OPTICAL PROPERTY

• a material’s response to exposure to

electromagnetic radiation and, in particular, to

visible light

– What is VISIBLE light?

– How do materials respond to visible light?

• What is VISIBLE light?

– a small band of frequencies visible to the human

eye among the larger electromagnetic (EM) wave

spectrum

ELECTROMAGNETIC WAVE

A transverse wave of mutually perpendicular, time-

varying electric and magnetic fields that propagate at

constant speed, c, in vacuum

electromagnetic radiation can have both wave-like and

particle-like properties

Travels as a wave

Reflection, refraction, diffraction, interference

Interacts with matter like a particle, photon

Photoelectric effect

THE ELECTROMAGNETIC SPECTRUM

http://www.andor.com/image_lib/lores/INTRODUCTION/Introduction%20(Light)/IntLight%201%20Small.jpg

Light Interactions with Solids

transparent: relatively little absorption and reflection

translucent: light scattered within the material

opaque: relatively little transmission

Outline

• BAND Theory of Solids

• Optical Properties of Metals

– Absorption

– Reflection

• Optical Properties of Non-metals

– Absorption

– Reflection

– Transmission

– Refraction

• Consider the electron energy levels of two atoms which are far

apart

• If the atoms are brought very close to each other, such as the case of the electrons in a SOLID, what will happen to the electron energy levels?

n=1 n=1

n=2 n=2

n=3 n=3

Atom 1 Atom 2

n=1 n=1

n=2 n=2

n=3 n=3

Atom 1 Atom 2

n=1

n=2

n=3

Atom 1 + 2

Band theory of a solid

• A solid will have millions of atoms close together in a lattice so these energy levels creates bands each separated by a gap.

n=1

n=2

n=3

Band theory of a solid

Optical Properties of METALS

• almost any frequency of light can be absorbed.

ABSORPTION

• So what happens to the excited electrons in the surface layers

of metal atoms if the energy absorbed is just enough to take

the electrons to a higher energy level ?a. they stay there forever

b. they relax again

• The energy lost by the descending electron is the same as the

one originally incident

• So the metal reflects the light very well – metals are both opaque and reflective

Optical Properties of METALS

and release photons as “reflected light”

REFLECTION

Optical Properties of METALS

http://d.yimg.com/a/p/rids/20100625/i/r3478875000.jpg?x=400&y=291&q=85&sig=tdBxysqz1mY2TafZXJ

Mh4g--

http://ecx.images-

amazon.com/images/I/31I68%2B2nlfL._AA300_.jpg

http://www.omnicoin.com/coins/969525.jpg http://www.coinfacts.com/colonial_coins/new_jersey_coppers/maris_21N_obv.jpg

Specular vs. Diffuse Reflection

• Smooth, shiny

surfaces have a

SPECULAR

reflection:

http://www.neilblevins.com/cg_education/chrome/chrome.jpg

http://www.racepartsdirect.com/images/EVUA-OR.jpg

Rough, dull surfaces

have a diffuse

reflection.

Diffuse reflection is

when light is scattered

in different directions

Non-metals can be opaque or transparent

to visible light

‒Reflection and Absorption

‒Refraction and Transmission

Optical Properties of Non-METALS

Semiconductors and insulators behave essentially the same

way, the only difference being in the size of the ………...

Optical Properties of Non-METALS

‒ If Egap < 1.8 eV

‒ full absorption;

appearance is black (Si,

GaAs)

‒ If Egap > 3.1eV

‒ Transmission ; transparent

(diamond)

‒ If 1.8 eV < Egap < 3.1eV

‒ partial absorption;

material has a color

ABSORPTION

• http://www.columbia.edu/itc/chemistry/chem-

c1403/lectures/_C1403_Lecture7_100404.ppt

• http://en.wikipedia.org/wiki/Ultraviolet_catastrophe

• http://nbsp.sonoma.edu/resources/teachers_materials/physical_01/light/light.ppt

• How Things Work by Louis Bloomfield

• http://www.molphys.leidenuniv.nl/monos/smo/basics/images/wave_anim.gif

• users.encs.concordia.ca/~mmedraj/mech221/lecture%2024.pdf

• http://www.kumc.edu/ophthalmology/timberlake/lectures/1-

Light%20&%20Refraction.ppt

• www.kyc.edu.hk/studteach/teacher/hlt/userfiles/11-4_refraction_of_light.ppt

• Materials Science and Engineering: An Introduction, 6th Edition by Callister