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 ?
The coherence length of a monochromatic laser refers to the distance over which the laser beam maintains its coherence, or the ability of all the photons in the beam to maintain a fixed phase relationship with each other.
The coherence length of a monochromatic laser is determined by the spectral bandwidth of the laser, which is the range of wavelengths contained in the laser beam. A narrower spectral bandwidth results in a longer coherence length.
The coherence length of a monochromatic laser is important in applications such as interferometry and holography, where the interference of light waves is used to create precise measurements or images. A longer coherence length allows for more accurate and detailed results.
Yes, the coherence length of a monochromatic laser can be increased by using techniques such as cavity enhancement, where the laser beam is reflected back and forth between two mirrors to amplify the coherence. Additionally, using a laser with a narrower spectral bandwidth can also increase the coherence length.
Yes, the coherence length of a monochromatic laser can change over time due to factors such as temperature fluctuations and vibrations, which can affect the spectral bandwidth of the laser. It is important to carefully control these factors in order to maintain a stable coherence length for precise applications.