Entropy flow of a laser beam
Abstract
A laser beam is often modelled by a pure coherent state. In fact, its state is mixed, even if it has coherent-state photon-number statistics (Poissonian), because the phase must vary. We consider such an ideal laser beam, with phase diffusion rate ℓ , equal to its (Lorentzian) spectral width. We show that the beam entropy is extensive, with an entropy flow of S ˙= k B N ˙ ℓ , where N ˙ is the number flow. We give an intuitive explanation for this remarkably simple result and compare it to the entropy flow of a unidirectional thermal beam.
Fields of Study & Subjects
Orbital Angular Momentum in Optics
Advanced Thermodynamics and Statistical Mechanics
Quantum Information and Cryptography
Publication details
- Journal / source
- Optics Letters
- Volume
- 51
- Issue
- 14
- Pages
- 3977–3977
- Publication date
- 24 June 2026
- Language
- EN