Optical tweezers utilize a focused laser beam to trap and manipulate small dielectric objects, which has significant applications in fields such as chemistry, physics, and biology. The document explains the operating principles, including the role of a Nd:YAG laser and the importance of objective lens selection, important for minimizing damage to biological specimens. Additionally, it highlights the use of optical tweezers in studying biological systems and measuring small forces.

1. OPTICAL TWEEZERS: THE
FORCE OF LIGHT

2. Introduction
General description
Working
Vedio of traping particle
Diagrams of instrument
Application

3. INTRODUCTION
Optical tweezers:
Light can exert forces on small dielectric
objects1, A tightly focused beam of light can
trap micron-sized objects, such as latex beads.
This “optical trapping” principle has found
many applications in chemistry, physics and
biology. It has found its most prominent use in

4. OPTICAL TWEEZERS ?
An optical tweezer is a scientific instrument that
uses a focused laser beam to provide an attractive
or repulsive force, depending on the index mismatch
(typically on the order of piconewtons) to physically
hold and move microscopic dielectric objects. Optical
tweezers have been particularly successful in
studying a variety of biological systems in recent
years.
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

5. Trapping a particle with light
5

6. Optical Tweezers
rolf
6

7. WORKING OF TWEEZER
YouTube - Protein crystal in optical tweezers.flv

8. WORKING
The Nd:YAG laser (1064 nm wavelength) is the
most common laser choice because biological
specimens
are most transparent to laser wavelengths
around 1000 nm. This assures as low an absorption
coefficient as possible, minimizing damage to
the specimen, sometimes referred to as opticution.
Perhaps the most important consideration in optical
tweezer design is the choice of the objective.

11. Basic Components
Laser
L1
L2
f1 + f2
L3
Objective Lens
f3
16 cm
Image created from Physlet at
http://webphysics.davidson.edu/Course_Material/Py230L/optics/lenses.htm Physlet by Dr. Wolfgang
Christian and Mike Lee

12. Schematic diagram
Laser line mirror
Laser
Beam expander
Cell
White Light Source
CCD
Color Filter
Laser line mirror
Objective
Tip
12

13. Dual beam tweezer design
13

14. Kinesin motor
motion
RAY OPTICS RADIATION
PATTERN
•A laser beam is expanded
and collimated. This
collimated beam is directed
through a microscope
objective into a flow cell.
Spheres with a higher index of
refraction than the medium in
the cell (water) will be
trapped at the focus of the
beam.

15. YouTube - real-life Tetris under a microscope.flv

16. APPLICATIONS
We will calibrate the strength of an optical
trap (Optical Tweezer)
Optical Tweezers may be used to measure
very small forces (femtoNewton, 10-15N)
Applications include Biophysics
16

17. k
YOU
FOR YOUR
ATTENTIO
N