In response to the question by simon Monard on air cooled or water cooled
lasers:

I would pick dry-- but choose the manufacturer carefully and definitely do QA
tests on laser stability in your system.

There is a major problem with laser stability on both UV and visible confocal
systems. Heat dissipation can definitely effect laser stability and in pronciple
wet is better than dry.  Improper temperature setting of a water chiller can
also effect the laser stability.  In the newer systems the problems appear not
to be so much with the laser RMS as with an incompatibility of laser light to
the optical polarization of the fiber. Does your system use an optical  fiber or
is it direct coupled?
I am not sure water cooling the laser would increase the stability of a good
argon laser in a fiber system. Changing the laser manufacturer would definitely
help the problem in either case. Also aligning your confocal system properly by
the service technician would help its system laser performance.  These factors
will be discussed in a manuscript soon to be submitted for publication entitled
"Evaluation of Confocal Microscopy System Performance."

We have a UV Coherent Enterprise laser and use an LP20 to cool it.
This laser is rated at under 1% RMS noise.  It delivers under 1% RMS noise.
However we have found laser instability at times to be over 10% due to fiber
polarization problems. Currently it fluctuates at 3% over a period of hours.

In the flow cytometry world, almost all clinical flow cytometers ( BD and
Coulter)  use 15mw argon air cooled lasers satisfactory. In that system
instability of a laser power is totally unacceptable for the quality of data
obtained. Note they are direct coupled and not fibber coupled. Apparently laser
instability  it is much more tolerated in the confocal systems as laser
instability of over 10% can be common with different manufacturers systems. No
one except a few concerned individuals seems to care about the problem. Everyone
doing live cell physiology experiments or quantification type experiments should
be very concerned about laser stability.

Bob
Robert M. Zucker, PhD
U.S. Environmental Protection Agency
MD 72
National Health and Environmental Effects Research Laboratory
Research Triangle Park, North Carolina, 27711
Tel: 919-541-1585; fax 919-541-4017
e-mail: [log in to unmask]