Hi all,
I am measuring the beat-signal between a tunable HeNe laser and a stabilized one, and seeing something like this:
http://www.youtube.com/watch?v=3arRbVKr9jQ

There is an overall slow drift (probably thermal expansion of the tunable laser cavity) which I can cope with, but I am not happy with the +/-5 MHz fast jumps of the beat-note.
I have tried this with two reference lasers, a HP5501A and a MarkTech 7900 and the results are similar - so I believe the tunable laser it at fault, not the reference laser.

Any ideas on what could cause this kind of rapid frequency shifting?
I have tried two powersupplies for the tunable laser. With a small brick-type PSU powered off +12V there is very large intensity modulation at 20-22 kHz. I am now using a better PSU which results in very small intensity noise.

A few photos of the tunable laser:
https://www.dropbox.com/sh/q4xruaiwlbhru1o/HtTelFz1j_
I believe this is an early version of the 5-color HeNe still on sale, e.g. this one:
http://www.edmundoptics.com/lasers/g...eon-laser/2550
The Littrow prism has been mounted on a piezo tube which allows electronic tuning of the laser.
I have tried looking at the beat-note with the piezo amplifier on/off, and with the piezo grounded - but I still see the same jumpy beat-signal.

Thanks in advance for any ideas & suggestions!

Anders