1. Joined
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    22 Jul '13 15:505 edits
    Is it possible to have a thin solid layer of mainly transparent material or optical filter that is, say, less than 1mm thick, that, ignoring any surface reflections (because can always use antireflective coatings ), selectively absorbs (and NOT reflects ) nearly all (say, more than 99% ) of an extremely narrow range of wavelengths of visible light (with a range of, say less than one nm difference in wavelength -so it is a very narrow absorption band ) while being virtually completely transparent (say, more than 99% transparency) to all other wavelengths of visible light?

    To help answer this above question; can anyone give me ANY example at all of a pigment molecule that can be incorporated either into a solid transparent matrix or dissolved in a transparent liquid that would selectively absorb an extremely narrow range of visible light while being transparent to all other wavelengths?
    Is it at least theoretically possible to fine-tine a semiconductor layer to do this?

    I am not being lazy here; I have read:

    http://en.wikipedia.org/wiki/Ultraviolet-visible_spectroscopy

    http://en.wikipedia.org/wiki/Conjugated_system

    http://en.wikipedia.org/wiki/Chromophore

    -but don't see how any of that helps answer any of my questions.

    I am also aware of UV filters that are transparent to all wavelengths of visible light but that is nothing like what I want here.
  2. Germany
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    22 Jul '13 16:33
    There are many substances with absorption spectra that are sharply peaked around multiple specific wavelengths (especially if they have no rotational or vibrational degrees of freedom), but I don't know of any substance that has an absorption spectrum about just one frequency.
  3. Subscribersonhouse
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    22 Jul '13 16:526 edits
    Originally posted by humy
    Is it possible to have a thin solid layer of mainly transparent material or optical filter that is, say, less than 1mm thick, that, ignoring any surface reflections (because can always use antireflective coatings ), selectively absorbs (and NOT reflects ) nearly all (say, more than 99% ) of an extremely narrow range of wavelengths of visible light (with a range are transparent to all wavelengths of visible light but that is nothing like what I want here.
    Can you give us the exact wavelength you want to be absorbed? Is this for a protective goggle, protecting you from an invisible beam, UV or IR? Ah, I see you mentioned visible light. So 600 to 400 ish. But exactly what wavelength. I don't think dye molecules will do the job, you would need some kind of engineered grating or some such, plasmonics maybe. Or an engineered multi layer filter, they can be tuned to specific frequencies but I don't know the bandwidth of that technology.

    I'm guessing you don't want an eye protection filter, you would want something a bit wider than 1 nm bandwidth. Maybe a hydrogen alpha line for telescopes? That would be 656 Nm. Nah, that would be a filter that rejects everything but 656. I think you want the opposite.

    Give me a nm # and I will see what pops up.
  4. Joined
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    22 Jul '13 19:298 edits
    Originally posted by sonhouse
    Can you give us the exact wavelength you want to be absorbed? Is this for a protective goggle, protecting you from an invisible beam, UV or IR? Ah, I see you mentioned visible light. So 600 to 400 ish. But exactly what wavelength. I don't think dye molecules will do the job, you would need some kind of engineered grating or some such, plasmonics maybe. Or thing but 656. I think you want the opposite.

    Give me a nm # and I will see what pops up.
    Can you give us the exact wavelength you want to be absorbed?

    ANY! As long as it is in the visible spectrum and a very narrow absorption band but the layer is still transparent to all other visible wavelengths.

    As for why I want to know this: this is a bit complicated but I want to know if it is possible to, while outside is relatively dark because it is night, light-up a room you are in with just one visible wavelength (probably using a laser bean that is first passed through a lens and then fogged glass) so you can see everything going on inside the room providing you are in the room (because almost all of the natural light passes through the window from outside to inside) BUT, the transparent and closed windows of this room is transparent to all wavelengths apart from that wavelength thus allowing you to see through that window everything outside that room without any significant or noticeable hindrance BUT without any of the light in that room escaping outside to cause light pollution outside that room (and I would explain why I want that on request but that is a more complicated explanation still ).

    Incidentally, this setup would have the side-effect of preventing anyone outside from seeing anything in the room through the window -but, although an interesting side-effect, that isn't the effect I am interested in this case.
  5. Joined
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    22 Jul '13 19:473 edits
    Originally posted by KazetNagorra
    There are many substances with absorption spectra that are sharply peaked around multiple specific wavelengths (especially if they have no rotational or vibrational degrees of freedom), but I don't know of any substance that has an absorption spectrum about just one frequency.
    (especially if they have no rotational or vibrational degrees of freedom)

    I can see how you can have a molecule with no rotational degrees of freedom but, and correct me if I am wrong which I could be here, I don't see how you can have a molecule with no vibrational degrees of freedom unless you are talking about single unbounded atoms or unbounded ions? (such as noble gas atoms) else wouldn't there always be vibration between two adjacent atoms joined be covalent/ionic bonds with atoms vibrating towards and away from each other?
    but I don't know of any substance that has an absorption spectrum about just one frequency.

    As long as it has an absorption spectrum of one wavelength in the visible spectrum, for what I want, that would do and it doesn't matter what its UV or infrared absorption spectrum is.
    Actually, it could have an absorption spectrum of several wavelengths and that would still work providing it still absorbs less than, say, 1% of natural light and is completely transparent to the rest.
  6. Subscribersonhouse
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    22 Jul '13 20:16
    Originally posted by humy
    (especially if they have no rotational or vibrational degrees of freedom)

    I can see how you can have a molecule with no rotational degrees of freedom but, and correct me if I am wrong which I could be here, I don't see how you can have a molecule with no vibrational degrees of freedom unless you are talking about single unbounded atoms or ...[text shortened]... still absorbs less than, say, 1% of natural light and is completely transparent to the rest.
    In that case I imagine you would want a red, a green, and a blue laser ganged together to make a simulated white light, each color tailored to add up to a perceived white, or close to it so you see things in natural-ish color. So the window would have three absorbing bands of those colors.

    Another way to do pretty much the same job is to just have a partially reflective coating like they use on those criminal line up rooms where the crim can't see the witness because the reflections are too strong and the rooms too bright.

    That would be a lot cheaper than a three color absorbing filter I would think.
    A smart dude could deduce something was going on if they had a wide band tuning laser spectrometer though. He would scan your window and the readout would show absorption at those three wavelengths.

    They would not be able to use that unless they could use a laser strong enough to punch a hole in the filter coatings, a couple hundred watt beam should do the job pretty well I would think. Then all would be revealed.

    The dude on the inside would probably not even notice anything odd since he would still see outside just fine. He would have to have some kind of counter laser spectrometer to see any skullduggery🙂 Spy Vs Spy!
  7. Joined
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    22 Jul '13 21:12
    Originally posted by sonhouse
    In that case I imagine you would want a red, a green, and a blue laser ganged together to make a simulated white light, each color tailored to add up to a perceived white, or close to it so you see things in natural-ish color. So the window would have three absorbing bands of those colors.

    Another way to do pretty much the same job is to just have a par ...[text shortened]... ould have to have some kind of counter laser spectrometer to see any skullduggery🙂 Spy Vs Spy!
    In that case I imagine you would want a red, a green, and a blue laser ganged together to make a simulated white light, each color tailored to add up to a perceived white, or close to it so you see things in natural-ish color. So the window would have three absorbing bands of those colors.

    My thinking exactly!
  8. Standard memberDeepThought
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    23 Jul '13 00:191 edit
    Originally posted by humy
    Can you give us the exact wavelength you want to be absorbed?

    ANY! As long as it is in the visible spectrum and a very narrow absorption band but the layer is still transparent to all other visible wavelengths.

    As for why I want to know this: this is a bit complicated but I want to know if it is possible to, while outside is rel ...[text shortened]... -but, although an interesting side-effect, that isn't the effect I am interested in this case.
    This is a classic dark room, use red light and a red filter, unless seeing red is important.
  9. Cape Town
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    23 Jul '13 05:54
    Originally posted by humy
    .. thus allowing you to see through that window everything outside that room without any significant or noticeable hindrance .
    Unless you have specific outside wavelengths you need, then you don't really need a single absorption band. You could probably live with many absorption bands so long as they match whatever laser light you are using in the room.
    My worry would be finding a laser that exactly matches the absorption band. Can laser frequency be adjusted easily?
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    23 Jul '13 06:071 edit
    Originally posted by twhitehead
    Unless you have specific outside wavelengths you need, then you don't really need a single absorption band. You could probably live with many absorption bands so long as they match whatever laser light you are using in the room.
    My worry would be finding a laser that exactly matches the absorption band. Can laser frequency be adjusted easily?
    If I remember correctly, although with most lasers their frequency is fixed, some types of lasers are designed to have their frequency adjusted and in the visible spectrum.
    I tried goggling this and I believe I got conformation of this:

    YouTube

    -but I have no idea how their frequency-adjustment mechanism actually physically works in these lasers.
  11. Joined
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    23 Jul '13 07:252 edits
    OK, I have a similar question but with a much less extreme requirement:

    Can anyone give any examples of either a semitransparent layer or a semitransparent pigment that completely absorbs a broad band of visible light wavelengths (for example, virtually all red light) while completely transmitting (i.e. being completely transparent to ) a broad band of visible light wavelengths (for example, virtually all blue and green light) while, ignoring any surface reflection due to differences in refractive indexes, reflecting NONE of the visible spectrum?

    I have looked at;

    http://en.wikipedia.org/wiki/Optical_filter

    but this doesn't give me an answer to that specific question.
  12. Subscribersonhouse
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    23 Jul '13 10:581 edit
    Originally posted by humy
    OK, I have a similar question but with a much less extreme requirement:

    Can anyone give any examples of either a semitransparent layer or a semitransparent pigment that completely absorbs a broad band of visible light wavelengths (for example, virtually all red light) while completely transmitting (i.e. being completely transparent to ) a broad band of visib ...[text shortened]... ipedia.org/wiki/Optical_filter

    but this doesn't give me an answer to that specific question.
    I think that depends on the size of the filter. Edmund Optical has lots of filters like that but only a few centimeters across for cameras and such. To put that technology into a large window, say one square meter would be prohibitively expensive.

    This is my go to shop for optical components:

    http://www.edmundoptics.com/
  13. Cape Town
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    23 Jul '13 11:13
    Not sure if this would help:
    http://en.wikipedia.org/wiki/Dichroic_filters
  14. Joined
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    23 Jul '13 11:355 edits
    Originally posted by twhitehead
    Not sure if this would help:
    http://en.wikipedia.org/wiki/Dichroic_filters
    Not quite because they work by selectively transmits a frequency band but reflects all the other frequencies (and I don't what something that reflects light here) and also exactly which frequency it transmits depends on the angle the light strikes its surface. Still, interesting. I am sure I can eventually come up with an imaginative use for them.
  15. Germany
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    23 Jul '13 13:37
    Originally posted by humy
    (especially if they have no rotational or vibrational degrees of freedom)

    I can see how you can have a molecule with no rotational degrees of freedom but, and correct me if I am wrong which I could be here, I don't see how you can have a molecule with no vibrational degrees of freedom unless you are talking about single unbounded atoms or ...[text shortened]... still absorbs less than, say, 1% of natural light and is completely transparent to the rest.
    I don't see how you can have a molecule with no vibrational degrees of freedom unless you are talking about single unbounded atoms or unbounded ions?

    Exactly! The problem I would see with using an atomic gas for such a purpose is that you would have to deal with fluorescence.
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