How Is Population Inversion Calculated in Laser Gain Switching?

[KFC]

Hi, many text about lasers introduces Q switching in detail and just mention gain switch briefly. We know the major difference b/w them is: Q-switching switches the loss from high to low while gain-switching switches the gain from low to high. But the time behavior is quite different in these two cases. In gain switching, does anyone know how to calculate the initial inversion of population when the photon starts to build up? and how to calculate the final inversion of population when the pulse just diminished to zero?

 

[Valerie Park]

To calculate the initial inversion of population when the photon starts to build up, you can use the equation: Population Inversion = (1/R) * (G - 1), where R is the rate of stimulated emission and G is the gain coefficient. To calculate the final inversion of population when the pulse just diminished to zero, you can use the equation: Population Inversion = (1/R) * (1 - 1/G), where R is the rate of stimulated emission and G is the gain coefficient.

 

[astrokreng]

Hello,

Thank you for bringing up the topic of laser gain switching. As you mentioned, the main difference between Q-switching and gain-switching is the change in gain or loss. In gain-switching, the gain is increased from a low level to a high level, allowing for the buildup of photons and the creation of a laser pulse.

To answer your question about calculating the initial and final inversion of population in gain-switching, it is important to understand the concept of population inversion. In a laser, population inversion refers to the state where there are more atoms or molecules in the excited state than in the ground state. This is necessary for laser action to occur.

In gain-switching, the initial inversion of population can be calculated by considering the pump rate, the decay rate, and the cross-section of the laser medium. The pump rate is the rate at which energy is being added to the system, while the decay rate is the rate at which the atoms or molecules in the excited state return to the ground state. The cross-section is a measure of the probability of an atom or molecule absorbing a photon.

As the pump rate increases, the population inversion also increases until it reaches a threshold level where laser action can occur. At this point, the photons start to build up and the laser pulse is generated. The final inversion of population can be calculated by considering the decay rate and the cross-section, as the population inversion decreases as the laser pulse is depleted.

It is important to note that the specific calculations for initial and final inversion of population may vary depending on the type of laser and its parameters. it is important to thoroughly understand the principles and equations behind laser gain switching in order to accurately calculate these values.

I hope this response provides some insight into the calculations involved in gain-switching and the importance of population inversion in this process. Thank you for your interest in this topic.