The Laser!!!!!

Purpose:

             The main objective of this laboratory experiment is to learn more in depth about the inside workings of a laser. This activity will use the online program of ActivPhysics to create an application that will allow the inside workings of a laser to be changed and adjusted to determine experimentally how the changes of the inside molecules affect the functional of the laser. This applet will allow us to discover more about the properties of spontaneous and stimulated emission.

Data Analysis:

            The following questions are the questions that were asked during the use of the program’s applet:

Question 1: Absorption
At any given time, the number of photons inputted into the cavity must be equal to the number that have passed through the cavity without exciting an atom plus the number still in the cavity plus the number of excited atoms. Verify this conservation law by stopping the simulation and counting photons.

-          This conservation is in fact verified through the running of the program. As the picture indicates bellow, at a random time, the number of photons inputted equals the number of photons passed while not exciting an atom plus the number of photons still in the cavity and those of the excited electrons. 

Question 2: Direction of Spontaneous Emission
During spontaneous emission, does there appear to be a preferred direction in which the photons are emitted?

-          No, the photons are not generated in a specific direction. The photons emitted by spontaneous emission propagate outwards into a random direction at a random time. 

Question 3: Lifetime of Excited State

Does there appear to be a constant amount of time in which an atom remains in its excited state?

-          No, there does not appear to be a constant time in which the atoms remain in an excited state. The atoms emit at random times and in random locations with no parameters that are noticeable to restrain them. 

Question 4: Stimulated Emission
Carefully describe what happens when a photon interacts with an excited atom. Pay careful attention to the phase and direction of the subsequent photons. (Can you see why this is called stimulated emission?)

-          When a photon hits an excited atom, that atom emits a photon. The previous photon that interacted with the atom initially, does not get absorbed and appears to be unaffected by the interaction. After the interaction, there is a total of two photons now that are both traveling in the same direction and phase as the originally present photon. 

Question 5: Pumping
Approximately what pumping level is required to achieve a population inversion? Remember, a population inversion is when the number of atoms in the excited state is at least as great as the number of atoms in the ground state.

-          The approximate pumping level appears to be present at around 90.

Question 6: Photon Emission
Although most photons are emitted toward the right in the simulation, occasionally one is emitted in another direction. Are the photons emitted at odd directions the result of stimulated or spontaneous emission?

-          These emitted photons must be as a result of spontaneous emission since the stimulated emission photons always appear to travel in the same direction of the entered photon. 

Conclusion:

            From this activity, it has been made more physical sense as to what quantum properties play a role in the production of an efficient laser. The gas that fills the interior of the laser must be set under very specific conditions for the laser to work properly. The gas must contain atoms that are in an excited state so as to increase the intensity of the beam. Another requirement is that the gas must contain a population inversion. Lastly, the photons that are being pumped into the laser’s gas chamber must be pumped at a specific rate so that the ratio of the atoms in an excited state to the atoms in a ground state remains relatively constant.