Photons etc

Question 1

Electron DIffraction

Answer 1

An electron gun with high voltage shoots an electron beam through a thin crystal foil. This creates a concentric circle pattern, an interference pattern.

Question 2

Photoelectric Effect Method

Answer 2

Light of high enough energy is shone on the emissive surface.
Circuit is completed with a cell to promote electron flow.
Current is detected by the nanoAmmeter.
[Labelled diagram]

Question 3

Photoelectric Effect

Answer 3

The emission of electrons from a surface when energetic enough photons fall on it.

Question 4

Stimulated Emission

Answer 4

An incident photon of specific energy travels through an atom.
This causes an excited electron to drop to a lower energy level.
As it does this, it releases a coherent, in-phase photon with the incident.

Question 5

Absorption

Answer 5

An incident photon of specific energy is absorbed by an atom. The photon disappears and an electron in the atom is excited to a higher energy level.

Question 6

Spontaneous Emission

Answer 6

Electron drops to a lower energy level randomly with the release of a photon.

Question 7

Pumping

Answer 7

Supplying amplifying medium with energy to excite electrons to a higher energy level / to create a population inversion.
So that there are more electrons on a higher energy level than lower, making stimulated emission more likely than absorption, which is essential for amplification.

Question 8

4 Level Population Inversion

Answer 8

We need more electrons in the third level than second.
Pump electrons to unstable fourth level, they drop to third spontaneously.
Population inversion achieved.
Because once electrons drop to second unstable level, they will quickly drop to G, keeping 2 empty almost at all times.

Question 9

Semiconductor Laser

Answer 9

• More efficient than regular laser (~60% of photons emitted rather than 1%)
• Cheaper to produce
• Used in CD or DVD players