Active Physics Laser

Purpose: 
The purpose of this activity is to explore the concept how the laser work by investigating the difference between stimulated emission and spontaneous emission. Students will use active modern physics website to understand the light absorption and emission throughout this activity.
  

1) As shown there are fourteen excited atoms and three loose photons. The number of photons pumped into the system are twenty two, the number of photons come out of the system are five. So, we can see the total number of excited atoms, loose photons and come out photons are equal to the number of photons pumped into the system.

2) As shown in the picture, there is no preferred direction for the photon emitted during spontaneous emission.

3) No, there is a large time difference in the time emission between atoms in spontaneous emssion.

4)For each input photon when it interacts with an excited atoms, It gains one more photon oriented same direction with the input.

5) Experimentally, the effect starts occurring at pumping level 70. The picture shows the pumping level 90, the population inversion occurs.

6) In the laser, the photon emits which non-direction is the spontaneous emission.

Summary:
According to the activity, the number of photon inputted into the system are equal to the number that come out of the system and excited atoms. In the spontaneous emission, the emitted photons do not have any specific direction; although, when a photon interacts with an excited atom in the stimulated emission, it gains another photon in the same its direction. By changing level of pumping, we found that the pumping level at least 70 is required to have population inversion. If one of photons is emitted in another direction, not in the incident's direction, the photon is emitted spontaneously.