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UltravioletPhotography

Some ideas


Stefano

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Some ideas that I accumulated since I started following this website, before becoming a member. I will try them too if I can.

For the people who can shoot in UVB (and below)

  1. Can you photograph silver at 310 nm (and compare it to other metals)? It should become black.
  2. Have you ever tried to stack the Invisible Vision 308 nm filter with an Hoya U-340 4 mm thick filter? It should block all visible leakage (it wasn’t a problem) and strongly reduce the IR leakage (which was the problem). It should raise the OD in the near infrared by at least 2.
  3. Have you tried UVB and UVC LEDs? They are weak and inefficient, but they exist.
  4. What about excimer lamps? According to Wikipedia they can go as low as 108 nm. I know that air starts to absorb UV strongly below 200 nm, mainly by oxygen, but in a nitrogen atmosphere it can propagate at shorter wavelengths.

For the people who want to try SWIR or already can shoot in SWIR

  1. Can you do it by “erasing” phosphorescence? Not many people know this, but if you shine light on a phosphorescent material with a per-photon energy lower than the energy required to activate it (for example red or infrared light), you can “erase” the glow. It will look brighter at first, and then darker. What happens is that you are giving energy to electrons in the metastable state to go to a slightly higher energy state from which they can return to the ground state, emitting a photon. Basically you discharge the material faster. I tried it and it requires a lot of light, but it works. Maybe using long-lasting phosphorescent materials and a lot of exposure an image can be formed.
  2. Never tried SWIR LEDs? As deep UV LEDs, deep IR LEDs exist and they are weak and inefficient, but probably nice to have.

For the people who can shoot in LWIR

  1. Can reflected LWIR photography be done? The problem is that at those wavelengths basically everything is incandescent, and this masks shadows and illumination. Maybe by subtracting two images, one “normal” and another one illuminated by, for example, a hot piece of metal can show shadows. But a shadow doesn’t necessarily mean a real, “optical” shadow, it can also mean that some areas have been heated up when illuminated.
  2. A carbon dioxide laser emits at 10.6 μm, in the range visible by LWIR cameras. At very low power (they can be extremely powerful), can they be seen like a normal laser pointer?

For everyone

  1. Never tried 340 nm LEDs?
  2. Can Terahertz waves be “seen” with an antenna? The frequency is crazy high and semiconductors basically stop working, but can a signal be detected? It can surely be done with longer wavelengths, such as millimeter or centimeter waves.
  3. Can a sound camera be built? Imagine something similar to a pinhole camera, an “illuminator” which uses ultrasound at MHz frequencies (the higher the frequency the lower the diffraction and the higher the resolution), and a sensor made with a matrix of microphones. I know that neither the speaker nor the microphones are designed to be responsive at that frequency, and very high frequency sounds travel short distances in air, but can this be done for short distances (~30 cm)? The only problem would be cavitation, which can damages tissues.
  4. Have someone tried (legally and very carefully) X-rays? If you really want to experiment with them, be extremely careful. Never expose yourself intentionally, use lead shielding, and power the tube far away. Also make sure that nobody is around.
  5. Ever tried violet photography (~400-430 nm)?

Hopefully this is all new and nobody already tried it on this website, hope most can be done.

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For the people who want to try SWIR or already can shoot in SWIR:

1. Can you do it by “erasing” phosphorescence? Not many people know this, but if you shine light on a phosphorescent material with a per-photon energy lower than the energy required to activate it (for example red or infrared light), you can “erase” the glow. It will look brighter at first, and then darker. What happens is that you are giving energy to electrons in the metastable state to go to a slightly higher energy state from which they can return to the ground state, emitting a photon. Basically you discharge the material faster. I tried it and it requires a lot of light, but it works. Maybe using long-lasting phosphorescent materials and a lot of exposure an image can be formed.

 

2. Never tried SWIR LEDs? As deep UV LEDs, deep IR LEDs exist and they are weak and inefficient, but probably nice to have.

 

1. Never heard of this -- will keep it in mind.

2. I looked into this at the beginning, when I first started playing with SWIR. They are very expensive, and as you said, not efficient. Whereas halogen lights put out a TON of SWIR, are cheap, and if you need a particular band you can always filter them. Not hard to find a halogen flashlight and put a 25mm filter on the front.

 

For the people who can shoot in LWIR
  • Can reflected LWIR photography be done? The problem is that at those wavelengths basically everything is incandescent, and this masks shadows and illumination. Maybe by subtracting two images, one “normal” and another one illuminated by, for example, a hot piece of metal can show shadows. But a shadow doesn’t necessarily mean a real, “optical” shadow, it can also mean that some areas have been heated up when illuminated.

 

1. When you take a photograph with a LWIR camera, you are seeing both the emitted + reflected light. HOWEVER, as discussed in another thread recently, the reflectivity = 1 - emissivity. What this means is that in situations (like with no sunshine) where the light is entirely due to emission, you can convert the photo to a reflectographic photo just by inverting the color scheme! This does not work perfectly because emitted light from one surface can reflect off of another surface, but it works well enough that inverting the color scheme gives something that's almost like a normal photo.

 

Consider the christmas tree scene I posted the other day. This is the version I posted.

post-94-0-15935900-1578261249.jpg

 

Inverting the color scheme gives something closer to a reflectographic photo:

post-94-0-85089300-1578261327.jpg

 

I would add, though, that even with our normal cameras, sometimes objects glow (incandescent light bulbs, hot stoves...) and we don't consider those to be non-reflectographic images even though they are plainly emitting as well as reflecting. The truth is that the world down there is REALLY ACTUALLY GLOWING (and also reflecting), so the original photo is the "truth." If I take a photo in sunshine, I can see reflected sun as well as emitted light. I will do one for you soon.

 

 

  • A carbon dioxide laser emits at 10.6 μm, in the range visible by LWIR cameras. At very low power (they can be extremely powerful), can they be seen like a normal laser pointer?

2. I don't have one, but I would assume so. The ones I've seen all look much too powerful for home experiments. My landlord will complain if I burn holes in the rug.

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For the people who can shoot in UVB (and below)

  1. Can you photograph silver at 310 nm (and compare it to other metals)? It should become black.
     
    I have a sterling silver bracket, will see if I can find it to image.
     
  2. Have you ever tried to stack the Invisible Vision 308 nm filter with an Hoya U-340 4 mm thick filter? It should block all visible leakage (it wasn’t a problem) and strongly reduce the IR leakage (which was the problem). It should raise the OD in the near infrared by at least 2.
     
    I don't have either of those filters.
     
  3. Have you tried UVB and UVC LEDs? They are weak and inefficient, but they exist.
     
    Too expensive for me to purchase and build. Mercury bulbs still the cheapest.
     
  4. What about excimer lamps? According to Wikipedia they can go as low as 108 nm. I know that air starts to absorb UV strongly below 200 nm, mainly by oxygen, but in a nitrogen atmosphere it can propagate at shorter wavelengths.
     
    Never heard about them. The XeCl and KrCl look interesting to me. Where are they for sale and how much. I only found papers on them from labs, but no commercial product.
     

For the people who want to try SWIR or already can shoot in SWIR

  1. Can you do it by “erasing” phosphorescence? Not many people know this, but if you shine light on a phosphorescent material with a per-photon energy lower than the energy required to activate it (for example red or infrared light), you can “erase” the glow. It will look brighter at first, and then darker. What happens is that you are giving energy to electrons in the metastable state to go to a slightly higher energy state from which they can return to the ground state, emitting a photon. Basically you discharge the material faster. I tried it and it requires a lot of light, but it works. Maybe using long-lasting phosphorescent materials and a lot of exposure an image can be formed.
  2. Never tried SWIR LEDs? As deep UV LEDs, deep IR LEDs exist and they are weak and inefficient, but probably nice to have.

For the people who can shoot in LWIR

  1. Can reflected LWIR photography be done? The problem is that at those wavelengths basically everything is incandescent, and this masks shadows and illumination. Maybe by subtracting two images, one “normal” and another one illuminated by, for example, a hot piece of metal can show shadows. But a shadow doesn’t necessarily mean a real, “optical” shadow, it can also mean that some areas have been heated up when illuminated.
  2. A carbon dioxide laser emits at 10.6 μm, in the range visible by LWIR cameras. At very low power (they can be extremely powerful), can they be seen like a normal laser pointer?

For everyone

  1. Never tried 340 nm LEDs?
     
    Too expensive for me.
     
  2. Can Terahertz waves be “seen” with an antenna? The frequency is crazy high and semiconductors basically stop working, but can a signal be detected? It can surely be done with longer wavelengths, such as millimeter or centimeter waves.
  3. Can a sound camera be built? Imagine something similar to a pinhole camera, an “illuminator” which uses ultrasound at MHz frequencies (the higher the frequency the lower the diffraction and the higher the resolution), and a sensor made with a matrix of microphones. I know that neither the speaker nor the microphones are designed to be responsive at that frequency, and very high frequency sounds travel short distances in air, but can this be done for short distances (~30 cm)? The only problem would be cavitation, which can damages tissues.
     
    Yes, researchers at the University of Toronto developed an optical tomography camera and were imaging inside tissues of small live animals. I saw this in the Medical Biophysics department, where I did my Ph.D.
     
  4. Have someone tried (legally and very carefully) X-rays? If you really want to experiment with them, be extremely careful. Never expose yourself intentionally, use lead shielding, and power the tube far away. Also make sure that nobody is around.
     
    Yes there is a thread here from someone whom modified a postal xray scanner.
    User name ultrapurple and his gallery
     
    Giles Read
     
  5. Ever tried violet photography (~400-430 nm)?
     
    Yes.
     

Hopefully this is all new and nobody already tried it on this website, hope most can be done.

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Also ultrasound imaging works using sound waves an gooey gell, you place on the surface of the skin.

You can inject air bubbles into someone to increase the contrast.

 

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  • Can Terahertz waves be “seen” with an antenna? The frequency is crazy high and semiconductors basically stop working, but can a signal be detected? It can surely be done with longer wavelengths, such as millimeter or centimeter waves.
  • Can a sound camera be built? Imagine something similar to a pinhole camera, an “illuminator” which uses ultrasound at MHz frequencies (the higher the frequency the lower the diffraction and the higher the resolution), and a sensor made with a matrix of microphones. I know that neither the speaker nor the microphones are designed to be responsive at that frequency, and very high frequency sounds travel short distances in air, but can this be done for short distances (~30 cm)? The only problem would be cavitation, which can damages tissues.
  • Have someone tried (legally and very carefully) X-rays? If you really want to experiment with them, be extremely careful. Never expose yourself intentionally, use lead shielding, and power the tube far away. Also make sure that nobody is around.

 

 

1. Terahertz waves are also millimeter waves (haha). Yes, people do imaging with them, they are very popular in airports for searching for bombs and making trans people miserable. Lenses are made of plastic and quite large. You don't use one antenna, you use an array of tiny ones. Microwaves imaging is also possible, down as far as 100MHz. Google "microwave imaging radiometer."

 

2. I've had the sound camera idea, and of course ultrasound machines do exist already. Ultrasound has the disadvantage that (as you said) it decays rapidly in air. You can buy an ultrasound for $1000 or so, they aren't all that expensive, but the applicability is pretty limited because they have to have good contact to image inside of something or the sound just reflects off the surface, and of course they aren't designed for imaging in air, which has a very different speed of sound from water, which the machines are designed for, so the raw data would have to be reprocessed. It could probably be done, but again, this is why I didn't pursue it much further.

 

3. Someone on this forum has tried X-rays and owns a machine. I forgot who it is.

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Terahertz waves are also millimeter waves (haha).

They are SUBmillimeter waves (according to Wikipedia). Frequency from 0.3 to 3 THz and wavelength from 0.1 to 1 mm. They are also the THF (Tremendously High Frequency) band.

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Also, I know of ultrasound machines, but I meant imaging in air. Imagine shooting a selfie with sound, or photographing a flower, something like that.
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Also, I know of ultrasound machines, but I meant imaging in air. Imagine shooting a selfie with sound, or photographing a flower, something like that.

 

You mean like radar. Yes its out there.

Hackers have even sent high frequency sound through Alexa devices and Google home, the used the microphone to map out the room. Kind of cool.

 

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They are SUBmillimeter waves (according to Wikipedia). Frequency from 0.3 to 3 THz and wavelength from 0.1 to 1 mm. They are also the THF (Tremendously High Frequency) band.

Like with infrared, I don't think anyone has really decided where the cutoffs are. Wikipedia notwithstanding. Most people use Terahertz and millimeter waves pretty interchangeably that I've seen.

Also, I know of ultrasound machines, but I meant imaging in air. Imagine shooting a selfie with sound, or photographing a flower, something like that.

How much sound (even ultrasound) do you think reflects off a flower? I'm not saying the whole idea is impossible, but I suspect we probably want to use sound in the 15 kHz range or something as a tradeoff between resolution and propagation distance. It would be a pretty big camera. 15 kHz => 2 cm or so, if speed of sound is 343 m/s. And expect to see only hard surfaces.

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Like with infrared, I don't think anyone has really decided where the cutoffs are. Wikipedia notwithstanding. Most people use Terahertz and millimeter waves pretty interchangeably that I've seen.

 

How much sound (even ultrasound) do you think reflects off a flower? I'm not saying the whole idea is impossible, but I suspect we probably want to use sound in the 15 kHz range or something as a tradeoff between resolution and propagation distance. It would be a pretty big camera. 15 kHz => 2 cm or so, if speed of sound is 343 m/s. And expect to see only hard surfaces.

Like with EMR, the shorter the wavelength, the rougher a surface appears. For example, something with 1 mm roughness should appear mirror-like under 10 cm waves.

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Like with infrared, I don't think anyone has really decided where the cutoffs are. Wikipedia notwithstanding. Most people use Terahertz and millimeter waves pretty interchangeably that I've seen.

 

How much sound (even ultrasound) do you think reflects off a flower? I'm not saying the whole idea is impossible, but I suspect we probably want to use sound in the 15 kHz range or something as a tradeoff between resolution and propagation distance. It would be a pretty big camera. 15 kHz => 2 cm or so, if speed of sound is 343 m/s. And expect to see only hard surfaces.

I expect to see something like dark sponges and bright walls. Diffraction is the same thing that makes f/32 images fuzzy. I really have to bring the wavelength down.
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You mean like radar. Yes its out there.

Hackers have even sent high frequency sound through Alexa devices and Google home, the used the microphone to map out the room. Kind of cool.

That's actually scary. If you listen for the echo delay you can map a 3D environment, like bats do.
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I expect to see something like dark sponges and bright walls. Diffraction is the same thing that makes f/32 images fuzzy. I really have to bring the wavelength down.

I don't think you can bring the wavelength down for an economical amount. I think you should accept the compromise of using audible sound, and go with 15kHz or 20kHz. There is plenty of sound in that range bouncing around freely outside to see things with, and you can use conventional tiny mics without having to shell out a lot of $$$.

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To add to the discussion Andy here is a cool new SWIR back side illuminated sensor:

 

http://image-sensors...imager.html?m=1

 

This maybe the sound sensor you want:

http://image-sensors...lodyne.html?m=1

Ooh, that top link looks nifty. But it will probably be ages before anything like that is on the market, and even longer before I can afford it.

 

The bottom one isn't a sound sensor? It is LiDAR, which is just like radar with light, and is based off the time of flight principle, rather than reflectography. The resulting images are not the same. I suppose you could combine them and use the amplitude of the returned wave as well as the phase difference?

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I don't think you can bring the wavelength down for an economical amount. I think you should accept the compromise of using audible sound, and go with 15kHz or 20kHz. There is plenty of sound in that range bouncing around freely outside to see things with, and you can use conventional tiny mics without having to shell out a lot of $$$.

If I use electromechanical microphones (with coils and magnets, the opposite of a speaker) I can still measure an AC voltage from them. The only problem is that the inductance (or better the inductive reactance) of the coil suppresses high frequencies. I can always add a capacitor to make a LC circuit tuned to the frequency I want. I don’t know how to deal with capacitive microphones, but maybe I can still use them above 20 KHz. And ultrasonic speakers aren’t difficult to get, and I can always drive a normal one to ultrasound frequencies, it just wouldn’t be very loud.
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Regular mics will just not be able to keep up with an ultrasonic wave. The diaphragm has to be able to vibrate fast enough, and ordinary mics are tuned to human auditory frequencies. I'm sure you can buy the right sort of mic, but if you make an array of them it's going to be too costly.
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Ever tried violet photography (~400-430 nm)?

 

Yes. I have a little violet LED and photographed in the dark with a longpass on the lens which cut out any overlap into the UV.

Some digital cameras are not very good at recording violet.

I will try to find the photos to post for you.


 

Stefano: Here's the part where I have to remind you and everyone else UVC IS DANGEROUS. I know Dabateman (David) knows how to be extremely careful below UVA, so please consult him before you mess around with UVC, OK? Thank you for listening.


 

Alexa devices and Google home

 

I absolutely will not have any of that stuff in my house! Or Nest or spying doorbells or whatever.

I even wonder about the Samsung TV sometimes laaaaaate at night. :devil: :devil: :devil:

 

However if my Samsung TV is spying on us, it must be very very BORED by what it sees or hears here in Nerdville where I and the SigOth and the two cats are living. :lol:

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Some interesting questions there.

 

The silver thing is quite cool, I never knew that. Looks as though the reflectance drops to zero around 310nm. Must try that (If I can find some silver in the house). How does the presence of oxide impact though - does it need to be cleaned/abraded back to bare metal for the test?

 

Never used 340nm, or shorter wavelength, LEDs - far too expensive at the moment for the amount of light they produce.

 

I have the invisible vision 308nm and some U340 4mm. Will try that at some point.

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Ever tried violet photography (~400-430 nm)?

 

Yes. I have a little violet LED and photographed in the dark with a longpass on the lens which cut out any overlap into the UV.

Some digital cameras are not very good at recording violet.

I will try to find the photos to post for you.


 

Stefano: Here's the part where I have to remind you and everyone else UVC IS DANGEROUS. I know Dabateman (David) knows how to be extremely careful below UVA, so please consult him before you mess around with UVC, OK? Thank you for listening.


 

Alexa devices and Google home

 

I absolutely will not have any of that stuff in my house! Or Nest or spying doorbells or whatever.

I even wonder about the Samsung TV sometimes laaaaaate at night. :devil: :devil: :devil:

 

However if my Samsung TV is spying on us, it must be very very BORED by what it sees or hears here in Nerdville where I and the SigOth and the two cats are living. :lol:

Yes, I have to be careful with UV. Even if UVB LEDs are not very powerful, can I get a suntan from them? I guess it isn't a very good idea to try it, but vith an LED that emits less than 20 mW of UV it is better to lay under the sun.
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Some interesting questions there.

 

The silver thing is quite cool, I never knew that. Looks as though the reflectance drops to zero around 310nm. Must try that (If I can find some silver in the house). How does the presence of oxide impact though - does it need to be cleaned/abraded back to bare metal for the test?

 

Never used 340nm, or shorter wavelength, LEDs - far too expensive at the moment for the amount of light they produce.

 

I have the invisible vision 308nm and some U340 4mm. Will try that at some point.

From previous tests, the Invisible Vision leaked IR, even if it is rated at OD 4. The Hoya U-340 is still very transparent in UVB at 4 mm, and reduces IR a lot. The only problem is that if it leaks upper UVA this stack will not prevent this.
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From previous tests, the Invisible Vision leaked IR, even if it is rated at OD 4. The Hoya U-340 is still very transparent in UVB at 4 mm, and reduces IR a lot. The only problem is that if it leaks upper UVA this stack will not prevent this.

Yes, I found that in sunlight the Invisible Vision did let some IR through. However keep in mind that the actual amount of UV at around 308nm in sunlight is absolutely tiny, while the IR levels are huge. So is it a surprise that when used for imaging in sunlight that some IR gets through? My copy showed very good blocking up to about 800nm which is as far as I can measure. It was definitely in the >OD3 range. However yes, adding a 4mm U340 would be a good test.

 

What light source (and lens) were you using? I normally use the Invisible Vision filter with a UVB light, so in that case it does not need extra blocking.

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