3D Optical Trapping via Tapered Optical Fibre at Extreme Low Insertion Angles Presentation by: Steven Ross The GERI Weekly Seminar Friday 18 th October.
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3D Optical Trapping via Tapered Optical Fibre at Extreme Low
Insertion Angles
Presentation by: Steven RossThe GERI Weekly Seminar
Friday 18th October 2013
Supervisors: Prof. D. R. Burton, Dr. F. Lilley & Dr. M. F. MurphyGeneral Engineering Research Institute (GERI), Coherent & Electro-Optics Research Group (CEORG), Liverpool John Moores University
(LJMU), GERI Building, Byrom Street, Liverpool, L3 3AF, UK.Email: s.ross@2002.ljmu.ac.uk
Introduction
• What is optical trapping?• Optical trapping history & basic theory• Optical trapping configurations• Pros & cons of “classical” and fibre systems• Tapered fibre optic tweezers(T-FOT’s) system• Optical fibre insertion angle issues & solutions• Maximum trapping range• Conclusion
What is Optical Trapping?
• Exploitation of the forces produced during the interaction between light and matter
• Allowing the deflection, acceleration, stretching, compression, rotation and confinement of organic & inanimate material
• Ranging in sizes from the microscopic down to the atomic level
• Optical forces can be in excess of 100 Pico Newton’s with sub-Nanometre resolution
• Excellent force transducers
The Origins of Optical Trapping
• 1969 -Arthur Ashkin – Bell Laboratories• Effects of electromagnetic radiation pressure
forces on microscopic particles• Witnessed Unusual phenomena• Expected – Particles driven in the direction of
the laser beam’s propagation• Unexpected - Particles located at the fringes of
the laser beam’s axis were drawn into the high intensity region of the axis
Optical Forces Acting on a Particle Ashkin's initial observations Total forces acting on a particle
Optical Trapping System Configurations
Counter propagating laser beams Particle levitation trap
Optical Trapping System Configurations
Multiple Optical Tweezers• Dual Optical tweezers
– Splitting the beam– Two laser sources
• Multiple trap systems– Fast Scanning time shared
laser beam– Diffractive optical element
(DOE)– Computer generated
holographic optical trap’s
Single Beam gradient force optical trap – “Optical tweezers”
Pros & Cons of “Classical” and fibre Based System Configurations
“Classical” optical tweezers
• Very large surface area required to mount the bulk optics
• Physically large compared to the miniaturised arena which they were built to serve
• Require a high numerical aperture (NA) microscope objective
• Expensive• Poor solution for project design
criterion
Fibre Based Optical Tweezers
• Reduced size and build costs• No bulk optics required • No high (NA) microscope
objective required• Therefore it can be decoupled
from the microscope• Optical fibre delivers the trapping
laser light to the sample chamber• Basic system consists of a laser
and an optical fibre • Ideal for project design criterion
Disadvantages of Fibre Based Optical Trapping Systems
Known Fibre Trapping Issues• Optical fibre is a physical
entity• The light exiting a Fibre is
divergent• Optical trapping efficiency of
fibre systems < “classical” systems
• Literature suggests that trapping cannot occur at fibre insertion angles below 20°
Problem Relating to the Project• Requires fixing and
manipulation• Fibre’s distal end requires
shaping to focus the light• Requires higher optical
powers to reach same level of forces
• Design criterion requires an insertion angle of ≤ 10° to pass under the atomic force microscope (AFM) head
Atomic Force Microscope (AFM)
AFM Head Optical Lever Detection System
Tapered Fibre Optic Tweezers (T-FOT’s) System
3D Trapping at 45° Insertion Angle
3D optical Trapping at 10° Insertion Angle
• Initial attempt to trap at a 10° Insertion angle failed at low optical output powers
• At extremely high optical output powers in excess of 500 mW 3D optical trapping was observed
• Leading to investigations as to why trapping only occurred at high optical output powers at an insertion angle of 10°
Investigation into Trapping Failure at Sub-45° Insertion Angles
Investigation into Trapping Failure at Sub-45° Insertion Angles
Fibre Taper Optimisation for 10° Insertion Angle Optical Trapping
Tip 44
Tip 96
Tip 92
Tip 94
Maximum Trapping Range
Maximum Trapping Range
Maximum Trapping Range92 94 96 Simulated
Maximum Trapping Range (µm) 9 13 13 0-12 [1]
Tapered Tip Movement (µm) 9 9 10
Actual Particle Displacement (µm) 6.27 6.11 8.2
Percentage error % 30.3 32.1 18
[1] Z. Liu, C. Guo, J. Yang and L. Yuan, “Tapered fiber optical tweezers for microscopic particle trapping: fabrication and application,” Opt. Express 14(25), 12510-12516 (2006)
Conclusion• Brief explanation of optical trapping, its origins,
basic theory behind the technique & the various system configurations
• Provided an evaluation of the pros & cons for both classical and fibre based systems
• Presented T-FOTs a 3D fibre based optical trapping system
• Offered a hypothesis for trapping failure at a 10° insertion angle & provided a viable solution for the problem
• Discussed the maximum trapping range
Thank You
Any Questions?
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