A ring-shaped laser trap based on axicons

OptoelectronicsComputing Group

A ring-shaped laser trap based on axicons

Bing Shao

University of California, San Diego

Del Mar Photonics

August 3rd, 2005

San Diego, CAOptics & Photonics 2005

The International Society for Optical Engineering


Photonics in Cell Based Bio-Chip Platforms

Photonics to augment fluidics chipse.g., for sample purification or sorting

Key features of Photonics• Remote manipulation

• reduces cross-contamination• wireless connectivity

• Individual selectivity of single cells or particles• Fast, highly parallel processing• Independent of environment of cells or medium• Essentially harmless to bio-molecules

Key features of Photonics• Remote manipulation

• reduces cross-contamination• wireless connectivity

• Individual selectivity of single cells or particles• Fast, highly parallel processing• Independent of environment of cells or medium• Essentially harmless to bio-molecules

Photonics to augment cell arraychipse.g., for pharmacological data extraction

Live Cells

Biocompatible Environment

Cell Array Platform -Fluidics Platform


Background on Optical Trapping

Discovered in 1970 [1] and demonstrated in 1986 [2] both by Ashkin, optical tweezers have been applied effectively for•Manipulation of biological cells, organelles and beads•Characterization and sorting of microparticles including cells•Generating and measuring molecular-scale forces for single molecule study

Scanning laser line optophoresis [4]

Kinesin Moving on a Microtubule[5]

Multiple-step yeast manipulation [3]

1. A. Ashkin, Physical Review Letters, v24, p154-159, 1970.2. A. Ashkin, et al., Optics Letters, v11, n5, p288-291, 1986.3. B. Shao et al., accepted for publication, Sensors & Actuators B Chemical,, 2005.4. A. Forster et al., Analytical biochemistry, v327, p 14-22, 2004.5. Koen Visscher, et al., Nature, v400, p184-189, 1999.


Optical Trapping Theory

hp k F t

Photon Momentum

* After A. Ashkin, Phys. Rev. Lett., 24, 156 (1970)

+r

+z

a

b

FDi

FDo

FRo

FRi

NetForce

Ray Optics Analysis for Large Particles (D >>) • Refraction at boundary transfers photon momentum to particle

• Force due to refraction (FD) is higher than that due to reflection (FR)• Restorative “trapping” force pushes particle toward z axis

• Arises from the gradient in the Gaussian envelope of the beam such that |a| > |b|. For a high NA lens, the gradient force will be in –z direction and acts to restore the

object to the focal point as well as to the z axis resulting in a Single Beam Optical Trap

Ray Optics Analysis for Large Particles (D >>) • Refraction at boundary transfers photon momentum to particle

• Force due to refraction (FD) is higher than that due to reflection (FR)• Restorative “trapping” force pushes particle toward z axis

• Arises from the gradient in the Gaussian envelope of the beam such that |a| > |b|. For a high NA lens, the gradient force will be in –z direction and acts to restore the

object to the focal point as well as to the z axis resulting in a Single Beam Optical Trap

• Optical tweezers form a stable three-dimensional trap that is created by the optical forces that arise in highly focused laser beams.

• These optical forces can be attributed to the transfer of momentum of a photon that occurs while undergoing a scattering event such as reflection or refraction.


A Ring trap

Facilitate single sperm study by preventing interference/competition

High efficiency bio-tropism study under equal-distance condition

• When studying self-propelling cells (e.g., sperm, algae, etc.) with single point trap, interference from untrapped cells need to be avoided.

• A Ring trap based speed bump could be used as a force shield to protect analysis area from other cells.

• Parallel sorting / separation of the cells based on their motility and response to attractants can be accomplished.– Only winners will make it to the attractant

stimuli


• Mechanical scanning---moving part, speed limitation (especially for fast moving target), reduced average exposure time, tangential drag force introduced by scanning focus

• Diffractive optics/Holography---lower efficiency, not suitable for power limiting system, dynamically adjustment of ring size and depth needs SLM.

• Axicon---low cost, high efficiency, easy implementation, ring size dynamically adjustable

Generating a uniform Ring Trap!

Axicon (rotationally symmetric prism), is a lens composed of a flat surface and a conical surface.


History of Axicon for Trapping1. Diffraction-free Bessel beam[13](Gaussian+Axicon)

)1(0

max

n

wZ

2. Hollow laser beam for atom trapping[14](Gaussian+Lens+Axicon)

Non-diffractive propagation distance for a quasi-Bassel beam

13. D. McGloin,et al., Spie’s oemagazine, p42-45, Jan 2003.

14. I. Manek, et al., Optics Communicatons, 147, p67-70, 1998.

Provide a large and dark inner region and the available laser power is used in an optimum way for creating the repulsive optical wall.


How to use Axicons to trap particles in a ring?

tan EFLring frTL

FL

f

f )sinarcsin(n

7. B. Shao et al., Proceedings of the SPIE, v5514, p62-72, 2004.

•Size---Trapping spot deviation from the optical axis input beam inclination [7].

•Uniformity---MO input is a cone of collimated beam intersecting at the back aperture with inclination angle .

•Strength---filling MO back aperture completely to ensure tight focusing input light cone thickness = diameter of MO back aperture


Ray Tracing Simulation

40x Oil

WD=0.2

fFL=100mm

fTL=400mm

ZEMAX simulation with 40x NA 1.3 oil immersion lens shows a ring-shaped focus at the sample plane whose diameter agrees with the theoretical calculation~220m.

sample plane spot diagram

Cross-section of annular focus

Immersion Oil 0.20mm

Coverglass 0.17mm

Water

0.077mm


Ray Tracing Simulation


Experimental Setup

06

1PPpostMO

Ytterbium

=1064nm

P0

Axiovert 200M


Experimental Setup


Experimental Results

40× MO NA=1.3 Oil (Zeiss)

PpostMO=80mW

15 micron polystyrene beads (Duke Scientific)

Buffer: Water

Experiment with microspheres verified the feasibility of the annular laser trap.

100m

P~2.4mW/microsphere Leftwards stage translation

Formation of the ring of microspheres

Rring~105m


Experimental ResultsPreliminary experiment with sperm shows an annular reaction zone

(a) (b)

(c) (d)

Rring~105m

Ptrap~30mW/sperm

Average trapping power: 100~200mW/sperm

6. J. Vinson, et al., Poster 5930-79, Optics & Photonics, SPIE 50th Annual Meeting, Jul. 31-Aug.4, San Diego, 2005.

[6]


Dynamically Adjustable Annular Trap?

• With fixed total power, changing the size of the ring trap leads to a change of trapping power per spot. This could be used for quantitative evaluating and sorting self-propelling cells with different swimming forces, motility patterns, and chemotaxis responses to chemo-attractants.

• The size of self-propelling cells varies dramatically. A variable annular trap enables study of different species without redesigning the system.


Optical System Design

tan EFLring fr

TLf

d 2tanarctan

Only should be changed (normal telescope lens pair also changes Din)!

•Introducing an axicon “telescope” pair in between the focusing lens and the tube lens

•Shift axicon2 along the optical axis while fixing other optics

•The incident angle is varied correspondingly while the filling of the objective back aperture is almost not changed.

d

drring

Din


Simulation Results

D=486m

D=84m

80 mm


Experimental Setup

40x oil NA=1.3

Ytterbium =1064nm

P0

l=66~126mm D=130~430m

Power throughput:

06

1~

5

1PPpostMO

P0



da2-a3=89mm da2-a3=68mm

40x Oil

NA=1.3

15m polystyrene

beads

Pout=0.5W PpostMO=90mW

Pout=0.3W PpostMO=55mW

100m

D~240m

100m

D~135m



P0=12W, Rring~55m Ptrap~70mW/sperm, 5×

P0=12W, ringm Ptrap~70mW/sperm, 3×

Fast sperm: not affected, swim across

Slow sperm: drawn to the ring and scattered out of the focus plane

Dead sperm and red blood cells: stably trapped to the ring and can freely move along the circumference.


ConclusionsTraditional applications of axicons lies in generating diffraction-free Bessel beam for communication or longitudinal partical confinement, and create central dark region for atom trapping

A new application of axicon has been explored to build an annular laser trap which confines particles into a ring-shaped pattern.

By adding two more axicons, and simply translating one of them along the optical axis, the diameter of the annular trap can be dynamically adjusted.

Although further optimization of the system is needed to improve the strength and stability of the annular trap, this system provides a prototype of an objective, automated, quantitative, and parallel tool for, cell motility and bio-tropism study.


Acknowledgements

Scripps Institute of Oceanography

Beckman Laser Institute

Beckman Center for Conservation and Research for Endangered Species (CRES) Zoological Society of San Diego


References

1. http://arbl.cvmbs.colostate.edu/hbooks/pathphys/reprod/semeneval/motility.html2. Y. Tadir, et al., Fertil. Steril. v52, p 870-873, 1989.3. Y. Tadir, et al., Fertil. Steril. v53, p 944-947, 1990.4. P. Patrizio, et al., Journal of Andrology, v21, p753-756. 2000.5. Z. N. Dantaset al., Fertil. Steril. v63, p185-188, 1995.6. M. Eisenbach et al., BioEssays, v21, p203-210, 1999.

7. J. Vinson, et al., Poster 5930-79, Optics & Photonics, SPIE 50 th Annual Meeting, Jul. 31-Aug.4, San Diego, 2005.

8. B. Shao et al., Proceedings of the SPIE, v5514, p62-72, 2004. 9. A. Ashkin, Physical Review Letters, v24, p154-159, 1970.10. A. Ashkin, et al., Optics Letters, v11, n5, p288-291, 1986.11. Koen Visscher, et al., Nature, v400, p184-189, 1999. 12. A. Forster et al., Analytical biochemistry, v327, p 14-22, 2004.13. A. Birkbeck, et al., Biomedical Microdevices, v5, n1, p47-54, 2003. 14. D. McGloin,et al., Spie’s oemagazine, p42-45, Jan 2003.

15. I. Manek, et al., Optics Communicatons, v147, p67-70, 1998.

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A ring-shaped laser trap based on axicons