Photophoresis

Photophoresis is physical phenomenon of suspension and moving of small droplets or solid clusters (say, of size between several nanometers and some hundreds microns) by the intensive (say, several watt) light beam in a gas or a liquid . The trapping and movement of particles may affected by the external electric and/or magnetic field .

Usually, the laser beam is used to suspend the particles. Some particles move in the direction of the beam (positive photophoresis) and some move in the opposite direction (negative photophoresis).

Usually the guiding (trapping) of the particles is attributed to the electric field (due to their dielectric succeptibility) while the movement is interpreted as the result of non-uniform heating of the particles. No simple "finger explanation" of this phenomenon is available, but Photophoresis is believed to allow the selective trapping of bacterias, viruses, etc. from a biological objects (for example, a blood).