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Thread: Measuring Wavelength

  1. #1
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    Default Measuring Wavelength

    Just wondering if anyone here knows of an easy way to measure the wavelength of a laser. I have an idea in mind, I was just wondering if you have an idea! Maybe something easier than my idea...

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    You might try passing it through some kind of optic that catches standing waves between the glass surfaces. If it worked over a range by rotating the glass, maybe you could figure it out by the angle of the glass to the laser beam.

    James.

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    Use a diffraction grating and some known sources to calibrate it? The principle of many small and cheap spectrophotometers is a calibrated diffraction grating mounted in front of a linear CCD sensor - each CCD element measures the intensity of a different wavelength.

    Best Regards, weartronics

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    Or you can use an interferometer

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    what accuracy are you trying to obtain 2nm, 1 nm, .1 nm ?
    Vis? IR ? UV?

    Steve

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    Cool

    Easiest way (in my opinion) is to use a prism and a long throw. You'll need a couple known lasers to calibrate... A Hene at 632.8 and a DPSS green at 532 work very well.

    Mount the prism in a sturdy mount that won't shift, then aim the 1st laser so the beam hits the prism and refracts, making a spot on the wall far away from the prism. (farther away is better; 20 to 30 feet would be great!) Tape a piece of paper on the wall and mark the spot where the first laser's dot appears, then label the wavelength.

    Now repeat the process with the second known laser. Make *certain* that the beam enters the prism at the same angle. (This is important! If the angle is off, the measurements will be off as well.) Mark the new spot on the paper and label it. Congratulations! You now have a calibrated laser frequency measurement device.

    Measure the linear distance between the two spots on the paper. Now subtract the two wavelengths to get the "spread" between them. There's your "nm/cm" conversion factor.

    Now install your mystery laser (again making sure the beam enters the prism at the same angle as the first two lasers), and measure the distance between the spot on the wall and one of the two known points. Use your "nm/cm" conversion factor to calculate the wavelength of the unknown laser.

    It's not perfect, mind you, but if you're careful and have a long throw, it will allow you to tell the difference between 632.8 nm and 635 nm.

    Adam

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    I used to work for a company (Optronic Laboratories, Inc in Orlando, FL) that made devices to measure the spectrum. I wrote software for spectroradiometers and they used gratings to split the light into its wavelength components. The gratings rotated so that the different light portions would be rotated onto a detector so that they could be measured for intensity.

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    I should have just asked, Do you want to borrow my manual monochromator ? 1 +/- .5 nm resolution

    Steve

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    Using a diffraction grating it can be done quite accurately. You'll find more info on this on page 2 & 3 of this thread:
    http://www.photonlexicon.com/forums/...elength&page=2
    I would not recommend the prism method as it is inaccurate.
    Last edited by Zoof; 09-20-2008 at 13:41.

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    Lightbulb This is a theory...

    You could use a dichro and a meter, assuming you know the specs of the dichro. Kinda like tuning a dichro based on the angle you're hitting if from. Find where it measures the highest and the angle... amd the wavelength and angle the dichro was made for...
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

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