Interference pattern for a laser beam through an AOM

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Discussion Overview

The discussion revolves around the observation of an interference pattern in the output of a laser beam passing through two acousto-optic modulators (AOMs). Participants explore the nature of the interference pattern, its potential causes, and the experimental setup involved. The scope includes technical explanations and exploratory reasoning regarding optical phenomena.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant describes a setup involving a continuous wave (CW) 1064 nm laser beam passing through two AOMs, noting the appearance of an interference pattern on the output beams from the second AOM.
  • Another participant suggests that the interference pattern may result from the combination of direct laser light and the output from the first AOM, implying different path lengths contribute to the observed effect.
  • A participant questions the meaning of "direct laser light" in the context of the setup, clarifying that the zeroth order beam is dumped and only the first order beam is sent to the second AOM.
  • There is a request for a diagram of the setup to better understand the arrangement and interactions of the beams.
  • A later reply inquires whether the original poster has determined the cause of the interference pattern, indicating ongoing uncertainty.

Areas of Agreement / Disagreement

Participants express differing views on the source of the interference pattern, with no consensus reached on its cause. The discussion remains unresolved regarding the explanation for the observed phenomenon.

Contextual Notes

Participants have not provided a complete diagram of the experimental setup, which may limit understanding of the interactions between the beams. There is also a lack of clarity regarding the specific conditions under which the interference pattern is observed.

Malamala
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Hello! I have a setup in which I send a laser beam (CW 1064 nm, 1 W) through an AOM (Acusto-optic modulator) and the 1st order beam coming out of it goes through a second AOM (they are both rated for this wavelength and more than 100 W of power). The original laser beam, as well as the first order (and zeroth order) coming out of the first AOM are TEM00 Gaussian beams (both in the specifications and as measured on a beam profiler). However, the beams coming out of the second AOM (both zero and first order), have a TEM00 Gaussian shape, but with an interference like pattern (wave-like) on top, along one direction (i.e. longitudinal pattern, not grid-like). Even when I don't apply any RF power at all to the second AOM, I still get this effect (in this case I only have the zeroth order beam). I even tried a different AOM as the second one and I am getting the same effect. I also measured the laser power reflected from the AOM crystal, and the reflection is <0.5%, as in the AR coating specifications. Has anyone seen this effect before?
 
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It looks like the interference pattern created by the direct laser light plus the output of the first AOM. Presumably these have different path lengths and hence the fast ripple.
 
tech99 said:
It looks like the interference pattern created by the direct laser light plus the output of the first AOM. Presumably these have different path lengths and hence the fast ripple.
What exactly do you mean by the direct laser light? In my case the laser light goes through the first AOM which generates a zeroth order and first order mode which go on different path (in my case I just dump the zeroth order beam in a beam dump). Then the 1st order beam goes through the second AOM, so there is no other laser light coming into the first AOM.
 
Malamala said:
What exactly do you mean by the direct laser light? In my case the laser light goes through the first AOM which generates a zeroth order and first order mode which go on different path (in my case I just dump the zeroth order beam in a beam dump). Then the 1st order beam goes through the second AOM, so there is no other laser light coming into the first AOM.
Could you send a diagram of the set up?
 
Did you ever figure out what was causing the unexplained interference pattern?
 

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