The Mechanical Effect Of Light On The Material

The mechanical effect of light has become one of hot research topics in the field of optics. Because the light carries energy and momentum, when light travels through the medium or reflected, energy will be passed on to the medium, leading to optical radiation pressure, which has been used for more and more widely in technical applications. Thus, research into the mechanical effect of light has important academic significance. On the other hand, particle image velocimetry (PIV) technology is a non-contact measurement technology. In this work, liquid flows were visualized by black particles which were then videoed by a CCD microscope. The liquid flows were driven by laser radiation. Afterwards, the screenshot images and taken from the video files and then were analyzed using a PIV software to obtain the speed field of flow. The advantages of the PIV technology are:(1) it can avoid the interference of instrument;(2) the velocity field of the whole flow field can be obtained directly through the PIV technology;(3) the precision of the measured data is high. In the recent decades, PIV technology has been becoming highly developed. It can be used to study both2d and3d flow fields of liquid. It has become an important technology for measurement of flow field.In the study of the project, we observed for the first time-that light radiation can drive tangential micro/mili-scale flows in vicinity of the liquid-liquid interface between two immiscible liquids. Then, an in-depth systematic study was made for this phenomenon via particle image velocimetry technology. The results show that the strength of these light-driven flows strongly depend on the radiation power of the excitation light used, the inclination of the liquid-liquid interface, the thickness of the top-layer liquid, and the concentrations of the liquid involved. The light used is provided from an optical-fiber coupled continuous-wave infra-red laser source, with a radiation power of14mw and a wave-length of1552.1nm. The laser beam is set to vertical down to a spot in the water-bubble area, where the local angle formed by the decane-water interface to the horizontal is about30°. With a radiation power of14mW, the fastest speed of the decane film can reach0.74mm/s. The strength of the flows increases with the laser power and inclination of the liquid-liquid interface but decreases with the thickness of top-layer liquid. Adding ethanol into water in the decane-water system weakens the strength of the flows remarkably. As a new physical phenomenon, its mechanism is yet unclear. In our work, we propose that the asymmetric deflection of the IR light is the most fundamental reason. Thermo-capillary effects caused by asymmetric heating and recoil effects associated with change in the momenta of photons, both occurring associated with the asymmetric deflection of the IR light used, are also proposed to be the possible physical mechanisms responsible behind the phenomena.