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“Nanophotonics and Optical Control of Single Nanoparticles”. Keonwoo Nam. Supervisor: Professor A. A. Fedyanin. Lomonosov Moscow State University, Faculty of Physics. Moscow 2012. Introduction to Optical Tweezers. Brief History of Optical Tweezers Principles of Optical Tweezers - PowerPoint PPT Presentation
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“Nanophotonics and
Optical Control of Single Nanoparticles”
Keonwoo Nam
Moscow 2012
Supervisor: Professor A. A. Fedyanin
Lomonosov Moscow State University, Faculty of Physics
Introduction to Optical Tweezers
OUTLINE
Brief History of Optical
Tweezers
Principles of Optical
Tweezers
Optical Trapping Forces
The Optical Tweezers Set up
&
The Experimental Method
Research Areas and Possible
uses
What is…Optical Tweezers - one of the techniques, which use a highly focused beam to control and hold microscopic particles.
History
Johannes Kepler (1571-1630): noticed comet's tail always
points away from the sun, because of the sun's radiation
pressure.
James Maxwell (1831-1879): existence of the light pressure
was demonstrated
P. N. Lebedev (1866-1912): measured the light pressure
Albert Einstein (1879-1955): confirmed that photons
possess its own momentum
Arthur Compton (1892-1962:) showed the existence of the
light momentum on his experimental work
Light transfers momentum to matter
In 1970 A. Ashkin proved that light can grab and
release nanometer particles by its momentum, using the
light Quantum Theory.
In 1986, A. Ashkin proved that he could trap 10nm
diameter dielectric particles only using gradient force
In 1987, A. Ashkin showed the damage-free
manipulation on cells using an infrared laser
Arthur Ashkin
History
Types of OT
Single Beam Optical Tweezers
Dual beam Optical Tweezers
Holographic Optical Tweezers
Principles of OT
Exert a laser beam to the very small particle, the
light will be reflected or refracted from the surface
of the particle. The momentum of photon, refracted
to the particle, will be changed and by the law of the
conservation of the momentum, the force of the
variation of momentum will be exerted to the small
particle.
(a) If the particle is to the left, say, of the center of the beam,it will refract more light from the right to the left, rather than vice versa.The net effect is to transfer momentum to the beam in this direction,so, by Newton’s third law, the particle will experience an equal andopposite force – back towards the center of the beam. In thisexample the particle is a dielectric sphere (b) Similarly, if the beam is tightly focused it is possible for the particle to experience a force that pushes back towards the laser beam. (c) We can also consider an energetic argument: when a polarizable particle is placed in an electric field, the net field is reduced. The energy of the system will be a minimum when the particle moves to wherever the field is highest – which is at the focus. Therefore, potential wells are created by local maxima in the fields.
How optical tweezers work Optical tweezers: the next generation, Kishan Dholakia,
2002, physics world
Conditions of OT
The Ray Optical Regime of Optical Tweezers Wonhoe Koo, Seoul, 2005
The Electromagnetic Regime of Optical Tweezers
Two Forces
The Electromagnetic Regime of Optical Tweezers
The Gradient Force
Two Forces
The Gradient Force
The Ray Optical Regime of Optical Tweezers Wonhoe
Koo, Seoul, 2005
The Basic OT Set up
A generic optical tweezers diagram with only the most basic componentsThe Optical Tweezers, Wikipedia
Research areasStudy and manipulate particles such as atoms,
molecules and small dielectric spheres
(in range from m to nm).Force measurements of biological objects in
piconewton range.Biological investigations involving cellsCutting and ablating biological objects
(Cell fusion and DNA cutting)Force measurements of cell structures and DNA
coilingElasticity measurements of DNA
Thank you ^-^
Keonwoo Nam