Two-Beam Photon Force Measurement System

Figure 7.3 shows the two-beam photon-force measurement system using a coaxial illumination photon force measurement system. Two microparticles dispersed in a liquid are optically trapped by two focused near-infrared beams ( 1 pm spot size) of a CW Nd YAG laser under an optical microscope (1064 nm, 1.2 MWcm , lOOX oil-immersion objective, NA = 1.4). The particles are positioned sufficiently far from the surface of a glass slide in order to neglect the interaction between the particles and the substrate. Green and red beams from a green LD laser (532 nm, 21 kWcm ) and a He-Ne laser (632.8 nm, 21 kW cm ) are introduced coaxially into the microscope and slightly focused onto each microparticle as an illumination light (the irradiated area was about 3 pm in diameter). The sizes of the illumination areas for the green and red beams are almost the same as the diameter of the microparticles (see Figure 7.4). The back scattered light from the surface of each microparticle is...

Figure 7.3 A schematic of a two-beam photon-force measurement system. Obj objective lens (lOOx oil immersion, N.A. 1.4), PBS polarization beam splitter, FI color filter for eliminating red illumination laser beam, F2 color filter for eliminating green illumination laser...

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