Re: Building Lasers

From: Sam Goldwasser (sam_at_saul.cis.upenn.edu)
Date: 07/27/04 

Date: 26 Jul 2004 21:23:21 -0400

jimzotos@yahoo.com (Laserman) writes:

> Hello all you laser gentle folk out there. A few years ago I was
> working for a laser company and they asked me to build this ring
> laser. This company had never built a ring laser before and the Phd
> assigned to the project had no idea how to do it. My supervisor
> handed me 4 lenses and said he wanted the beam 5 inches above the
> board. That's it! So I scoured the lab and assembled all the
> necessary ingredients and put it together. Next I had to worry about
> alignment. This ring laser was to be a double pumped nd:YAG with
> input about 30 watts from the power supply and output as much as I
> could tweak it. I relized very quickly that if I was to follow normal
> procedure for alignment that I might be there for days trying to set
> it straight so I carefully alligned the lenses BY EYE, turned on the
> power supply, double pumped the nd:YAG and started tweaking the output
> lens. I set up the Infrared detector and started looking for a sign.

Lenses or mirrors?

> nd:YAG puts out 1064 nm infrared cw. About 30 minutes of tweaking and
> I saw a green flash across the detector. IT WORKED!! I was so happy
> I yelled out, "I GOT A SPARK!" Everyone in the lab came over but the
> flash was gone. Ten minutes later I was able to sustain the spark a
> few seconds, I knew it was only a matter of time because I had faith
> in Einstiens theory of stimulated emission. A half hour later I had
> 1064 nm cw so I carefully tightened the lens (the other 3 lenses were
> screwed in solid)
> I brought the infrared detector closer to the output mirror and saw
> that I had 2 green dots. A few minutes of carefull consideration and
> I realized what was happening. There were 2 laser beams inside the
> optical cavity traveling in opposite directions because tha nd:YAG was
> being pumped from opposite sides! I measured both beams with a power

Nothing to do with being double pumped (whatever you exactly mean by that!),
but rather that without some means of forcing a single direction usch as using
an optical isolator or Faraday rotator, there will naturally be two
beams traveling in opposite directions, and thus two output beams where
the output mirror is at a vertex of the ring.

> meter and they were each about 7 watts. I put a power meter on one of
> the beams and blocked the other one with a laser mount, the goal being
> to "walk the beam around" so as to maximize the power output. I set
> up the power meter and started tweaking the lenses. At some point I
> wanted to change the position of the power meter because it was
> slightly burnt but the laser mount blocking the beam was in the way so
> I went around and with my right hand moved the mount that was blocking
> the other beam. I was not interfering with any part of the laser
> itself. WHAT DO YOU THINK HAPPENED?? If you are interested let me
> know. I'll explain in a few days but give you some time to think
> about it for now.

Not sure what you're leading up to here but if your movement resulted in
a reflection back into the laser cavity, quite a lot could have happened.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
 Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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>
> Yours Truly
> Laserman

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