AN ENERGY MODEL ON THE ENIGMATIC PHENOMENA INDUCED BY THE FOCUSED AND UNFOCUSED INCIDENT CW LIGHT BEAM
Biao Wang (Sun Yat-sen University)
Prager Medal Symposium in honor of George Weng: Micromechanics, Composites and Multifunctional Materials
Wed 1:30 - 2:50
MacMillan 117
It is a well-known fact that light can produce a force on the medium. Long time ago, Maxwell (1891) showed a calculation of pressure exerted by the sunlight at the surface of the Earth. Recently, optical tweezers become a very efficient tool to manipulate the soft materials and particles by using a light beam. One century ago, Minkowski and Abraham proposed two quite different formulae for the light momentum in the dielectric media, which dominants the force on the media. Many scientists have been working hard to clarify the two expressions of the light momentum. Some experimental results seem to support the Minkowski form, whereas some seem to support Abraham form. The problem to determine which momentum is correct has become the famous Abraham-Minkowski dilemma. A very famous experiment was carried out by Ashkin and Dziedzie in 1973. They observed an outward bulge at the water-air interface when a 60 ns tightly focused light pulse enters (or leaves) the water. Just recently, She et.al. showed experimentally that a focused CW 532 nm light beam was incident onto the surface of a week absorption film of white mineral oil on the surface of pure water, an outward bulge really occured; however, when the incident beam was unfocused, it induced a concave at the oil surface due to the optical pressure. To give a consistent explanation, an energy model based on the virtual displacement principle was established, and the theoretical prediction is shown in coincidence with the experimental results.