note on fringe-locking green/red

Joe Farina · Post by **Joe Farina** » Mon Sep 26, 2011 1:17 pm

In case anyone's interested, I wanted to report the results of fringe-locking a combined green/red beam. I had been worried that if the fringes of the green light were locked, the compensations (by the locker's mirror) would not be optimal for the longer red wavelength. I'm still not sure about how the locking of green relates to the simultaneous locking of red, but from visual observation, the red fringes look nicely locked, in addition to the green. I picked off a little of the combined light of the interferometer (after the final spreading lens) with a dichroic which reflects red, but transmits green. In the photos, the locker was set into the green fringes, while the red fringes were projected into another part of the room (on the side of a portable oven). The red fringes are still somewhat polluted with green, but are visible. So locking green and red at the same time seems OK.

Johnfp · Post by **Johnfp** » Mon Sep 26, 2011 2:35 pm

Hey Joe, I had never even thought of trying to fringe lock two colors at the same time. Pretty cool technique.

BobH · Post by **BobH** » Fri Sep 30, 2011 11:28 pm

I've just used a color filter in front of the detectors of the fringe locker to lock a multi-colored system with one of the colors. Stable is stable, regardless of how many wavelengths are in the system.

Joe Farina · Post by **Joe Farina** » Sat Oct 01, 2011 6:58 am

Thanks Bob, it does indeed look like "stable is stable." The reason I went through the exercise is because Rallison said in one of his pappers that the amount of mirror movement is not exactly the same for different wavelengths. He was talking about red versus blue. But it didn't sound like a very big deal, the way he described it. The green/red lock looked fine to me, and I'm glad you confirmed it.