Breaking the coherence of an optical signal

[narra]

Hi,

I am curious to know if there any passive (or simple active) methods to convert a very coherent signal into an incoherent one? I suppose I would need to find a way to chirp the signal and a non-linear medium might be one method. Any ideas?

Thanks

narra

 

[Jolb]

This is a pretty vague question... certainly a nonlinear medium could be used to dephase parts of a signal... but it is true that any coherent optical signal has a finite "coherence length", which basically is the length over which the light travels while maintaining a certain degree of coherence. So you could just increase length of the path over which your signal travels (maybe if you have a long fiber optic cable?). But coherence of an optical signal can be a tricky thing, especially for lasers, where coherence can come in and out as you increase path lengths.

Can you be any more specific with your question?

 

[Jano L.]

In theory, you can lead the light into scattering medium, low pressure gas or other rarified substance and collect the radiation at right angle. If the distances of the scatterers are larger than the wavelength, they will give you incoherent light of the same frequency, as they have random positions. I do not know whether it is practicable though.

 

[Andy Resnick]

I am curious to know if there any passive (or simple active) methods to convert a very coherent signal into an incoherent one?<snip>

The standard way to produce (spatially) incoherent light is to pass it through counter-rotating ground glass sheets. If, on the other hand, you want to decrease the *temporal* coherence, I'm not sure you can do it without complicated nonlinear processes, although it may be possible to simply use a length of photonic-crystal ("holey") fiber.

 

[Claude Bile]

You can use an optical diffuser;

http://www.edmundoptics.com/optics/windows-diffusers/optical-diffusers/

If you don't mind changing wavelengths; you could always pump a population of fluoroescent centres. A non-phase matched SHG signal will work as well.

Claude.