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Changing light wavelength.

  1. Jan 25, 2008 #1
    Hello, I am new to this forum and in no way a physics major. My question for you guys is "can the wavelength of light photons being emitted from a bulb be shortened". If it can, how? Please don't get too over my head. I am basically trying to find the best or easiest way to shorten the wavelength coming from a mercury vapor bulb and then focus the light toward something.
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  3. Jan 25, 2008 #2


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    Changing the wavelength of light in the way you're hoping to do, is not practical with today's technology. The only instances I know are -

    the light from chemical dye lasers can be tuned very slightly,
    photonic band gap crystals can 'split' a UV photon into two green ones.

    If the spectrum of your lamp is not suitable for your purpose, there's not much you can do about it.

    Of course, there may have been some kind of breakthrough I don't know about yet...
  4. Jan 26, 2008 #3
    Crystals such as ones in laser pointers in a dpss system could achieve this. http://en.wikipedia.org/wiki/Neodymium_doped_yttrium_orthvanadate [Broken]
    This is a simple crystal that takes the infrared wavelength of 1064nm and cuts it in half to 532nm which is green light.
    Last edited by a moderator: May 3, 2017
  5. Jan 26, 2008 #4
    Theoretically, any energy field - e. g., gravitational or electromagnetic - can change the frequency of light passing through it. If the energy potential increases with light passage the frequency diminishes, and vice versa.

    In practice, this may be difficult. Mentz114 gives two good examples. Would increasing the pressure in a mercury bulb alter its frequency?
  6. Jan 26, 2008 #5


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    Er... I think everyone seems to have missed something here.

    Typically, light coming from Hg lamp has several wavelengths/frequencies. In intro physics, we often give a Hg discharge lamp in labs to study emission spectra using a diffraction grating and a spectrometer. You'll see several distinct emission lines.

    So what does the OP means by "shortening THE wavelength" here, since there are several? If one has the right set of filters, one can select one wavelength after another and another, etc. So to me, this question is puzzling.

  7. Jan 26, 2008 #6
    If you mean to shorten any wavelenght of light emitted by a lamp, another (very uneasy) way is to approach the lamp at high speed to the detecting apparatus (Doppler effect).
  8. Jan 28, 2008 #7

    Andy Resnick

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    Other posters have pointed out several obvious issues, let me add a few more.

    A wavelength, which corresponds to momentum, can be shortened by passing into a material with a higher refractive index. A frequency, which corresponds to energy, cannot be raised without adding energy into the system: frequency doublers, for example.

    If you want to extract out the short-wavelength lines from a Hg bulb, I advise caution: the lines are in the UV and I know of a technician that gave himself a sunburn on his corneas. No permanent damage, but a painful night was spent in the hospital.
  9. Mar 31, 2008 #8
    Basically, I was wondering if it was possible to take the light emitted from an Hg bulb and shorten the wavelength below 180 NM. Or find some sort of device that can emit very low wavelength light.
  10. Mar 31, 2008 #9


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    Don't fluorescent tubes accomplish this? The EM freqs (UV) emitted from the terminals is not the same as that which ultimately reaches our eyes (visible light).

    Actually, that's exactly backwards to what the OP asked...
  11. Mar 31, 2008 #10


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    When you say low wavelength, you mean short wavelength, right? You want to raise the frequency, right?
  12. Apr 1, 2008 #11
    Do you basically want a UV or an x-ray source?
  13. Apr 1, 2008 #12

    Andy Resnick

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    Here's the standard spectrum from a Hg bulb:


    (near the bottom)

    As you can see, there's not much below 300 nm. Here's the spectrum of a deuterium source:


    Which also peters out below 200 nm. I don't know of any common source that has substantial emission below 200 nm, and you would need to be working in a vacuum as the air will absorb the light.

    AFAIK, there is no common technology to frequency double 360 nm light to 180 nm. One can frequency quadruple Nd:YAG light to 266 nm using standard equipment.
  14. Apr 1, 2008 #13
    I guess so, however, X-rays just sound dangerous. Are there really any short wavelength/ X-ray sources available for reletivly cheap? Like a few hundred dollars?
  15. Apr 1, 2008 #14
    Yes, you are right. I meant short.
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