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

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Discussion Overview

The discussion revolves around the nature of laser light, specifically how it can be understood through both quantum mechanics and classical physics. Participants explore the implications of stimulated emission, coherence, and the definitions of classical versus quantum light sources.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that the physics of lasers, particularly stimulated emission, can only be explained through quantum mechanics and questions how lasers can also be considered classical light sources.
  • Another participant seeks clarification on what constitutes a "classical light source."
  • A participant defines a classical light source as one that can be described using classical electromagnetism and raises concerns about the implications of photon coherence on the uncertainty principle.
  • Some participants argue that while quantum mechanics is essential for describing the production of laser light, the light itself can be described classically as a solution to Maxwell's equations, contrasting it with states of light that lack a classical description.

Areas of Agreement / Disagreement

Participants express differing views on the classification of laser light, with some supporting the idea that it can be both quantum and classical, while others question the implications of coherence and the uncertainty principle. The discussion remains unresolved regarding the definitions and classifications of light sources.

Contextual Notes

Participants reference specific states of light, such as coherent and squeezed states, to illustrate their points, but the discussion does not resolve the implications of these classifications on the nature of laser light.

Muthumanimaran
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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?
 
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What's a "classical light source"?
 
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?
 
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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
 
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atyy said:
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
 

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