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Craig's point is a good excuse to bring up one of my favorite physics
questions: if you use a plane wave to stimulate a pointlike fluorophore to
emit, is the fluorophore's emission a plane wave, or a spherical* outgoing
wave?

Other ways to phrase the question include:
* Does stimulated emission from an isolated pointlike emitter carry
information about the emitter location?
* Can we use lenses to form images with stimulated emission?

We showed some results at the last Focus on Microscopy:
 https://goo.gl/9Sr812
...and I think there's lots of fun follow-up questions.


*dipole-shaped, of course, not spherically symmetric, but you know what I
mean.

On Wed, Nov 8, 2017 at 9:10 PM, Craig Brideau <[log in to unmask]>
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.
> *****
>
> Very good point George, although I doubt most people would notice the
> stimulated emission at the same wavelength as the depletion laser. That
> said, I'm sure there are applications for pump-probe experiments that would
> take advantage of the driven emission using lock-in amplification or the
> like. It's funny to think of the fluorophore as an optical gain medium, but
> here we are!
>
> Craig
>
> On Wed, Nov 8, 2017 at 6:53 PM, George McNamara <[log in to unmask]
> >
> 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.
> > *****
> >
> > neither a nor b, since emission are emissions.
> >
> > There are two different emissions in STED experiments:
> >
> > 1. stimulated emission at exactly the wavelength of the depletion laser
> > wavelength.
> >
> > 2. fluorescence emission, detected at whatever wavelength range the light
> > path to the detector allows.
> >
> > enjoy,
> >
> > George
> >
> >
> > On 11/8/2017 12:44 PM, Craig Brideau 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.
> >> *****
> >>
> >> You are reducing the emission volume, not preventing excitation. In
> >> practice you excite a gaussian-ish spatial volume, then deplete with an
> >> annular pattern (+'barbell' for 3D) before the molecules can emit.
> >>
> >> Craig
> >>
> >> On Wed, Nov 8, 2017 at 9:53 AM, Juan Luis Ribas <[log in to unmask]> wrote:
> >>
> >> *****
> >>>
> >>> This topic has started a nice discussion in our staff Facility. The
> STED
> >>> effect, has to be considered in the excitation or the emission volume?
> >>>
> >>> Which is the right phrase in STED definition?
> >>>
> >>> a) The improving in lateral an axial resolution is provided by reducing
> >>> the volume of the _emission_ by the fenomenon of stimulated emission.
> >>>
> >>> b) The improving in lateral an axial resolution is provided by reducing
> >>> the volume of the _excitation_ by the fenomenon of stimulated emission.
> >>>
> >>> Basically, the term STED is lacking some other explanations behind.
> Does
> >>> someone has a better one than "Stimulated Emission Depletion"?
> >>>
> >>> Thank you very much in advance.
> >>>
> >>> Best regards
> >>>
> >>> Juan Luis
> >>>
> >>>
> >>> El 31/01/2017 a las 16:09, Matthias Reuss escribió:
> >>>
> >>> *****
> >>>> 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.
> >>>> *****
> >>>>
> >>>> Dear Joost,
> >>>>
> >>>> This is probably a question everyone stumbles across sooner or later
> >>>> when
> >>>> thinking about the mechanisms behind STED.
> >>>>
> >>>> It is correct that the effective volume of the excitation spot is
> shrunk
> >>>> by the STED beam. In other words, the region from which spontaneous
> >>>> fluorescence is allowed is much smaller than the original
> >>>> diffraction-limited excitation volume. Also, your student is
> absolutely
> >>>> correct that the image of this reduced volume on the detector is again
> >>>> diffraction limited.
> >>>>
> >>>> The solution to your question lies in realizing that it doesn’t
> matter!
> >>>>
> >>>> It’s often helpful to picture an extreme situation, so let’s imagine
> >>>> that
> >>>> we are able to reduce the effective focal volume to a very, very small
> >>>> point. Fluorescence from a molecule located at this point will
> propagate
> >>>> back through the optical system and end up diffracted on the detector,
> >>>> spread out and with Airy rings and all. However, what we’re interested
> >>>> in
> >>>> is not the image of the molecule per se, but we'd like to know *where*
> >>>> the
> >>>> molecule is.
> >>>>
> >>>> The punchline is that with STED, we are able to get an accurate fix on
> >>>> the molecule, simply because we know the position of the zero point of
> >>>> the
> >>>> STED-PSF. For example, if we do beam scanning, we know where we’re
> >>>> currently pointing the beam, we therefore know where the intensity
> zero
> >>>> of
> >>>> the STED-donut is, and we therefore know that the molecule can only be
> >>>> at
> >>>> this very place. If it was at another place just a few nanometers
> away,
> >>>> the
> >>>> molecule would see a non-zero STED intensity and would currently not
> be
> >>>> able to emit. Without STED, we could only know that it is somewhere
> >>>> within
> >>>> an approx. 200 nm region, the size of the diffraction-limited
> excitation
> >>>> distribution.
> >>>>
> >>>> All this is 100% independent of the image of the molecule on the
> >>>> detector
> >>>> and whether it is diffraction-limited there or not.
> >>>>
> >>>> Hope this helps.
> >>>>
> >>>> Best,
> >>>> Matthias
> >>>>
> >>>>
> >>>> Matthias Reuss, Dr.
> >>>> Head of Marketing & Sales
> >>>> Abberior Instruments GmbH
> >>>> Hans-Adolf-Krebs-Weg 1
> >>>> 37077 Goettingen
> >>>> Germany
> >>>>
> >>>> phone: +49 (551) 30724 175
> >>>> fax: +49 (551) 30724 171
> >>>> http://www.abberior-instruments.com
> >>>> mailto:[log in to unmask]
> >>>>
> >>>> Managing Director: Dr. Gerald Donnert | Trade Register: Göttingen HRB
> >>>> 201844 | VAT Reg. No.: DE 283588727
> >>>>
> >>>>
> >>>> --
> >>> Juan Luis Ribas
> >>> Servicio de Microscopía
> >>> Centro de Investigación, Tecnología e Innovación
> >>> Universidad de Sevilla
> >>> Av. Reina Mercedes 4b
> >>> 41012 Sevilla
> >>> Spain
> >>>
> >>>
> > --
> >
> >
> > George McNamara, PhD
> > Baltimore, MD 21231
> > [log in to unmask]
> > https://www.linkedin.com/in/georgemcnamara
> > https://works.bepress.com/gmcnamara/75   (may need to use Microsoft Edge
> > or Firefox, rather than Google Chrome)
> > http://www.ncbi.nlm.nih.gov/myncbi/browse/collection/44962650
> > http://confocal.jhu.edu
> >
> > July 2017 Current Protocols article, open access:
> > UNIT 4.4 Microscopy and Image Analysis
> > http://onlinelibrary.wiley.com/doi/10.1002/cphg.42/abstract
> > supporting materials direct link is
> > http://onlinelibrary.wiley.com/doi/10.1002/cphg.42/full#hg0404-sec-0023
> > figures at
> > http://onlinelibrary.wiley.com/doi/10.1002/cphg.42/figures
> >
>