Trident Laser Laboratory

F.L. Archuleta, R.B. Gibson, R.P. Gonzales, T.R. Hurry, R.P. Johnson, N.K. Okamoto, T.A. Ortiz, T. Shimada (P-24)

Lasers—light amplification by stimulated emission of radiation—are among the most varied and versatile tools of modern science and technology. LANL has been a leader in laser technology since the early 1970s, particularly in the arena of high-energy pulsed lasers. The latest of these is Trident, a multipurpose laboratory that principally supports ICF, HED physics, and basic research. Since becoming operational in 1993, Trident has fired over 800 high-energy target shots (Figure 1) each year for experiments requiring high-energy pulsed laser light.

The Trident laser laboratory provides varied and flexible experimental configurations for a wide variety of experiments. It features a powerful Nd:glass laser driver with flexible characteristics in pulse shape, duration, intensity, and focus; two well-instrumented vacuum target chambers with a suite of resident optical and x-ray diagnostics; and ancillary equipment and facilities for optical fabrication and diagnostic checkout. A dedicated staff maintains and operates the Trident laboratory and assists users. The Target Fabrication Facility in the MST Division at LANL designs, fabricates, and characterizes targets for experiments conducted on Trident. Users from more than a dozen major research institutions have executed ~ 200 experimental campaigns in the past decade, including studies of x-ray generation and diffraction, plasma waves and instabilities, shock waves in solids and gases, energetic proton and ion generation, and EOS and other material properties. In addition, high-speed plasma and x-ray diagnostic techniques and instruments are routinely developed and tested at the laboratory for use on Trident and at other major laser laboratories.

Trident Laser Driver

Trident’s laser driver produces several hundred joules of energy over a pulse-length duration that spans more than 6 orders of magnitude from less than a picosecond to several microseconds. It uses an Nd:YLF master oscillator and three chains of Nd:glass rod and disk amplifiers in a conventional master-oscillator power-amplifier (MOPA) configuration (Figure 2) operating at 1,054-nm wavelength. Trident’s main A and B beam lines, which use 14-cm-aperture amplifiers, produce the highest energy after frequency doubling and conversion into the 527-nm green light shown in Figure 1. The third C beam line, which uses 10-cm-aperture final amplifiers, produces lower energy but is more flexible with better beam quality, focus, and ability to be converted to other wavelengths. (Three beams—hence the name “Trident”!) The high-energy stages of the amplifier chain are shown in Figure 3. The laser-driver system operates in three different modes, depending on the pulse-length range. For microsecond-length pulses, one regenerative amplifier is used as an oscillator and the frequency-doubling crystals are bypassed. For nanosecond-length pulses, output from the master oscillator is temporally shaped (Figure 4) before amplification. The C beam line pulse can be independently shaped and timed. It is also normally frequency-doubled to 527 nm but can also run at a fundamental output of 1,054 nm, at a third harmonic output of 351 nm, or at a fourth harmonic output of 263 nm. It can also be operated at reduced energy in a single-hot-spot (SHS) mode in which the spot on target is nearly diffraction-limited. For pulses in the picosecond range, the output of the master oscillator is frequency-broadened and “chirped” before amplification in the C beam line. The 1,054nm output is then compressed with a pair of large diffraction gratings before being focused on target. Energies available on target are summarized in Table 1 and Figure 5.

Target Chambers

Experiments are regularly conducted in two high-vacuum target chambers, each in its own room. The south target chamber is a cylinder approximately 150 cm long and 75 cm in diameter (Figure 2). Single- or double-sided target illumination is possible through several 20-cm-diam ports on each end of the chamber. More than 40 smaller ports are available for diagnostic instrumentation. Individual targets are inserted through an airlock. The target insertion and positioning mechanism provides xyz and rotation adjustment under computer control with 1-µm linear resolution and 350-µrad angular resolution. The three-axis, target-viewing system has 20-µm resolution. The chamber is fitted with a Nova-standard six-inch instrument manipulator (SIM) to accept all SIM-based instruments for checkout, characterization, or use.

Trident’s north target chamber is a sphere with an inside diameter of 145 cm (Figure 2). This target chamber is capable of very flexible target illumination and diagnostic placement geometry because of the 92 ports, ranging in diameter from 2 in. to 14 in., distributed around the chamber surface. The target insertion and positioning mechanism is similar to that in the south chamber. The chamber is fitted with a standard ten-inch instrument manipulator (TIM) that accepts all TIM- and SIM-based instruments.

Trident Target Diagnostics

Optical diagnostics routinely used on Trident include illumination and backscattered-light calorimeters, backscattered-light spectrometers, and high-bandwidth (5 GHz) and streak-camera-based power monitors. Both point and line VISARs are also available. Filtered, photoconductive diamond detectors and x-ray streak cameras with < 10-ps resolution monitor the emission of x-rays from the target. A gated, filtered, x-ray imager provides 16 frames with 80-ps resolution. Various filtered x-ray power and spectral diagnostics covering 0 to 35 keV can be installed as needed. Static x-ray pinhole cameras are also available.

Table 2 summarizes the diagnostic instrumentation available on Trident. Most can be installed on either the north or south target chamber. Users are also welcome to provide their own unique instruments; interfacing information is provided upon request.

Administration

The Plasma Physics Group (P-24) operates Trident as a multipurpose facility for LANL and outside users (national laboratories, universities, and industry). Trident is funded largely through the Laboratory’s Thermonuclear Experiments program element. The quality of proposed research and its relevance to Laboratory missions are major criteria in determining what experiments are fielded on Trident. Proposals are normally solicited annually each winter for the following federal fiscal year.

Trident is located at LANL’s Technical Area 35—an area open to visitors without security clearances. However, security plans are in place to permit appropriately cleared personnel to conduct classified experiments, if necessary.

Figure Captions

Figure 1. View inside Trident's target chamber. Targets may be illuminated with up to several hundred joules of energy in pulses ranging from picoseconds to microseconds in length.

Figure 2. Trident's laser driver uses a conventional MOPA architecture. Main laser pulses (A and B beam lines) and auxiliary laser pulses (C beam line) are amplified sequentially through the front end of the laser system before they are routed to separate disk amplifier chains for further amplification. Shaping and timing can be controlled separately.

Figure 3. Trident's two power amplifier chains feature 10- and 14-cm-aperture Nd:glass disk amplifiers (bray boxes) and a fully enclosed beam transport system (blue vacuum spatial filters and transport tubes).

Figure 4. Pulse-stacker output. These figures are examples of the diverse pulse shapes made possible by the coherent pulse stacker, which follows the master oscillator.

Table 1. Trident target environment. (see PDF file above)

Figure 5. The laser driver operates over more than 6 orders of magnitude in pulse length. The solid lines show the energy that can presently be produced in one beam line. The dashed lines indicate energies that would be possible with modest enhancements. Red indicates 1,054 nm (infrared), green is 527 nm (green light), and blue is 351 nm (ultraviolet).

Table 2. Trident target diagnostics. (see PDF file above)

Acknowledgment

Many individuals beyond those presently operating Trident have contributed to its construction and operational success over the years, including Hank Alvestad, Tom Archuleta, Bentley Boggs, Max Byers, Paula Diepolder, Scott Evans, Jim Faulkner, George Faulkner, Jody Godard, Sam Letzring, Kent Moncur, Danielle Pacheco, Sam Reading, Tom Sedillo, Bob Watt, and scores of others. Trident is funded by the DOE Secondaries and Inertial Fusion Division.

PDF file of this highlight

For more information, contact Robert Gibson at rbg@lanl.gov or visit the Trident Web site.