Undergrad How Can LASER Be Both a Quantum and Classical Light Source?

[Muthumanimaran]

My question is the physics behind the LASER such as stimulated emission can be only explained by quantum mechanics only. We can represent LASER as coherent state in quantum mechanics only. Then how can we say LASER can be thought of a classical light source?

 

[berkeman]

What's a "classical light source"?

 

[Muthumanimaran]

According to my understanding, classical light source is something we can able to describe using classical electromagnetism. I have this confusion because, when you say LASER, we talk bunch of photons in phase. Does this violate uncertainty principle between phase and photon number? $$\Delta{N}\Delta{\phi}\geq 1$$
so we can regard them as classical light source?

 

[atyy]

Quantum mechanics is needed to describe the production of laser light, but the light itself can be called "classical" as it can be described as a solution of the classical Maxwell equations. This is in contrast to states of light that have only quantum description, without being solutions of the classical Maxwell equations.

Coherent state (has classical description): https://en.wikipedia.org/wiki/Coherent_state
Squeezed state (has no classical description): https://en.wikipedia.org/wiki/Squeezed_states_of_light

 

[Muthumanimaran]

Quantum mechanics is needed to describe the production of laser light, but the light itself can be called "classical" as it can be described as a solution of the classical Maxwell equations. This is in contrast to states of light that have only quantum description, without being solutions of the classical Maxwell equations.

Coherent state (has classical description): https://en.wikipedia.org/wiki/Coherent_state
Squeezed state (has no classical description): https://en.wikipedia.org/wiki/Squeezed_states_of_light

got it