-8) disks. It is powered by an LLE-designed power conditioning unit capable of delivering up to a total of 275 kJ when charged to its maximum voltage of 14.8 kV. The unit contains 12 pulse-forming networks, one for each of the flash-lamp circuits contained within the laser amplifier. Each of the 12 networks is composed of a 210-μF capacitor (ICAR model D-65B-1500), a 160-μH inductor (Pulse Systems model X-1090), and a 52-in. flash lamp. Peak current in each circuit is approximately 7 kA with a pulse width of 550-μs full width half maximum (FWHM). A preionization and lamp check (PILC) circuit allows for reliable operation even at reduced capacitor bank voltages. Ignitron vacuum tubes are used to switch the high voltage and current. A single “D”-size ignitron (Richardson model NL8900R) switches the main bank of the pulse-forming network, while a single “A”-size ignitron (Richardson model NL7218H-100R) switches the PILC pulse. In the event of an aborted shot sequence, the capacitors are discharged into a dump resistor (HVR model K07KGA431K) via high-voltage relays (Ross model E25-NC-25-0-27-XQ). Since flash-lamp pumping deposits a significant amount of heat in the amplifying glass disks, thermally induced changes in refractive index as well as thermal expansion can affect the beam profile and pointing if the laser is fired too soon after a previous shot. For this reason, a 20-min delay between shots is enforced through the control software. The amplifier housing shown in Fig. 8 lies between the two laser tables. To maximize the amount of energy extracted and maintain beam uniformity, the beam is angularly multiplexed both vertically and horizontally through the amplifier over six passes. As energy builds, the beam size is expanded to maintain intensity levels that are safe for all downstream optics. Magnifying image relays before passes 1, 3, and 5 increase the beam diameter by a factor of 1.6 each, resulting in a final diameter of 8 cm. While flash lamps may be fired at voltages as high as 14.8 kV, the laser is designed to be operated at 10 kV to lengthen the lifetimes of the flash lamps. Under these conditions, the small-signal gain from a single pass is ∼3. After six passes through the amplifier, the final IR energy of the laser is >200 J.

After the disk amplifier, no further amplification takes place and the beam is transported to the second table (shown in Fig. 9), where SSD and frequency conversion to the third harmonic take place. This table also houses the bulk of a number of important diagnostics that are indispensable in assessing laser performance. The remaining back-end optics lie within the target chamber. A final diagnostic, the equivalent target plane (ETP), is also mounted on the chamber, providing essential information about beam size, profile, and smoothing on target.

In the case of the DCS laser, SSD is implemented in only one dimension, as in the NIF laser.²³ This allows all of the modulation to be applied in the front end and the gratings left until after the final stage of amplification. This arrangement is beneficial because the beam is not angularly dispersed throughout each amplification stage, and spectral narrowing from beam clips in spatial filters is not a concern. In addition, modulation can be carried out in fiber-based systems, which are much more robust than large-diameter modulators in which uniform modulation across the beam front can be difficult. One consequence of this increased bandwidth early in the amplification chain is that it requires all subsequent stages of amplification to be capable of supporting the SSD bandwidth.

The design SSD of 66 μrad/Å is achieved with a pair of transmission gratings. Both gratings are held in a Littrow configuration but are oriented to diffract opposite first orders, resulting in an overall dispersion that is smaller than that of either grating alone. This geometry allows for low angular dispersion with more easily manufactured rulings. The gratings are positioned and oriented in such a way that their output points directly through the frequency-conversion crystals.

The DCS laser’s frequency-conversion crystals consist of three KDP crystals cut for type-II phase matching. They are oriented in a configuration intended for very high (70%–80%) third-harmonic conversion efficiency and modeled after those of the OMEGA laser.²⁴ The first two crystals are 22 mm thick and perform second- and third-harmonic generation, while the third crystal is 16 mm thick and is intended to add bandwidth to the third-harmonic–generation process.²⁵ Polarization going into the crystals is set to 34.8° with respect to the doubler o axis with a wave plate immediately preceding the crystals.

The high-efficiency conversion scheme implemented with the first two crystals is based on achieving an ideal ratio of fundamental and second-harmonic photon numbers along the appropriate axes in the tripler. To this end, polarization going into the doubler is chosen such that the intensity is twice as high along the o axis as that along the e axis. Crystal thickness is chosen so the second-harmonic–generation (SHG) process is saturated, resulting in equal numbers of fundamental photons along the o axis as the second harmonic along the e axis. The tripler is then oriented with its axes at 90° with respect to the doubler, where a significant fraction of the incoming light is converted into the UV. This geometry can be optimized to achieve 80% conversion efficiency for a single given intensity. Since the DCS laser fires multiple pulse shapes with varying intensities, final values of design parameters such as crystal thickness and input polarization are determined by modeling and are adjusted to achieve low sensitivity to varying inputs such as pointing and intensity. This results in a lower conversion efficiency of around 50% but with the much higher shot-to-shot fidelity required for the DCS application.

While a two-crystal conversion setup can achieve the target energy of 100 J in the UV for a wide range of pulse shapes with varying input intensities, conversion of the shortest desired pulse shapes is less efficient. This is because the associated phase-matching curves have the smallest bandwidth at higher intensities. Because all of the pulses out of the main amplifier have roughly the same energy, conversion of the entire SSD bandwidth is more difficult for shorter pulses. For this reason, a second tripler is utilized to increase spectral coverage. Implementation involves orienting both triplers slightly off phase matching in opposite directions so that their phase-matching curves cover different portions of the laser spectrum. Since the relative phases of all harmonics propagating between the tripler pair are important to the conversion process, care has been taken to set the longitudinal distance between triplers to be a multiple of the dephasing length (∼4 cm) associated with propagation of these wavelengths in air.

The majority of the remaining space on the second table is reserved for a suite of diagnostics covering energetics, beam pointing and centering, pulse shape, and conversion efficiency. Light leaking through a turning mirror following the main amplifier is used for diagnostics designed to measure both IR pulse shape and near field immediately after the disk amplifier. The remaining diagnostics are fed by a pickoff consisting of a large-diameter meniscus optic with antireflection sol-gel coating on one side. The uncoated reflecting surface of the pickoff has a long focal length of 3.3 m and serves as the focusing optic for pointing cameras. Along the path to that camera, additional pickoffs and dichroic mirrors are used to feed UV beam and energy diagnostics for each harmonic.

After frequency conversion, the fundamental and second-harmonic photons are passively filtered out by UV dielectric transport mirrors. Laser light is periscoped under the table and passed through a 2× telescope (not shown in the figure), which increases its diameter to 16 cm before exiting the laser room. The laser beam enters the adjacent x-ray hutch and is directed into the chamber through an enclosure connected to the laser room, effectively extending the positive pressure and clean room space of the laser room up to the target chamber’s input port. This is essential since a number of sensitive and high-fluence final optics lie in this beam path.

The DCS target chamber is a spherical chamber located in the x-ray hutch. It is designed to house samples under vacuum and facilitate time-resolved x-ray measurements of laser-driven compression. The chamber is capable of horizontal and vertical translation as well as rotation in order to accurately point laser energy onto the sample at angles of 0°, 45°, 90°, and 135° relative to the x-ray beam. It is an integral part of the laser because it houses the final beam-conditioning optics, a focusing lens, and a target-plane diagnostic.

The beam path through the chamber is shown in Fig. 10. It begins close to the ground and encounters two periscopes in order to properly point the beam into the chamber. The first periscope begins directly underneath the chamber, pointing the beam upward and collinear with the chamber’s axis of rotation. The second periscope elevates the beam to target height and directs it into the chamber port. Two mirrors (M2 and M3 in Fig. 10) along this path are motorized to remotely center and point the beam along its final path. These periscope optics are housed within an arm capable of rotating 135° around the center of the chamber to address samples at various angles of incidence. The vertical portion of this arm consists of an expandable column in which both the DPP and DPR are mounted. Its flexibility is necessary since the upper mirror of the periscope must move to match the height of the target.

Because the beam path into the chamber utilizes a periscope that can change its propagation direction, both polarization and SSD direction are different at each chamber orientation. While most of the back-end optics are insensitive to such changes, the DPR requires a specific orientation with respect to both beam properties to function properly. For this reason, each time the chamber is rotated, the DPR must be accessed and manually rotated accordingly. Since the DPP must be swapped out to change the focal-spot size, the DPP and the DPR are both mounted behind a removable panel where they can be easily accessed.

After the last turning mirror, the beam is directed into a final 1-m aspherical focusing lens that focuses the beam to the center of the target chamber through a disposable debris shield. The surfaces of this lens were designed to avoid formation of secondary images that focus at or near the other optical components in the path. These “ghost” images, formed by single or multiple surface reflections, can be potentially damaging to optics because of excessively high beam fluence or phase-to-amplitude modulation “spikes” produced by the DPP. This design aspect determined the rotating arm length and was an important consideration for positioning most of the optical surfaces in the chamber’s periscopes and DPP/DPR beam path.

A final important diagnostic, the equivalent target plane (ETP), rests atop the chamber arm in a 1-ft × 2-ft self-contained enclosure. Its purpose is to image a focus equivalent to that of the full-energy beam on target. The diagnostic lies beyond the final turning mirror in the chamber path and utilizes 1% of the beam that leaks through it. The leaked beam encounters a separate replica of the final focusing lens and an attenuator before entering the diagnostic. The resulting focus is then imaged with a pair of lenses onto a 2048 × 2048 resolution camera. The lens pair is mounted on a single assembly that can be adjusted to scan its focal plane. Figure 11 shows an image collected by the ETP upon installation. From these data, the rms variation in intensity across the face of the beam was determined to be ±8.7%.

The DCS laser facility is intended to be operated by a single laser scientist, able to efficiently align, operate, and diagnose all aspects of laser operation. An advanced control system is necessary to meet this operational requirement. A web-based client-server system has been developed that consolidates all laser operations in a single system. A Microsoft Windows server interfaces with all laser equipment. Custom software, written in Python, collects all diagnostic information, including beam images, oscilloscope traces, and energy data, as well as data from the laser amplifiers, and logs it on a regular basis. Real-time data are provided to the operator through a graphical interface on a web-based client. The operator can connect to the system through a web browser on any computer on the local intranet, connected via either Ethernet or wireless connection. This allows the operator to take the entire laser control and diagnostic system with them from the control room to the laser room to facilitate alignment and troubleshooting.

The main page of the user interface displays real-time diagnostic information, allowing the operator to see any anomalous behavior. Separate pages show detailed diagnostic information for each amplifier stage and also allow one to control the amplifiers and system timing. Full system shots are operated through a wizard that takes the operator through the system setup and then initiates an automated charging and firing sequence, including an audible countdown. After the shot, the system saves all diagnostic information and summarizes the laser shot in a single performance sheet. Experimenters can log in directly to the server and view a diagnostic summary, which provides information on shot status and laser performance.

The DCS laser is a one-of-a-kind shock driver designed to meet requirements specific to a user facility geared toward studying shock physics, which include specific performance parameters as well as reliability and ease of use. The 351-nm laser is capable of firing 100-J shots on a 20-min cycle, with minimal need for adjustments or maintenance. A number of ICF-derived technologies are employed in this new context to achieve flexibility in pulse shape and a smooth beam on target within a uniform super-Gaussian spot. A suite of diagnostics measuring pulse shape, beam profile, and energetics provides feedback on collective performance, demonstrating stability in energy to within a few percent and pulse shape to within ±10% per shot. This laser represents the current state of the art in shock-driving technology in that it offers a higher repetition rate as well as increased experimental flexibility when compared with more-traditional mechanical shock-driving methods.

The design and construction of this laser would not be possible without the following individuals, who contributed greatly to the project through engineering support, testing, and management of logistics: W. Bittle, B. Brannon, B. Byrne, T. Clark, Z. Currier, K. D’Amico, J. Engler, B. Erich, T. Flannery, D. Guy, R. Huff, N. Kephalos, D. Kuhn, D. Paskvan, A. Rigatti, J. Russell, J. Schoen, M. Scipione, M. Sharpe, T. Smith, J. Szczepanski, and B. Williams.

This publication is based upon work performed for the Dynamic Compression Sector, which is operated by Washington State University under the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) Award No. DE-NA0002442. Additional support was provided by the DOE NNSA under Award No. DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority.

This report was prepared as an account of work sponsored by an agency of the U.S. government. Neither the U.S. government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. government or any agency thereof.