An Introductory Information

about Optical Tweezers

Mustafa Yorulmaz

Koç University,

Material Science and Engineering

February 20, 2008 Koç University, Material Science and Engineering

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Outline

History of optical tweezers Basics of optical tweezers Physics beyond optical trapping Types of optical tweezers Possible uses and research areas A typical setup of optical tweezers Illustrative examples from our laboratory

February 20, 2008 Koç University, Material Science and Engineering

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History of Optical Tweezers

The technique of trapping was first applied in 1984 at Bell Laboratories

In 1986, they showed a demo of optical tweezers

They showed the damage-free manipulation on cells using an infrared laser in 1987.

1970 - Optical Tweezers: A. Ashkin (*)

(*) http://www1.bell-labs.com/org/physicalsciences/timeline/1970_ashkin_pop.html

February 20, 2008 Koç University, Material Science and Engineering

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Basics of Optical Tweezers Optical Tweezers are examples of optical trapping which is a

subfield of laser physics. They are used to trap and manipulate particles (in range from m

to nm) and also to measure the forces (in range from 1 to 100 pN) on these particles

A strongly focused laser beam is used for trapping the particles. The particles that are of interest has to show dielectric property.

* http://www.physics.uq.edu.au/lp/tweezers/papers/nieminen2001jqsrt70/

February 20, 2008 Koç University, Material Science and Engineering

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Physics Beyond Optical Trapping Trapping occurs due to radiation

pressure of laser which results by the momentum change of light.

There are two forces that let the particle to be hold in trap: Scattering force: due to reflection of

light (to push object) Gradient force: due to refraction of

light (to pull object)

nparticle>nmedium so that Fgradient>Fscattering

Using high NA objectives and high power lasers maximizes the trapping force.

Schematic diagram showing the force on a dielectric sphere due to both reflection and refraction of two rays of light.

February 20, 2008 Koç University, Material Science and Engineering

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Types of Optical Tweezers

Single beam optical tweezers

Holographic Optical Tweezers

Experimental setup for our aerosol holographic tweezers

http://people.sabanciuniv.edu/meric/projects/twz1.jpg

http://www.dundee.ac.uk/elecengphysics/tweezers/Research/aerosols_HOT.htm

Dual beam optical tweezers

http://www.the-scientist.com/article/display/15545/

http://www.ffn.ub.es/ritort/research.html

February 20, 2008 Koç University, Material Science and Engineering

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Possible uses and research areas

By using optical tweezers, it is possible to study and manipulate particles like

atoms, molecules and small dielectric spheres (in range from m to nm).

make force measurements of biological objects in piconewton range.

Dielectric objects are attracted to the center of the beam, slightly above the beam waist, as described in the text. The force applied on the object depends linearly on its displacement from the trap center just as with a simple spring system.

http://www.answers.com/topic/optical-tweezers?cat=technology

Optical tweezer for force measurements

In the lasest research; this technique has been used forbiological investigations involving cellscutting and ablating biological objects (cell fusion and DNA cutting)force measurements of cell structures and DNA coilingelasticity measurements of DNA

So, optical tweezers has opened up several important new areas of study in biophysics

February 20, 2008 Koç University, Material Science and Engineering

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A Typical Setup of Optical Tweezers

CCDCCD

Collimationf1f2

M1

M2 M3

M4

f5O1

Telesentricf4f3

ComputerComputer

MicroscopeMicroscope

IlluminationIllumination

Nd: YAG Laser (1064nm)Nd: YAG Laser (1064nm)

February 20, 2008 Koç University, Material Science and Engineering

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Illustrative Examples From Our Laboratory: Manipulation of Microspheres

Thanks to Ahmet Faruk Coşkun

February 20, 2008 Koç University, Material Science and Engineering

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Illustrative Examples From Our Laboratory: Manipulation of Vibrio Cholerae

Thanks to Ahmet Faruk Coşkun

February 20, 2008 Koç University, Material Science and Engineering

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Thanks..

Questions?