Trapping of multiple particles by space speckle field and infrared microscopy

Optical tweezer technology is widely used in trapping and manipulating micro- and nano-sized particles, mainly including the trapping of transparent particles in water and the trapping of absorbing particles in air. In this paper, a frosted glass diffuser is irradiated by laser beam, and a subjective speckle field is generated in the image plane of a lens after the laser has transmitted the lens. The speckle field is spatially distributed, and contains multiple bright spots and dark spots. A large number of dark spots surrounded by bright spots are spatial energy traps, and can be used to trap a large number of absorbing particles. The sizes and densities of trapped particles are about 2-8 mu m and 1-2 g/cm(3). In addition, an infrared microscope is used to record the infrared images of the particles trapped by the speckle field, and the infrared images show that the temperature of trapped particles rises by absorbing the light energy, which verifies that the mechanism of trapping absorbing particles by speckle field is photophoretic force.