Alignment of a coupled-cavity Q-switched laser
- From: "John Travolta Sardus" <pireddag@xxxxxxxxxxx>
- Date: Thu, 28 Jul 2005 11:59:28 -0400
Hi all,
in my lab I have trouble aligning a Q-switched laser and I hope someone can
give me some useful indication.
It is a Nd:Yag laser, pumped with flashlamps. The cavity is formed by three
mirrors. The back mirror is convex. I do not know the radius of curvature of
the output coupler (reflectivity around 50%). Inside the cavity there is a
third mirror, which might be planar and has a reflectivity of around 60%.
The Nd:Yag rod is between the output coupler and the middle mirror, while
the Q-switch, a passive saturable absorber, is between the middle mirror and
the back mirror, pretty close to the last one. There is a pinhole close to
the output coupler.
I can get the laser to Q-switch if I remove the middle mirror, but the
temporal shape of the pulse has some oscillations whose period is a
roundtrip superimposed on the near-gaussian overall shape. With the middle
mirror, the cavity formed by the middle mirror and the output coupler lases
by itself (without adjusting the output coupler from its previous position,
where it makes the longer cavity lase); there is of course an output
directed towards the back mirror through the middle mirror and I have
verified that this beam does not follow the path of the beam that is formed
when the long cavity lases in absence of the middle mirror. When the middle
mirror is in, there is no Q-switching.
I hope that despite the explanation is tangled it is possible to understand
something. The laser was working fine before I had to change the flashlamps
(to do this I had to remove the Nd:Yag rod + flashlamps assembly from the
cavity, which ruined the alignment).
My questions are
- why does the structure appear on top of the Q-switched pulses?
- why a coupled cavity design?
- how do I get the to cavities co-aligned?
- will co-alignment make the structure disappear and yield a nice looking
pulse?
Thanks in advance for any indication or suggestion.
Giovanni
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