lateral trap anisotropy S, evaluated at x-offset= 50nm(with --offset adjusted to yield maximum lateral trapping force Fr), is seen in Fig. 6 to be positive for small particle diameters, negative when the particle size is comparable to the wavelength of the trap beam, and weakly positive for d> 1. 4um (a) Objective /(=147) +1.0(c) y(um) x(um) +1.0-1.0 x(um) +10 Fig. 7(a)A linearly-polarized Gaussian beam having wavelength 20=532nm and 1/e(ampli- tude) radius ro=4.0mm is focused through a 1. 4NA oil immersion objective lens, The lens has focal length f=3.0mm and aperture radius(at the entrance pupil)Ra=2. 85mm; the refrac- tive index of the immersion oil is 1.47. a glass plate of the same index as the oil separates the oil from the water(rater =1. 33), where the focused spot is used to trap various dielectric beads. The marginal rays are lost by total internal reflection at the glass-water interface, there ome degree of apodization due to Fresnel reflection at this interface, but the phase aber- induced by the transition from oil/glass to water are ignored in our calculations. The of the spherical aberrations thus induced is justifiable, so long as the trap is not too far from the oil/water interface, Ref. [12].(b-d) Logarithmic plots of the intensity distribu- tion for x-, y, and --components of the E-field at the focal plane. The relative peak intensi- es are lExl-: Eyl- E-F- 1000: 9: 200. The total intensity distribution at the focal plane 1(x,y)=Ex+Erk+E-l (not shown) is elongated in the x-direction, the full-width at half- maximum intensity(FWHM)of the focused spot is 300nm along x and 196nm along y. The transmission efficiency of the oil/glass-to-water interface is 92.6%, that is, the overall loss of optical power to total-internal and Fresnel reflections at this interface is 7.4% #67575-$15.00USD Received 15 February 2006, revised 7 April 2006, accepted 10 April 2006 (C)2006OSA 17 April 2006/Vol 14, No 8/OPTICS EXPRESS 3667lateral trap anisotropy sl, evaluated at x-offset = 50nm (with z-offset adjusted to yield maximum lateral trapping force Fx), is seen in Fig. 6 to be positive for small particle diameters, negative when the particle size is comparable to the wavelength of the trap beam, and weakly positive for d > 1.4μm. (b) -1.0 x (μm) +1.0 -1.0 x (μm) +1.0 +1.0 y (μm) -1.0 (c) (d) (a) Glass Plate (n = 1.47) Water (n = 1.33) Oil (n = 1.47) x z Objective E Fig. 7. (a) A linearly-polarized Gaussian beam having wavelength λ0=532nm and 1/e (ampli￾tude) radius r0= 4.0mm is focused through a 1.4NA oil immersion objective lens. The lens has focal length f =3.0mm and aperture radius (at the entrance pupil) Ra=2.85mm; the refrac￾tive index of the immersion oil is 1.47. A glass plate of the same index as the oil separates the oil from the water (nwater=1.33), where the focused spot is used to trap various dielectric beads. The marginal rays are lost by total internal reflection at the glass-water interface; there is also some degree of apodization due to Fresnel reflection at this interface, but the phase aber￾rations induced by the transition from oil/glass to water are ignored in our calculations. The neglect of the spherical aberrations thus induced is justifiable, so long as the trap is not too far from the oil/water interface, Ref. [12]. (b)-(d) Logarithmic plots of the intensity distribu￾tion for x-, y-, and z-components of the E-field at the focal plane. The relative peak intensi￾ties are |Ex| 2:|Ey| 2: |Ez| 2≈ 1000 : 9 : 200. The total intensity distribution at the focal plane, I(x,y) = |Ex| 2 +|Ey| 2 +|Ez| 2, (not shown) is elongated in the x-direction; the full-width at half￾maximum intensity (FWHM) of the focused spot is 300nm along x and 196nm along y. The transmission efficiency of the oil/glass-to-water interface is 92.6%; that is, the overall loss of optical power to total-internal and Fresnel reflections at this interface is 7.4%. #67575 - $15.00 USD Received 15 February 2006; revised 7 April 2006; accepted 10 April 2006 (C) 2006 OSA 17 April 2006 / Vol. 14, No. 8 / OPTICS EXPRESS 3667