PRINCE AHMAD GANAI

Nature of Light

Department of Physics-National Institute of Technology Srinagar

What is light. Vision and comprehension of light. Illusions. Physics of Light. Newton and Huygen. Youngs experiment Maxwells EM- theory Quantum theory of light Research still in progress

LIGHT:

Light can confuse you

Physics of Light

How does it behave? Reflection Refraction Dispersion What models can we use to: understand light predict other behaviour How can we apply our knowledge to do something useful: microscopes, telescopes, . . .

Optics

Ray theory of light

Dispersion

Light as wave

The Wave Nature of Light

Interference : Thomas Young (1803):

Light as wave

Interference

Diffraction

Polarization

Light: Particles or Waves? In 1700s the particle model of light

was assumed By 1830, the wave theory was

generally accepted By 1900, light was known to be an

electromagnetic wave

Electromagnetic Theory of Light

Maxwell’s Equations

0

0

00

B

E

t

EB

t

BE

EM- wave equation

t

BB

Similarlyt

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Wt

ESHR

EEESHL

Bt

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2

2

002

2

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have e

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EM-Spectrum:

http://en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edit.svg

EM- THEORY

• First successful theory of unification.• Electricity, Magnetism, and Light• Origin of Light- explained.• Microscopic explanation to reflection and ref.• Radio wave production and transmission.• But wait------- Next century will hit you

Light is still a problem

Two mega theories are born ,because we want to answer the basic question, What is light?

1. Special theory of relativity.2. Quantum Mechanics.

Relativity

Theory was perceived for invariance requirements of Maxwell’s equations.

Constancy of light becomes basic postulate of the first mega theory of 20th century.

Experiments verified the theory and the concept of space and time changes for ever.

Quantum Physics

•Origin of light challenged.•How can atom be stable.•New rules required.•Wave concept in trouble.• No explanation to-

1. Photo electric effect.2. Compton effect3. Pair production

The Photoelectric Effect

Compton Scattering

Pair production.

Light and matter are different manifestations of same thing.

Quantum theory of Light

Double slit experiment

http://images.google.co.in/imgres?imgurl=http://abyss.uoregon.edu/~js/images/photon_double_slit3.gif&imgrefurl=http://abyss.uoregon.edu/~js/cosmo/lectures/lec08.html&usg=__WbQQPwrNbBjEYhjdvs14JSauUpg=&h=420&w=348&sz=104&hl=en&start=102&um=1&tbnid=j0lBY7MYtLHIgM:&tbnh=125&tbnw=104&prev=/images?q=Quantum+double+slit+experiment&start=90&ndsp=18&um=1&hl=en&sa=N

http://images.google.co.in/imgres?imgurl=http://www.daviddarling.info/images/Youngs_double-slit_experiment.jpg&imgrefurl=http://www.daviddarling.info/encyclopedia/L/light.html&usg=__zfrjB2qoSSU-cGQV9scc2yLPMN8=&h=284&w=300&sz=22&hl=en&start=26&um=1&tbnid=VdlOipMgyV5ALM:&tbnh=110&tbnw=116&prev=/images?q=Quantum+double+slit+experiment&start=18&ndsp=18&um=1&hl=en&sa=N

http://images.google.co.in/imgres?imgurl=http://www.blacklightpower.com/theory/DoubleSlit/Fig_37-1_Two_Slit_Particles.jpg&imgrefurl=http://www.blacklightpower.com/theory/DoubleSlit.shtml&usg=__GwIaKB65_dYzJCXgJSvhOch5Uiw=&h=315&w=300&sz=16&hl=en&start=95&um=1&tbnid=pVqm5o8C2ppXJM:&tbnh=117&tbnw=111&prev=/images?q=Quantum+double+slit+experiment&start=90&ndsp=18&um=1&hl=en&sa=N

Quantum theory of light

•Light is both wave and particle•Observer decides the choice.

•Giving light yet another new twistE. Plum, J. Zhou, J. Dong, V. A. Fedotov, T. Koschny, C. M. Soukoulis, and N. I.

Zheludev

Phys. Rev. B 79, 035407 (2009) – Published January 12, 2009

CURRENT RESEARCH

Future applications.

Thankx