What Is Coherence Distance in Laser Interferometers?

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SUMMARY

The discussion centers on the importance of coherence distance in selecting light sources for laser interferometers. Participants emphasize that coherence distance significantly influences the design and functionality of the instrument. Ranger Mike seeks affordable light sources with a coherence distance of at least 5mm, highlighting the challenge of finding this information on company data sheets. The conversation concludes that laser diodes and gas lasers are viable options for achieving the necessary coherence length.

PREREQUISITES
  • Understanding of laser interferometry principles
  • Knowledge of coherence length and its relation to bandwidth
  • Familiarity with light sources such as laser diodes and gas lasers
  • Basic budget management for scientific equipment
NEXT STEPS
  • Research coherence distance specifications for various laser diodes
  • Explore the characteristics of gas lasers suitable for interferometry
  • Investigate budget-friendly light sources for optical experiments
  • Learn about the impact of bandwidth on coherence length in lasers
USEFUL FOR

This discussion is beneficial for hobbyists, researchers, and educators involved in optical physics, particularly those designing or building laser interferometers on a budget.

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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