Sub-millimeter thruster-in-water powered by a remote laser pulse

•We fabricated sub-millimeter thruster-in-water powered by remote laser pulses.•There is no internal moving part in the thruster.•The conversion efficiency to kinetic energy increased significantly in smaller thruster.•The thrusters also move reliably at low Reynolds number regime of ∼0.0001.

Thrusters with 900–2000 μm in lengths and 340–800 μm in diameters are fabricated from glass tubes and light-absorbing graphite cores. The smallest thruster moves ∼2300 μm in water powered by a remote laser beam of 1.1 W for 30 ms. The thrusters also move reliably at low Reynolds number of ∼10−4 in glycerol. The conversion efficiency from thermal energy of a laser pulse to kinetic energy increases significantly as the size of the thruster decreases. This simple mechanism can be utilized for the propulsion engines of a μm-sized untethered swimmer in water at low Reynolds number regime.