system
Given the following post, respond as if you're commenting on Reddit:
human
How can lasers get hotter by going through a magnifying glass?

Doesnt this violate conservation of etendue? Can anyone help me understand what's going on here.
gpt
I looked a bit further into your explanation involving negative temperature.

Negative temperature doesn't violate COE, in a laser it requires that there is population inversing in the lasing material. That's well know. A statistical definition of temperature as related to entropy is used to describe these systems. This is not the same way we think about systems with positive temperature, where thats a measure of kinetic energy of particles.

The laser beam itself does not have negative temperature by this definition. It just works the same as lasers are known to work. The "negative temperature" being refered to just focuses on the inverted population of the lasing material. Which transfers heat in the sense that the higher energy states relax and disperse that energy into the vibrational modes of the material.

So there really isn't any law being broken here.