“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