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.