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Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 5 — Mar. 11, 2013
  • pp: 6186–6195

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Morphology-dependent resonance of the optical forces on Mie particles in an Airy beam

Yang Yang, Wei-Ping Zang, Zi-Yu Zhao, and Jian-Guo Tian  »View Author Affiliations


Optics Express, Vol. 21, Issue 5, pp. 6186-6195 (2013)
http://dx.doi.org/10.1364/OE.21.006186


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Abstract

Morphology-dependent resonance (MDR) of the optical forces for a particle illuminated by Airy beams is investigated with respect to its internal field distribution. We find the ring structures arising from the resonance transform significantly with the parametric evolution of Airy evanescent wave, and the interference of the internal waves have a great impact on the Q factor and the background of the resonant peak, but it’s not proper for Airy transmitted wave. The multiple reflections of the evanescent wave between the particle and the interface are also investigated, which show significant impacts on the region where the energy concentrate in.

© 2013 OSA

1. Introduction

Since the first demonstration of optical trapping of a dielectric particle by Ashkin [1

A. Ashkin, “Acceleration and Trapping of Particles by Radiation Pressure,” Phys. Rev. Lett. 24(4), 156–159 (1970). [CrossRef]

], optical tweezers have been widely used for manipulating micro-particles without mechanical contact [2

P. H. Jones, E. Stride, and N. Saffari, “Trapping and manipulation of microscopic bubbles with a scanning optical tweezer,” Appl. Phys. Lett. 89(8), 081113 (2006). [CrossRef]

–6

S. Kawata and T. Sugiura, “Movement of micrometer-sized particles in the evanescent field of a laser beam,” Opt. Lett. 17(11), 772–774 (1992). [CrossRef] [PubMed]

]. The observed variation of the optical forces as a function of the wavelength or the size of a spherical particle shows a regular series of resonance peaks which is generally known as Morphology-dependent resonance (MDR) [7

J. U. Nöckel and A. D. Stone, “Ray and wave chaos in asymmetric resonant optical cavities,” Nature 385(6611), 45–47 (1997). [CrossRef]

–12

M. L. Gorodetsky and V. S. Ilchenko, “Optical microsphere resonator: optimal coupling to high-Q whispering-gallery modes,” J. Opt. Soc. Am. B 16(1), 147–154 (1999). [CrossRef]

]. Extensive researches have been made on this phenomenon, such as MDRs in a dielectric sphere with tiny inclusions [13

P. T. Leung, S. W. Ng, K. M. Pang, and K. M. Lee, “Morphology-dependent resonances in dielectric spheres with many tiny inclusions,” Opt. Lett. 27(20), 1749–1751 (2002). [CrossRef] [PubMed]

], in stimulated Raman scattering [14

J. B. Snow, S. X. Qian, and R. K. Chang, “Stimulated Raman scattering from individual water and ethanol droplets at morphology-dependent resonances,” Opt. Lett. 10(1), 37–39 (1985). [CrossRef] [PubMed]

], in a bisphere system [15

H. Miyazaki and Y. Jimba, “Ab initio tight-binding description of morphology-dependent resonance in a bisphere,” Phys. Rev. B 62(12), 7976–7997 (2000). [CrossRef]

], and in a plane evanescent wave [16

J. Ng and C. T. Chan, “Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes,” Appl. Phys. Lett. 92(25), 251109 (2008). [CrossRef]

].

Recently, the Airy beam which was first experimentally realized in 2007 [17

G. A. Siviloglou and D. N. Christodoulides, “Accelerating finite energy Airy beams,” Opt. Lett. 32(8), 979–981 (2007). [CrossRef] [PubMed]

, 18

G. A. Siviloglou, J. Broky, A. Dogariu, and D. N. Christodoulides, “Observation of accelerating Airy beams,” Phys. Rev. Lett. 99(21), 213901 (2007). [CrossRef] [PubMed]

], can be well applied into the conventional optical tweezers [19

J. Baumgartl, M. Mazilu, and K. Dholakia, “Optically mediated particle clearing using Airy wavepackets,” Nat. Photonics 2(11), 675–678 (2008). [CrossRef]

, 20

J. Baumgartl, G. M. Hannappel, D. J. Stevenson, D. Day, M. Gu, and K. Dholakia, “Optical redistribution of microparticles and cells between microwells,” Lab Chip 9(10), 1334–1336 (2009). [CrossRef] [PubMed]

], which can avoid divergence and diffraction within a certain propagating distance for its unique features: “non-diffracting” and transverse accelerations. A. V. Novitsky et al. analyzed the dynamics of nonparaxial Airy beams which show the role of evanescent waves [21

A. V. Novitsky and D. V. Novitsky, “Nonparaxial Airy beams: role of evanescent waves,” Opt. Lett. 34(21), 3430–3432 (2009). [CrossRef] [PubMed]

]. And we have investigated the optical forces exerted on a Mie particle in the Airy evanescent field theoretically [22

Y. Yang, W. P. Zang, Z. Y. Zhao, and J. G. Tian, “Optical forces on Mie particles in an Airy evanescent field,” Opt. Express 20(23), 25681–25692 (2012). [CrossRef] [PubMed]

]. Here, we present a systematic study on the MDRs of the optical forces for a particle illuminated by an Airy beam passes through the interface with respect to the electric field distribution inside the particle which reflects the motions of the internal wave.

We find the ring structures arising from the resonances change significantly with different incident angle and transmitted distance for Airy evanescent wave, and the interference strength of the internal wave have a great influence on the Q factor and the background of the resonant peak. E.g., travelling wave patterns correspond to high Q peaks, while strong interference patterns for high background peaks. But the key structure of the internal field for the Airy transmitted wave won’t change. The quality factor Q of the resonant peaks for a damped wave is much larger than that for a propagating wave. The multiple reflections of the Airy evanescent wave between the particle and the interface are also investigated, which show significant impacts on the region where the energy concentrate in.

2. Theory and description

The schematic diagram of the scattering problem is shown in Fig. 1 . The origin of coordinate system coincides with the center of the spherical particle at a distance d from the interface. The refractive indices of the mediums below and above interface are n1 = 1.5 and n2 = 1.0, representing the glass-air interface. The refractive index of dielectric sphere is n3. The parameters of the incident two-dimensional (2D) Airy beam are chosen as: wavelength λ = 750 nm, the characteristic lengths x0 = y0 = 2 μm, the aperture coefficient which determines the beam propagating distance a0 = 0.1. The Airy beam center is at (xc, yc, zc). The input power P = 1 W. We take x-z plane as the plane of incidence and ( x^, y^, z^) as unit vectors.

Fig. 1 An Airy beam is incident from below with incident angle θ1. A spherical particle with radius a is located above the interface ( z>−d).

For a perpendicular polarized 2D Airy beam in y-direction, the vector potential A can be expressed in terms of its angular spectrum representation:
A= y^ C i k0 ∬ d sxd syΦ ( sx, sy)exp [ i fi ( x,y,z)],
(1)
where Φ ( sx, sy)is its Fourier spectrum:
Φ ( sx, sy)∝exp [ i3 ( x¯03 sx3+ y¯03 sy3−3 a02 x¯0 sx−3 a02 y¯0 sy)− a0 ( x¯02 sx2+ y¯02 sy2)].
(2)
sx= nxcos θ1− nzsin θ1,   sy= ny,  sz= nxsin θ1+ nzcos θ1,  x¯0= n1 k0 x0,   y¯0= n1 k0 y0.
(3)
where fi ( x,y,z)= n1 k0 [ nx ( x− xc)+ ny ( y− yc)+ nz ( z− zc)],C is the normalization factor, (nx, ny, nz) denote the dimensionless direction cosines of the wave vector k1 along the Cartesian coordinate axes. The integration is over the domain of sx2+ sy2<1and nz>0.

The electromagnetic fields E and H can be derived through the Maxwell equations in the Gaussian system of units:
E= i n12 k0∇×∇× A,  H=∇× A,
(4)
Substituting Eq. (1) into Eq. (4), we derive the incident electromagnetic fields of Airy beam as follows:
E ( i)=C ∬ d sxd sy nx s^i+ ny nz p^i 1− nz2Φ ( sx, sy)exp [ i fi ( x,y,z)],
(5)
H ( i)= n1C ∬ d sxd sy ny nz s^i− nx p^i 1− nz2Φ ( sx, sy)exp [ i fi ( x,y,z)],
(6)
where
s^i=− ny x^+ nx y^,  p^i= ( nx x^+ ny y^) nz− ( 1− nz2) z^.
(7)
representing the vectors perpendicular and parallel to the plane of incidence, respectively. Then coupled with the transmitted Fresnel amplitude coefficients for p polarization and s polarization, respectively,
Tp= 2 n1 nz n1ξ+ n2 nz,  Ts= 2 n1 nz n1 nz+ n2ξ.
(8)
where ξ= [ 1− ( n1/ n2)2 ( nx2+ ny2)] 1/2, the expressions for the transmitted electromagnetic fields though the dielectric interface can be derived as:
E ( t)=C ∬ d sxd sy nx Ts s^t+ ny nz Tp p^t 1− nz2Φ ( sx, sy)exp [ i ft ( x,y,z)],
(9)
H ( t)= n2C ∬ d sxd sy ny nz Tp s^t− nx Ts p^t 1− nz2Φ ( sx, sy)exp [ i ft ( x,y,z)],
(10)
where

s^t=− ny x^+ nx y^,  p^t= ( nx x^+ ny y^)ξ− ( n1/ n2) ( 1− nz2) z^.
(11)
ft ( x,y,z)= n1 k0 [ nx ( x− xc)+ ny ( y− yc)− nz ( zc+d)]+ n2 k0 ( z+d)ξ.
(12)

On paraxial condition, nx≈sin θ1,  ny≈0, if θ1> θ crit,  ( θ crit= sin −1 ( n2/ n1)≈0.73 rad), the parameter ξ will be an imaginary number, the incident Airy beam is totally reflected on the interface and an evanescent electromagnetic wave is generated on the side of the medium n2. In this case, the integral domain is ( n1/ n2)2 ( nx2+ ny2)>1.

By substituting the expressions in Eq. (9)–(12) into the Arbitrary-Beam theory (ABT) [23

J. P. Barton, D. R. Alexander, and S. A. Schaub, “Internal and near-surface electromagnetic fields for a spherical particle irradiated by a focused laser beam,” J. Appl. Phys. 64(4), 1632–1639 (1988). [CrossRef]

, 24

J. P. Barton, D. R. Alexander, and S. A. Schaub, “Theoretical determination of net radiation force and torque for a sphereical particle illuminated by a focused laser beam,” J. Appl. Phys. 66(10), 4594–4602 (1989). [CrossRef]

], after using a great deal of recursions and orthogonal relationships, the coefficients A lmand B lm of the expansions of the Airy transmitted field can be derived as follows:
A lm= Ac ∬ d sxd syΦ ( sx, sy)exp [ i⋅g ( r0)] ( nx−i ny)m ( 1− nz2) ( m+1)/2 [ i nx β lm (ξ) Ts+ ny nz α lm (ξ) Tp],
(13)
B lm= Bc ∬ d sxd syΦ ( sx, sy)exp [ i⋅g ( r0)] ( nx−i ny)m ( 1− nz2) ( m+1)/2 [ i nx α lm (ξ) Ts+ ny nz β lm (ξ) Tp],
(14)
where Acand Bcare constants:
Ac=−C i l+1 l ( l+1) α2 π ( 2l+1) ( l−m)! ( l+m)!,  Bc= n2C il l ( l+1) α2 π ( 2l+1) ( l−m)! ( l+m)!,
(15)
g ( r0)=− n1 k0 [ nx xc+ ny yc+ nz ( zc+d)]+ n2 k0ξd.
(16)
the functions α lm (ξ)and β lm (ξ)are defined as
α lm (ξ)=ξ [ Pl m+1 (ξ)+ ( l+m) ( l−m+1) Pl m−1 (ξ)]−2m ( 1− ξ2) 1/2 Plm (ξ),
(17)
β lm (ξ)= Pl m+1 (ξ)− ( l+m) ( l−m+1) Pl m−1 (ξ).
(18)
The expansion coefficients aland bl which correspond to the l th scattered electric wave and magnetic wave term by the particle respectively are found to be:
al= ψ′l ( n˜α) ψl (α)− n˜  ψl ( n˜α) ψ′l (α) n˜  ψl ( n˜α) ξl (1)  ′ (α)− ψ′l ( n˜α) ξl (1) (α),
(19)
bl= n˜  ψ′l ( n˜α) ψl (α)− ψl ( n˜α) ψ′l (α) ψl ( n˜α) ξl (1)  ′ (α)− n˜  ψ′l ( n˜α) ξl (1) (α).
(20)
where k0= 2π/λ, α= n2 k0a,  n˜= n3/ n2,a, n3 is radius and refractive index of the particle, respectively. ξl (1)= ψl−i χl, ψland χl are the Riccati-Bessel functions.

So we derive the force expressions for the Airy transmitted wave based on ABT. It is known that the MDRs of the optical forces originate from the specific coefficients aland blof partial scattering waves in resonance, which is Re ( al)=1and Im ( al)=0, or Re ( bl)=1and Im ( bl)=0 [9

P. Chylek, J. T. Kiehl, and M. K. W. Ko, “Optical levitation and partial-wave resonances,” Phys. Rev. A 18(5), 2229–2233 (1978). [CrossRef]

].

3. Results and discussions

The data programs were written in double-precision FORTRAN. The coefficients Alm and Blm appear in Eq. (13)–(14) obtained by two-dimensional integral. We computed the integral with trapezoidal method. The integral range and step size have been chosen carefully to ensure the absolute errors less than 10−6. In general, the expression for the radiation force, written symbolically as Fl= ∑ fl,has to be truncated at some upper value of l. Our general choice was to terminate the series when | F l+1/ Fl−1|< 10 −4.

First, we investigate the behaviors of the optical forces as a function of the particle radius in different conditions in Fig. 2 : for Airy evanescent wave, θ1 = 0.9 rad ( θ1> θ crit), (a) d = a, n3 = 1.59, (b) d = a, n3 = 1.59 + 10−3i, (c) d = 2.1a, n3 = 1.59; (d) for Airy transmitted wave, θ1 = 0.3 rad ( θ1< θ crit),d = a, n3 = 1.59; (e) enlarged plot of Fx of b18 in (a) with its resonant item l = 18. While size parameter α varies from 12.4 to 14.9 (1.48<a<1.78 μm), xc = yc = 0, zc = −(d + λ).

Fig. 2 Optical forces Fx (black line) and Fz (red line) as a function of particle radius: for Airy evanescent wave, θ1 = 0.9 rad, (a) d = a, n3 = 1.59, (b) d = a, n3 = 1.59 + 10−3i, (c) d = 2.1a, n3 = 1.59; (d) Airy transmitted wave, θ1 = 0.3 rad, d = a, n3 = 1.59; (e) enlarged plot of Fx of b18 in (a) with its resonant item l = 18.

As we can see, all the optical force curves exhibit strong oscillations of MDR that originate from the resonance of the partial scattering waves, but the shape of them are very different. Each peak in Fig. 2 can be directly related to the first-order resonance indicated. Higher-order resonances of lower modes [9

P. Chylek, J. T. Kiehl, and M. K. W. Ko, “Optical levitation and partial-wave resonances,” Phys. Rev. A 18(5), 2229–2233 (1978). [CrossRef]

] are not observable within this range of size parameters. For Airy evanescent wave in (a), the peaks of Fx are much sharper than those for Airy transmitted waves in (d). If we define Q = ares/△a, where ares is the resonant radius, △a is the width of the radius range of which the force is half of its maximum ares. For b19 peak in (a), Q≈104. This high Q properties of the optical forces can be utilized for accurate sorting of micro-particles, which select resonant ones, and leaving those at non-resonance untouched.

In Fig. 2(b), we added a small imaginary part in its refractive index, n3 = 1.59 + 10−3i this time. As we can see, the absorptions generated by the complex refractive index make the peaks a considerable decline, while △a increased. If the imaginary part increases further, (e.g. for nickel, n3 = 1.5 + 3.1i), the oscillations would disappear by strong absorptions [22

Y. Yang, W. P. Zang, Z. Y. Zhao, and J. G. Tian, “Optical forces on Mie particles in an Airy evanescent field,” Opt. Express 20(23), 25681–25692 (2012). [CrossRef] [PubMed]

]. With a transmitted distance of d = 2.1a shown in Fig. 2(c), al peaks emerge, dominating with respect to the bl peaks on this occasion, while the Q factor is much smaller, meaning a less size-selective manipulation. Figure 2(e) shows a detailed plot of Fx of b18 compared with its resonant item l = 18, as observed, the resonant item accounts for the majority of the peak.

The red lines show the gradient forces that act on the particle along z direction. As we can see in Fig. 2(a) and 2(b), the gradient force can be attractive or repulsive with the source of evanescent wave; the reason is that the optical force is a bilinear product of the incident field and the scattering coefficients al and bl [9

P. Chylek, J. T. Kiehl, and M. K. W. Ko, “Optical levitation and partial-wave resonances,” Phys. Rev. A 18(5), 2229–2233 (1978). [CrossRef]

, 16

J. Ng and C. T. Chan, “Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes,” Appl. Phys. Lett. 92(25), 251109 (2008). [CrossRef]

]. But for transmitted wave in Fig. 2(d), both Fx and Fz are resonant scattering forces and exhibit similar shape.

In order to understand the formation of the resonant peaks, we investigate the distributions of the electric field magnitude | E| of which the Airy evanescent wave interacted with the polystyrene spherical particle situating on the interface in Fig. 3 : (a) y-z plane (x = 0), (b) x-y plane (z = 0), (c) x-z plane (y = 0) are for the resonant peak b18 and (d) x-z plane (y = 0) is for non-resonant case. The unit of electric field magnitude is statvolt/cm and 1statvolt/cm = 3 × 104 V/m. We can see: most energy is distributed in the incident x-z plane. With regard to b18 (α = 14.01, a = 1.6725 μm) in Fig. 3(a), almost all the incident wave is coupled into the particle which is confined near the surface by total internal reflection. The arrows denote the directions of Poynting vectors, indicating the internal wave travelling along the surface.

Fig. 3 Distributions of the electric field magnitude |E| of Airy evanescent wave incident upon a polystyrene spherical particle situating on the interface: (a) y-z plane (x = 0), (b) x-y plane (z = 0), (c) x-z plane (y = 0) are for b18 (α = 14.01); (d) x-z plane (y = 0) for the non-resonant case (α = 13.56). While d = a, n3 = 1.59, xc = yc = 0, zc = −(d + λ), θ1 = 0.9 rad. The unit of electric field magnitude is statvolt/cm and 1 statvolt/cm = 3 × 104 V/m.

But for the non-resonant case shown in Fig. 3(d) (α = 13.56, a = 1.619 μm, where Fz changes its sign between b17 and b18), a considerable part of the energy have not transmitted into the particle, and the internal field exhibit a chaotic distribution which would lead to the offset and loss of the energy, that causes the bottom of Fx. In y-z plane Fig. 3(a) and x-y plane Fig. 3(b), the internal field is mainly distributed in the upper and lower, left and right sides of the particle, respectively. Moreover, through the propagating directions of Poynting vectors, the conclusion can be drawn that the polystyrene sphere plays a focusing lens role.

As we know from Fig. 3, the occurrence of the resonant peak would accompany a ring structure of the surface wave in the internal field. So it is interesting to see how this structure varies with different incident angle and transmitted distance. Figure 4 shows the transformation of the internal field patterns of the resonant peaks for the polystyrene particle illuminated by Airy evanescent wave for b18, 4(a)–4(c), θ1 = 0.9 rad while transmitted distance: 4(a) d = 1.3a, 4(b) d = 1.7a, 4(c) d = 2.1a; 4(d)–4(f), d = 2a with incident angle: 4(d) θ1 = 0.75 rad, 4(e) θ1 = 0.9 rad, 4(f) θ1 = 1.05 rad; 4(g) a17, θ1 = 0.9 rad, d = 2.1a. And illuminated by Airy transmitted wave, b18: 4(h) θ1 = 0.2 rad, d = a, 4(i) θ1 = 0.5 rad, d = 2a.

Fig. 4 Variations of the ring structures of the resonant peaks: b18, (a)–(c), θ1 = 0.9 rad with transmitted distance: (a) d = 1.3a, (b) d = 1.7a, (c) d = 2.1a; (d)–(f), d = 2a, with incident angle: (d) θ1 = 0.75 rad, (e) θ1 = 0.9 rad, (f) θ1 = 1.05 rad; (g) a17, θ1 = 0.9 rad, d = 2.1a, the above for Airy evanescent wave. (h) θ1 = 0.2 rad, d = a, (i) θ1 = 0.5 rad, d = 2a, for Airy transmitted wave b18.

As we can see, for the damped wave, the ring structures exhibit significant changes with the variations of incident angle and transmitted distance. Specifically, in Fig. 4(a) with d = 1.3a, the internal field shows a traveling surface wave pattern. In Fig. 4(b) with d = 1.7a, the solid ring change to a lap of bigger bright spots (2l) [10

P. Chylek, J. D. Pendleton, and R. G. Pinnick, “Internal and near-surface scattered field of a spherical particle at resonant conditions,” Appl. Opt. 24(23), 3940–3942 (1985). [CrossRef] [PubMed]

], representing the standing wave which is caused by the interference of the counter-propagating internal waves. With the transmitted distance increase further, with d = 2.1a in Fig. 4(c), the spots become smaller, and will stabilize with further increasing of d. Moreover, the wave fronts can be seen clearly this time which is propagating in the positive x-direction, indicating a much stronger interference of the internal wave.

With the increasing of the incident angle θ1 from 0.75 to 1.05 rad, the ring structures present a different transformation process shown in Figs. 4(d)–4(f). Figure 4(g) shows the internal field distribution of a17 in Fig. 2(c). We can see, for this high background, low-Q peak, the spots around the surface disappear. But for illumination by the transmitted wave, as shown in Figs. 4(h) and 4(i), the internal field patterns present no change essentially, only the propagating directions vary with the incident angle. Likewise, the shape of its corresponding resonant peaks won’t change.

Next we investigate the relationships between the resonance peak and its corresponding internal field distribution. The resonant peaks of the optical forces in Figs. 5(a) –5(d) correspond to Figs. 4(a)–4(c), and 4(g), respectively. As we can see, the resonant peak in Fig. 5(a) of which corresponding to a solid ring of travelling wave pattern has a high Q factor (Q≈1.5 × 103), and its background approaches zero. For a larger spots of standing wave pattern which originate from the weak interference of the internal wave, as shown in Fig. 5(b), the height of its corresponding peak is reduced, the width and the background increases, leading to a lower Q factor (Q≈1.37 × 103). Furthermore, with a stronger interference pattern in Fig. 5(c), its corresponding peak has a very high background which exceeding the half of its peak value, that reduce the Q factor greatly. In Fig. 5(d) for a17, also exhibit a strong interference pattern, but the spots around the surface disappear, its resonant peak width is broadened further.

Fig. 5 The resonant peaks of the optical forces correspond to the internal wave distributions in Figs. 4(a)-(c), and 4(g), respectively.

In a summary of the above analysis, we can see that the strong interference of the internal wave around the particle would reduce the Q factor of the resonant peak, and enhance the background of the optical forces.

Finally, we investigate the impacts of multiple scattering of the Airy evanescent wave between the particle and the interface on the optical forces [25

S. Chang, J. T. Kim, J. H. Jo, and S. S. Lee, “Optical force on a sphere caused by the evanescent field of a Gaussian beam; effects of multiple scattering,” Opt. Commun. 139(4-6), 252–261 (1997). [CrossRef]

] as a function of particle radius in Fig. 6 . For convenience of comparison and clarity, the particle radius is chosen to vary in the range of (0.2<a<0.8) μm, while xc = yc = 0, n3 = 1.59, d = a, zc = −(d + λ), θ1 = 0.9 rad. The multiple scatterings considered here is up to five orders: the black lines denote the optical forces without reflection; the red, magenta, yellow, green, and blue lines represent the evanescent wave is reflected between the particle and the interface for once, twice, three, four and five times, respectively.

Fig. 6 Effects of multiple scattering of the Airy evanescent wave between the particle and the interface on the optical forces as a function of particle radius. The curves near the left arrow and near the right arrow represent Fx and Fz, respectively: the black lines denote the optical forces without reflection; the red, magenta, yellow, green, and blue lines represent the evanescent wave is reflected for once, twice, three, four and five times, respectively. While xc = yc = 0, n3 = 1.59, d = a, zc = −(d + λ), θ1 = 0.9 rad. The inset is the variation of the peaks of Fz versus the reflected times.

As we can see, the optical forces exhibit strong oscillations of MDR with the variation of particle radius, the impacts of the multiple scattering are more and more significant with the resonance enhanced, while in off-resonance regions are negligible. This is not difficult to understand: most photons of the evanescent wave are gathered in the resonance regions where the optical force is stronger, so the absorptions and dissipations from the reflections between the particle and the interface are more significant in these regions, which make the optical force reduced greatly. On the contrary, in off-resonance regions where little photons distributed in, the loss of the transmitted photons is negligible. The inset is the variation of the peaks of Fz versus the reflected times. As we can see, after experiencing five times of the reflections of the evanescent wave, the optical forces converge ultimately.

Figure 7 shows the impacts of multiple scattering on the optical forces as a function of the beam center’s displacements xc, while yc = 0, a = 0.8 μm, other parameters are the same as in Fig. 6. As we can see, the optical forces exhibit strong oscillations which are corresponding to the distributions of main lobe and the sideways of the Airy evanescent field. And the effects of the multiple scattering are more significant in the regions of bigger lobes of the Airy beam. For the same reason, most photons are distributed in where big lobes located, the more serious loss of energy there lead to the results.

Fig. 7 Effects of multiple scattering on the optical forces: as a function of beam center’s displacements xc, while yc = 0, a = 0.8 μm, other parameters are the same as in Fig. 6.

4. Conclusions

In summary, we have investigated the MDR properties of the optical forces for a Mie particle illuminated by the Airy beam transmitted through an interface. Numerical results show that the distributions of the electromagnetic field inside the particle would affect its corresponding resonant peak structure greatly. The multiple reflections of the evanescent wave between the particle and the interface are also considered. We believe that the theoretical works presented in this paper would provide better guidance on the investigations of optical micro-manipulations and near-field optics.

Acknowledgments

We acknowledge financial supports from the Natural Science Foundation of China (grant 11074130, 61275148), Chinese National Key Basic Research Special Fund (2011CB922003), and 111 Project (B07013).

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2.

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S. Kawata and T. Sugiura, “Movement of micrometer-sized particles in the evanescent field of a laser beam,” Opt. Lett. 17(11), 772–774 (1992). [CrossRef] [PubMed]

7.

J. U. Nöckel and A. D. Stone, “Ray and wave chaos in asymmetric resonant optical cavities,” Nature 385(6611), 45–47 (1997). [CrossRef]

8.

P. T. Korda, M. B. Taylor, and D. G. Grier, “Kinetically Locked-In Colloidal Transport in an Array of Optical Tweezers,” Phys. Rev. Lett. 89(12), 128301 (2002). [CrossRef] [PubMed]

9.

P. Chylek, J. T. Kiehl, and M. K. W. Ko, “Optical levitation and partial-wave resonances,” Phys. Rev. A 18(5), 2229–2233 (1978). [CrossRef]

10.

P. Chylek, J. D. Pendleton, and R. G. Pinnick, “Internal and near-surface scattered field of a spherical particle at resonant conditions,” Appl. Opt. 24(23), 3940–3942 (1985). [CrossRef] [PubMed]

11.

B. R. Johnson, “Theory of morphology-dependent resonances: shape resonances and width formulas,” J. Opt. Soc. Am. A 10(2), 343–352 (1993). [CrossRef]

12.

M. L. Gorodetsky and V. S. Ilchenko, “Optical microsphere resonator: optimal coupling to high-Q whispering-gallery modes,” J. Opt. Soc. Am. B 16(1), 147–154 (1999). [CrossRef]

13.

P. T. Leung, S. W. Ng, K. M. Pang, and K. M. Lee, “Morphology-dependent resonances in dielectric spheres with many tiny inclusions,” Opt. Lett. 27(20), 1749–1751 (2002). [CrossRef] [PubMed]

14.

J. B. Snow, S. X. Qian, and R. K. Chang, “Stimulated Raman scattering from individual water and ethanol droplets at morphology-dependent resonances,” Opt. Lett. 10(1), 37–39 (1985). [CrossRef] [PubMed]

15.

H. Miyazaki and Y. Jimba, “Ab initio tight-binding description of morphology-dependent resonance in a bisphere,” Phys. Rev. B 62(12), 7976–7997 (2000). [CrossRef]

16.

J. Ng and C. T. Chan, “Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes,” Appl. Phys. Lett. 92(25), 251109 (2008). [CrossRef]

17.

G. A. Siviloglou and D. N. Christodoulides, “Accelerating finite energy Airy beams,” Opt. Lett. 32(8), 979–981 (2007). [CrossRef] [PubMed]

18.

G. A. Siviloglou, J. Broky, A. Dogariu, and D. N. Christodoulides, “Observation of accelerating Airy beams,” Phys. Rev. Lett. 99(21), 213901 (2007). [CrossRef] [PubMed]

19.

J. Baumgartl, M. Mazilu, and K. Dholakia, “Optically mediated particle clearing using Airy wavepackets,” Nat. Photonics 2(11), 675–678 (2008). [CrossRef]

20.

J. Baumgartl, G. M. Hannappel, D. J. Stevenson, D. Day, M. Gu, and K. Dholakia, “Optical redistribution of microparticles and cells between microwells,” Lab Chip 9(10), 1334–1336 (2009). [CrossRef] [PubMed]

21.

A. V. Novitsky and D. V. Novitsky, “Nonparaxial Airy beams: role of evanescent waves,” Opt. Lett. 34(21), 3430–3432 (2009). [CrossRef] [PubMed]

22.

Y. Yang, W. P. Zang, Z. Y. Zhao, and J. G. Tian, “Optical forces on Mie particles in an Airy evanescent field,” Opt. Express 20(23), 25681–25692 (2012). [CrossRef] [PubMed]

23.

J. P. Barton, D. R. Alexander, and S. A. Schaub, “Internal and near-surface electromagnetic fields for a spherical particle irradiated by a focused laser beam,” J. Appl. Phys. 64(4), 1632–1639 (1988). [CrossRef]

24.

J. P. Barton, D. R. Alexander, and S. A. Schaub, “Theoretical determination of net radiation force and torque for a sphereical particle illuminated by a focused laser beam,” J. Appl. Phys. 66(10), 4594–4602 (1989). [CrossRef]

25.

S. Chang, J. T. Kim, J. H. Jo, and S. S. Lee, “Optical force on a sphere caused by the evanescent field of a Gaussian beam; effects of multiple scattering,” Opt. Commun. 139(4-6), 252–261 (1997). [CrossRef]

OCIS Codes
(140.7010) Lasers and laser optics : Laser trapping
(170.4520) Medical optics and biotechnology : Optical confinement and manipulation
(350.4855) Other areas of optics : Optical tweezers or optical manipulation

ToC Category:
Optical Trapping and Manipulation

History
Original Manuscript: January 22, 2013
Revised Manuscript: February 20, 2013
Manuscript Accepted: February 22, 2013
Published: March 4, 2013

Citation
Yang Yang, Wei-Ping Zang, Zi-Yu Zhao, and Jian-Guo Tian, "Morphology-dependent resonance of the optical forces on Mie particles in an Airy beam," Opt. Express 21, 6186-6195 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-5-6186


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References

  1. A. Ashkin, “Acceleration and Trapping of Particles by Radiation Pressure,” Phys. Rev. Lett. 24(4), 156–159 (1970). [CrossRef]
  2. P. H. Jones, E. Stride, and N. Saffari, “Trapping and manipulation of microscopic bubbles with a scanning optical tweezer,” Appl. Phys. Lett. 89(8), 081113 (2006). [CrossRef]
  3. L. Bosanac, T. Aabo, P. M. Bendix, and L. B. Oddershede, “Efficient optical trapping and visualization of silver nanoparticles,” Nano Lett. 8(5), 1486–1491 (2008). [CrossRef] [PubMed]
  4. Z. J. Li, Z. S. Wu, and Q. C. Shang, “Calculation of radiation forces exerted on a uniaxial anisotropic sphere by an off-axis incident Gaussian beam,” Opt. Express 19(17), 16044–16057 (2011). [CrossRef] [PubMed]
  5. M. Nieto-Vesperinas and J. J. Saenz, “Optical forces from an evanescent wave on a magnetodielectric small particle,” Opt. Lett. 35(23), 4078–4080 (2010). [CrossRef] [PubMed]
  6. S. Kawata and T. Sugiura, “Movement of micrometer-sized particles in the evanescent field of a laser beam,” Opt. Lett. 17(11), 772–774 (1992). [CrossRef] [PubMed]
  7. J. U. Nöckel and A. D. Stone, “Ray and wave chaos in asymmetric resonant optical cavities,” Nature 385(6611), 45–47 (1997). [CrossRef]
  8. P. T. Korda, M. B. Taylor, and D. G. Grier, “Kinetically Locked-In Colloidal Transport in an Array of Optical Tweezers,” Phys. Rev. Lett. 89(12), 128301 (2002). [CrossRef] [PubMed]
  9. P. Chylek, J. T. Kiehl, and M. K. W. Ko, “Optical levitation and partial-wave resonances,” Phys. Rev. A 18(5), 2229–2233 (1978). [CrossRef]
  10. P. Chylek, J. D. Pendleton, and R. G. Pinnick, “Internal and near-surface scattered field of a spherical particle at resonant conditions,” Appl. Opt. 24(23), 3940–3942 (1985). [CrossRef] [PubMed]
  11. B. R. Johnson, “Theory of morphology-dependent resonances: shape resonances and width formulas,” J. Opt. Soc. Am. A 10(2), 343–352 (1993). [CrossRef]
  12. M. L. Gorodetsky and V. S. Ilchenko, “Optical microsphere resonator: optimal coupling to high-Q whispering-gallery modes,” J. Opt. Soc. Am. B 16(1), 147–154 (1999). [CrossRef]
  13. P. T. Leung, S. W. Ng, K. M. Pang, and K. M. Lee, “Morphology-dependent resonances in dielectric spheres with many tiny inclusions,” Opt. Lett. 27(20), 1749–1751 (2002). [CrossRef] [PubMed]
  14. J. B. Snow, S. X. Qian, and R. K. Chang, “Stimulated Raman scattering from individual water and ethanol droplets at morphology-dependent resonances,” Opt. Lett. 10(1), 37–39 (1985). [CrossRef] [PubMed]
  15. H. Miyazaki and Y. Jimba, “Ab initio tight-binding description of morphology-dependent resonance in a bisphere,” Phys. Rev. B 62(12), 7976–7997 (2000). [CrossRef]
  16. J. Ng and C. T. Chan, “Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes,” Appl. Phys. Lett. 92(25), 251109 (2008). [CrossRef]
  17. G. A. Siviloglou and D. N. Christodoulides, “Accelerating finite energy Airy beams,” Opt. Lett. 32(8), 979–981 (2007). [CrossRef] [PubMed]
  18. G. A. Siviloglou, J. Broky, A. Dogariu, and D. N. Christodoulides, “Observation of accelerating Airy beams,” Phys. Rev. Lett. 99(21), 213901 (2007). [CrossRef] [PubMed]
  19. J. Baumgartl, M. Mazilu, and K. Dholakia, “Optically mediated particle clearing using Airy wavepackets,” Nat. Photonics 2(11), 675–678 (2008). [CrossRef]
  20. J. Baumgartl, G. M. Hannappel, D. J. Stevenson, D. Day, M. Gu, and K. Dholakia, “Optical redistribution of microparticles and cells between microwells,” Lab Chip 9(10), 1334–1336 (2009). [CrossRef] [PubMed]
  21. A. V. Novitsky and D. V. Novitsky, “Nonparaxial Airy beams: role of evanescent waves,” Opt. Lett. 34(21), 3430–3432 (2009). [CrossRef] [PubMed]
  22. Y. Yang, W. P. Zang, Z. Y. Zhao, and J. G. Tian, “Optical forces on Mie particles in an Airy evanescent field,” Opt. Express 20(23), 25681–25692 (2012). [CrossRef] [PubMed]
  23. J. P. Barton, D. R. Alexander, and S. A. Schaub, “Internal and near-surface electromagnetic fields for a spherical particle irradiated by a focused laser beam,” J. Appl. Phys. 64(4), 1632–1639 (1988). [CrossRef]
  24. J. P. Barton, D. R. Alexander, and S. A. Schaub, “Theoretical determination of net radiation force and torque for a sphereical particle illuminated by a focused laser beam,” J. Appl. Phys. 66(10), 4594–4602 (1989). [CrossRef]
  25. S. Chang, J. T. Kim, J. H. Jo, and S. S. Lee, “Optical force on a sphere caused by the evanescent field of a Gaussian beam; effects of multiple scattering,” Opt. Commun. 139(4-6), 252–261 (1997). [CrossRef]

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