UV-C Death Ray works!

[Lou Jost]

I now have a good system for macrophotography using deep ultraviolet light. 254nm, (UV-C). Glass is completely opaque at this wavelength, so this is harder than one might expect.

The lens has to be made of quartz or fused silica or fluorite or a few other things. The glass cover slip over the sensor of the camera also has to be removed. Light sources are rarely pure at this wavelength, so special (non-glass) filters are needed and must block unwanted light over a much larger range of wavelengths than is normal for visible-light filters.

But it all came together for me now, with the chance discovery on eBay of a reasonably priced little monochrome 8Mp USB camera with no cover glass over the sensor. It came with a quartz lens. I got a 254nm filter from Edmund Optics that blocks unwanted wavelengths all the way to the far infrared and deep UV, and I got a germicidal UV-C lamp. Here are some test results. The ordinary glass is black and opaque:

A reminder: UV-C is dangerous, TAKE APPROPRIATE PRECAUTIONS.

[rjlittlefield]

Very nice!

But of course my curiosity is instantly aroused... Why does the label on the flask go black at 365 nm ?

--Rik

[Lou Jost]

That's the most surprising part of the whole experiment. I have no idea why this happens. It seems strange that a substance would be so uniformly reflective across all visible wavelengths, yet so completely and suddenly absorbing for shorter wavelengths. Do you know what material these glassware labels are made of?

[rjlittlefield]

Do you know what material these glassware labels are made of?

I have no idea. My first thought was that the label is etched in, and that what we're seeing is the increased absorbance of many interactions with a material that is noticeably absorbent at that wavelength. But when I mentally zoom in to look at the microscopic scale, I can't make the details work out.

--Rik

[Beatsy]

Images by the light of doom! I'm enjoying watching your progress with this. Very much looking forward to seeing images taken through your microscope too. Hurry up man!!

[Lou Jost]

Do you know what material these glassware labels are made of?

I have no idea. My first thought was that the label is etched in, and that what we're seeing is the increased absorbance of many interactions with a material that is noticeably absorbent at that wavelength. But when I mentally zoom in to look at the microscopic scale, I can't make the details work out.

--Rik

I took a closer look at the white areas, and they seem to be raised rather than subtracted from the beaker surface.

[jmc]

Very nice. With regards to the white label, my girst thought us that it has a high proportion of TiO2 and has been baked onto yhe glass. This would appear white in thr visible spectrum and then start to scatter and absorb uv as the wavelength decreases.

[Lou Jost]

Jonathan, yes, it does look baked on, with heat crackling visible under magnification. You are probably right.

[shades]

Hello,

If I'm not mistaken this is your UV-C lamp? http://www.michaelfastphotography.com/g ... 33623a.jpg

I'm very curious on how you built the shroud/frame that holds the ZWB2 filtered glass. You might remember talking to me about snagging a 365nm diode but it turned out the 175watts was too much power for my batteries. I finally saved up enough to make a smaller 100watt version but am hoping you can help source where you got the shroud or provide a how to, or just more detailed pictures of how it all secures together. Is it just a plastic 3d print you might still have the STL file for or is this metal that was cut and folded into a trapezoid?


Thanks!

[JW]

Real exciting stuff Lou - and do be safe. We've built a 2000 Watt (yes, 2 kW) UV-A 365 nm source at work for air purification applications, using LED elements, but nothing like this. Looks like fun!

[Lou Jost]

Hello,

If I'm not mistaken this is your UV-C lamp? http://www.michaelfastphotography.com/g ... 33623a.jpg

I'm very curious on how you built the shroud/frame that holds the ZWB2 filtered glass. You might remember talking to me about snagging a 365nm diode but it turned out the 175watts was too much power for my batteries. I finally saved up enough to make a smaller 100watt version but am hoping you can help source where you got the shroud or provide a how to, or just more detailed pictures of how it all secures together. Is it just a plastic 3d print you might still have the STL file for or is this metal that was cut and folded into a trapezoid?


Thanks!

Oh no, that's a real death ray! But the one in your picture is just UV-A. I'm working at a much shorter wavelength (the lamp in your photo will not produce the effects I've shown above) but MUCH lower power. My lamp is a little mercury tube I bought on eBay for a few dollars, only 6W. That's all you need if you have good fused silica lenses.

Last night I did a series of experiments with other light sources-- will report shortly.

[ray_parkhurst]

The last electronics swap for the year was yesterday, and I ended up picking up a couple UV-C bulbs in a mix of other stuff. I got a 6W and an 8W. Not sure if anyone has use for this but if anyone is interested I can measure the lengths. I might have a fixture to run them but am not so sure I want to play around with UV-C.

[Lou Jost]

They might be interesting; did they come with ballasts?

Coincidentally I have spent the last three days testing UV-C light sources. UV-C fluorescent bulbs have some advantages over UV-C LEDs, because the the bulbs emit extremely monochromatic spectral lines. With sharp spectral lines, UV-apochromatic optics (which are very rare) are not necessary. Light sources that have a broader spectral distribution will cause chromatic aberrations with most UV optics.

On the other hand, LEDs are more compact light sources that are easier to manage in microscope condensers and other microscope illumination methods.

[ray_parkhurst]

They might be interesting; did they come with ballasts?

Coincidentally I have spent the last three days testing UV-C light sources. UV-C fluorescent bulbs have some advantages over UV-C LEDs, because the the bulbs emit extremely monochromatic spectral lines. With sharp spectral lines, UV-apochromatic optics (which are very rare) are not necessary. Light sources that have a broader spectral distribution will cause chromatic aberrations with most UV optics.

On the other hand, LEDs are more compact light sources that are easier to manage in microscope condensers and other microscope illumination methods.

No ballasts, just the bulbs.

You say "fluorescent" but these seem to have no coatings in the tubes, just the electrodes and whatever gases are present to do the emission. I'd expect these to have narrow emission lines per whatever the gases dictate.

[enricosavazzi]

[..]
You say "fluorescent" but these seem to have no coatings in the tubes, just the electrodes and whatever gases are present to do the emission. I'd expect these to have narrow emission lines per whatever the gases dictate.

Basically, these bulbs are made in the same way as (true) fluorescent bulbs, but without a fluorescent lining that absorbs UV and re-emits the energy at longer wavelengths. "Germicidal" is a more common commercial term for these "non-fluorescent" tubes.

By changing the composition and pressure of the gas, the emission spectrum can be tailored to specific needs. The wavelength of individual emission lines of course remains constant, but their relative intensity can change.

After a long time (years) of use, the fluorescent lining of tubes used for ordinary domestic illumination breaks down, and some of the UV starts leaking out. I once took pictures of a car tunnel in NY, illuminated 24 h a day with fluorescent tubes that apparently are replaced only when they don't light up any more, and they emitted a sizable amount of UV (brighter than the UV in direct sunlight).

An example of emission spectra of different tubes: https://www.researchgate.net/publicatio ... cent_lamps
(not a particularly good paper, but that's what came up first on Google)