Laser interference fringes fading in and out of view

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Discussion Overview

The discussion revolves around the fading and reappearance of interference fringes in a Mach-Zehnder interferometer setup used in quantum optics. Participants explore potential causes for this phenomenon, including coherence issues, laser stability, and mode changes, while seeking solutions to the observed behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the issue may relate to the coherence of the laser, proposing the use of a spectrum analyzer to measure it.
  • Another participant estimates a coherence time of about 6 seconds based on the fading pattern of the fringes, questioning the polarization of the input beam.
  • Concerns are raised about potential varying losses in one leg of the interferometer affecting the peak amplitude of the fringes.
  • Frequency stability is discussed as a possible factor, with some participants questioning whether this would cause the interference pattern to move across the screen.
  • There is speculation about the laser potentially switching modes, which could introduce new frequencies and affect the interference pattern.
  • Participants discuss the implications of different transverse modes and their relevance to the observed interference, with some asserting that only TEM modes propagate in free space.
  • One participant mentions the importance of having a single mode source for effective interferometry and discusses methods to detect higher order modes in lasers.
  • Another participant introduces the idea of evanescent modes and their potential effects, suggesting that different rules may apply in various contexts.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the causes of the fading fringes, including coherence, frequency stability, and mode changes. The discussion remains unresolved, with no consensus on the primary issue or solution.

Contextual Notes

Participants note the complexity of laser behavior and the importance of understanding the specific type and model of the laser being used, which remains unspecified in the discussion.

  • #31
We ended up writing a program to correct for the blurriness in the interference. We gave up trying to fix it haha.
 
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