Re: 1W 405 source

Posted by Zdenek Svindrych-2 on
URL: http://confocal-microscopy-list.275.s1.nabble.com/1W-405-source-tp7591310p7591328.html

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Hi Ben,

I'm glad LEDs work for you. Absolutely, if 10 mW/mm^2 is enough, LEDs are
the way to go!
We've used Luminus Phlatlight LEDs in the past, they are much brighter (in
terms of W/mm^2/sr) than most. But they are also more pricey.
I'm surprised how much better the LEDs are now, especially in the 400 nm
range with 1 W optical output from 1 mm^2 chip...

Importantly, there is no reason why a LED-based fluorescence illumination
system *with* DMD should be dramatically dimmer than *without* it. The
optical efficiency of a DMD is 70%. Still, even in commercial LED light
sources most of the light is wasted, as the chips are too big (but it makes
the optical design easier).

Lasers make things more complicated, but my favorite arrangement -
multimode fiber shaker and critical illumination - work most of the time.
The DMD acts as a very poor blazed grating, so it's tricky to make it work
efficiently, especially with multiple laser wavelengths. But with a 1 W 405
nm laser you still have plenty of light for photoconversion, photobleaching
and photodamage experiments.

Finally, I have never heard of microlens homogenizer used together with a
DMD. All DLP projectors (I've had the pleasure to take apart) use a light
pipe homogenizer, maybe except for the tiniest ones. I wasn't lucky enough
to get my hands on a LightCrafter or similar stuff... For microscopy
equipment, I don't see a reason for a homogenizer (exactly for that same
reason - the etendue of the source is so much bigger than what the
objective lens can use).

Best, zdenek


On Tue, Sep 22, 2020 at 4:02 PM Benjamin Smith <[hidden email]>
wrote:

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>
> Attaching DMDs to microscopes is actually pretty common in optogenetics and
> retinal research.  Here is an image of a DMD coupled into a BX-51 arm in
> one of the labs I work with using one of the high power LEDs:
> https://drive.google.com/file/d/1oFL0CQynji-hmkIDca002IZMmitwtksd/
>
> In this setup we wanted a high power 450 nm output for optogenetics (>10
> mW/mm^2 at the sample plane) while still having it usable as a fluorescent
> microscope, so we used a 10W 450 nm LED (the one with the CPU cooler
> attached) for the high power channel combined with a liquid light guide
> from a xenon arc lamp for longer wavelengths.
>
> Originally we tried a 3W 450 nm laser we bought off of eBay for $50 (which
> to our surprise really was 3W optical output), but quickly realized that
> the vast majority of losses in a DMD are at the microlens array used to
> make the light uniform across the DMD.  Additionally the coherence of the
> laser caused a strong speckling issue, which we tried to abate with 10m of
> multimode fiber but was still pretty strong. We also had to couple at an
> odd four degree of freedom offset to try to get as much of the field
> covered as we could.
>
> We then switched to the 10W LED, and since it covers the whole microlens
> array, the field of illumination was perfectly uniform, and did not require
> any odd 4 degree-of-freedom alignments.
>
> One thing to keep in mind is that the DMD array itself is fairly big, so as
> along as the LED die is appreciably smaller than the DMD itself, then the
> etendue really won't cause a loss in intensity due to coupling, and will
> only work in your favor to have a more uniform field of illumination.
> Additionally, since these LEDs are intended to be used with DMDs, some of
> them even have dies with a 4:3 or 16:9 aspect ratio for even better
> efficiency.
>
> And a quick side note, for anyone who want's to couple a DMD into a
> microscope, I strongly recommend using the BX-51 arm.  It is easy to pull
> out the lenses, and a Thorlabs SM1 lens tube fits neatly inside with only
> minor modification.  You can also fit a TTL200 tube lens right behind the
> manual shutter, giving you the perfect spacing to the back focal plane of
> the objective.
>
> Cheers,
>    Ben Smith
>
> On Tue, Sep 22, 2020 at 8:57 AM Zdenek Svindrych <[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 Antonio,
> >
> > We used to buy from Dragon lasers (China) many years back, now CNI Laser
> > (again China) seems like a great source (no commercial interest).
> >
> > If you want to go super cheap, you can search eBay for laser engraving
> > modules, some are 405 nm (but mostly 445 nm), you want something like
> "7W"
> > at least, as it's the electric input power... And don't stare into the
> beam
> > with your remaining eye!
> >
> > Andor uses a fiber shaker to homogenize the beam (and critical
> > illumination, like their Borealis technology) for their Mosaic DMD
> devices,
> > but I can't guarantee the amount of light you can couple into a 50 um or
> > 100 um fiber from the eBay laser modules...
> >
> > UV LEDs sound cool, but the problem is the coupling efficiency (etendue).
> > If your source is a 1 mm^2 LED chip, you can illuminate 1 mm^2 with a 1
> NA
> > objective lens with good efficiency (if you try hard). If you try to
> focus
> > the light down to 0.3 mm^2, 90% of the light is lost... And higher power
> > (more LED chips) won't help you get more light trough, only the optics
> may
> > be simpler... Of course on top of that another 99% of light is blocked if
> > you only have few DMD pixels "on"...
> >
> > I've seen papers where folks bolted a DMD digital projector to a
> > microscope. Lie this one:
> > https://drive.google.com/file/d/1IEfgKvZ0JrCUaaUPdnRFhUzT3phJO-D-/
> >
> > Best, zdenek
> >
> > On Mon, Sep 21, 2020 at 10:11 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.
> > > *****
> > >
> > > Dear all,
> > >
> > > I'm looking for a 0.5-1W , 405nm, can have many spatial as well as
> > > longitudinal modes, 405nm laser. This is to feed a photoconversion
> module
> > > (Mosaic), a DMD-based system that wastes most power. That's why we need
> > > such high power source.
> > >
> > > I appreciate if you could give suggestions on low-budget options, which
> > > I'm failing to find ...
> > >
> > > Thank you so much,
> > > Antonio
> > >
> > >
> > >
> > > Antonio Pereira
> > > CID lab
> > > i3S/IBMC, Universidade do Porto
> > > Room 001.S2B, [phone] Ext. 6127
> > >
> >
> >
> > --
> > --
> > Zdenek Svindrych, Ph.D.
> > Research Scientist - Microscopy Imaging Specialist
> > Department of Biochemistry and Cell Biology
> > Geisel School of Medicine at Dartmouth
> >
>
>
> --
> Benjamin E. Smith, Ph. D.
> Imaging Specialist, Vision Science
> University of California, Berkeley
> 195 Life Sciences Addition
> Berkeley, CA  94720-3200
> Tel  [phone]
> Fax [phone]
> e-mail: [hidden email]
>
> https://vision.berkeley.edu/faculty/core-grants-nei/core-grant-microscopic-imaging/
>

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