Interaction of light (scattering)

Question 1

What happesn when light enters a homogenous material

Answer 1

Reflection, refraction and absorption

Question 2

What happens when light enters a non-homogenous material

Answer 2

Scattering

Question 3

What is transmission

Answer 3

When incident light passes through a medium

Question 4

What is absorption

Answer 4

Light incident on the medium is inhibited or absorbed

Selective absorption
- where certain wavelengths are absorbed more than others

Question 5

How does the medium type affect transmission and absorption

Answer 5

Transparent
- transmission increase, absorption decrease

Translucent
- Partial transmission and absorption

Opaque
- transmision decrease, absorption increase

Question 6

What is scattering

Answer 6

When light is incident on anon homogenous material and is absorbed and re radiated

Question 7

What affects scattering

Answer 7

Size of particles

Distance between particles

Strength of interaction between light and particles

Question 8

What is coherance scattering

Answer 8

Particles in material closer than coherance length of light

Constructive and destructive interference of light occurs

Resultant scattered wave is refracted wave

Question 9

What is incoherant scattering and what affects it

Answer 9

When the space betweem particle in material is greater than the coherence length of light

Is affected by the size of particles

Question 10

What are the three types of incoherant scattering and give examples of each type

Answer 10

When particle size is bigger than the wavelength of light
- reflection and refraction takes place
- wavelength independent
- eg: fog and clouds

What particle size is similar to the wavelength of light
- spreads out in a more even direction
- wavelength dependent
- halos seen through fogged up car window

When particle size is smaller than the wavelength of light
- scatters short wavelengths more than long wavelengths
- the blue sky

Question 11

What is continous spectrum

Answer 11

Produced by hot soilds and liquids and high denisty gases

Continous range of wavelength

Question 12

What is absorption spectrum

Answer 12

The spectrum formed by electromagnetic radiation tha has passed through a medium in which radiation of certain frequencies is absorbed

Question 13

What is emission spectrum

Answer 13

Process by whuich a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon

Question 14

What are the two types of emission

Answer 14

Spontaneous and stimualted

Question 15

Define sponatenous emission

Answer 15

Excited electron at a higher energy level in the atom will after a short time return to a lower energy level with the emission of a photon

Question 16

Define stimulated emission

Answer 16

When an excited atom is struck by a photon of the same energy, it will emit a photon and return to a lower energy level. This is an amplification process (one photon goes into atom, two photons emitted)

Both photons are coherent (same freq, wavelength, direction and phase)

Question 17

What is the full name of LASER

Answer 17

Light amplification by Stimulated Emission of Radiation

Question 18

How is LASER produced

Answer 18

Pumping system supplies energy to laser material

Resulting in orbital electrons acheiving excited energy lvl

population inversion occurs, where more electrons are excited to higher energy lvl

Populationg inversion results in the emission of photons whihc are reflected back and forth the laser material

there is an increase in the number of photons through stimulated emission as there is an amplification process as when one phton enters an atom, two photons are emitted

some photons arriving at partially reflecting mirror are reflected while other consistute laser beams and are emitted

Question 19

What are the charasteristic of a LASER

Answer 19

DMCF

Highly directional
Highly monochromatic
Highly coherent
Can be sharply focused

Question 20

What are the applications of LASER

Answer 20

Non-clincial uses
- computer, printer
- fax machine
- circuit board production

Clinical uses
- LASIK
- photocoagulation