Why is there a temperature gradient in lasers causing thermal lensing?

AI Thread Summary
Thermal lensing occurs due to a temperature gradient in active media, where the core is hotter than the outer parts. This temperature difference arises because the inner sections experience less heat loss compared to the outer sections, which lose heat more rapidly. The analogy of penguins in a storm illustrates this concept, as those in the center remain warmer than those on the outside. Each part of the medium converts the same input power into heat, leading to varying equilibrium temperatures. Understanding this principle clarifies the dynamics of thermal lensing in laser systems.
DariusP
Messages
50
Reaction score
3
Hello, I wanted to ask about thermal lensing. Thermal lensing is when a temperature gradient from the center of the medium to the outermost part of the medium is created. This causes a varying refractive index throughout the medium.

What I want to ask is: Why is the core of the rod(or any other active medium) always hotter and the outermost part - cooler?
 
Science news on Phys.org
DariusP said:
Why is the core of the rod(or any other active medium) always hotter and the outermost part - cooler?
Same reason as the penguins at the centre of a colony in a storm are warmer than those on the outside (or why there is a temperature gradient across any cooling body). Each part of the laser is transferring the same amount of input power per unit volume into heat, the outer parts have a higher net loss than the inner parts so the equilibrium temperatures will be different.
 
  • Like
Likes DariusP and gleem
sophiecentaur said:
penguins at the centre of a colony
Thanks, that's a marvelous metaphor.

Water always flows downhill. Heat always flows from warmer to colder. Consider just 3 penguins; center, middle, outer. For heat to flow, temperature at center must be hotter than middle, and temperature at middle must be hotter than outer.
 
  • Like
Likes sophiecentaur
anorlunda said:
Thanks, that's a marvelous metaphor.
Cheers. I saw some Emperor Penguins on the TV last night and the metaphor just thrust itself into my mind this morning.
 
  • Like
Likes anorlunda
sophiecentaur said:
Same reason as the penguins at the centre of a colony in a storm are warmer than those on the outside (or why there is a temperature gradient across any cooling body). Each part of the laser is transferring the same amount of input power per unit volume into heat, the outer parts have a higher net loss than the inner parts so the equilibrium temperatures will be different.
So simple now when I think about it (net gains and net losses). Thanks.
 

Similar threads

Back
Top