interaction of light with matter

Question 1

what is stimulated emission?

Answer 1

when an excited atom at a higher energy level is struck by a photon of the same energy level, it will emit a photon and return to a lower energy level.

• amplification process
• both photons gave same frequency, wavelength, direction and phase(coherent)

Question 2

what is spontaneous emission?

Answer 2

excited electron, at a higher energy level in an atom will, after a short time, return to a lower energy level w the emission of a photon.

Question 3

what is continuous spectrum

Answer 3

• produced by hot solids, liquids, and gases of high density.
• continuous range of wavelength.

Question 4

what is absorption spectrum?

Answer 4

the spectrum formed by electromagnetic radiation that has passed through a medium in which radiation of certain frequencies is absorbed.

Question 5

what is emission spectrum?

Answer 5

process by which a high energy quantum mechanism state of a particle is converted to a lower one with the emission of a photon.

Question 6

what is LASER?

Answer 6

• Laser Amplification by Stimulated Emission of Radiation

- amplifying light wave using energy stored in atoms through stimulated emission

Question 7

what are the components of LASER?

Answer 7

- lasing material
> solid, liquid, gas
- pumping system
> optical/electric/chemical
- optic cavity
> contain lasing material
> bounded by mirrors at ends
> one end w full reflector, other partially reflection

Question 8

LASER operation

Answer 8

• pumping system supplies energy to laser material
• energy absorbed by laser material, resulting in orbital electrons achieving excited energy level
• storage of electron in higher state, means more electrons are excited to higher energy level
• population inversion results in emitting of photons that stimulate other electrons
• photons are reflected back and forth laser material where the chain reaction increase number of photons
• some photons arriving at partially reflection mirror reflected, other constitute laser beam

Question 9

what are the characteristics of LASER?

Answer 9

• highly monochromatic
• highly coherent
• highly directional
• can be sharply focused

Question 10

what are the applications of LASER?

Answer 10

• non-clinical uses
  > computer & printer
  > fax machine
  > circuit welding & circuit board production

- clinical uses
> LASIK
> photocoagulation 
> trabeculoplasty 
> capsulotomy
> laser peripheral iridotomy

Question 11

what is coherent scattering?

Answer 11

• particles in material closer together then coherence length of light
• constructive & destructive interference of light occurs
  > resultant scattered wave is refracted wave
• e.g. corneal stroma

Question 12

what is incoherent scattering?

Answer 12

• space between particle in material greater than coherence length of light
• affected by particle size
• particle size bigger than wavelength of light
  > reflection & refraction
  > wavelength independent
  > e.g. fog, clouds, haze
• particle size similar to wavelength of light
  > spread out more evenly
  > wavelength dependent
  > sensitive to particle size
  > e.g. haloes seen through fogged up car window
• particle size is smaller than wavelength of light
  > scatter short wavelength more than long wavelength (Rayleigh scattering)
  > e.g. blue sky