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Lasers can be used to ionize air...

  1. Sep 25, 2015 #1
    By surfing the net I learned that lasers can be used to ionize air and even produce "bangs" for some reason. Now, what I'm after is to ionize hydrogen or deuterium gas, at either 1 atm pressure or reduced pressure, say 40 mbar. Now what kind of laser light would be best to use? A hideously strong green laser perhaps? Or a strong 405 nm laser? Which is cheapest per watt laser light? UV lasers are probably too expensive. What about using a strong UV-lamp?

    There are apparently two ways for ionization; either multiphoton or some sort of resonance of the electrons in the changing electric field of the laser light; now which applies to ionization of hydrogen or deuterium?

    All input welcome!
  2. jcsd
  3. Sep 25, 2015 #2


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    Infrared CO2 lasers at high power probably, that doesn't mean it has to be the best for ionization.

    What is the application of your ionization? How much do you want to ionize? Is there any other gas present apart from hydrogen?

    Do you want to ionize hydrogen molecules or hydrogen atoms? The first happens at significantly lower energies, but then you'll probably get a mixture of ionized molecules and free (non-ionized) atoms.
  4. Sep 25, 2015 #3
    Primarily I want deuterons or protons. Also I want them as "cold" as possible too. It doesn't matter if there are other species present also such as D, D2+, even D-.

    Soft X-rays could do the job best perhaps. They even sell soft X-ray generators for ionizing air to remove static electricity.

    The question is if a very strong green or violet laser could do the job too, reasonably efficiently? Actually testing it yourself may be the only way of finding out.
  5. Sep 25, 2015 #4


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    Multi-photon ionization requires huge intensities. Ionization of hydrogen needs 13.6 eV, so even for two-photon ionization you would need a laser with 7 eV. With 3-4 eV you need 4-5 photons, which makes the rate even lower.

    An x-ray source might be interesting. I have no idea how well an electron beam would work.
    It is possible to make a plasma by heating a small volume in the laser focus, not sure if that would give a relevant ionization rate for hydrogen.
  6. Sep 27, 2015 #5


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    It's not the beam intensity per se that matters, but the peak field strength. In practice that means using a pulsed laser. Typically, the average beam power will be quite small but even a quite modest average power corresponds to enormous field strength if all the energy is squashed up into pulses a few picoseconds long. Lensing due to air ionisation is a common problem with mode-locked q-switched YAG and YLF lasers if you focus the beam too tightly.
  7. Oct 10, 2015 #6


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    I have recently joined this forum and have a question:If p3 and p4 represent the optical pumping power for a 3level and 4 level laser respectively, then what is the relation between them?
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