AW: Objective phosphorescence

Posted by Gerhard Holst on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Objective-phosphorescence-tp7587588p7587605.html

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Dear all,

from my experiences with fiber optics and microscopes, I would expect that the additional luminescence might come more from the used glue to fix the lenses within the objectives. I guess for manufacturing reasons, to reduce the times for polymerization often UV hardening might be used. As long as a light beam just passes the lenses, there is only little issue (we are using laser light for widefield illumination of the microscope stage, but we don't have issues with such a background), in case the LED light is able to be spread within the objective casing, some luminescence might excited within the glue and part of it will be guided through the optical system as well.

Could the LED light be better shaped, such that I travels mainly through the lenses?

with best regards,

Gerhard


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Von: Confocal Microscopy List [mailto:[hidden email]] Im Auftrag von Martin Wessendorf
Gesendet: Mittwoch, 22. November 2017 00:16
An: [hidden email]
Betreff: Re: Objective phosphorescence

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Interesting.  I was using the widefield 'scope in my lab today and saw something that I've seen a thousand times before, but never thought
about: Near-UV excitation causes the optics in my sub-stage condenser to fluoresce yellow.  However, as others have said, I don't know whether the source is the glue, the glass, or the housing.

Martin Wessendorf




On 11/20/2017 9:33 PM, Benjamin E Smith wrote:

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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-3f03c7
> bc0c80/1.1/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
>

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