Measurement of laser absorption in underdense plasmas using near-field imaging of the incident and transmitted beams

Journal Article · Wed Dec 14 00:00:00 EST 2022 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/5.0100084· OSTI ID:1925160

Katz, J. ^[1]; Turnbull, D. ^[2]; Ivancic, S. T. ^[2]; Milder, A. L. ^[2]; Froula, D. H. ^[2]

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1. Univ. of Rochester, NY (United States); Laboratory for Laser Energetics, University of Rochester
2. Univ. of Rochester, NY (United States)

Measurements of laser absorption in high-temperature, underdense plasmas produced at the Omega Laser Facility are made using two near-field imaging detectors that diagnose the spatial profile and energy of the port P9 beam before and after it transmits through the plasma. The incident beam is sampled using a partial reflection from a full-aperture, (30 cm-diam) uncoated wedge pickoff located before the target chamber vacuum window and final focus lens assembly. A concave mirror reduces the reflected beam size, allowing it to be recorded directly using a charged-coupled device (CCD) camera. The P9 transmitted beam diagnostic (P9TBD) characterizes the transmitted light by terminating the expanded beam on a semi-transparent diffuser and imaging the illuminated surface using a lens and CCD camera. The P9TBD samples a numerical aperture twice as large as the input beam, allowing the energy of transmitted beams with moderate levels of beam spray to be measured accurately. Calibration shots with no plasma provide a path to infer absorption without absolute photometric calibration of either detector. Lastly, the cross-calibration between the two detectors was measured to remain stable at ±200 ppm, enabling measurements of total beam absorption below 1% with ±0.07% error.

• Research Organization: Univ. of Rochester, NY (United States). Lab. for Laser Energetics
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0003856
• OSTI ID: 1925160
• Alternate ID(s): OSTI ID: 1905182
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 12 Vol. 93; ISSN 0034-6748
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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