The discussion revolves around measuring the coherence length of a monochromatic laser, with participants exploring experimental methods and theoretical concepts related to this topic.
Some participants have provided guidance on using a Michelson interferometer and the importance of high-resolution spectrometers for measuring bandwidth. However, there remains uncertainty about the specific procedures and equipment needed, as well as the relationship between bandwidth and coherence length.
Participants note the requirement for high-resolution measurements and the challenge of selecting appropriate equipment. There is mention of the need for clarity on how to practically implement the measurements discussed.
But the teacher ask for also long coherent length.I learn that I can use a spectrometry to find bandwith and then calculate the coherent length.But I couldn't find how can I get bandwith measurement? And I wonder up to what coherent length I can use michelson interferometerehild said:You can use a Michelson interferometer and see how long is the path difference when the interference is not blurred yet.
But lasers can have very long coherence lengths. Choose a not too good laser.
I think I read all of them before asking that question :) But I need to describe how can use a spectrometer to measure bandwith ? what is the procedure...etc.For michelson I know what I need to do.Also do you know which spectrometer should I use ?ehild said:To measure the spectral bandwidth of the laser radiation you need very high resolution of the spectrometer. The resolution must be much better than the bandwidth of the laser.
The coherence length L is c/Δf, where Δf is the bandwidth, difference of the frequencies where the power is half the maximum.
The coherence length of He-Ne lasers are in the range of several cm - several dm. But high-quality lasers can have even 100 m coherence length.
Some things to read:
http://en.wikipedia.org/wiki/Coherence_length
http://www.rp-photonics.com/coherence_length.html
http://www.answers.com/Q/What_are_the_coherence_lengths_of_the_different_types_of_lasers
elif said:I think I read all of them before asking that question :) But I need to describe how can use a spectrometer to measure bandwith ? what is the procedure...etc.For michelson I know what I need to do.Also do you know which spectrometer should I use ?