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
OptoelectronicsComputing Group
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
OptoelectronicsComputing Group
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.
OptoelectronicsComputing Group
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.
OptoelectronicsComputing Group
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
OptoelectronicsComputing Group
• 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.
OptoelectronicsComputing Group
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.
OptoelectronicsComputing Group
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
OptoelectronicsComputing Group
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
OptoelectronicsComputing Group
Ray Tracing Simulation
OptoelectronicsComputing Group
Experimental Setup
06
1PPpostMO
Ytterbium
=1064nm
P0
Axiovert 200M
OptoelectronicsComputing Group
Experimental Setup
OptoelectronicsComputing Group
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
OptoelectronicsComputing Group
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]
OptoelectronicsComputing Group
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.
OptoelectronicsComputing Group
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
OptoelectronicsComputing Group
Simulation Results
D=486m
D=84m
80 mm
OptoelectronicsComputing Group
Experimental Setup
40x oil NA=1.3
Ytterbium =1064nm
P0
l=66~126mm D=130~430m
Power throughput:
06
1~
5
1PPpostMO
P0
OptoelectronicsComputing Group
Experimental Results
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
OptoelectronicsComputing Group
Experimental Results
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.
OptoelectronicsComputing Group
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.
OptoelectronicsComputing Group
Acknowledgements
Scripps Institute of Oceanography
Beckman Laser Institute
Beckman Center for Conservation and Research for Endangered Species (CRES) Zoological Society of San Diego
OptoelectronicsComputing Group
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.