Fig. 1

ISO-FLUCS: homogeneous laser scanning for an even time-averaged temperature distribution on the sample while still inducing net thermoviscous flows. a Optical layout of the FLUCS setup capable of simultaneous imaging and inducing intracellular flows. The flow-inducing infrared laser beam is x/y-scanned by an acousto-optic deflector (AOD) and relayed by a telescope onto a dichroic mirror, thereby combining it with the imaging path. Both are coupled to the back focal plane of a high-numerical-aperture, custom-coated microscope objective lens. Flows are generated by laser-induced relative temperature increase within the region of interest (ROI). The absolute temperature within the ROI is controlled through adjunctive heating or cooling of the whole sample by Peltier elements connected to a highly conducting sapphire slide. b Simulated temperature distribution produced by repeatedly scanning an infrared laser along a single line. The highly localized heating entails a relatively strong temperature increase along the track. c A two-step scan pattern heats the entire ROI uniformly: forward followed by backward scans aim to cancel net flows everywhere except on the ‘flow line’ (middle line) where scans point in the same direction and their effects are reinforced