Posted by
Antonio Jose Pereira-2 on
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Hi all,
Thank you so much Zdenek, Craig, Peter, for the suggestions and literature. I'll certainly try some pre-compensation using l/2 and l/4 waveplates. I don't have the system built yet, so I'm just anticipating the difficulties...
Mirrors are problematic too, not so much for (protected?) metallic ones. Regarding the 'mirror pair' that we will use for beam co-alignment (as is often needed in general optical setups), I was considering making the two reflections define orthogonal planes. Like a periscope 'looking to the side', so that an s-component reflection in the 1st mirror becomes a p-reflection in the 2nd mirror. I guess this compensation strategy is either well-known or just wrong. If it would really work, I might even consider dielectric mirrors, maybe.
Anyway, thanks for your help.
Antonio
i3S, University of Porto - Portugal
----- Original Message -----
From: "Peter Brunt AVR" <
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To: "CONFOCALMICROSCOPY" <
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Sent: Thursday, 1 April, 2021 16:21:55
Subject: Re: polarization and dichroics
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Hi Antonio,
A quick disclaimer- AVR Optics is the research distributor for Semrock in the US and Canada.
This is something we have come across in the past from groups working on polarization sensitive projects. Due to the nature of interference coatings, different polarization states will behave differently as the propagate through the coating lasers. This effect can be controlled but to a certain degree but this becomes more challenging at 45 degrees versus zero degrees for example. For linear states this tends to manifest in the form of a simple efficiency change but for mixed states, this can cause ellipticity.
One option that we have suggested in the past where you are seeing a polarization change as a result of the dichroic is to pre-compensate for the polarization prior to the dichroic. If the effect of the dichroic is known, then you can work with that to correct the issue. In your case this may be challenging as you're also interested in the return state but this could be worth exploring.
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-----Original Message-----
From: Confocal Microscopy List <
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Sent: Wednesday, March 31, 2021 3:47 PM
To:
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Subject: Re: polarization and dichroics
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Polarization is actually one of my research focuses. The primary dichroic in particular can alter your polarization fairly strongly. This is mainly an issue if you don't have pure S or P states (+) relative to the dichroic surface. Any 45 or -45 content (x) will be likely ellipticized by the coating layers, and if you already have elliptical light then it starts becoming very complicated. This is problematic as we discovered that under certain conditions fluorophores exhibit "interesting" responses to polarized light. We actually observed different fluorescence rises with calcium concentration using XRhod using different polarization states for excitation. This implies that if you use certain polarization states you will get significantly different results with your experiment! Here's a couple of our papers on the subject, and a couple additional papers on my similar work with polarized CARS microscopy.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5459219/https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8207/82076C/Polarization-dependent-responses-of-fluorescent-indicators-partitioned-into-myelinated-axons/10.1117/12.908976.shorthttps://www.researchgate.net/publication/258711286_Automated_Control_of_Optical_Polarization_for_Nonlinear_Microscopyhttps://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-24/issue-4/046502/Excitation-parameters-optimized-for-coherent-anti-Stokes-Raman-scattering-imaging/10.1117/1.JBO.24.4.046502.fullEnjoy!
Craig
On Wed, Mar 31, 2021 at 11:37 AM Antonio Jose Pereira <
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>
> Hi all,
>
> I'm resorting to those of you who are experienced with anisotropy
> measurements or polarization optics in general. I might need a
> long-pass dichroic beamsplitter at 45º, but where the longer
> wavelengths
> (fluorescence) will pass through the dichroic backwards. I mean that
> light from the source is to be reflected, whereas the fluorescent
> light is to be transmitted back to the source. Polarization
> preservation upon reflection is not important for me, but preservation upon (backwards) transmission is.
>
> I reckon that taming polarization states with dichroics (and virtually
> all optical elements) is already an issue. I wonder how much more it
> will be by using the dichroic in such geometry.
> Or maybe there other optical elements better suited for this purpose?
>
> Thanks in advance for any comment or suggestion, Antonio
>