Begishev I A, Brent G, Carey S, Chapman R, Kulagin I A, Romanofsky M H, Shoup M J, Zuegel J D, Bromage J
Opt Express. 2021 Jan 18;29(2):1879-1889. doi: 10.1364/OE.415691.
High-energy deep ultraviolet (UV) sources are required for high-density plasma diagnostics. The fifth-harmonic generation of large-aperture neodymium lasers in ammonium dihydrogen phosphate (ADP) can significantly increase UV energies due to the availability of large ADP crystals. Noncritical phase matching in ADP for (ω + 4ω) was achieved by cooling a 65 × 65-mm crystal in a two-chamber cryostat to 200 K. The crystal chamber used helium as the thermally conductive medium between the crystal and the crystal chamber, which was surrounded by a high-vacuum chamber with a liquid nitrogen reservoir. A temperature variation of 0.2 K across the crystal aperture was obtained. The total conversion efficiency from the fundamental to the fifth harmonic at 211 nm was 26%.
高密度等离子体诊断需要高能深紫外（UV）源。由于大尺寸磷酸二氢铵（ADP）晶体的可得性，在磷酸二氢铵中利用大孔径钕激光器的五次谐波产生可以显著提高紫外能量。通过在双腔低温恒温器中将一块65×65毫米的晶体冷却到200 K，实现了ADP中（ω + 4ω）的非临界相位匹配。晶体腔使用氦气作为晶体与晶体腔之间的热传导介质，晶体腔被一个带有液氮储存器的高真空腔包围。晶体孔径上的温度变化为0.2 K。在211 nm处从基波到五次谐波的总转换效率为26%。
