Rapid melting and revitrification of cryo samples: concept and experimental demonstration. (a) Illustration of the geometry of the cryo sample, which is prepared on a holey gold film supported by a gold mesh. The sample is irradiated in situ with a laser beam that is centered onto a grid square. (b) In the vicinity of the laser focus, the sample rapidly melts, allowing embedded particles to undergo equilibrium dynamics in the liquid phase. When the laser is switched off the sample rapidly revitrifies, trapping the particles, so that they can subsequently be imaged. (c)–(f) Micrographs of a cryo sample of apoferritin (c, d) and of the same sample after melting and revitrification with a 20 µs laser pulse (e, f). The laser focus is aligned to the central hole, which is marked with a crosshair. The outline of the revitrified area is indicated in (e) with a dashed semicircle. Adjacent regions have crystallized. The scale bars are 50 nm in (c) and 5 µm in (d).