Laser Active Physics Simulation

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.

- the sum of the photon output and number of excited atoms is always equal to the photon input.

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

- there does not appear to be a preferred direction in which the photons are emitted

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?

- there does not appear to be a constant amount of time for which the atoms are in an excited state. They appear to decay randomly

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 interacts with an excited atom the atom emits a secondary photon in the same phase and direction as the initial photon

Question 5: PumpingApproximately 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.

- A population inversion occurs with a pumping level of about 70

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?

- the photons emitted at odd directions are usually the result of spontaneous emission, but can also be a result of stimulated emission if a spontaneously emitted photon interacts with another excited atom.