Joseph,
Your problem may be that the Transverse mode (TEM) of your I70 has
degraded from the 00 to 01 or higher. The transverse mode number represents
the number of nulls that appear in the cross section of the beam. As the
number increases, the beam diameter as well as the divergence increase. This
may result in a doughnut shaped beam. If this happens, your cell now passes
effectively through 2 or more beams, which will generate a broader pulse
(with peaks and valleys) from your PMT, hence the wider CV's. The most
common cause of this problem is the tube sagging over time, although there
may be other causes.
If your I70 has an aperture try decreasing the setting. Your power
output will probably decrease, but your beam quality that intercepts the
cell may improve. Ask your service engineer to compare the beam quality of
your I90 to your I70. There are a few companies that sell laser beam
characterization test equipment that not only measures power, but also
measures beam shape as well as intensity profile. Hope this helps.
Best Regards,
Ray Lannigan
Tritech Field Engineering Inc.
2014 Renard Ct. Suite I
Annapolis, MD 21401
800-886-7004
410-266-1522
www.tritechinc.com
P.S. We are thinking of providing laser beam characterization services for
our customers and would like to get feedback from flowers that would be
interested ( or not) in that service. Any responses are greatly appreciated.
-----Original Message-----
From: Joseph Webster <J.Webster@centenary.usyd.edu.AU>
To: cyto-inbox
Date: Monday, May 08, 2000 5:09 PM
Subject: Another laser question...
>
>Hi All,
>Has anyone compared the Coherent I-70c with I-90/5UV for
>visible light performance, particularly stability?
>
>I was running the I-90 as primary laser, 488/200mW, last week
>swapped the I-70 into that role.
>
>I'm not happy with the result....
>
>I don't have equipment to measure output power jitter,
>but the CV of bead peaks is around 2-3 times more with the I-70
>compared to the same measurement done with the I-90; the FSC
>is now lots murkier than before.
>
>I would expect similar results from the two lasers running in
>exactly the same conditions, but the Coherent engineer is not
>convinced there is anything wrong.
>
>Any experience from the real world would be appreciated.
>
>Thanks, Joseph.
>--
>Joseph Webster, Flow Cytometry Facility
>Centenary Institute, Sydney AUSTRALIA.
>
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