1. Development of a 3-D Fibre Based Laser Light Force Optical Trap
Steven Ross
GERI-CEORG
Supervisors:
Prof. D. Burton, Dr. F. Lilley and Dr. M. Murphy

2. Introduction Objective of the project Optical Trapping Theory
Why Fibre Based Trapping?
Shaping Fibre For 3-D Optical Trapping
System Design
Results
Particle Tracking and Force Determination
Future Work
Summary

3. Objective of the project
To aid current investigations of the mechanical properties of cells
Normal cells like to attach themselves
Pathological cells, such as cancer are not so friendly
OT can also be used to apply forces
LASER scanning confocal and holographic Microscopy

4. Optical Trapping Theory
Scattering force
Propels particles in the direction of the beams propagation
Gradient force
Pulls particles into the high intensity region of the beams axis

5. Optical Trapping Theory
Counter propagating dual beam trap
Net opposing scattering force at E
Optical levitation trap
Scattering force balanced with gravity at E
Images taken from [1]

6. Optical Trapping Theory
Single beam gradient force optical trap - “optical tweezers”
Gradient force greater than scattering force
Tightly focusing laser through high NA microscope objective lens
Gradient force F slightly below focal point f
Image taken from [1]

7. Why Fibre Based Trapping?
Advantages
Reduced size and costs
Decoupled from the microscope
Light delivered to sample chamber via optical fibre
No need for position detection
Disadvantages
System complexity increases with additional trap
Fibre ends prone to damage require maintenance

8. Shaping Fibre for 3-D Optical Trapping
Focused ion beam milling [2]
Fibre polishing [3]
Laser micro-machining [4 ]
Chemical etching [5]
Heating and drawing [6]
4 Axis lapping [3]
Chemical etching [5]

9. System Design Heating & Drawing Fibre heated with 20W CO2 laser
Microcontroller controlled allowing a wide range of tapers
Simple, rapid & repeatable fabrication of taper
Core/cladding ratio maintained
Sutter P-2000/F Micropipette Puller

10. System Design
100 X Magnification
7000 X Magnification

11. System Design

13. Particle Tracking & Force Determination
IDL
Doesn’t like working with video
Allows the user to track a specified particle
Records specific particle data
LabView
Does like working with video
Tracks multiple particles simultaneously
Records data for all particles

14. Particle Tracking & Force Determination

15. Particle Tracking & Force Determination
Trapping force determination-dynamic measurement method
Obtained as a function of the beads displacement

16. Particle Tracking & Force Determination
Newton's second law and the stokes law
fopt = 6∏nrŚ + mŜ [7]
Trapping force-1st & 2nd derivatives of the beads position as a function of time
Displacement-in a certain time can be calculated from the beads position

17. Further Work Develop particle tracking software
Define optical trap parameters
Trap strength
Trap stiffness
Continue to find the optimum optical fibre taper
Trapping of non adhered cells
Integrate laser trap with other microscopy systems

18. Summary Objective of the project Optical Trapping Theory
Why Fibre Based Trapping?
Shaping Fibre For 3-D Optical Trapping
System Design
Results
Particle Tracking and Force Determination
Future Work
Summary

19. References
[1] Ashkin A 1997 Optical trapping and manipulation of neutral particles using lasers proc. Natl. Acad. Sci. 19 (8) pp [2] Minzioni P, Bragheri F, Liberale C, Di Fabrizio E and Crisiani I 2008 A novel approach to fibre-optic tweezers: numerical analysis of the trapping efficiency IEEE journal of selected topics in quantum electronics 14 (1) pp [3] I-En Lin S A lensed fibre workstation based on the elastic polishing plate method Precision Engineering 29 pp [4] Presby H M, Benner A F and Edwards C A 1990 Laser micromachining of efficient fiber microlenses Applied Optics 29 (18) pp [5] Luo J, Fan Y, Zhou H, Gu W and Xu W 2007 fabrication of different fine fibre tips for near field scanning optical microscopy by simple chemical etching technique Chineese Optics Leters 5 pp. S232-S234 [6] Liu Z, Guo C, Yang J and Yuan L 2006 Tapered fiber optical tweezers for microscopic particle trapping: fabrication and application Optics Express 14 (25) pp [7] Hu Z, Wang J and Liang J 2006 Experimental measurement and analysis of the optical trapping force acting on a yeast cell with a lensed optical fiber probe optics and laser technology 39 pp