UV-driven high-harmonic generation occurs in Kr gas within a vertical, end-sealed glass capillary. Bright emission (center) results from the ionized atoms, while colors from the laser fundamental, second-harmonic, and green pump lasers in the lab reflect within the vacuum chamber. For details see Wang et al. Nature Commun. 6, 7459 (2015) and Buss et al. Rev. Sci. Instrum. 90, 023105 (2019). Unprocessed image taken with Iphone XS (Halide app) in the Kaindl group at Lawrence Berkeley National Lab.
—Robert A. Kaindl, Lawrence Berkeley National Lab
20 Nov 2019