Two points about filters "burning out"...

(1) We have had this happen only with mercury burner excitation lamps,
not with laser sources (but we usually use our only low laser power -
typically 1%). It takes about two to three years of regular use (up to
six hours per day) before the central part of the filter burns out - ie
goes dark, with a separation of the various layers that make up the
filter.

(2) It only happens with the excitation filters for green fluorophores
(ie excitation centred around 488nm or so)

The problem seems to be worse with filters that have very narrow
bandpasses. Most of our filters are custom-made made by Chroma - they
have replaced the burnt out ones at minimal charge, which is good of
them, since you could make a case that there is not much you can do
about this problem. We have tried putting heat absorbing filters into
the excitation light path (they are routinely there!), but it doens't
seem to make much difference. I assume that the problem is caused by the
filter heating up as a result of absorbed light and associated heat...
If you really want to see what all the focussed light / heat can do ,
have a look at the back (ie light side) of the light stop / shutter that
you use to cut off the light path in a fluorescence microscope - ours
all have really nice little zones burnt into them, heat / IR filters
notwithstanding!!

Hope that helps a bit

IAN



Weijun Qian wrote:
>
> Dear Dr. Robinson,
>
> I'm glad you brought up this issues. I have been working on a NIkon RCM
> confocal system for over a year.  It is also equipped with a Coherent
> enterprise laser.  I found the same  problem for the
> excitation filter.  Actually i have replaced the 488 nm excitation filter
> two times during the past year.  The maximum laser output for the visible
> light of my system is 1 W.  I have been always wondering if some
> companies supply high quality exciters which can hold several walts of
> laser power.
>
>    One thought I'm going to try is to put a ND filter infront of
> the excitaiton filter.  But I'm not sure whether the ND filter will
> degrade if high power laser light keeps shining on it.  I will welcome any
> interesting discussions on this issue.
>
> Best!
>
> Weijun Qian
>
> ------------------------------------------------------------------------
> Weijun Qian
> Department of Chemistry, P.O. Box 117200
> Gainesville, 32611-7200
> Phone: 352-846-0838(O)
>
> On Fri, 29 Oct 1999, J.Paul Robinson wrote:
>
> > Colleagues:
> > I 'd like to report on a recent problem that caused us some lost time on our
> > confocal microscope (BioRad MRC 1024 UV/Vis system). We have been
> > doing a lot of reflection imaging lately and recently encountered a situation
> > where the quality of the images suddenly dropped off badly.
> >
> > It turns out the problem was a burned filter. It was hard to identify because
> > it was one of those problems that did not have an obvious solution (well not
> > to me anyway).
> >
> > I took some photos for those interested and they can be seen on
> > http://www.cyto.purdue.edu/flowcyt/confocal/cfcl4.htm
> >
> > The bottom line is yes - filters do degrade and excitation filters can be
> > damaged eventually. We have been using the system continuously for 5
> > years.  These particular filters are excited by the Coherent Enterprise laser.
> > They only have the visible lines going through them. Has anyone else seen
> > this problem?
> >
> > Thanks
> >
> > Paul Robinson
> >
> >
> > J.Paul Robinson, PhD             PH:(765)4940757
> > Professor of Immunopharmacology
> > Professor of Biomedical Engineering
> > Purdue University          FAX:(765)4940517
> > EMAIL:[log in to unmask]
> > WEB: http://www.cyto.purdue.edu
> >

--
Professor Ian Gibbins
Anatomy & Histology
Flinders University of South Australia
GPO Box 2100, Adelaide, SA 5001
Australia

Phone:  +61-8-8204 5271
FAX:    +61-8-8277 0085
Email:  [log in to unmask]