ActivPhysics Lab - 18.3 The Laser

ActivPhysics Lab: 18.3 Atomic Physics: The Laser

Introducation:
The purpose of this experiment is to understand how does a laser works by investigating the difference between the spontaneous and stimulated emission.


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.

 Answer: The difference of photons in and out is the excited state atoms.


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

Answer:  During spontaneous emission, the amount of the photons out equals the amount of the atoms changed from excited state to ground state. Therefore, the photons are emitted have completely different directions and phases. 

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

Answer: There is no constant amount of time in which an atom remains in its excited state.

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. 

Answer: The amount of the photons out is the sum of the photons in and the atoms changed from excited state to ground state.

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.

Answer: To achieve a population inversion, a pumping level 70 is required.

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?

Answer: In stimulated emission, the photons emits at an order direction; but in spontaneous emission, the photons emits at odd directions.