Minimizing spatial hole burning

[Niles]

Hi

Say I am looking at a linear laser cavity consisting of a gain medium filling the *entire* cavity, please refer to the attached picture. The cavity will have standing waves in it, which will result in spatial hole burning of the gain medium at the antinodes of the optical field.

Say the intracavity field starts out by being P-polarized at point A. Then it propagates to point B, where I put a device that changes the polarization to S. Then it propagates back to point where, where a device makes it P-polarized again, etc..

Assuming the gain-medium is birefringent, this should in principle minimize spatial hole burning, right? Because the optical path length of P- and S-polarized beams are different, so the standing-wave pattern would also change as well?


Niles.

 

[tommw]

Interesting thought.. Do you consider the points A and B to be inside the cavity as well? (By the way, I don't see any picture attached.)
Any thoughts about how such a "device" would look like?
Normally you'd use a Halfwaveplate to rotate polarization. This will, however, not work in your case. But a quartewaveplate could do the trick.
The latter has been proposed by Siegman, named twisted-mode-technique, see Applied Optics, Vol. 4, Issue 1, pp. 142-143 (1965) It works in the inverse way as you suggested: The polarization within the gain medium will be circular.

I also think that with your suggestion you will implicitely create a ring-cavity (there won't be any standing waves at all because p- and s-polarizations won't interfere).

 

[Niles]

I forgot the attachment, thanks to berkeman for letting me know. In principle the gain medium should fill the whole cavity.


Niles.

 

[Niles]

Thanks. I haven't thought much about how I would do it in practice, I just thoight of the theory. But you say quarter waveplates? I don't see how that could work. So first time it passes through and becomes circular, then changes direction when reflection of the mirror, and then it gets a 90 degree phase shift again, which is a total of 360 degrees. So we just end up with the same as initially?