This document discusses the history and principles of optical tweezers, which use laser light to manipulate microscopic objects. Optical tweezers were invented in 1970 and can trap and manipulate particles ranging from micrometers to nanometers in size. They work by using the forces exerted by a strongly focused laser beam, including radiation pressure and gradient forces, to hold dielectric particles in the trap. Optical tweezers have various applications, such as manipulating cells in biological investigations and performing force measurements on cell structures and DNA.

1. A revolution in otical
manipulation
SHASHI KANT
ROLL NO. :- 16PH62R13
SOLID STATE TECHNOLOGY
M.TECH 1st YEAR

2. Outline
• History
• Optical tweezers
• Priciple
• Application
• Refrence

3. History
• In 1970 Arthur Ashkin invented a devide that
uses light to manipulate objects.
• In 1987 Arthur Ashkin By using optical
tweezer to trap single cells.
• They also showed the damage-free
manipulation on cells using an infrared laser .

4. Optical tweezer
• 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 mm 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.

5. Principle
• Case 1. d << λ
• Case 2. d >> λ

6. Case 1. d << λ
 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.

7. Case 2. d >>λ
• Presence of the objects in the beam path
leads to
- reflection
- refraction
- scattering

8. Types of optical tweezers
1. Single beam optical tweezers
2. Dual beam optical tweezers

9. Set up of Optical tweezers

10. Application
In the lasest research; this technique has been used for
– biological investigations involving cells
– cutting and ablating biological objects (cell fusion
and DNA cutting)
– force measurements of cell structures and DNA
coiling
– elasticity measurements of DNA

11. Refrence
• 1. Ashkin, A., Dziedzic, J. M., Bjorkholm, J. E. & Chu, S. Observation
of a single-beam gradient force optical trap for dielectric particles.
Opt. Lett. 11, 288–290 (1986).
• 2. Ashkin, A. History of optical trapping and manipulation of small-
neutral particle, atoms, and molecules. IEEE J. Sel. Top. Quantum
Elec. 6, 841–856 (2000).
• 3. Ashkin, A. Forces of a single-beam gradient laser trap on a
dielectric sphere in the ray optics regime.
Methods Cell Biol. 55, 1–27 (1998).
• 4. Svoboda, K. & Block, S. M. Optical trapping of metallic Rayleigh
particles. Opt. Lett. 19, 930–932
(1994).
• 5. Ke, P. C. & Gu, M. Characterization of trapping force on metallic
Mie particles. Appl. Opt. 38, 160–167 (1999).