polarization and dichroics

[Antonio Jose Pereira-2]

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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

[Antonio Jose Pereira-2]

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Just to add the inverting orientation might of course make sense, given reflected polarization state is not as important. But there may be better options...?

----- Original Message -----
From: Antonio Jose Pereira <[hidden email]>
To: [hidden email]
Sent: Wed, 31 Mar 2021 18:35:39 +0100 (WEST)
Subject: polarization and dichroics

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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

--
This message has been scanned for viruses and
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[Zdenek Svindrych-2]

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Hi Antonio,

I never got all the way to actually doing polarization experiments, but I
once used (literally once) some software (FilmStar) to see how interference
filters change polarization. It might not be that useful for you since you
don't know the prescription for the dichroic in question, but you may ask
the manufacturer...

One trick I've seen in some paper (can't find it now) is that the light
passes through two identical dichroics, one at 45° combines/splits the
emission and excitation, and the other one at -45° compensates the
polarization effects of the first one... But i can't really tell how severe
these effects are in the first place.

Another option would be a low incidence dichroic, but that may limit the
useful field of view due to geometrical constraints. Note that at zero aoi
(normal incidence) the interference filter will cause wavelength-dependent
group delay and what not, but no polarization effects, as there is no
preferred axis.

Or, if you can separate the excitation and emission spatially at some
point, you can use 100% mirrors. Alternatively, something like this (
https://drive.google.com/file/d/1OtdjLG31ZhTfTker4XAkis12DIR2dMcl ) - I
don't know what to call it, a "holey mirror"? - might work. This one is
from a dual-cuvette spectrophotometer - spectrally flat and no polarization
effects on transmission, as the light (or 50% of it) is passing through
empty space!

Best, zdenek


On Wed, Mar 31, 2021 at 1:37 PM Antonio Jose Pereira <
[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> 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
>

--
--
Zdenek Svindrych, Ph.D.
Research Scientist - Microscopy Imaging Specialist
Department of Biochemistry and Cell Biology
Geisel School of Medicine at Dartmouth

[Craig Brideau]

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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.short

https://www.researchgate.net/publication/258711286_Automated_Control_of_Optical_Polarization_for_Nonlinear_Microscopy

https://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.full

Enjoy!
Craig

On Wed, Mar 31, 2021 at 11:37 AM Antonio Jose Pereira <
[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> 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
>

[Peter Brunt AVR]

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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.


Best Regards
 
Peter Brunt
(he/him/his)


Peter Brunt (MPhys)
VP of Sales

Direct Dial:              585.312.0510
General Office:       585.445.7588
Email:                     [hidden email]
Web:                      www.avr-optics.com

AVRO Inc., a Delaware Corporation doing business as AVR Optics, 187 N Water Street, Rochester, NY 14604
This email and any attached files are confidential and solely for the use of the original intended recipient. This communication represents the originator's personal views, which do not necessarily reflect those of AVR Optics. If you are not the original recipient or person responsible for delivering email to the intended recipient, this email has been received in error. Any unauthorized use, dissemination, forwarding, printing, or copying of the email (or any attachments thereto) is strictly prohibited. If you have received this email in error, please notify [hidden email] and permanently delete the original and any copies of this email and any attachments. This message and its attachments have been scanned for viruses. However, please rely on your own virus scanner for absolute security.

-----Original Message-----
From: Confocal Microscopy List <[hidden email]> On Behalf Of Craig Brideau
Sent: Wednesday, March 31, 2021 3:47 PM
To: [hidden email]
Subject: Re: polarization and dichroics

*****
To join, leave or search the confocal microscopy listserv, go to:
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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.short

https://www.researchgate.net/publication/258711286_Automated_Control_of_Optical_Polarization_for_Nonlinear_Microscopy

https://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.full

Enjoy!
Craig

On Wed, Mar 31, 2021 at 11:37 AM Antonio Jose Pereira < [hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> 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
>

[Antonio Jose Pereira-2]

*****
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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" <[hidden email]>
To: "CONFOCALMICROSCOPY" <[hidden email]>
Sent: Thursday, 1 April, 2021 16:21:55
Subject: Re: polarization and dichroics

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

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.


Best Regards
 
Peter Brunt
(he/him/his)


Peter Brunt (MPhys)
VP of Sales

Direct Dial:              585.312.0510
General Office:       585.445.7588
Email:                     [hidden email]
Web:                      www.avr-optics.com

AVRO Inc., a Delaware Corporation doing business as AVR Optics, 187 N Water Street, Rochester, NY 14604
This email and any attached files are confidential and solely for the use of the original intended recipient. This communication represents the originator's personal views, which do not necessarily reflect those of AVR Optics. If you are not the original recipient or person responsible for delivering email to the intended recipient, this email has been received in error. Any unauthorized use, dissemination, forwarding, printing, or copying of the email (or any attachments thereto) is strictly prohibited. If you have received this email in error, please notify [hidden email] and permanently delete the original and any copies of this email and any attachments. This message and its attachments have been scanned for viruses. However, please rely on your own virus scanner for absolute security.

-----Original Message-----
From: Confocal Microscopy List <[hidden email]> On Behalf Of Craig Brideau
Sent: Wednesday, March 31, 2021 3:47 PM
To: [hidden email]
Subject: Re: polarization and dichroics

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

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.short

https://www.researchgate.net/publication/258711286_Automated_Control_of_Optical_Polarization_for_Nonlinear_Microscopy

https://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.full

Enjoy!
Craig

On Wed, Mar 31, 2021 at 11:37 AM Antonio Jose Pereira < [hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> 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
>

[Craig Brideau]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
Post images on http://www.imgur.com and include the link in your posting.
*****

Hi Antonio, metal mirrors tend to preserve the polarization state while
dielectric mirrors will alter it much like a dichroic. The dielectric
stacks can act like weak waveplates in certain conditions.
Regarding S and P flipping with a periscope, I have actually used this
method myself when I wanted a particular linear direction out of a
microscope. This method turns the frame of reference to flip the state.
Finally, all mirrors preserve polarization if you reflect at exactly 90
degrees as long as they have no birefringence from strain in the coatings.
Metal mirrors are much more forgiving even if your reflections are not a
perfect 90 degrees and will tend to preserve the state.

Craig

On Tue., Apr. 6, 2021, 7:05 a.m. Antonio Jose Pereira, <
[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> 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" <[hidden email]>
> To: "CONFOCALMICROSCOPY" <[hidden email]>
> Sent: Thursday, 1 April, 2021 16:21:55
> Subject: Re: polarization and dichroics
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> 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.
>
>
> Best Regards
>
> Peter Brunt
> (he/him/his)
>
>
> Peter Brunt (MPhys)
> VP of Sales
>
> Direct Dial:              585.312.0510
> General Office:       585.445.7588
> Email:                     [hidden email]
> Web:                      www.avr-optics.com
>
> AVRO Inc., a Delaware Corporation doing business as AVR Optics, 187 N
> Water Street, Rochester, NY 14604
> This email and any attached files are confidential and solely for the use
> of the original intended recipient. This communication represents the
> originator's personal views, which do not necessarily reflect those of AVR
> Optics. If you are not the original recipient or person responsible for
> delivering email to the intended recipient, this email has been received in
> error. Any unauthorized use, dissemination, forwarding, printing, or
> copying of the email (or any attachments thereto) is strictly prohibited.
> If you have received this email in error, please notify
> [hidden email] and permanently delete the original and any
> copies of this email and any attachments. This message and its attachments
> have been scanned for viruses. However, please rely on your own virus
> scanner for absolute security.
>
> -----Original Message-----
> From: Confocal Microscopy List <[hidden email]> On
> Behalf Of Craig Brideau
> Sent: Wednesday, March 31, 2021 3:47 PM
> To: [hidden email]
> Subject: Re: polarization and dichroics
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> 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.short
>
>
> https://www.researchgate.net/publication/258711286_Automated_Control_of_Optical_Polarization_for_Nonlinear_Microscopy
>
>
> https://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.full
>
> Enjoy!
> Craig
>
> On Wed, Mar 31, 2021 at 11:37 AM Antonio Jose Pereira <
> [hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > 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
> >
>

[Zdenek Svindrych-2]

*****
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*****

Hi Antonio,
my description of the trick with the second (compensating) dichroic was not
accurate (let's face it, I was plainly wrong). This is what I had in mind:
https://onlinelibrary.wiley.com/doi/abs/10.1002/jbio.201400116
So yes, swapping s and p is exactly what you want!
zdenek

On Tue, Apr 6, 2021 at 9:05 AM Antonio Jose Pereira <
[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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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" <[hidden email]>
> To: "CONFOCALMICROSCOPY" <[hidden email]>
> 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.
>
>
> Best Regards
>
> Peter Brunt
> (he/him/his)
>
>
> Peter Brunt (MPhys)
> VP of Sales
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> -----Original Message-----
> From: Confocal Microscopy List <[hidden email]> On
> Behalf Of Craig Brideau
> Sent: Wednesday, March 31, 2021 3:47 PM
> To: [hidden email]
> 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.short
>
>
> https://www.researchgate.net/publication/258711286_Automated_Control_of_Optical_Polarization_for_Nonlinear_Microscopy
>
>
> https://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.full
>
> Enjoy!
> Craig
>
> On Wed, Mar 31, 2021 at 11:37 AM Antonio Jose Pereira <
> [hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > 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
> >
>

--
--
Zdenek Svindrych, Ph.D.
Research Scientist - Microscopy Imaging Specialist
Department of Biochemistry and Cell Biology
Geisel School of Medicine at Dartmouth