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Thread: Looking for an economical calibration light source at ~ 400nm

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    Default Looking for an economical calibration light source at ~ 400nm

    I recently purchased a spectrometer from Science Surplus, and have calibrated it using known stable DPSS wavelengths (473, 532, 561, 589 and 593.5). With the spectrometer's default diffraction grating, I can get a range of a bit over 200nm. While the DPSS approach has worked great so far, I'm looking to re-calibrate my spectrometer to cover the 400 to 600 nm range.

    This means that I really need to locate a calibration light source, of some sort, in the very low 400s (or even in the high 300s). Can anyone brainstorm a creative calibration light source that would fit the bill? (my bill, by the way, is something I hope to keep to under $30). The light source doesn't need to provide anything other than the low 400 spectral line. I can use a 473, 532, and 561/589/593.5 for the rest.

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    use a 405nm blueray diode...

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    Quote Originally Posted by slicklasers View Post
    use a 405nm blueray diode...
    Well in a perfect world that would work, but since it's not, a blueray diodes isn't going to work. Not sure what would work best for this. I know there's argon and krypton lines in that region but not sure about dpss.

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    He asked for an economical way... his 532 and 473 will have a shift of +/-5nm so IMO the blu-ray would be the cheapest way at under $100...

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    532 and 473 will have a shift of +/-5nm
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    Maybe I'm wrong, but I've never heard of DPSS lasers having a drift of +/-5nm. Maybe in the pump diode which results in a loss of power, but not a drift, as far as I know...

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    Quote Originally Posted by DZ View Post
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    Maybe I'm wrong, but I've never heard of DPSS lasers having a drift of +/-5nm. Maybe in the pump diode which results in a loss of power, but not a drift, as far as I know...
    No, you're not wrong. DPSS doesn't drift +/- 5nm. Lol, I think that notion is the product of the same Chinese laser sellers that will advertise "Portable Blue 532nm 10,000 mW Square Beam Laser 1x 16340". In other words, copy and pasted specs for cheap lasers, that they often indicate a +/- DPSS drift even though that's not backed up by science or reality. If the 808nm pump wanders in wavelength, that only impacts the pumping efficiency. The resulting output wavelength remains incredible stable, with less than 1nm (less than 0.1nm if memory serves) of drift.

    A 405nm laser is obviously not the same deal. That will have a wandering wavelength that changes with heat, and from diode to diode. No good as a calibration source. Argon has a strong line at:
    358.844021 (which is too low)
    440.098598 (which is a little bit high)

    Neon was another obvious choice in terms of cheap availability, bit it looks like neon's prominant line is 352.04714 - again too low.

    The perfect element would be mercury. There's a REALLY prominent line at 398. Mercury would be fantastic. I'm thinking about this:
    http://www.amazon.com/Regent-Mercury.../dp/B000HM9HFU

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    That's what I thought. I had run a test on a couple blueray diodes for dave at LPF a year or two ago and used 532nm and 473nm as the stage to determine the blueray diodes wavelength, knowing that 532 and 473 should be dead on. If I remember correctly, I had one as short as 402nm and one as long as 416nm.

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    I recall that your average nightclub blacklight fluorescent-tube has a ~370 nm peak.
    It won't get cheaper than that.
    Not sure about the spectral bandwidth, pretty broad, probably like 20nm.

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    400 nm LED flashlight ? (Don't know how accurate that would be) http://www.amazon.com/Ultra-Violet-B.../dp/B001VZC5LA
    Maybe a noble-gas lamp?

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    +/- 5 Nanometer shift? Someone's dreaming.

    532.05 nm is the main peak of a 1.1 nanometer wide doubled 1064.1 nm laser laser line. Ring lasers, such as the Coherent compass, were narrower, but the center frequency does NOT drift from 1064.1

    There is NO hobbyist measured drift in the 532 nm wavelength. If you switched to Vandate or ND:YLF hosts there is about half a nanometer shift going to vandate and a 17 nm shift going to ND:YLF. No company is going to make a ND:YLF DPSS unless you request it and pay considerably extra for it. ND:YLF slowly rots on exposure to moisture, anyways.

    That wavelength is locked, I mean solidly locked, to the 1064.1 F manifold transition.

    946, the source of 473, is even narrower and much lower gain, so it does not shift either.

    I did 72 hour spectral runs on Coherent Compasses and cheap hobby 532 nm lasers at the university while looking to see if we could use one to replace a Argon. The compass mode hopped three times in 10 hours. A mode shift is a few 10s of Gigahertz. The CNI mode hopped every few minutes across about 10-20 modes.

    While both are much wider lines then a ion laser or hene laser when free running, there is no significant drift that a CCD spectrometer with 2 nm resolution is going to see.

    One they are lasing, low cost DPSS lase over a very narrow band and its stable. You would be hard pressed to measure the ND:YAG lasing curve on anything less then a 3/4 meter spectrometer.

    High pressure metal vapor lamps, incandescent lamps, some LEDs and all unstabilized diode lasers shift spectra.
    Almost nothing else does.

    What you need is a low pressue argon, mecury, or neon lamp. The lines are narrow and fixed. Not a mercury arc lamp, they have band spectra.

    Positive column Neon lamps have a weak line at 347 nm, you may see it weakly in a 2$ Radio Shack NE2 lamp if the envelope (Type 80 lead glass) transmits it.

    Google Penray lamp. I have a few argon/mercury penray tubes, I may be able to sell you one.

    http://www.uvp.com/pdf/Pen-RayLampSpectra.pdf

    I can do the glassware and pump a pure argon lamp for you if you need it. So can any neon sign shop.
    I can also do krypton, they wont have it on station. Cost would be not cheap, but still cheaper then a pen-ray.

    GE AR2s show up on Epay from time to time for about 20$-30$,in fact there are about 10 AR1s on ebay right now.

    They will have the spectra of Argon, possibly a few Neon lines from the Penning mixture used as a fill, and maybe a weak, very weak, Barium line spectrum from the cathodes.

    The $9.99 175W mercury lamp, which you should buy as a collectors item, will source your lines if you drive it with 10-20 mA. You'll need 2Kv for it to break down, and then Vlamp will drop to about 80 volts. A car ignition coil of the old Ford style is 14.95 at Autozone and if you run it off a Variac, at about 12-24 VAC it should light the lamp. At least thats how I did it as a kid.

    Pure Mercury arcs for outdoor lighting just got outlawed, replacement lamps and fixtures will no longer be made. That is why that lamp is so cheap.

    Sam has a pic of the HENE sidelight spectrum on the FAQ some place

    Here's Helium, this would run off a HENE PSU if you add a ballast resistor. Try 56K or 75K, 2-3 watts.

    http://www.homeschoolingsupply.com/u...nt-spthe01.htm

    Steve
    Last edited by mixedgas; 01-25-2012 at 08:09.

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