CH 21 - Optical Properties

Question 1

What is a photon?

Answer 1

quantum unit of light

Question 2

What is refraction?

Answer 2

• transmitted light distorts e- clouds

- velocity of light in a material is lower than in a vacuum

Question 3

What is the optical classification of materials?

Answer 3

• transparent = single crystal
• translucent = polycrystalline dense
• opaque = polycrystalline porous

Question 4

What is luminescence?

Answer 4

• reemission of light by a material
• material absorbs light at one frequency and reemits it at another (lower) frequency
• trapped (donor/acceptor) states introduced by impurities/defects

Question 5

How does phosphorescent light happen?

Answer 5

-residence time in trapped state is relatively long (>10^-8 s)

Question 6

How does fluorescent light happen?

Answer 6

residence in trapped state is relatively short (

Question 7

What kind of light waves does a laser generate?

Answer 7

waves that are in phase and travel parallel to one another

Question 8

What is population inversion?

Answer 8

more e- in excited energy states than in ground states

Question 9

How is light produced in a laser?

Answer 9

• apply strong forward bias across semiconductor layers, metal & heat sink
• e-hole pairs generated by e- that are excited across the band gap
• recombination of an e-hole pair generates a photon of laser light

Question 10

What is the difference between CD’s and DVD’s?

Answer 10

CD’s use red light, DVD’s use blue light

-blue light has a shorter wavelength, so it can store more information over the same surface area