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Figure 1
Practical differences between potential regions of light contamination in fixed targets and HVEs. (a) A comparison of pump–probe in HVEs and fixed targets, highlighting the increased access of environmental stray photons to the sample when mounted in fixed targets compared with jets. (b) A simplified schematic drawing demonstrating pump-laser contamination in an HVE. Crystal n is currently illuminated with X-rays. As the jet descends, crystals n + 1, n + 2, etc., will descend into the X-ray path. The pump laser is also currently illuminating n, but is also partially illuminating n + 1 and leading to light contamination. (c) A schematic drawing of a 1:1 interleaved light:dark setup in a MISP chip with an incompatibly large laser spot for the experiment. Each `light well' (A1, A3, A5, etc.) is correctly illuminated. The laser will also weakly illuminate any crystals in the `dark wells' (A2, A4, A6, etc.) and lead to light contamination. Importantly, however, the light contamination will occur between both consecutive apertures (A1 to A2, 10 ms at 100 Hz) and adjacent apertures, i.e. A1 to B1. The contamination of these adjacent apertures gives rise to much longer reaction timescales; A1 to B1 = 3.24 s. (d), (e) Schematic drawings of the two potential orientations of an apertured fixed target in a pump–probe experiment. The sample area is shown in yellow, the cavities in grey and the X-ray in red. The stage path is depicted as a dashed cyan line and the pump laser is shown in blue.

IUCrJ
Volume 11| Part 5| September 2024|
ISSN: 2052-2525
https://doi.org/10.1107/S2052252524005591