Spectralon fluorescence?

[Cadmium]

Maybe you or someone else has some, and can test that?

 

Actually, i will drop my discussion about this for now, maybe in a year. Maybe two...

What's the point anyway, right? What difference does it make to anyone if Spectralon/PTFE/Teflon fluoresces or not?

Do we use it for fluorescence photography? I never do. It may be a great reflected UV white balance target, but not for UVIVF, UVIIRF or V(G)IIRF.

Personally, I still think without further proof that all of the above and pretty much everything fluoresces, new and old, baked or fried...

Maybe someone can demonstrate the contrary, that would be interesting, but still, it is slightly academic given that we don't use it as such.

Perhaps there is some reason to worry about it in some related way, but I could use a little down time, more sleep, I am getting tired of the subject.

Get some food, do some work.

So that's it for me, for now.

[JMC]

Andrea, thanks for following up with Labsphere. I am not however convinced by their response - 'Spectralon does not fluoresce' is a little too definitive, and sounds very much like towing the company line.

 

I will continue to dig a bit on this with my disks when I have more time (after months of being fairly quiet, I've got more work than I know what to do now that needs to be finished before the end of Dec 31st).

 

If I'm reading it right, the general consensus on here seems to be that it's not a huge issue whatever it may be. I'd agree with that. If I'm in a dark room and shine a strong UV source on my Spectralon samples I can see some visible light come off from them. However that's because I am in a dark room and with some pretty powerful light sources (and yes I am wearing UV eye protection whenever I am doing that). Is it fluorescence or reflection or a combination of both? I've not done a definitive a job of filtering my light source as Steve did with his huge filter stack, so I cannot prove it either way, and more work is needed.

[dabateman]

Do the Labsphere spectralon targets have a shelf life or expiry?

The colorchecker passport standards are only rated for 2 years. Its recommended to replace after 2 years for most accurate colors. I am wondering if the spectralon is similar?

[JMC]

Not that I am aware of David, but as far as I recall they recommend having standards rechecked regularly depending on application.

 

Sorry if this is a repost, but this article - https://www.hou.usra...16/pdf/2362.pdf - looks at Raman spectroscopy of Spectralon, and does talk about the fluorescence observed during the measurements, and that was from 532nm laser irradiance for the measures. They do talk about possible reasons for this.

[Stefano]

Regarding the "low but non-zero" fluorescence issue:

 

I have a 405nm line laser (100mW) coming late this month, and I am planning to try LASER-INDUCED fluorescence. (I am not yet comfortable playing with UV lasers, even if I could find an affordable one, so this will be violet fluorescence rather than UV induced.) Allegedly, according to this paper, laser induced fluorescence brings out a lot of faint stuff that would otherwise be hard to photograph, simply due to the high fluxes involved.

That's interesting. The big advantage with lasers is that they are very narrow and shouldn't emit anything outside their narrow band. And the fact that their light is collimated means you can be even more sure what you are seeing is fluorescence since no light contamination has the shape of a dot several meters away. It's like the torch, but even more extreme.

 

I am sure you will be, but be careful with these lasers, talking about personal experience (I had a yellow afterimage last three days in my right eye due to a very stupid me playing with a 405 nm "5 mW" laser pointer (5 mW shouldn't heat up my lips, as that laser did...)). 405 nm is a beautiful color, a nice, deep violet.

 

That's a 375 nm laser pointer:

 

He was really lucky to find the diode for $80.

[Stefano]

Anyway, the snow test seems a better and better idea to me, the more I think of it, the more I am convinced of that. Snow really doesn't fluoresce, and reflects UV. A side by side comparison would really prove that indeed Spectralon does fluoresce.

[Andy Perrin]

Stefano- will start a separate thread re the laser when it arrives. But I already bought laser safety goggles designed to cover 405nm. Also it’s a LINE laser, not a dot, which spreads the beam and lowers the flux.

[dabateman]

Not that I am aware of David, but as far as I recall they recommend having standards rechecked regularly depending on application.

 

Sorry if this is a repost, but this article - https://www.hou.usra...16/pdf/2362.pdf - looks at Raman spectroscopy of Spectralon, and does talk about the fluorescence observed during the measurements, and that was from 532nm laser irradiance for the measures. They do talk about possible reasons for this.

There you have it Cadmium. Your sphere was contaminated as you may not have used correct seals and ultra pure CO2 for storage.

 

I also found a paper from 1960s on teflon indicating that the chain ends do fluorescence and the breakdown of large chains over time to smaller units will increase the fluorescence. But I couldn't see the data. So I am not confident on if there are other factors involved in the results.

[Andy Perrin]

David- he said freshly cut PTFE still glows so I don’t think it’s surface damage. But it could be breakdown over time or the hydrocarbons.

[Stefano]

PTFE should be pretty stable, so shouldn't breakdown much?

[Andy Perrin]

Stefano - that's contradicted by the papers linked above! It does break down.

[Andrea B.]

I've got some sonw here. I'll go out tonight with Spectralon, PTFE, and a UV-LED to see what happens.

 

FWIW, I agree that something is happening with Spectralon and PTFE. Probably some kind of manufacturing imputities.

 

BTW, don't go baking Spectalon/PTFE on your own. It might release fumes or something at high temps.

[Andrea B.]

BTW: Let me be CLEAR.

 

Labsphere said that Spectralon does not fluoresce in the sense that it does not absorb photons and release lower energy light.

 

The part about "not arguing with physics" is mine. Maybe I should have phrased it like: "OK, then, I guess you can't argue with physics???" Followed by a "Whatever!"

 

I'll try to speak with one of Labsphere's R & D people to get a better explanation of what we are seeing.

 

I should remind you that the photo I posted in Post #8 was an illustration *to me* (and to me alone, apparently!) of the unblocked violet light reaching my sensor when using the BaaderU as a filter for the UV-LED instead of the U-340 filter. I did not look at that and see fluorescence. But as I've always said, I'm always willing to be proved wrong. I hold no patent on either facts or truth. :wink:

[Andrea B.]

Here we go.......

 

Three photos:

• PTFE Disk in Snow
  
• Spectralon 99% White Standard in Snow
  
• Snow
  

It was cold out there when handling metal flashlights and tripod legs! Wooh!!

No moon. The sky was clouded over. We turned off all house lights. The nearest ambient lights appeared to be about a mile away. We do have houses closer than that, but slopes and shrubs and the garden wall block closer light.

 

I might have to repeat the series because I messed up the snow exposure time. But I will wait until I get some feedback from anyone who might have suggestions.

 

Files were converted in Capture NX2 so I could show them exactly as I shot them. No sharpening.

Labels and downsizing were made in Photo Mechanic. The white balance was an existing pre-set made in sunlight against Spectralon.

 

PTFE Disk in Snow

Obviously my PTFE disk is showing some "dirt" &/or contamination.

 

 

Spectralon 99% White Standard in Snow

No comment.

 

 

Snow

This is the snow depression made by the PTFE disk. I accidently doubled the exposure time, but this is still what it looked like to my naked eye. If the "inner"snow is not fluorescent, then it is performing a good simulacrum of fluorescence. Alternately there is a lot of fluorescent dust and bits of fluorescent this and fluorescent that which are creating the glow. I'm not sure exactly what is going on here. The top outer surface of the snow doesn't glow much.

 

 

---

I am kinda seeing why Mom was always telling us not to eat snow. It's got stuff in it.

---

 

Spectralon 99% White Standard in Snow, Longer Exposure

This exposure is 8" long, 4 times as long as the preceding version.

[otoien]

...

Snow

This is the snow depression made by the PTFE disk. I accidently doubled the exposure time, but this is still what it looked like to my naked eye. If the "inner"snow is not fluorescent, then it is performing a good simulacrum of fluorescence. Alternately there is a lot of fluorescent dust and bits of fluorescent this and fluorescent that which are creating the glow. I'm not sure exactly what is going on here. The top outer surface of the snow doesn't glow much.

---

I am kinda seeing why Mom was always telling us not to eat snow. It's got stuff in it.

---

 

Yes, lots of stuff in the snow. The blue-green tones shining through are usually dog or cat pee...

So bring a UV light and only collect snow at dark before eating it .

 

(It could actually make sense for winter camping when collecting snow for tea water.)

[dabateman]

Andrea, first sorry for inadvertently calling you stupid. I know you know what physics is, the mathematical explanation of the physical world with limits and assumptions. As in we need to first assume the chicken is perfectly spherical. Old physics joke. Its not doctrine that is and can only be the way of things. Assumptions and mistakes are made.

 

Second, You have snow!!

It was 60 F here today in DC area. I love snow.

 

Thirdly, your photos add weight to the end groups of teflon (ptfe) being fluorescent. I can image that in your samples based on the dots you are seeing. I think that is what we are seeing.

 

It looks like you really dirtied up the snow there. Very cool (literally) experiment.

[Andrea B.]

Not to worry, David, I didn’t think anybody was calling me stupid.

 

It snowed about 5” a few days ago. Then melted down a lot. Then a bit more snow. And more melting. And then again. In between the snows there has been a lot of wind here which blows up dust and leaf bits and assorted high desert-y stuff to mix in with the snow and settle during the melts. So that is my attempted explanation of the glowy bits we see in the snow.

 

The area of snow I picked had no footprints, birdy tracks or little rodent-y tracks. It sure looked clean and nice in daylight.

 

My PTFE disk certainly does need a clean-up. But there is obvious fluoresence from the disk which isn’t going to disappear after cleaning. I don’t know what kind of PTFE this is.

 

It is clear to me that my particular Spectralon standard does not fluoresce, although there is a very minor bit of glow just on the sharp edge of the little cake where it has become a bit contaminated from handling and being bumped during lid replacement. When sanding the Spectralon, I place it face down on the sandpaper on a flat surface, but I’ve never worked along the edge. Maybe I should next time I clean it up.

 

I’m thinking that because I bought calibrated Spectralon standards, they might possibly be a higher grade? I will try to find out.

 

I’m thinking that this experiment should be done against some kind of flat black super absorbing background?

[Stefano]

I didn't expect snow to be so fluorescent. Fresh snow should work best?

 

 

[dabateman]

I didn't expect snow to be so fluorescent. Fresh snow should work best?

 

Problem is thats too hard to come by. Andrea would be better to make some ice cubes and shave them with a cheese grater. That the freshest you would be able to get.

 

Using a black 3.0 or black 2.0 background might also work well.

I still need to paint mine, I got some 3.0 months ago and haven't painted my boards yet.

[Andrea B.]

I didn't expect snow to be so fluorescent. Fresh snow should work best?

 

Yeah, Stefano, I didn't either !!

I can try this again in fresh snow whenever we get some.

 

But the surface of the snow was non-fluorescent enough to show the difference between the dirty PTFE and the clean Spectralon.

 

(Remember that not all PTFE may behave like mine does. There are different kinds of PTFE.)

[Andrea B.]

I just went outside to look again at the surface of the snow with my Convoy + U-340.

I saw no fluorescence from the top surface.

 

I did observe that it is mandatory to wear non-fluorescent clothing when making fluorescence observations.

 

And I noticed something a little bit strange, so I have a question. With my “old” eye, I could only see a very weak trace of reflected Convoy light off the snow - a weak blue-gray. With my “new” good eye, I could see a definite bright reflected violet circle of Convoy light. No surprise there as I’ve known the left lens implant restores color in the violet/blue region. But here’s the question: Does UV-LED light pulse?? This violet circle slowly pulsed on/off. Or maybe I’m going nuts from staring at too much UV. Or could maybe the battery need replacing in the torch?

 

Answer: See Post #74 and Post #75 below. Low temperature is the culprit here.

[Stefano]

You may be going nuts (hope not!), I never saw UV pulse, not even 340 nm. Don't know about low battery effects, maybe it pulses. Laser pointers start strong and then dim after like half a second with a low battery.

[Andrea B.]

wondering if it had something to do with the eyes trying to become dark adapted.

a rods/cones thing.

[ulf]

It could also be a temperature related issue.

The threshold voltage of the LEDs is rather close to the output voltage of the batteries in normal temperatures.

Both voltages change with lower temperature.

The output from the battery goes down and the LEDs threshold voltage goes up, both making less current flow.

With less current there is less light but also less self-heating counteracting the thermal issue.

 

I think that you might have discovered a thermo-electric oscillator.

Somewhere in the structure there can be something with just the right amount of thermal mass to allow this.

 

In my youth there were low voltage lamps with an intentionally created function like this by the inclusion of a bi-metal strip inside the lamp, making it blink.

The frequency was voltage dependent.

[Andrea B.]

Bingo! I think that the low temperatures are indeed what caused the slow ebb & flow of the violet.

 

Tonight I tested the two Convoys again. I left one torch inside and put the other one outside to cool down in the 24°F/-4.4°C temperatures. Later when I tested them, the warm torch did not fluctuate, but the cold torch slowly lost its violet then slowly the violet came back.

Overall, the cold torch seemed to have a lower output because a fluorescent leaf in the snow glowed a little bit more brightly with the warm torch than it did with the cold one. (Both batteries were fully charged.)

The experiment did not last too long because the warm torch cooled down rather quickly and so did I !!