High-efficiency, large-aperture fifth-harmonic: Generation of 211-nm pulses in ammonium dihydrogen phosphate crystals for fusion diagnostics

Journal Article · 04 March 2019 · SPIE Seminar Proceedings (Online)

DOI: https://doi.org/10.1117/12.2506557 · OSTI ID:1505789

Begishev, Ildar ^[1]; Romanofsky, Mark ^[2]; Carey, Sean ^[2]; Chapman, Raymond ^[2]; Brent, Gregory ^[2]; Shoup, Milton ^[2]; Zuegel, Jonathan ^[2]; Bromage, Jake ^[2]; Haefner, Constantin L. ^[2]; Awwal, Abdul A. ^[2]

---

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

High-energy ultraviolet (UV) sources are required to probe hot dense plasmas from fusion experiments by using Thomson scattering resulting from the lower self-generated background from the plasma in the 180 to 230-nm spectral region. Although recently we demonstrated efficient, joule-class fifth harmonic conversion of 1053-nm pulses using a cesium lithium borate (CLBO) crystal, larger crystals are necessary for increased UV energy. This paper presents an alternative approach for fifth-harmonic generation of a large-aperture neodymium laser using ammonium dihydrogen phosphate (ADP). An Nd:YLF laser was optimized to produce square pulses with a flattop, square beam profile (1053 nm, 1 to 2.8 ns, 12 x 12 mm, ≤1.5 J, ≤5 Hz). Noncritical phase matching in ADP suitable for sum–frequency mixing the fourth harmonic with residual fundamental light was achieved by cooling the crystal (65 x 65 x 10 mm) in a two-chamber cryostat to 200 K. The crystal chamber used helium (1 atm) as the thermally conductive medium between the crystal and the crystal chamber, which in turn was surrounded by a high-vacuum chamber that contained a liquid nitrogen reservoir to cool the crystal chamber. Temperature variation of 0.4 K across the crystal aperture was obtained using two 50-W heaters with active feedback. The total conversion efficiency from the fundamental to the fifth harmonic, including surface losses and absorption, was 26%.

• Research Organization: Univ. of Rochester, Rochester, NY (United States). Lab. for Laser Energetics
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0003856
• OSTI ID: 1505789
• Report Number(s): 2018-204, 1484; 2018-204, 1484, 2443
• Journal Information: SPIE Seminar Proceedings (Online), Journal Name: SPIE Seminar Proceedings (Online) Vol. 10898; ISSN 1996-756X
• Publisher: SPIECopyright Statement
• Country of Publication: United States
• Language: English