As the name implies, optical tweezers are tweezers formed by light, which is based on the principle of light radiation pressure.

principle

The proposal of light radiation pressure originated from Kepler and Newton's era. At that time, the theory thought that light was a particle, and according to Newton's mechanical principle, the moving particle beam would produce pressure. In astronomy, the comet's tail is always facing away from the sun, which is a typical example of light radiation pressure. However, the existence of light pressure and Maxwell's theoretical prediction of radiation pressure were proved by experiments in the laboratory at the beginning of the 20th century.

history

In 1960s, when laser appeared as a coherent light source with extremely high brightness, the research on optical pressure had a revolutionary change. In the early 1970s, people began to make a comprehensive and in-depth study of the radiation pressure of laser, especially the theoretical discussion and experimental observation of the nature and mechanism of the radiation pressure on atoms under different conditions, thus developing experimental technologies such as laser beam deflection, laser cooling, photon viscose and atomic fountain, and at the same time using light pressure to study atomic capture and particle manipulation. It is because of the pioneering research on laser cooling that the famous Chinese scientist, Professor Steven Chu of Stanford University and two others won the 1997 Nobel Prize in Physics.

As we know, light source has both thermal effect and radiation effect. For ordinary light sources, the pressure generated by thermal effect is several orders of magnitude larger than that generated by simple momentum exchange, so it is difficult to obtain sufficient radiation pressure. The appearance of laser changed this situation and fully reflected the radiation pressure of light. At the same time, the cross-section distribution of laser beam has a simple and clear mathematical expression, which is convenient for theoretical treatment and makes it possible to study optical traps and optical levitation. Laser optical tweezers use the mechanical effect of momentum transfer between laser and matter to form a three-dimensional optical potential well.