Objective phosphorescence

Posted by Benjamin Smith on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Objective-phosphorescence-tp7587588.html

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Hey microscopists,
   We observed an odd phenomenon today on a microscope and was wondering if
anyone else has ever seen it.  We were using a DMD do a full field flash
with 420nm light during the flyback of the scanning mirror on a 2P imaging
rig.  We noticed that after the light was turned off, there was a
millisecond long slewing of the signal that looked a lot like
phosphorescence.  In the following image, you can see that the LED is on
for the first portion of the scan, then turns off and the apparent
afterglow: https://goo.gl/2ENHwL

This afterglow was also apparent with an oscilloscope looking at the PMT
and fast mirror signals: https://goo.gl/2AMsvB

   We then systematically removed components from the optical path, and
cleaned everything, and we were eventually able to determine that the glass
in the objective itself was glowing, where if the objective was removed and
the DMD image was shined onto a piece of lens paper or metal, the afterglow
went away:
https://goo.gl/arXYF5
https://goo.gl/cVo2Ev

    The final nail in the coffin to our suspicions was when we then mounted
a plano-convex N-BK7 lens onto the microscope and the effect came back, and
the thicker the lens, the stronger the effect. Also, the effect went away
when we used 540nm light.

With a bit of internet searching I also came across this paper that
confirms there is some visible fluorescence in glass due to trace elements:
http://www.schott.com/d/advanced_optics/87330898-4e56-4d70-965a-3f03c7bc0c80/1.1/schott_tie-36_fluorescence_of_optical_glass_us.pdf

Even when I saw the slew, and the first thing that came to mind was
phosphorescence, the last thing that came to mind was that the glass in the
objective itself was the offender, so I wanted to post this to both give
other people a heads-up, and also to see if anyone else has run into this
phenomenon.

Cheers,
   Ben Smith

--
Benjamin E. Smith, Ph. D.
Imaging Specialist, Vision Science
University of California, Berkeley
195 Life Sciences Addition
Berkeley, CA  94720-3200
Tel  [phone]
Fax [phone]
e-mail: [hidden email]
http://vision.berkeley.edu/?page_id=5635 <http://vision.berkeley.edu/>