The NIF facility commissioned the Advanced Radiographic Capability (ARC) short-pulse laser system in 2015. The ARC high-energy backlighting capability is required for the Stockpile Stewardship Program (SSP)-High-Energy-Density (HED) and SSP-Inertial Confinement Fusion (ICF) programs. Two beams in a single NIF quad (Q35T) are converted into four ARC “beamlets;” the infrastructure to convert the other two beams in the quad to four more beamlets is partially installed in the NIF Target Bay. A layout of the ARC system is shown in Figure 4-19. Conversion of NIF beamlines to high-intensity, picosecond operation requires three top-level changes to the existing NIF beam lines:
- Addition of the High Contrast ARC Front End (HCAFE), which provides dual regenerative amplifiers for split beam injection.
- Improved amplifier isolation for backscatter protection.
- Pulse compression in the NIF Target Bay and final focusing optics.
The HCAFE uses short-pulse optical parametric amplifier technology3 to meet the high temporal contrast requirement of 80 dB for t < -200 ps before the main pulse (70 dB at TCC). The dual amplifiers on the ARC Dual Regen Table and split beam injection produce two beamlets that can be independently timed (0–30 ns currently), pointed (0–1 mm currently) to a target, and configured for compressed pulse duration. The B353 and B354 beamlet pairs can be independently pointed within the ARC focal spot volume (±50, ±50, +10/-45) mm and B353 can be delayed up to 3.6 ns after B354. The short-pulse output of the compressor is diagnosed using the ARC Diagnostic Table (ADT) during system shots. The ADT is capable of measuring key short-pulse laser performance metrics (near-field and far-field intensity patterns, pre-pulse levels, spectrum, and energy in the compressed pulse, etc.) on system shots. The measured focal spot performance goal for a 1.5-kJ beamlet with 30 ps FWHM Gaussian pulse is 50 percent of the energy with ≥1017 W/cm2 irradiance and contained in 150-µm spot size.
Currently, ARC is commissioned at 4 pulse widths, each having a different beamlet energy limit: 1kJ@38 ps, 0.9 kJ@30 ps, 0.6 kJ@10 ps, and 0.25 kJ@~1 ps. As ARC optics are upgraded and laser performance optimized, the maximum energy will increase to 1.5 kJ at 30-ps pulse length. As new user requirements are developed for future missions, ARC will be commissioned at different operational parameters (pulse length, beamlet timing and pointing, etc.).
3C. Dorrer et al., “High-contrast optical-parametric amplifier as a front end of high-power laser systems,” Optics Letters 32 (15), 2143 (2007).
