Unit 2.8: Lasers Flashcards
What is photon absorption?
When an electron is excited to a higher energy level by absorbing the energy of an incoming photon
What is photon emission?
The decay of an electron from one energy state to a lower energy state results in the creation of a photon
What is spontaneous emission?
When a photon is created spontaneously
What is stimulated emission?
The emission of a photon triggered by a passing photon of equal energy to the energy gap. The emitted photon has the same frequency, phase and direction of propagation as the passing atom
What is population inversion:N2>N1?
A population inversion is a situation in which a higher energy state in an atomic system is more heavily populated than a lower energy state of the same system.
For a laser to work, there must be population inversion between…?
The energy levels
What is pumping?
Pumping is feeding energy into the amplifying medium of a laser to produce a population inversion. This ensures that stimulated emission can occur
How do semiconductor lasers work?
They use electrical current to pump electrons to produce a high population inversion and the mirrors used transmits up to 60% of the photons
How are semiconductor lasers better than conventional lasers.
They are smaller, cheaper and far more efficient
Is it possible to create a population inversion on a 2 level energy system?
No. The best it can create is NL=Nu
Is it possible to create a population inversion on a 3 level energy system?
Yes. The pumping frequency and the laser frequency are different. Half of the electrons in the lower level must be promoted to ensure a higher number in level U, this takes a lot of energy.
Explain how a 3 level system works?
1.Electrons are pumped up to level 3, which is not stable, so the electrons quickly drop to level 2
2. Level 2 is metastable so the electron will stay in this level long enough for a photon of the laser frequency to cause stimulated emission
What is the typical structure of a laser?
A typical laser has an amplifying medium between 2 mirrors, one of which reflects only 99% of the photons. The other 1% of photons are transmitted, this is the laser light
Explain how a 4 level system works?
1.Electrons are pumped to level 4, which is not stable so the electrons quickly drop to level 3
2. Level 3 is metastable so the electron will stay in this level long enough for the laser frequency to cause stimulated emission
3. Level 2 is not stable so the electrons quickly drop to level 1.
Why is population inversion easier to create on a 4 level system?
Because stimulated emission occurs between level 2 and 3, and level 2 is almost always empty
Therefore, only a small number of electrons need to be pumped to ensure population inversion
