What Is Coherence Distance in Laser Interferometers?

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Discussion Overview

The discussion revolves around the concept of coherence distance in laser interferometers, particularly in the context of selecting an appropriate light source for building an interferometer. Participants explore the implications of coherence distance on design and functionality, as well as practical considerations regarding budget and light source options.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • One participant expresses a need for a light source with a coherence distance of at least 5mm and mentions budget constraints as a pensioner.
  • Another participant inquires about the budget available for purchasing the light source.
  • A participant reflects on past experiences with white light sources in school interferometers, noting that coherence length is inversely proportional to bandwidth and suggesting that laser diodes or gas lasers might suffice for producing measurable fringes.
  • There is a mention of a misunderstanding regarding laser operation, with one participant indicating a belief that lasers continuously operate without restarting, which they have since corrected.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the best light source or the implications of coherence distance, and multiple viewpoints regarding suitable options and experiences remain present.

Contextual Notes

Limitations include the lack of specific coherence distance data on company sheets and the potential variability in coherence lengths among different light sources.

Who May Find This Useful

Individuals interested in building interferometers, those exploring the properties of light sources in optical applications, and participants in educational settings related to optics and laser technology.

poor mystic
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Hi people :)
I want to build an interferometer.
In the course of looking for a suitable light source for my instrument I have been advised to check the 'coherence distance' of the sources; it is clear to me that this distance places practical limits on the design of the machine. However 'coherence distance' is not mentioned on the company data sheets for the devices I have been looking at.
I need to find a light source that I can afford, with as short a wavelngth as possible and a coherence distance of at least 5mm. Can anyone help me please?
 
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what kind of budget do you have? how much $ do you have to spend on this ?
 
Thanks for your question Ranger Mike :)
I have very little money, being a pensioner.
The design I'm using is one I cooked up for myself in the olden days (ended last week) when I believed that lasers just continuously lased, and did not continually restart as seems to be the case.
 
The original interferometers we used in school, used a white light source, and with a smooth hand you could find the "white light fringes". Coherence length is inversely proportional to the bandwidth. I think even a laser diode would have a decent enough coherence to show and measure fringes. Almost any gas laser will work also.
 

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