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Hi Lu,
For very broadband coupling in the visible, I'm not sure which objectives
would work best. Most likely a 10x achromatic objective would be fine,
although a fluorite may be needed if you are very sensitive to chromatic
aberration. I've mostly worked in the NIR however, so I can't recommend
you a specific objective.
The beam expander optics will also introduce aberrations. How much this
matters depends a lot on what your system will look like. Unfortunately,
it is very difficult to understand precisely how aberrations will propagate
through a microscope system as objective vendors rarely if ever provide
technical details or model files for their optics. Fortunately, designing
diffraction limited beam expanders is usually not very difficult. If you
use relatively long focal length achromats, and use a Galilean expander
(not Keplerian) you will likely be fine. And try to avoid any elements with
focal lengths less than 100 mm (positive or negative).
If you have access to Zemax however, I recommend simulating to be
certain. For example, just trying an ACN254-100A and an AC254-200A to
build a 2:1 6 mm to 12 mm expander into a 20x high NA paraxial objective, I
get less than 500 nm of focal shift over your entire range, and 0.013 waves
of spherical aberration (so well below diffraction limited) because the
aberration from the positive and negative elements almost entirely cancels
out.
Mike
On Thu, Nov 6, 2014 at 7:43 PM, Yan, Lu <[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.
> *****
>
> Hi Mike,
>
> You are right that a reflective collimator might be the best option. We
> have a reflective collimator (
> http://www.thorlabs.com/thorproduct.cfm?partnumber=RC12FC-P01) used in
> another project. But the problem with mine is that, we will be using a
> specialty designed fiber for the future STED system, and the fiber is not
> connectorized (at least not now). We flat cleave the fiber, and put it on a
> V-groove fiber holder, but the reflective collimator has a sealed connector
> for APC or PC. We used to try to use it but we were never be able to
> precisely align the fiber tip w.r.t. the focal point. We also tried a 90
> deg off-axis parabolic mirror, but the alignment is so tricky that we could
> not get it proper aligned. Thorlabs said they are working on some documents
> on the aligning procedure but they have not get back to me since several
> month ago.
>
> For the microscope objective, do you have any suggestion which one(s) to
> consider? BTW, intermediate optics such as telescope (to change beam size
> to match the back aperture of the high NA objective) consisting of two
> regular achromats will add chromatic and spherical aberration, right?
>
> Thanks,
> Lu
>
> -----------------------------------------------------
> Lu Yan
> Nanostructured Fibers and Nonlinear Optics Laboratory
> Electrical and Computer Engineering
> Boston University
> 8 St. Mary St., Boston, MA, 02215
> (617)353-0286
> [log in to unmask]
> -----------------------------------------------------
>
> On Wed, Nov 5, 2014 at 5:16 PM, Michael Giacomelli <[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.
> > *****
> >
> > From your test results, the only components left would be the beam
> splitter
> > or the mirrors. That seems unlikely, but its worth removing each one in
> > sequence just to be sure you don't have a defective or damaged component
> > somewhere.
> >
> > Regarding sted, an achromat is better than a singlet, but probably not
> > adequate given the large bandwidth you want to use. I recommend getting
> a
> > good microscope objective or even a reflective collimator. Zemax gives a
> > 0.3 diopter focal shift over that bandwidth for instance.
> >
> > Mike
> >
> >
> > On Wed, Nov 5, 2014 at 3:34 PM, Yan, Lu <[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.
> > > *****
> > >
> > > Hi everyone,
> > >
> > > I have updated the linked page a bit, and included some images I took
> > > yesterday. FYI, the link is:
> > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > >
> > >
> > > Hi Mike,
> > >
> > > I am using a achromat since we will be doing multicolors (in 500~750
> nm,
> > > ultimately we would like to build a STED illumination system using
> > > fibers.). For the lens orientation, yes I checked that, and there is
> > also
> > > an arrow mark indicating the direction of collimated wavefront on the
> > lens
> > > housing. The problem with the aspheric is that, for multiple colors if
> I
> > am
> > > not mistaken, I will get significant chromatic aberration provided that
> > my
> > > objective lens (Olympus UPLSAPO 60X) will have quite good correction on
> > > chromatic aberration, i.e. it focuses collimated multiple colors on to
> > the
> > > same focal plane so if I have multiple beams with different divergent
> > > angles it will focus them at different z positions. So a good achromat
> > > seems the only option.
> > >
> > > For the coupler alignment, I am using a throlabs 3-x stage (
> > > https://www.thorlabs.com/thorproduct.cfm?partnumber=MBT616D) with a
> > fiber
> > > holder. I also tried 6-x stage but it does not give me better results.
> I
> > am
> > > using flat cleaved fiber.
> > >
> > > I have updated the linked page and added some images of the beam at
> > > different position in the system. Hope that can clear something out.
> > >
> > > Thanks,
> > > Lu
> > >
> > > -----------------------------------------------------
> > > Lu Yan
> > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > Electrical and Computer Engineering
> > > Boston University
> > > 8 St. Mary St., Boston, MA, 02215
> > > (617)353-0286
> > > [log in to unmask]
> > > -----------------------------------------------------
> > >
> > > On Wed, Nov 5, 2014 at 1:40 PM, Michael Giacomelli <[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.
> > > > *****
> > > >
> > > > Hi Lu,
> > > >
> > > > Regarding your collimator, using short focal length achromats is
> > usually
> > > a
> > > > bad idea unless you are using a very broadband laser (E.g. short
> pulse
> > > > ti:saph or supercontinuum). Instead, aspheric couplers are usually
> > used
> > > as
> > > > an achromat will have significant spherical aberration. If you do
> use
> > an
> > > > achromat, make sure that do not use it backwards (always minimize
> > > > glass-wavefront curvature - flatter face into diverging wavefront,
> > curved
> > > > face into collimated wavefront) and if possible simulate in zemax to
> be
> > > > sure before trying it. Just simulating the AC254-30-A, putting the
> > lens
> > > in
> > > > backwards results in a massively abberated beam. I would double
> check
> > > that
> > > > first. Alternatively, buying an aspheric may be a better idea.
> > > Technically
> > > > the AC254-30-A is ok, but only just, only if perfectly aligned. You
> > have
> > > > little margin for error.
> > > >
> > > > If you haven't already, I recommend aligning the coupler to the grid
> of
> > > > your table, and running the beam quite far out and ensuring that it
> is
> > > > truly parallel to that grid (and thus perpendicular to lens face).
> > > Because
> > > > of the short focal length, you must be very precise here, with an
> error
> > > of
> > > > about a quarter of a millimeter in centration introducing noticeable
> > > > astigmatism. I recommend a good 3 axis kinematic.
> > > >
> > > > Regarding tilt of the fiber face, usually fibers are angle cleaved,
> and
> > > > then mounted in a coupler with a matching tilt. Make sure that if
> you
> > > used
> > > > an APC fiber, you have an APC mount, and if you used a flat cleaved
> > > fiber,
> > > > you have an un-angled mount.
> > > >
> > > > Regarding mirrors, a standard thorlabs mirror used in one of their
> > mounts
> > > > will have negligible astigmatism when used with a beam of your
> > diameter.
> > > > It is true that mirrors can and do introduce aberration into beams,
> but
> > > > with such a narrow beam diameter, even a relatively poor mirror will
> > not
> > > > introduce noticeable phase error. These problems are much more
> common
> > at
> > > > 2" and above.
> > > >
> > > > By the way, do you have access to a beam profiler? Taking an image
> of
> > > this
> > > > focal spot and posting it might give some clues.
> > > >
> > > > Mike
> > > >
> > > >
> > > >
> > > >
> > > > On Wed, Nov 5, 2014 at 1:11 AM, Yan, Lu <[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.
> > > > > *****
> > > > >
> > > > > Hi Mike,
> > > > >
> > > > > Thanks for promote reply. Like you said for an on axis system
> > > (especially
> > > > > simple as mine), astigmatism should not be there, and that why it
> > > > confused
> > > > > me a lot. I am currently using a Thorlabs air-spaced achromatic
> lens
> > > > > (f=30mm) (
> > > > http://www.thorlabs.com/thorproduct.cfm?partnumber=ACA254-030-A)
> > > > > for the collimation. The fiber I have tried are SMF600 and RBG 400,
> > > both
> > > > of
> > > > > which are single mode at 632 nm. I usually looked at the back
> > > reflection
> > > > > (from surfaces of the lens) formed interference pattern (concentric
> > > > rings)
> > > > > to align my fiber w.r.t. my fiber facet.
> > > > >
> > > > > For your comments on my questions:
> > > > >
> > > > > 1) I am using the multimode fiber as the pinhole to achieve
> confocal.
> > > > > 2) Looking at the beam spot after the collimation lens, it was not
> > > > changing
> > > > > much even at several meters away from the lens. The spot changed
> > > rapidly
> > > > > around the focal plane if the beam was reimaged through another
> lens
> > > > (e.g.
> > > > > L2 or L3 in the linked page). I think the NA is large enough for
> the
> > > > fiber
> > > > > I am using.
> > > > > 3) I was thinking maybe the fiber tip is tilted with respect to the
> > > > > collimation lens plane? Would that cause problem? OR would that
> still
> > > > give
> > > > > me concentric rings pattern centered at my fiber tip (if the fiber
> is
> > > > > tilted w.r.t. the lens plane)?
> > > > >
> > > > > Thanks,
> > > > > Lu
> > > > >
> > > > > -----------------------------------------------------
> > > > > Lu Yan
> > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > Electrical and Computer Engineering
> > > > > Boston University
> > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > (617)353-0286
> > > > > [log in to unmask]
> > > > > -----------------------------------------------------
> > > > >
> > > > > On Wed, Nov 5, 2014 at 12:37 AM, Michael Giacomelli <[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.
> > > > > > *****
> > > > > >
> > > > > > Hi Lu,
> > > > > >
> > > > > > In an on axis system like you have drawn there should be no
> > > astigmatism
> > > > > if
> > > > > > the fiber is well centered on the optic. Assuming you've
> correctly
> > > > > aligned
> > > > > > the collimator, I would think it is some other aberration you are
> > > > seeing.
> > > > > >
> > > > > > Regarding your questions in that linked page:
> > > > > >
> > > > > > 1) It depends on what you want to collect. 4f (or some other
> > > imaging
> > > > > > condition) will give you maximum light collection, which is
> likely
> > > what
> > > > > you
> > > > > > want if you have selected a multimode fiber. Alternatively, if
> > this
> > > > is a
> > > > > > confocal system, it is probably not necessary.
> > > > > >
> > > > > > 2) The diagram shows a collimated single mode fiber. That
> should
> > be
> > > > > > independent of distance. If you find that your spot is changing
> > > > rapidly
> > > > > > with distance, likely something is wrong with the collimation.
> > What
> > > > are
> > > > > > you using a collimator? Is it suitable for the NA and
> > > > > wavelength/bandwidth
> > > > > > of your source? Is it well aligned? What is the exact model of
> > > fiber
> > > > > you
> > > > > > are using.
> > > > > >
> > > > > > 3) Most likely it is a problem with your coupler.
> > > > > >
> > > > > > Mike
> > > > > >
> > > > > > On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[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.
> > > > > > > *****
> > > > > > >
> > > > > > > Hi folks,
> > > > > > >
> > > > > > > I am building a fiber based confocal microscopy setup (with
> > sample
> > > > > stage
> > > > > > > scanning). But I always got some astigmatism aberration in PSF
> > > > > > measuremnts.
> > > > > > > The similar aberration was there even I replaced the objective
> > lens
> > > > > with
> > > > > > a
> > > > > > > regular lens and imaged my illumination beam through that lens
> > > with a
> > > > > > > camera. I got elongated beam 'spot' on both sides of the focal
> > > plane,
> > > > > and
> > > > > > > the orientation of the two 'spot' were orthogonal. I think that
> > is
> > > > > > > astigmatism aberration if I am not mistaken. I draw a schematic
> > in
> > > > > > Evernote
> > > > > > > so I can include it here. Here is the link:
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> > > > > > > (copy and paste if the link does not work in email)
> > > > > > >
> > > > > > > I tried to adjust both lens in xy to avoid off-axis incident,
> but
> > > the
> > > > > > > aberration would go away. So I got confused where they came
> > from. I
> > > > > hope
> > > > > > > someone here could lead me a direction to further look into it.
> > > > > > >
> > > > > > > Thanks very much,
> > > > > > > Lu
> > > > > > > -----------------------------------------------------
> > > > > > >
> > > > > > >
> > > > > > > Lu Yan
> > > > > > > Nanostructured Fibers and Nonlinear Optics Laboratory
> > > > > > > Electrical and Computer Engineering
> > > > > > > Boston University
> > > > > > > 8 St. Mary St., Boston, MA, 02215
> > > > > > > (617)353-0286
> > > > > > > -----------------------------------------------------
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
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