Transcript A ring-shaped laser trap based on axicons

A ring-shaped laser trap based on
axicons
Bing Shao
University of California, San Diego
Del Mar Photonics
August 3rd, 2005
San Diego, CA
Optics & Photonics 2005
The International Society for Optical Engineering
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Photonics in Cell Based Bio-Chip Platforms
Photonics to augment cell array chips
e.g., for pharmacological data extraction
Photonics to augment m-fluidics chips
e.g., for sample purification or sorting
Live Cells
Biocompatible
Environment
Cell Array Platform
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
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m-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
Multiple-step yeast
manipulation [3]
Scanning laser line
optophoresis [4]
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.
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Kinesin Moving on a
Microtubule[5]
Optical Trapping Theory
• 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.
FDi
a
FRi
+z
FDo
+r
FRo
Net
Force
Photon Momentum
p  k  h  F t

b
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
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* After A. Ashkin, Phys. Rev. Lett., 24, 156 (1970)
A Ring trap
• 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
Facilitate single sperm study by
preventing interference/competition
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High efficiency bio-tropism study under
equal-distance condition
Generating a uniform Ring Trap!
•
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
Axicon (rotationally symmetric prism), is a lens composed of a flat surface and a
conical surface.
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History of Axicon for Trapping
1. Diffraction-free Bessel beam[13](Gaussian+Axicon)
Non-diffractive propagation distance for a quasi-Bassel beam
Z max 
2. Hollow laser beam for atom trapping[14](Gaussian+Lens+Axicon)
Provide a large and dark inner region and the
available laser power is used in an optimum way for
creating the repulsive optical wall.
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13. D. McGloin,et al., Spie’s oemagazine, p42-45, Jan 2003.
14. I. Manek, et al., Optics Communicatons, 147, p67-70, 1998.
w0
(n - 1)
How to use Axicons to trap particles in a ring?
  arcsin( n sin  ) - 
f FL


fTL
rring    f EFL  tan  
•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
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7. B. Shao et al., Proceedings of the SPIE, v5514, p62-72, 2004.
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Ray Tracing Simulation
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~220mm.
40x Oil
WD=0.2
Water
Immersion Oil
0.20mm
0.077mm
fFL=100mm
fTL=400mm
Coverglass
0.17mm
sample plane spot diagram
Cross-section of annular focus
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Ray Tracing Simulation
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Experimental Setup
Ytterbium
=1064nm
P0
1
PpostMO  P0
6
Axiovert
200M
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Experimental Setup
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Experimental Results
Experiment with microspheres verified the feasibility of the annular laser trap.
40× MO NA=1.3 Oil (Zeiss)
PpostMO=80mW
15 micron polystyrene beads (Duke Scientific)
Rring~105mm
Buffer: Water
100mm
Formation of the ring of microspheres
P~2.4mW/microsphere
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Leftwards stage translation
Experimental Results
Preliminary experiment with sperm shows an annular reaction zone
(a)
(b)
Rring~105mm
Ptrap~30mW/sperm
Average trapping power:
100~200mW/sperm
(c)
(d)
[6]
6. J. Vinson, et al., Poster 5930-79, Optics &
Photonics, SPIE 50th Annual Meeting, Jul. 31Aug.4, San Diego, 2005.
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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.
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Optical System Design
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r
ring
d
Din
 d  tan  2 
  arctan 

fTL


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rring    f EFL  tan  
Simulation Results
80 mm
D=486mm
D=84mm
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Experimental Setup
Ytterbium
=1064nm
P0
P0
l=66~126mm
D=130~430mm
40x oil NA=1.3
Power throughput:
PpostMO 
1 1
~ P0
5 6
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Experimental Results
40x Oil
NA=1.3
D~240mm
15mm
polystyrene
beads
100mm
da2-a3=89mm
Pout=0.5W PpostMO=90mW
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D~135mm
100mm
da2-a3=68mm
Pout=0.3W PpostMO=55mW
Experimental Results
P0=12W, Rring~55mm
Ptrap~70mW/sperm, 5×
P0=12W, Rring~55mm
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.
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Conclusions
Traditional 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.
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Acknowledgements
Scripps Institute of Oceanography
Beckman Laser Institute
Beckman Center for
Conservation and Research for Endangered Species (CRES)
Zoological Society of San Diego
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References
1.
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/reprod/semeneval/motility.html
2.
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 50th 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.
Optoelectronics
Computing Group