NanophotonicsandOpticalControlofSingle纳米光子学和光学控制单.ppt

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1、Introduction to Optical TweezersOUTLINEv Brief History of Optical Tweezersv Principles of Optical Tweezersv Optical Trapping Forcesv The Optical Tweezers Set up & The Experimental Method v Research Areas and Possible usesWhat isOptical Tweezers - one of the techniques, which use a highly focused bea

2、m to control and hold microscopic particles. HistoryvJohannes Kepler (1571-1630): noticed comets tail always points away from the sun, because of the suns radiation pressure.vJames Maxwell (1831-1879): existence of the light pressure was demonstratedvP. N. Lebedev (1866-1912): measured the light pre

3、ssurevAlbert Einstein (1879-1955): confirmed that photons possess its own momentumvArthur Compton (1892-1962:) showed the existence of the light momentum on his experimental workLight transfers momentum to mattervIn 1970 A. Ashkin proved that light can grab and release nanometer particles by its mom

4、entum, using the light Quantum Theory. vIn 1986, A. Ashkin proved that he could trap 10nm diameter dielectric particles only using gradient forcevIn 1987, A. Ashkin showed the damage-free manipulation on cells using an infrared laserArthur Ashkin HistoryTypes of OTv Single Beam Optical Tweezersv Dua

5、l beam Optical Tweezersv Holographic Optical TweezersPrinciples of OTvExert a laser beam to the very small particle, the light will be reflected or refracted from the surface of the particle. The momentum of photon, refracted to the particle, will be changed and by the law of the conservation of the

6、 momentum, the force of the variation of momentum will be exerted to the small particle.(a) If the particle is to the left, say, of the center of the beam,it will refract more light from the right to the left, rather than vice versa.The net effect is to transfer momentum to the beam in this directio

7、n,so, by Newtons third law, the particle will experience an equal andopposite force back towards the center of the beam. In thisexample the particle is a dielectric sphere(b) Similarly, if the beam is tightly focused it is possible for the particle to experience a force that pushes back towards the

8、laser beam. (c) We can also consider an energetic argument: when a polarizable particle is placed in an electric field, the net field is reduced. The energy of the system will be a minimum when the particle moves to wherever the field is highest which is at the focus. Therefore, potential wells are

9、created by local maxima in the fields.How optical tweezers work Optical tweezers: the next generation, Kishan Dholakia, 2002, physics worldConditions of OT The Ray Optical Regime of Optical Tweezers Wonhoe Koo, Seoul, 2005 The Electromagnetic Regime of Optical Tweezers Two ForcesThe Electromagnetic

10、Regime of Optical Tweezers The Gradient ForceTwo ForcesThe Gradient ForceThe Ray Optical Regime of Optical Tweezers Wonhoe Koo, Seoul, 2005 The Basic OT Set upA generic optical tweezers diagram with only the most basic componentsThe Optical Tweezers, WikipediaResearch areasvStudy and manipulate part

11、icles such as atoms, molecules and small dielectric spheres (in range from mm to nm).vForce measurements of biological objects in piconewton range.vBiological investigations involving cellsvCutting and ablating biological objects (Cell fusion and DNA cutting)vForce measurements of cell structures and DNA coilingvElasticity measurements of DNAThank you -Keonwoo Nam