Dabbling with fluorescence on a budget

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Lou Jost
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Post by Lou Jost »

Chris, theoretically you can diffuse and de-cohere a laser beam by shining it through a colloidal suspension like milk.

ChrisR
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Post by ChrisR »

Might milk not impart its own colours?
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Lou Jost
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Post by Lou Jost »

Not unless it flouresces; a monochromatic beam can't change color otherwise.

ChrisR
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Post by ChrisR »

Certainly but it might fluoresce! And the milk might "go off".
Perhaps gelatin, or grey paint.
A tank of liquid might absorb too much UV, too?
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jcb
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Post by jcb »

@Johan : here you are.

Some theory first :
  • the blue line is the transmission of the blue Lee 721 filter
    the red one the transmission of the Heliopan red R25 filter
    the green solid lines are the wavelengths that excite the chlorophylle
    the dotted green lines the luminescence wavelengths
Image

As you see, no light passes through both filters superimposed.

Image

The setup is basic. Having a white background helps to identify possible problems : if you see the background in the picture you are not photographing luminescence...

Image

Here is the result (Gloiocladia_repens).

Image

harisA
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Post by harisA »

This is a photo of the nichia led.


Image

From the following link:
http://www.nichia.co.jp/en/product/uvled.html#NVSU333A

the only that matches is NCSU276A u365 at the middle of the page

typical optical power 780mw at 500ma.This is a yield of aprox 35%.Rather amazing i would say.

Lou Jost
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Post by Lou Jost »

Chris, I don't know about gelatin. The idea is to have biggish diffractors moving around rapidly (relative to exposure time) in water.

Lou Jost
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Post by Lou Jost »

Here is everything anyone would ever want to know (and more!) about using milk to reduce laser speckle patterns below the threshhold of human vision:

https://www.google.com/url?sa=t&rct=j&q ... Au4j8vZLpA

See Chapter 7. Diluted whole milk is best.

ChrisR
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Post by ChrisR »

Has to be homogenised. apparently!
I'm aware milk, gelatin, and Dettol are used, it's the spectral behaviour I queried.
The article doesn't mention fluorescense. Best would be to try it. Also UV may get absorbed somewhere.

I did find (P88)
“Tamron TT18” objective which has a focal length of 18 mm and a working distance of 9.7 cm.
Hmmm!
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ChrisR
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Post by ChrisR »

The laser was informative - I read, that in discussion of chlorophyll spectra
fluorescence spectra are invariate, and the same spectrum will be obtained regardless of which wavelengths are used for excitation:
I don't think that's entirely true, particularly in terms of amplitude, but with that in mind, these pop up in the first few Google hits::

Image
and

Image

and
Image

Therefore, "about 405nm" leds are useful, because they're short without being too dangerous.
They provide spectral separation for either
filtering out the excitation colour from the light reflecting off the subject, or
filtering out the emission colour from the light hitting the specimen.

Chlorophyll in living plants, doesn't have exactly the same spectrum as in solution (such as ethanol).
Also, in the plant, there is a quenching effect. After first exposure to the excitation, the level of emission drops (Kautsky curve).
Chris R

johan
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Post by johan »

jcb wrote:@Johan : here you are.
Thanks, very interesting!
My extreme-macro.co.uk site, a learning site. Your comments and input there would be gratefully appreciated.

Pau
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Post by Pau »

As you can see in the graphs (and my very limited experience agrees) the best red fluorescence of chlorophyll can be obtained around 450nm, a royal blue 450-455nm Cree XT-E is my most adequate light excitation source for it.
UV has the big advantage of providing blue fluorescence of cell walls like for example at the delightful Jacek's last images here:
http://www.photomacrography.net/forum/v ... hp?t=33177
Pau

ChrisR
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Post by ChrisR »

Good point, Pau - with Charles' image here, too http://www.photomacrography.net/forum/v ... 608#204608 .

Next question, If we use 365nm to excite, is a 420nm long pass filter better than say a 400nm?
What is it in the walls which fluoresces blue, and at what wavelength? Something over 450nm I would guess -?
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Post by Pau »

The devil is in the details, in principle 400nm or 420nm emission filters will work equally well for blue emission with 365nm excitation IF you actually use excitation radiation no longer than 400nm and the filter is perfect.
If you use the adequate excitation filter as I do with my filter cubes it is but in Charles setup without excitation filter the violet tail of the LED emission can obscure fluorescence, so the longer emission filter is much more adequate.

I've just ordered a Nichia UV NVSU233A-D1 365nm. When received and mounted I will be able to test it, at the moment my UV LEDs aren't adequate for this test.

This is a table fom a paper I downloaded*
Image

https://www.google.ca/url?sa=t&rct=j&q= ... vfOCZrBx7g

So likely that blue fluorescence comes from cutin or lignin, more likely from cutin in epidermic cells

Cellulose is not fluorescent at this wavelength
http://chemistry.stackexchange.com/ques ... luorescent
Pau

enricosavazzi
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Re: Dabbling with fluorescence on a budget

Post by enricosavazzi »

Charles Krebs wrote:When I came across some relatively inexpensive flashlights with Nichia 365nm UV LEDs I decided to give it a try. These are the flashlights:

(picture)

They were purchased from this site:
http://www.gearbest.com/led-flashlights/pp_277704.html
I just ordered two of these because they are extremely cheap (right now 50% discount according to the web site, although this seems to be the same for many other items on the site) compared to the MTE UV torches that probably use the same or similar LEDs (I think I paid about 250 US$ for one a few years ago). If they turn out to have a comparable UV emission, these new ones are a real bargain. In fact, they are even cheaper than the retail price for one of these LEDs from some online EU sources.

Once they arrive, I can make a direct comparison of the two torch models.
--ES

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