3D Optical Trapping via Tapered Optical Fibre at Extreme Low

3D Optical Trapping via Tapered
Optical Fibre at Extreme Low
Insertion Angles
Presentation by: Steven Ross
The GERI Weekly Seminar
Friday 18th October 2013
Supervisors: Prof. D. R. Burton, Dr. F. Lilley & Dr. M. F. Murphy
General Engineering Research Institute (GERI), Coherent & ElectroOptics Research Group (CEORG), Liverpool John Moores University
(LJMU), GERI Building, Byrom Street, Liverpool, L3 3AF, UK.
Email: [email protected]
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
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
Counter propagating laser beams
Particle levitation trap
Optical Trapping System
Single Beam gradient force
optical trap – “Optical tweezers”
Multiple Optical Tweezers
• Dual Optical tweezers
– Splitting the beam
– Two laser sources
• Multiple trap systems
– Fast Scanning time shared
laser beam
– Diffractive optical element
– Computer generated
holographic optical trap’s
Pros & Cons of “Classical” and
fibre Based System Configurations
“Classical” optical tweezers
Fibre Based 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
• Expensive
• Poor solution for project design
• 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
• The light exiting a Fibre is
• Optical trapping efficiency
of fibre systems < “classical”
• Literature suggests that
trapping cannot occur at
fibre insertion angles below
Problem Relating to the Project
• Requires fixing and
• 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
• 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 92
Tip 94
Tip 96
Maximum Trapping Range
Maximum Trapping Range
Maximum Trapping Range
Maximum Trapping Range (µm)
0-12 [1]
Tapered Tip Movement (µm)
Actual Particle Displacement (µm)
Percentage error %
[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)
• 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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