A four-level system of transitions in a laser employs a few key ...

[jake]

A four-level system of transitions in a laser employs a few key methods to produce coherent laser light. All of the following are vital to the four-level systems' working EXCEPT:
  a. forbidden transitions
  b. metastable states
  c. tunable emission wavelengths
  d. external source of energy
  e. population inversion

Question 2

A magnet of solid metal is placed in a magnetic field. Within the magnet, the magnetic field is greater than that outside (but still oriented in the same direction). The magnet is then heated by an external source to a very high temperature. The magnetic field inside the magnet is now significantly weaker but still greater than the outside field. What kind of magnet is this?
 

a. Ferromagnet
  b. Paramagnet
  c. Diamagnet
  d.a or c. It is impossible to tell which with the information given.
  e.a or b. It is impossible to tell which with the information given.

[mk6555]

Answer to Question 1

Although the ability to tune the wavelengths of output of the laser is useful in many scientific applications, it is not a necessary feature of the four-level system.
c.

Answer to Question 2

It is impossible to tell between a ferromagnet and paramagnet in this case. When place in an external magnetic field, both the ferromagnet and paramagnet could have a greater internal field than outside. When heated past the Curie point for a ferromagnet, the ferromagnet becomes a paramagnet with lesser magnetization. Also, the paramagnet's magnetization is inversely proportional to the temperature.
e.

[jake]

Excellent

[Joy Chen]

Gracias!