Laser Physics: Saturation, Two-Level System & Pump Field

[KFC]

What does saturation mean in laser physics? I am reading some material on two-level system, in which it mentions something call "saturating pump field", what does this field mean?

 

[Andy Resnick]

In the two-state approximation (ground state and excited state), a pump field can move atoms from the ground state to excited state. When the efficiency of pumping goes to zero (which is reached at a 50-50 population distribution, IIRC), the laser medium is said to be 'saturated'- no additional atoms can be moved into the excited state without some returning to the ground state.

Population inversion (lasing with gain) requires at least three states.

 

[astrokreng]

In laser physics, saturation refers to the point at which the number of excited atoms or molecules in a laser gain medium reaches its maximum capacity. This occurs when the population of excited states is equal to the population of ground states, and any additional energy input will not result in further amplification of the laser beam.

In a two-level system, the laser gain medium has only two energy levels - a ground state and an excited state. When the pump field, which is the energy source that excites the atoms or molecules in the gain medium, reaches a certain intensity, it can cause a large number of atoms or molecules to reach the excited state. This results in a high population of excited states and leads to saturation.

The term "saturating pump field" refers to the pump field that is strong enough to saturate the gain medium, meaning it has reached the maximum capacity for amplification. This is an important concept in laser physics as it determines the maximum output power of a laser.

In summary, saturation in laser physics refers to the point at which the gain medium can no longer amplify the laser beam, and a saturating pump field is the energy source that causes this saturation to occur.