Net flow generated by laser beam with rotating polarization in proximity of side wall. (a) If the center of the laser beam is close to the side wall of a microfluidic channel, which imposes non-slip boundary condition, part of the vortex is suppressed. Inset shows the beam direction (red arrow) and the plane at which the cross-section of the relevant fields is drawn (in green). (b) Oscillation of the flow rate through the channel and its time average. Net flow rate in the channel is along the x direction. (c) Optimization of the beam center position in the channel. Too close to the boundary, the director field is strongly conditioned by the surface anchoring and does not follow the electric field. If the laser beam is centered in the middle of the channel, flow field is bidirectional with zero net flow. (d) Optimization of the flow rate with respect to rotation frequency (in units of electric field time scale τE and director relaxation time scale τdir). At low frequencies the director field follows the electric field, but the flow magnitude is small, because of slow rotation of the director field. Linear response to the rotation frequency is shown by the dotted line. At higher frequencies, net flow generation is diminished. In given geometry, an optimal rotation frequency is ≈ 14/τdir.