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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 6 — Mar. 14, 2011
  • pp: 5232–5243
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Microparticle movements in optical funnels and pods

José A. Rodrigo, Antonio M. Caravaca-Aguirre, Tatiana Alieva, Gabriel Cristóbal, and María L. Calvo  »View Author Affiliations


Optics Express, Vol. 19, Issue 6, pp. 5232-5243 (2011)
http://dx.doi.org/10.1364/OE.19.005232


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Abstract

Three-dimensional microparticle movements induced by laser beams with a funnel- and tubular pod-like structure, in the neighbourhood of the focal plane of an optical trapping setup, are experimentally studied. The funnel and pod beams constructed as coherent superpositions of helical Laguerre-Gaussian modes are synthesized by a computer generated hologram using a phase-only spatial light modulator. Particle tracking is achieved by in-line holography method which allows an accurate position measurement. It is experimentally demonstrated that the trapped particle follows different trajectories depending on the orbital angular momentum density of the beam. In particular applying the proposed pod beam the particle rotates in opposite directions during its movement in the optical trap. Possible applications of these single-beam traps for volumetric optical particle manipulation are discussed.

© 2011 Optical Society of America

1. Introduction

Optical microparticle manipulation by a single-beam trap is a well-known tool with numerous applications in the fields of biology, chemistry and physics [1

1. A. Ashkin, Optical Trapping and Manipulation of Neutral Particles Using Lasers: A Reprint Volume With Commentaries (World Scientific Publishing Company, 2006). [CrossRef] [PubMed]

]. It is usually studied at the focal plane of a microscope’s objective where a particle may be trapped or moved along certain trajectory according to the field distribution of the applied beam. Different types of beams have been proposed for this task. For example, optical vortices such as the helical Laguerre-Gaussian (LG) modes yield rotation of a dielectric particle around the beam axis [2

2. M. Padgett and L. Allen, “Light with a twist in its tail,” Contemp. Phys. 41, 275–285 (2000). [CrossRef]

4

4. A. Jesacher, S. Fürhapter, C. Maurer, S. Bernet, and M. Ritsch-Marte, “Holographic optical tweezers for object manipulations at an air-liquid surface,” Opt. Express 14, 6342–6352 (2006). [CrossRef] [PubMed]

]. The rotation velocity depends on the orbital angular momentum carried by the beam, apart from the particle’s characteristics (weight, size, form, material, etc.) and the surrounding medium. Certain combinations of the LG modes produce spiral beams [5

5. L. Paterson, M. P. MacDonald, J. Arlt, W. Sibbett, P. E. Bryant, and K. Dholakia, “Controlled rotation of optically trapped microscopic particles,” Science 292, 912–914 (2001). [CrossRef] [PubMed]

7

7. T. Alieva, E. Abramochkin, A. Asenjo-Garcia, and E. Razueva, “Rotating beams in isotropic optical system,” Opt. Express 18, 3568–3573 (2010). [CrossRef] [PubMed]

] which maintain the form of their transversal intensity distribution apart from rotation and scaling. Such a type of beam was used for example in order to induce the Archimedes spiral movement of the particle [8

8. E. Abramochkin, S. Kotova, A. Korobtsov, N. Losevsky, A. Mayorova, M. Rakhmatulin, and V. Volostnikov, “Microobject manipulations using laser beams with nonzero orbital angular momentum,” Laser Phys. 16, 842–848 (2006). [CrossRef]

]. On the other side, the sum of LG modes with opposite topological charge was found useful for particle sorting [9

9. A. Jesacher, S. Fürhapter, S. Bernet, and M. Ritsch-Marte, “Size selective trapping with optical cogwheel tweezers,” Opt. Express 12, 4129–4135 (2004). [CrossRef] [PubMed]

, 10

10. K. Dholakia, M. P. MacDonald, P. Zemanek, and T. Cizmár, Laser manipulation of cells and tissues methods in cell biology (Elsevier, 2007), chap. Cellular and colloidal separation using optical forces, pp. 467–495. [CrossRef]

].

Apart from setups designed for plane-curve particle movements, there are more sophisticated trapping systems based on a spatial light modulator (SLM) which provide an interactive three dimensional (3D) control of the particle position almost in real time [11

11. D. G. Grier and Y. Roichman, “Holographic optical trapping,” Appl. Opt. 45, 880–887 (2006). [CrossRef] [PubMed]

, 12

12. M. J. Padgett, J. E. Molloy, and D. Mcgloin, eds., Optical Tweezers: Methods and Applications (CRC Press, 2010). [CrossRef]

]. These systems, commonly known as optical tweezers, use the computer generated holograms (CGHs) that allow the fast optical beam modification for particle manipulation. They play a relevant role in many applications ranging from the measurement of biological forces to the construction of micro-machines and micro-components [12

12. M. J. Padgett, J. E. Molloy, and D. Mcgloin, eds., Optical Tweezers: Methods and Applications (CRC Press, 2010). [CrossRef]

], but a high amount of computational resources is required for real time synthesis of the CGHs. Nevertheless pre-designed 3D particle movements which are important for example for micro-robotics, can be induced by a single-beam trap. Notice that such an optical setup might use an analogue hologram for beam generation and therefore it is more compact and cheap than using a single SLM [5

5. L. Paterson, M. P. MacDonald, J. Arlt, W. Sibbett, P. E. Bryant, and K. Dholakia, “Controlled rotation of optically trapped microscopic particles,” Science 292, 912–914 (2001). [CrossRef] [PubMed]

].

2. Beam design for the optical trap

As basic elements for the optical beam-trap design we use linearly polarized monochromatic helical LG modes given by [13

13. A. E. Siegman, Lasers (University Science Books, 1986).

]
LGp,l±(r;z)=w1(z)2p!π(p+l)!(2x±iyw(z))lpl(2r2w2(z))×exp(r2w2(z))exp(iπr2λR(z))exp(i(2p+l+1)ζ(z)),
(1)
with r = (x, y) being a transversal position vector, r2 = x2 + y2, w(z) = w0 (1 + (z/zR)2)1/2, where w0 is the minimum beam waist at the propagation distance z = 0, zR=πw02/λ being Rayleigh range, ζ(z) = arctan(z/zR) corresponding to Gouy phase, and R(z) = z(1 + (zR/z))2 representing the wavefront curvature radius. Here pl stands for the Laguerre polynomial with radial index p and azimuthal index l. This choice is explained by mode orthonormality, stability under the propagation through the isotropic paraxial systems (which besides a well-known limitations remain a good model for the conventional optical tweezers) and simple expression for the longitudinal component of the orbital angular momentum (OAM), Jz, carried by one mode or their linear superposition [14

14. R. Zambrini and S. M. Barnett, “Angular momentum of multimode and polarization patterns,” Opt. Express 15, 15214–15227 (2007). [CrossRef] [PubMed]

].

It has been reported in numerous publications that the beams carrying OAM produce particle rotation at the trapping plane, see for example [2

2. M. Padgett and L. Allen, “Light with a twist in its tail,” Contemp. Phys. 41, 275–285 (2000). [CrossRef]

4

4. A. Jesacher, S. Fürhapter, C. Maurer, S. Bernet, and M. Ritsch-Marte, “Holographic optical tweezers for object manipulations at an air-liquid surface,” Opt. Express 14, 6342–6352 (2006). [CrossRef] [PubMed]

]. Nevertheless, to the best of our knowledge, the obvious 3D spiral like trajectory of the particle in the neighbourhood of the focal plane has not been observed yet. Thus, one of the beam trap used for this study is a single helical LG mode
1(r)=LG1,18+(r;0),
(2)
carried the global OAM Jz = 18. The choice of the beam indices as well as its waist parameter is explained by the limitations of our experimental setup (named, laser power, numerical aperture of the objective, particle size, etc.) and is not relevant for further discussions.

We underline that two beams may have the same OAM but their interaction with a particle may differ due to the different intensity and OAM density distributions, which play an important role in the optical trap performance. The OAM density distribution of a beam constructed as a linear superpositions of the LG modes p,lap,lLGp,l±(r;0), where ap,l are constants, is given by the expression [15

15. A. M. Caravaca-Aguirre and T. Alieva, “Orbital angular moment density of beam given as a superposition of Hermite-Laguerre-Gauss functions,” in “PIERS 2011, Marrakesh,” (2011).

]
jz(r)=p,l,p,l±|ap,l|2|LGp,l±(r;0)|2l±Re[ap,l*ap,lLGp,l(r;0)LGp,l±(r;0)](l+l).
(3)
It is easy to see that the OAM density for a single LG mode is proportional to the intensity distribution jz(r)=±|LGp,l±(r;0)|2l. The global OAM, Jz, is obtained by integration over the x and y coordinates: Jz = ∑p,l±|ap,l|2l.

To study the dependence of particle trajectory from the OAM density distribution we use the following superposition of the LG modes
2(r)=[LG1,17+(r;0)+LG1,19+(r;0)]/2,
(4)
with the same global OAM, Jz = 18, and similar beam size as ℱ1. Moreover ℱ2 belongs to the class of the spiral beams mentioned above. From the analysis of mode indices it can be concluded (see for example [6

6. E. G. Abramochkin and V. G. Volostnikov, “Spiral light beams,” Phys. Usp. 47, 1177 (2004). [CrossRef]

, 7

7. T. Alieva, E. Abramochkin, A. Asenjo-Garcia, and E. Razueva, “Rotating beams in isotropic optical system,” Opt. Express 18, 3568–3573 (2010). [CrossRef] [PubMed]

]) that the intensity distribution of ℱ2 performs clockwise rotation at π/2 during free space propagation. The beam focusing accelerates the rotation near the focal plane. Notice that opposite rotation corresponds to the complex conjugate beam 2*.

The intensity, phase and OAM density distributions of these three beams are shown in Fig. 1. We observe that the maxima of the OAM densities almost coincide with the maxima of the intensity distribution for ℱ1 and ℱ2. The nonuniform distribution of the OAM over the rings for ℱ2 yields to the larger OAM density in some regions and smaller for others than for ℱ1. It is expected that particle plane rotation induced by ℱ2 will be limited by the region with large OAM density and intensity distribution.

Fig. 1 Intensity, phase and OAM density distributions of the beams ℱ1 (a), ℱ2 (b), ℱ3 (c), displayed in the first, second and third row respectively, at the minimum beam waist plane z = 0.

All three beams form a funnel-like structure in the neighbourhood of the focal plane (z = 0) as it can be appreciated from Fig. 2. For the numerical simulations we used the parameters corresponding to the experimental setup: a 100× microscope objective lens (MO) with 1.32 NA, wavelength λ = 532 nm and 0.25× relay optics (telescope). Then a minimum beam waist value of w0 = 3 μm is reached at the focal plane of the MO. As observed in Fig. 2, while the ℱ1 and ℱ3 beams remain invariant (except scaling), the ℱ2 one presents an additional clockwise rotation yielding a double helix intensity structure. We also note, that since the diameter of the particle used in the experiments for the analysis of 3D movement is 10 μm, then the average intensity distribution over the particle cross-section is almost the same for the beams ℱ1 and ℱ3. Therefore the main difference in their interaction with the particle is the presence of the OAM in the case of ℱ1 beam.

Fig. 2 Three-dimensional representation for the propagation of beams ℱ1 (a), ℱ2 (b), ℱ3 (c). Minimum beam waist w0 = 3 μm is obtained at focal plane (z = 0) of the 100× microscope’s objective lens.

It is also possible to design other attractive trapping beams by combining two or more optical funnels. Along the last decade, different techniques were proposed to generate beams with cylindrical hollow axial structure (so-called optical bottles) [16

16. R. Ozeri, L. Khaykovich, N. Friedman, and N. Davidson, “Large-volume single-beam dark optical trap for atoms using binary phase elements,” J. Opt. Soc. Am. B 17, 1113–1116 (2000). [CrossRef]

18

18. N. Bokor and N. Davidson, “A three dimensional dark focal spot uniformly surrounded by light,” Opt. Commun. 279, 229–234 (2007). [CrossRef]

]. Here we consider the collinear superposition of two optical funnels with a controlled focusing for each one then allowing generation a beam with pod-like structure. Indeed the position of the minimum beam waist value can be displaced a distance d away from the focal plane by modulating the input beam ℱn (r) with a spherical phase distribution
g(d)=exp(i2πnmdr2λf2d),
(6)
where f is the focal length of the microscope objective lens and nmd is the refractive index of the medium (water in our case). Then several optical funnels focused at different distances can be combined to construct a tubular-like trap. In this work we consider the superposition of two optical funnels described as
𝒫n,m(r)=a1n*(r)+a2m(r),
(7)
where a1,2 = |a1,2|g(d1,2) is the weight complex function that takes into account the focusing shift. In particular, we study the 𝒫1,1 and 𝒫2,2 beams with a1=g(d)/2, a2=1/2 and d = −20 μm that yields a tubular pod-like structure near to the focal region as displayed in Fig. 3(a) and 3(b), respectively. The peculiarity of these beams lies in the change of the OAM sign of their part interacting with the particle. Thus, it is expected to observe the particle rotation at the opposite directions at different distances z.

Fig. 3 Three-dimensional representation for the propagation of beam 𝒫1,1 (a) and 𝒫2,2 (b). To help visualization a 3D cut-out view of such beams is displayed in the second row.

The cross sections of the intensity distribution for all beams studied in this work at the distances z = 0 (first row) and z = −11 μm (second row) are shown in Fig. 4.

Fig. 4 Transversal intensity distributions for propagation distance z = 0 (first row) and z = −11 μm (second row) for the beams: ℱ1 (a), ℱ2 (b), ℱ3 (c), 𝒫1,1 (d) and 𝒫2,2 (e).

3. Experimental implementation

To generate these trapping beams we used a conventional holographic optical tweezers setup (see Fig. 5), which consists from a hand-made inverted light microscope with Zeiss 100× objective (1.32 NA, oil immersion, Plan-Apochromat), a reflective LCoS-SLM (Holoeye LCR-2500, twisted nematic, 8-bit grayscale signal, pixel size δ = 19 μm) operating in phase-only modulation, and Nd:YAG laser with wavelength λ = 532 nm and 400 mW. Theory and experimental implementation of such systems are studied in [19

19. B. Sun, Y. Roichman, and D. G. Grier, “Theory of holographic optical trapping,” Opt. Express 16, 15765–15776 (2008). [CrossRef] [PubMed]

] and [20

20. E. Martín-Badosa, M. Montes-Usategui, A. Carnicer, J. Andilla, E. Pleguezuelos, and I. Juvells, “Design strategies for optimizing holographic optical tweezers set-ups,” J. Opt. A, Pure Appl. Opt. 9, S267 (2007). [CrossRef]

], to name a few. The CGH is addressed onto a phase-only SLM that modulates a collimated laser beam. The resulting beam, B1, is focused over the sample by using a Keplerian telescope and the microscope objective, as sketched in Fig. 5.

Fig. 5 Schematic representation of the holographic optical trapping system. SLM displays the hologram that is imaged into the back focal plane of the microscope objective (MO) by using two relay lenses, L1 and L2, working as 0.25× telescope. The sample is illuminated by an additional laser beam B2 in order to acquire its image as in-line hologram, which is recorded in real time by a CCD camera.

Particle tracking is achieved by using an additional collimated laser beam B2 (in our case λ = 532 nm and 10 mW) that replaces the conventional incandescent illuminator, see Fig. 5. Its irradiance is comparable to that of conventional microscope illumination and therefore it does not exert measurable forces on the illuminated particles (suspended in the sample). Light scattered by the sample is recorded by a CCD camera (pixel size of 4.6 μm and 30 frames per second) in real time as an in-line hologram, which can be numerically analyzed in order to obtain the 3D particle position. In this work we use Rayleigh-Sommerfeld (RS) back-propagation for the in-line hologram reconstruction because it permits faster particle tracking. This technique was studied in detail for holographic video microscopy in [21

21. F. C. Cheong, B. J. Krishnatreya, and D. G. Grier, “Strategies for three-dimensional particle tracking with holographic video microscopy,” Opt. Express 18, 13563–13573 (2010). [CrossRef] [PubMed]

] and was found successful for micro-sized colloidal spheres of polystyrene and silica tracking. The in-line hologram results from interference between the light scattered by the particle and the unscattered portion of the illumination laser beam B2 at the focal plane of the objective. In our case this hologram is 100× magnified by the MO lens and recorded as a raw-video file by using a CCD camera (exposure time was 1 ms). The hologram reconstruction is achieved by computing the RS diffraction integral which makes possible to render a volumetric reconstruction of the light scattered by the particle. The particle’s position is found by locating maxima in such a volumetric reconstruction [21

21. F. C. Cheong, B. J. Krishnatreya, and D. G. Grier, “Strategies for three-dimensional particle tracking with holographic video microscopy,” Opt. Express 18, 13563–13573 (2010). [CrossRef] [PubMed]

].

Since the SLM operates in phase-only modulation, the beam complex amplitude distribution has to be encoded into the phase hologram. In the last decades several types of CGHs have been proposed to overcome this problem, see for example [22

22. J. P. Kirk and A. L. Jones, “Phase-Only Complex-Valued Spatial Filter,” J. Opt. Soc. Am. 61, 1023–1028 (1971). [CrossRef]

24

24. V. Arrizón, U. Ruiz, R. Carrada, and L. A. González, “Pixelated phase computer holograms for the accurate encoding of scalar complex fields,” J. Opt. Soc. Am. A 24, 3500–3507 (2007). [CrossRef]

]. To shape both amplitude and phase of the trapping beam we consider the method described in [24

24. V. Arrizón, U. Ruiz, R. Carrada, and L. A. González, “Pixelated phase computer holograms for the accurate encoding of scalar complex fields,” J. Opt. Soc. Am. A 24, 3500–3507 (2007). [CrossRef]

], that yields an accurate beam synthesis [25

25. T. Ando, Y. Ohtake, N. Matsumoto, T. Inoue, and N. Fukuchi, “Mode purities of Laguerre–Gaussian beams generated via complex-amplitude modulation using phase-only spatial light modulators,” Opt. Lett. 34, 34–36 (2009). [CrossRef]

] ensuring its stability under propagation.

Let us now describe the beam generation approach. It is well-known [22

22. J. P. Kirk and A. L. Jones, “Phase-Only Complex-Valued Spatial Filter,” J. Opt. Soc. Am. 61, 1023–1028 (1971). [CrossRef]

] that an arbitrary scalar complex field described by s(x, y) = a(x, y) exp[(x, y)], where a(x, y) and ϕ(x, y) are the amplitude and phase distribution respectively, can be encoded as a phase CGH with a transmittance function H(x, y) = exp[(a, ϕ)]. To obtain an appropriate dependence of ψ(a, ϕ), function H(x, y) has to be represented as a Fourier expansion in the domain of ϕ(x, y). As demonstrated in [24

24. V. Arrizón, U. Ruiz, R. Carrada, and L. A. González, “Pixelated phase computer holograms for the accurate encoding of scalar complex fields,” J. Opt. Soc. Am. A 24, 3500–3507 (2007). [CrossRef]

], the encoded signal s(x, y) is recovered from first-order term of such Fourier expansion by using the following hologram phase modulation:
ψ(a,ϕ)=f(a)sinϕ,
(8)
provided that the condition J1 [f(a)] = a is fulfilled for every value of amplitude a(x, y) in the interval [0, 1], by choosing the appropriate value of f(a) according to Bessel function J1(ρ). To isolate the encoded field s(x, y) from the other terms of the Fourier expansion it is necessary to perform spatial filtering by adding a linear carrier phase φc = 2π(u0x + v0y), with spatial frequencies (u0, v0), to the phase of the encoded field. Fortunately, this spatial filtering can be optically achieved using the Keplerian telescope (4-f system), see Fig. 5, where the SLM is placed at the back focal plane of the first relay lens. Notice that the reconstruction of the encoded signal s(x, y) is performed by spatial filtering of the first-order difracction term in the CGH Fourier spectrum plane [24

24. V. Arrizón, U. Ruiz, R. Carrada, and L. A. González, “Pixelated phase computer holograms for the accurate encoding of scalar complex fields,” J. Opt. Soc. Am. A 24, 3500–3507 (2007). [CrossRef]

]. In our case the overall diffraction efficiency (light guided into the first diffraction order) of the LCoS display is about 45%, see [26

26. I. Moreno, A. Lizana, A. Márquez, C. Iemmi, E. Fernández, J. Campos, and M. J. Yzuel, “Time fluctuations of the phase modulation in a liquid crystal on silicon display: characterization and effects in diffractive optics,” Opt. Express 16, 16711–16722 (2008). [CrossRef] [PubMed]

] for further details. Because of such a filtering process the maximum beam output power is about one half of the one corresponding to the input collimated beam.

Wavefront distortion φab arising from the SLM non-flatness, mainly astigmatism and spherical aberration, was calibrated following the suggestions reported in [20

20. E. Martín-Badosa, M. Montes-Usategui, A. Carnicer, J. Andilla, E. Pleguezuelos, and I. Juvells, “Design strategies for optimizing holographic optical tweezers set-ups,” J. Opt. A, Pure Appl. Opt. 9, S267 (2007). [CrossRef]

]. The SLM also allows compensating the wavefront aberrations corresponding to the optical setup, see Refs. [27

27. Y. Roichman, A. Waldron, E. Gardel, and D. G. Grier, “Optical traps with geometric aberrations,” Appl. Opt. 45, 3425–3429 (2006). [CrossRef] [PubMed]

, 28

28. C. López-Quesada, J. Andilla, and E. Martín-Badosa, “Correction of aberration in holographic optical tweezers using a Shack-Hartmann sensor,” Appl. Opt. 48, 1084–1090 (2009). [CrossRef]

]. To compensate such aberrations and therefore to optimize the optical trap performance, the hologram phase modulation Eq. (8) is evaluated as ψ(a,ϕφab + φc) mod 2π. Notice that aberrations such as coma and astigmatism mainly degrade the lateral trapping efficiency while the spherical aberration mostly degrades the axial trapping performance [27

27. Y. Roichman, A. Waldron, E. Gardel, and D. G. Grier, “Optical traps with geometric aberrations,” Appl. Opt. 45, 3425–3429 (2006). [CrossRef] [PubMed]

]. A further wavefront correction can be achieved as proposed in [28

28. C. López-Quesada, J. Andilla, and E. Martín-Badosa, “Correction of aberration in holographic optical tweezers using a Shack-Hartmann sensor,” Appl. Opt. 48, 1084–1090 (2009). [CrossRef]

].

Fig. 6 Experimental results ( Media 1): Transversal sections at z = 0 (first row) and z = −11 μm (second row) for the beams: ℱ1 (a), ℱ2 (b), ℱ3 (c), 𝒫1,1 (d) and 𝒫2,2 (e).

4. Microparticle manipulation: experimental results

We start from the analysis of particle movements (2 μm diameter polystyrene sphere, Spherotech SPV-20-5 Lot W01) at the focal plane of the MO, which in this case is near to the upper covering glass in order to compensate the axial scattering force. Figure 7 shows the motion of the trapped particle along the multiringed beam profile following the exerted torques (see also Media 2 and Media 3). As expected, the particle is confined in the high-intensity circular fringes and rotates around the beam ℱ1 axis whereas for the case of beam ℱ2 it only rotates in the angular range limited by the nonzero OAM density. The trapping with the beam ℱ3 does not produce any rotation due to zero OAM density.

Fig. 7 In-line holograms showing the trapped particle (2 μm diameter) for the beam ℱ1 Media 2 and ℱ2 Media 3, first and second row respectively.

Let us now consider the 3D motion of 10 μm diameter polystyrene spheres (Duke Scientific Lot 9949) suspended in water, which is induced by the proposed trapping beams. The flow-cell thickness is about 120 μm and the particle motion starts from the lower coverslip surface. Figure 8(a)–8(c) displays the particle’s tracking for the beams ℱ1, ℱ2 and ℱ3, respectively. Although both beams ℱ1 and ℱ2 have the same OAM (Jz = 18), they exert different forces and torques on the particle according to the geometry of their 3D intensity and OAM density distributions. This yields different types of helix-like trajectories, see Fig. 8(a) Media 4 and Fig. 8(b) Media 5. In contrast, the beam ℱ3 does not transfer OAM and therefore the particle just goes up to the minimum beam waist plane (z = 0), see Fig. 8(c). Notice that these trapping beams are displayed for the trap-region of interest, given between the lower coverslip surface at z = −30 μm and the focal plane z = 0. Several video snapshots corresponding to the in-line holograms obtained for the case ℱ1, ℱ2 and ℱ3 are also showed in Fig. 8(d)–8(f). We underline that clockwise rotation direction is obtained for the complex conjugate beams 1* and 2*.

Fig. 8 3D particle-tracking reconstruction for the beams: ℱ1 (a) Media 4, ℱ2 (b) Media 5, ℱ3 (c). Particle’s trajectory is also projected into x − y, x − z and y − z planes (grey lines). It is experimentally measured from in-line holograms stored as video as the ones showed in (d) Media 6, (e) Media 7, and (f), correspondingly. The trajectories start from the lower coverslip surface at t = 0 s (z = −30 μm) and ends at the focal plane z = 0 μm.

Since the intensity distribution of the beams ℱ1 and ℱ3 posses angular symmetry the particle may be trapped in any point of the plane where the light force is sufficient, while for the beam ℱ2 there are two well-defined regions around the intensity maxima where it may happens. Moreover, due to the relatively big particle size, two particles can be simultaneously trapped by beam ℱ2 following different helical channels as it is observed in Fig. 8(b) and 8(e). This may be useful for the organization of different sorting particle flows in the same cell for the observation of their interaction in the focal plane.

While the direction of the particle rotation trapped by the considered optical funnels is fixed, it may varies with the distance for the pod-like structures. As an example, we consider the 3D particle movement induced by the beam 𝒫1,1. Figure 9(a) together with Media 8 show the particle trajectory. For better visualization a cut-out view of the beam and the particle’s trajectory are represented in Fig. 9(b). The video snapshots, several of them are presented in Fig. 9(c), corresponding to the in-line holograms used for the 3D particle-tracking reconstruction are found in Media 9. In this case the particle describes a spiral trajectory from the starting point A [z = −30 μm, see Fig. 9(b)] with clockwise rotation (due to the 1* beam), until it reaches the distance z = −25 μm corresponding to the point B. At this point the particle is simultaneously trapped by both optical funnels 1* and ℱ1, which exert opposite torques over the particle according with their OAM value (Jz = ∓18, respectively). Therefore the particle goes straight up until the point C, in which its interaction with the ℱ1 becomes stronger. From the point C to D the particle, as expected, follows a new spiral trajectory with anticlockwise rotation. The relatively short elevation (with respect to the funnel trapping) of the particle during spiral movement (A–B and C–D tracks) is explained by the fact that only one half of the beam energy is participated in light-particle interaction in these regions. We underline that the movements of such particles, induced by the designed beams, have been systematically reproduced. For smaller polystyrene sphere the longer spiral trajectories are expected due to the lager longitudinal regions where the particle is trapped by only one of the funnels ( 1* or ℱ1) composed the pod.

Fig. 9 3D particle-tracking reconstruction for the trapping beam 𝒫1,1 (a) Media 8 and (b). Particle’s trajectory is also projected into xy, xz and yz planes (grey lines). The in-line holograms (as the ones shown in (c)) used for the reconstruction are stored as video, see Media 9.

This pod beam allows trapping of multiple particles, which simultaneously rotate in clockwise and anticlockwise directions at different distances z. It could be useful for twisting of rod-like particles or filaments which ends are trapped in the regions with opposite OAM sign.

5. Conclusions

The design of funnel and pod beams suitable for volumetric optical trapping and the method for their correct generation have been discussed. The interaction of these beams with dielectric colloidal particles was experimentally observed. It has been demonstrated that the trapped particles describe a 3D spiral trajectory governed by the forces and torques exerted by the beam carrying OAM. In contrast to a single helical-LG funnel the double-helix funnel beam provides two well-defined 3D channels for the particle movement. The capacity of the proposed bifocal pod beam to exert opposite particle rotations, at different planes during its propagation, is attractive for various micro-object manipulation techniques including all-optical twisting. Moreover the trapping of a rod-like particle by a similar pod beam with the same OAM sign in both focal regions could be used for optically driven stirring or pumps. These facts result useful for volumetric trapping and provide an additional level of control over the trapped particles. The manipulation of particles with different geometries, size and material by these and other funnel and pod beams will be the subject of further research.

While the described setup uses the SLM for the single-beam trap generation, the application of analogue hologram for this task will significantly increase the energetic layout of such optical traps providing setup compactness and reducing its cost.

Acknowledgments

The financial support of the Spanish Ministry of Science and Innovation under projects TEC2008-04105, TEC2009-5545-E/TEC are acknowledged. J. A. Rodrigo and A. M. Caravaca-Aguirre gratefully thank a “Juan de la Cierva” grant and fellowship from “Obra Social Ibercaja (Beca Ibercaja de Investigación 2010)”, respectively. The authors appreciate valuable comments from J. R. Arias-González.

References

1.

A. Ashkin, Optical Trapping and Manipulation of Neutral Particles Using Lasers: A Reprint Volume With Commentaries (World Scientific Publishing Company, 2006). [CrossRef] [PubMed]

2.

M. Padgett and L. Allen, “Light with a twist in its tail,” Contemp. Phys. 41, 275–285 (2000). [CrossRef]

3.

K. Ladavac and D. Grier, “Microoptomechanical pumps assembled and driven by holographic optical vortex arrays,” Opt. Express 12, 1144–1149 (2004). [CrossRef] [PubMed]

4.

A. Jesacher, S. Fürhapter, C. Maurer, S. Bernet, and M. Ritsch-Marte, “Holographic optical tweezers for object manipulations at an air-liquid surface,” Opt. Express 14, 6342–6352 (2006). [CrossRef] [PubMed]

5.

L. Paterson, M. P. MacDonald, J. Arlt, W. Sibbett, P. E. Bryant, and K. Dholakia, “Controlled rotation of optically trapped microscopic particles,” Science 292, 912–914 (2001). [CrossRef] [PubMed]

6.

E. G. Abramochkin and V. G. Volostnikov, “Spiral light beams,” Phys. Usp. 47, 1177 (2004). [CrossRef]

7.

T. Alieva, E. Abramochkin, A. Asenjo-Garcia, and E. Razueva, “Rotating beams in isotropic optical system,” Opt. Express 18, 3568–3573 (2010). [CrossRef] [PubMed]

8.

E. Abramochkin, S. Kotova, A. Korobtsov, N. Losevsky, A. Mayorova, M. Rakhmatulin, and V. Volostnikov, “Microobject manipulations using laser beams with nonzero orbital angular momentum,” Laser Phys. 16, 842–848 (2006). [CrossRef]

9.

A. Jesacher, S. Fürhapter, S. Bernet, and M. Ritsch-Marte, “Size selective trapping with optical cogwheel tweezers,” Opt. Express 12, 4129–4135 (2004). [CrossRef] [PubMed]

10.

K. Dholakia, M. P. MacDonald, P. Zemanek, and T. Cizmár, Laser manipulation of cells and tissues methods in cell biology (Elsevier, 2007), chap. Cellular and colloidal separation using optical forces, pp. 467–495. [CrossRef]

11.

D. G. Grier and Y. Roichman, “Holographic optical trapping,” Appl. Opt. 45, 880–887 (2006). [CrossRef] [PubMed]

12.

M. J. Padgett, J. E. Molloy, and D. Mcgloin, eds., Optical Tweezers: Methods and Applications (CRC Press, 2010). [CrossRef]

13.

A. E. Siegman, Lasers (University Science Books, 1986).

14.

R. Zambrini and S. M. Barnett, “Angular momentum of multimode and polarization patterns,” Opt. Express 15, 15214–15227 (2007). [CrossRef] [PubMed]

15.

A. M. Caravaca-Aguirre and T. Alieva, “Orbital angular moment density of beam given as a superposition of Hermite-Laguerre-Gauss functions,” in “PIERS 2011, Marrakesh,” (2011).

16.

R. Ozeri, L. Khaykovich, N. Friedman, and N. Davidson, “Large-volume single-beam dark optical trap for atoms using binary phase elements,” J. Opt. Soc. Am. B 17, 1113–1116 (2000). [CrossRef]

17.

J. Arlt and M. J. Padgett, “Generation of a beam with a dark focus surrounded by regions of higher intensity: the optical bottle beam,” Opt. Lett. 25, 191–193 (2000). [CrossRef]

18.

N. Bokor and N. Davidson, “A three dimensional dark focal spot uniformly surrounded by light,” Opt. Commun. 279, 229–234 (2007). [CrossRef]

19.

B. Sun, Y. Roichman, and D. G. Grier, “Theory of holographic optical trapping,” Opt. Express 16, 15765–15776 (2008). [CrossRef] [PubMed]

20.

E. Martín-Badosa, M. Montes-Usategui, A. Carnicer, J. Andilla, E. Pleguezuelos, and I. Juvells, “Design strategies for optimizing holographic optical tweezers set-ups,” J. Opt. A, Pure Appl. Opt. 9, S267 (2007). [CrossRef]

21.

F. C. Cheong, B. J. Krishnatreya, and D. G. Grier, “Strategies for three-dimensional particle tracking with holographic video microscopy,” Opt. Express 18, 13563–13573 (2010). [CrossRef] [PubMed]

22.

J. P. Kirk and A. L. Jones, “Phase-Only Complex-Valued Spatial Filter,” J. Opt. Soc. Am. 61, 1023–1028 (1971). [CrossRef]

23.

J. A. Davis, D. M. Cottrell, J. Campos, M. J. Yzuel, and I. Moreno, “Encoding amplitude information onto phase-only filters,” Appl. Opt. 38, 5004–5013 (1999). [CrossRef]

24.

V. Arrizón, U. Ruiz, R. Carrada, and L. A. González, “Pixelated phase computer holograms for the accurate encoding of scalar complex fields,” J. Opt. Soc. Am. A 24, 3500–3507 (2007). [CrossRef]

25.

T. Ando, Y. Ohtake, N. Matsumoto, T. Inoue, and N. Fukuchi, “Mode purities of Laguerre–Gaussian beams generated via complex-amplitude modulation using phase-only spatial light modulators,” Opt. Lett. 34, 34–36 (2009). [CrossRef]

26.

I. Moreno, A. Lizana, A. Márquez, C. Iemmi, E. Fernández, J. Campos, and M. J. Yzuel, “Time fluctuations of the phase modulation in a liquid crystal on silicon display: characterization and effects in diffractive optics,” Opt. Express 16, 16711–16722 (2008). [CrossRef] [PubMed]

27.

Y. Roichman, A. Waldron, E. Gardel, and D. G. Grier, “Optical traps with geometric aberrations,” Appl. Opt. 45, 3425–3429 (2006). [CrossRef] [PubMed]

28.

C. López-Quesada, J. Andilla, and E. Martín-Badosa, “Correction of aberration in holographic optical tweezers using a Shack-Hartmann sensor,” Appl. Opt. 48, 1084–1090 (2009). [CrossRef]

29.

Y. Roichman, I. Cholis, and D. G. Grier, “Volumetric imaging of holographic optical traps,” Opt. Express 14, 10907–10912 (2006). [CrossRef] [PubMed]

OCIS Codes
(090.1760) Holography : Computer holography
(140.3300) Lasers and laser optics : Laser beam shaping
(140.7010) Lasers and laser optics : Laser trapping
(090.1995) Holography : Digital holography

ToC Category:
Optical Trapping and Manipulation

History
Original Manuscript: December 21, 2010
Revised Manuscript: February 10, 2011
Manuscript Accepted: February 13, 2011
Published: March 4, 2011

Virtual Issues
Vol. 6, Iss. 4 Virtual Journal for Biomedical Optics

Citation
José A. Rodrigo, Antonio M. Caravaca-Aguirre, Tatiana Alieva, Gabriel Cristóbal, and María L. Calvo, "Microparticle movements in optical funnels and pods," Opt. Express 19, 5232-5243 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-6-5232


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References

  1. A. Ashkin, Optical Trapping and Manipulation of Neutral Particles Using Lasers: A Reprint Volume With Commentaries (World Scientific Publishing Company, 2006). [CrossRef] [PubMed]
  2. M. Padgett, and L. Allen, "Light with a twist in its tail," Contemp. Phys. 41, 275-285 (2000). [CrossRef]
  3. K. Ladavac, and D. Grier, "Microoptomechanical pumps assembled and driven by holographic optical vortex arrays," Opt. Express 12, 1144-1149 (2004). [CrossRef] [PubMed]
  4. A. Jesacher, S. Fürhapter, C. Maurer, S. Bernet, and M. Ritsch-Marte, "Holographic optical tweezers for object manipulations at an air-liquid surface," Opt. Express 14, 6342-6352 (2006). [CrossRef] [PubMed]
  5. L. Paterson, M. P. MacDonald, J. Arlt, W. Sibbett, P. E. Bryant, and K. Dholakia, "Controlled rotation of optically trapped microscopic particles," Science 292, 912-914 (2001). [CrossRef] [PubMed]
  6. E. G. Abramochkin, and V. G. Volostnikov, "Spiral light beams," Phys. Usp. 47, 1177 (2004). [CrossRef]
  7. T. Alieva, E. Abramochkin, A. Asenjo-Garcia, and E. Razueva, "Rotating beams in isotropic optical system," Opt. Express 18, 3568-3573 (2010). [CrossRef] [PubMed]
  8. E. Abramochkin, S. Kotova, A. Korobtsov, N. Losevsky, A. Mayorova, M. Rakhmatulin, and V. Volostnikov, "Micro-object manipulations using laser beams with nonzero orbital angular momentum," Laser Phys. 16, 842-848 (2006). [CrossRef]
  9. A. Jesacher, S. Fürhapter, S. Bernet, and M. Ritsch-Marte, "Size selective trapping with optical cogwheel tweezers," Opt. Express 12, 4129-4135 (2004). [CrossRef] [PubMed]
  10. K. Dholakia, M. P. MacDonald, P. Zemanek, and T. Cizmár, Laser manipulation of cells and tissues methods in cell biology (Elsevier, 2007), chap. Cellular and colloidal separation using optical forces, pp. 467-495. [CrossRef]
  11. D. G. Grier, and Y. Roichman, "Holographic optical trapping," Appl. Opt. 45, 880-887 (2006). [CrossRef] [PubMed]
  12. M. J. Padgett, J. E. Molloy, and D. Mcgloin, eds., Optical Tweezers: Methods and Applications (CRC Press, 2010). [CrossRef]
  13. A. E. Siegman, Lasers (University Science Books, 1986).
  14. R. Zambrini, and S. M. Barnett, "Angular momentum of multimode and polarization patterns," Opt. Express 15, 15214-15227 (2007). [CrossRef] [PubMed]
  15. A. M. Caravaca-Aguirre, and T. Alieva, "Orbital angular moment density of beam given as a superposition of Hermite-Laguerre-Gauss functions," in "PIERS 2011, Marrakesh," (2011).
  16. R. Ozeri, L. Khaykovich, N. Friedman, and N. Davidson, "Large-volume single-beam dark optical trap for atoms using binary phase elements," J. Opt. Soc. Am. B 17, 1113-1116 (2000). [CrossRef]
  17. J. Arlt, and M. J. Padgett, "Generation of a beam with a dark focus surrounded by regions of higher intensity: the optical bottle beam," Opt. Lett. 25, 191-193 (2000). [CrossRef]
  18. N. Bokor, and N. Davidson, "A three dimensional dark focal spot uniformly surrounded by light," Opt. Commun. 279, 229-234 (2007). [CrossRef]
  19. B. Sun, Y. Roichman, and D. G. Grier, "Theory of holographic optical trapping," Opt. Express 16, 15765-15776 (2008). [CrossRef] [PubMed]
  20. E. Martín-Badosa, M. Montes-Usategui, A. Carnicer, J. Andilla, E. Pleguezuelos, and I. Juvells, "Design strategies for optimizing holographic optical tweezers set-ups," J. Opt. A, Pure Appl. Opt. 9, S267 (2007). [CrossRef]
  21. F. C. Cheong, B. J. Krishnatreya, and D. G. Grier, "Strategies for three-dimensional particle tracking with holographic video microscopy," Opt. Express 18, 13563-13573 (2010). [CrossRef] [PubMed]
  22. J. P. Kirk, and A. L. Jones, "Phase-Only Complex-Valued Spatial Filter," J. Opt. Soc. Am. 61, 1023-1028 (1971). [CrossRef]
  23. J. A. Davis, D. M. Cottrell, J. Campos, M. J. Yzuel, and I. Moreno, "Encoding amplitude information onto phase-only filters," Appl. Opt. 38, 5004-5013 (1999). [CrossRef]
  24. V. Arrizón, U. Ruiz, R. Carrada, and L. A. González, "Pixelated phase computer holograms for the accurate encoding of scalar complex fields," J. Opt. Soc. Am. A 24, 3500-3507 (2007). [CrossRef]
  25. T. Ando, Y. Ohtake, N. Matsumoto, T. Inoue, and N. Fukuchi, "Mode purities of Laguerre-Gaussian beams generated via complex-amplitude modulation using phase-only spatial light modulators," Opt. Lett. 34, 34-36 (2009). [CrossRef]
  26. I. Moreno, A. Lizana, A. Márquez, C. Iemmi, E. Fernández, J. Campos, and M. J. Yzuel, "Time fluctuations of the phase modulation in a liquid crystal on silicon display: characterization and effects in diffractive optics," Opt. Express 16, 16711-16722 (2008). [CrossRef] [PubMed]
  27. Y. Roichman, A. Waldron, E. Gardel, and D. G. Grier, "Optical traps with geometric aberrations," Appl. Opt. 45, 3425-3429 (2006). [CrossRef] [PubMed]
  28. C. López-Quesada, J. Andilla, and E. Martín-Badosa, "Correction of aberration in holographic optical tweezers using a Shack-Hartmann sensor," Appl. Opt. 48, 1084-1090 (2009). [CrossRef]
  29. Y. Roichman, I. Cholis, and D. G. Grier, "Volumetric imaging of holographic optical traps," Opt. Express 14, 10907-10912 (2006). [CrossRef] [PubMed]

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