Optical properties of engineering materials

In electromagnetic radiation, what are the orientations of the electric field, magnetic field and direction of propagation in relation to each other?

Electric field and magnetic field perpendicular to each other

both components perpendicular to direction of waves propagation

What form of radiation has the largest wavelength?

radio waves

What form of radiation has the highest energy?

Gamma rays

What colour in the visible light spectrum has the longest wavelength?

red

What is the approximate range of wavelengths for visible light?

0.4μm to 0.7μm

What is the equation of visible light, c?

c = 1/ rt(ε0*μ0)

What is the result of interaction between the electric field in a light wave and the electron cloud surrounding the atom in a material?

electronic polarisation

electron cloud temporarily distorted creating a temporary dipole moment

one side of electron cloud slightly positive and the other slightly negative

Effect of overlapping energy in metallic materials and partially filled bands on optical properties

electrons easily absorb photon energy and move to higher energy states

near total absorption of visible light makes materials fundamentally opaque

What causes high reflectivity of light in metallic materials?

Absorbed photons are rapidly re-emitted

Effect of band gap separating fully occupied valence band and empty conduction bands on optical properties of non metallic materials

can exhibit` wide array of optical properties

dependent on size of band gap

Refraction in nonmetal

velocity of light reduced due to electronic polarisation

light bends

When does reflection occur?

at the interface between two materials with different refractive indices

When does transmission occur in non metals? (transparency)

if non metals band gap is larger than the energy of visible light photons

passes through without being absorbed

What happens when band gap of non metals is smaller than energy of the photons?

photons are absorbed

leading to opacity

What are the three causes of internal light scattering in non metals?

porosity

grain boundaries

secondary phases

How does porosity impact light scattering in non metals

pores of gas in ceramic or polymer material

light scatters at boundaries of pores due to significant difference in indices of refraction

How do grain boundaries cause light scattering in polycrystalline materials?

variations in crystallographic orientation between adjacent grains

leads to different refractive indices across boundaries

causes scattering

How do secondary phases impact scattering in materials?

Composite materials or materials that contain secondary phase particles have a mismatch in refractive indices between components

causing dispersion of incoming light