Optical trapping force

S. B. Smith, Y. Cui, and C. Bustamante, An optical-trap force transducer that operates by direct measurement of light momentum. Methods Enzymol. 361, 134-162 (2003). 

Kurachi M, Hoshi M, Tashiro H (1995) Buckling of a single microtubule by optical trapping forces direct measurement of microtubule rigidity. Cell Motil Cytoskeleton 30(3) 221-228... 

Fig. 55 The origin of optical trapping force, which provides various mechanisms for micro-nanodevice optical actuating... 

Figure C 1.4.8. (a) An energy level diagram showing the shift of Zeeman levels as the atom moves away from the z = 0 axis. The atom encounters a restoring force in either direction from counteriDropagating light beams, (b) A typical optical arrangement for implementation of a magneto-optical trap.

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...

J. E. and Chu, S. (1986) Observation of a single-beam gradient force optical trap for dielectric particles. Opt. Lett., 11, 288-290. 

Hotta, J., Takasaki, H., Eujiwara, H. and Sasaki, K. (2002) Precise analysis of optically trapped particle position and interaction forces in the vidnity of an interface. Int. J. Nanosci., 1, 645-649. 

In optical tweezer experiments, the optical scattering force is used to trap particles, but the force can also be used to control the shape of liquid droplets26. An infrared laser with 43-mW power focused onto a microdroplet on a superhydrophobic surface enabled up to 40% reversible tuning of the equatorial diameter of the droplet26. Such effects must naturally also be taken into account when exciting laser modes in droplets in experiments with levitated drops. 

Hopkins, R. J. Mitchem, L. Ward, A. D. Reid, J. P., Control and characterisation of a single aerosol droplet in a single beam gradient force optical trap, Phys. Chem. Chem. Phys. 2004, 6, 4924 4927... 

Tadir, Y., Wright, W.H., Vafa, O., Ord, T., Asch, R.H., and Bems, M.W., Force generated by human sperm correlated to velocity and determined using a laser generated optical trap, Fertil. Steril., 53, 1990, 944-947. 

Fig, 9. (a) Optical trapping (b) The use of an optical trap to estimate extensions and forces in single macromolecules. Adapted from Bennink [82], For details see text. 

Using optical traps, Cui and Bustamante [76] stretched isolated chicken erythrocyte fibers, and Bennink et al. [77] pulled on fibers directly reconstituted in the flow cell from X-DNA and purified histones with the help of Xenopus extracts (see Fig. 10a for a schematic of the latter experiment). Up to 20 pN, the fibers underwent reversible stretching, but applying stretching forces above 20 pN led to irreversible alterations, interpreted in terms of removal of histone octamers from the fibers with recovery of the mechanical properties of naked DNA. 

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