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Thread: LPC 826 658nm diode tests/infos

  1. #11
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    Quote Originally Posted by p1t8ull View Post
    I have no hard data on these but the DVD diodes I have looked at tended to hover round about .3nm per deg/C shift.

    Norrra lot!

    well, the max t diff of a tec (at least the widely available off fleabay) is 67 degrees celcius

    assuming an ambient temp of 25 degrees, we could easily drop to -30. this is a 55 degrees diff x 0.3 nm/C gives a wavelength of 660-(55*0.30) = 643.5.

    maybe it is worth it after all

    nice to hear from you sir simon, long time, no see. hope all is well there
    "its called character briggs..."

  2. #12
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    It would be very interesting to see how a -30 LD chill down session goes..

    Quote Originally Posted by LaNeK779 View Post
    nice to hear from you sir simon, long time, no see. hope all is well there
    All gravy thanks, a bit hectic but still tuned in
    A little bit werrrr, a little bit weyyyyyy, a little bit arrrrgggghhh

  3. #13
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    One thing you do need to pay attention to is to localize the 'chill' as much as possible. The mini TEC modules somebody mentioned could be a very good tool for this, so you would only cool down the diode and mount, not the base plate.

    Especially in a multi-diode array you would want to keep the base plate near ambient to keep everything in alignment. (Or align the whole thing in sub-zero, which has a considerable risk of condensing up)

    The added bonus is that you can cool the individual diodes to your needs, and get a very neat wavelength mix if you want. A well tuned quad could be running a 4-line mix from 660nm down to 645nm, resulting in a very rich red colour.

  4. #14
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    What lasing threshold difference did you see between the diodes? The lasing threshold can be an indicator of design decisions that relate to maximum power output.

  5. #15
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    Dr lava, welcome back. I will look at threshold vs. temp. That will be easy. Don't worry about condensation. As long as you seal the space in front of the optics the surrounding cold metal surfaces act like a getter and pull the moisture away from the lens. The glass lens I am using does not shift in position in the threaded cold plate nor dose the focus shift all the way down to -50C. I've tested three 815 diodes down to this temperature and the wavelength shift is consistently 0.2nm/C. I have reached 643 nm. with these diodes and when compared to room temp. operation they are MUCH brighter. I'm still not sure why anyone is interested in the 826 diodes as I haven't seen any evidence that they are different from the $10 LOC815 diodes











    dr lava

  6. #16
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    Quote Originally Posted by drlava View Post
    What lasing threshold difference did you see between the diodes? The lasing threshold can be an indicator of design decisions that relate to maximum power output.
    Hi Andrew, my tests revealed differing lasing thresholds between 815 and 826, 80mA vs 90mA approximately.

    See here http://www.photonlexicon.com/forums/...754#post189754
    This space for rent.

  7. #17
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    Default chilling...

    well, with regards to chilling diodes, i tried a first approach today. made myself two mini rigs today, using the same method: huge alu heatsink with a 12cm fan blowing air on it and this was attached to the hot side of a tec. then, a much smaller piece of alu was attached to the cold side of the tec

    i did not get the results i was expecting. a 5v / 4a tec managed to reach 5.5 celcius on its cold side while its hot side was around 30celcius. a 12v / 5a tec managed just below 0 while its hot side was around 28celcius

    i did not use a tec controller, i just hooked the tecs to a psu with enough current to drive them properly. ambient temp was around 20celcius

    i was expecting much more... am i missing something here? did not attach any diodes to this, just cooling the metal to see where it takes me. any thoughts?
    "its called character briggs..."

  8. #18
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    Try to keep the cold side more insulated. It will heat up due to influence from the ambient air.

    Getting it cold is the hard part, once it's sub-zero, keeping the thing cool should be quite easy.

    Also, try to cover the entire cold side of your TEC with alu, since you need as much conductive surface as possible. A 0,25x0,25" piece of aluminium on a 4x4" TEC is not going to work.

  9. #19
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    well, the entire cold side of the tecs was covered, to be more precise, the tec is not visible at all, burried underneath the alu block. i also took extra care so that the screws holding the pieces together are thermally insulated, too.

    i will try insulating the cold piece of alu from the environment. i don't want to cool the air, i want the chill to remain within the alu, so i'll "dress it up" in some sort of foamy insulating material. i got some minor condensation in the process, so insulation will also improve things to that end fo things, too.

    the good side of this is that as the hot side did not run too hot just using air, so i will not have to assemble a watercooling rig for the time being
    "its called character briggs..."

  10. #20
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    As you can see from my entry several days ago I have reached very low temps and the process was not difficult, but you need to meet a couple of important requirements. Use a LARGE TEC. It does not need to be high performance,yet with low tech and practical insulation you will need 100-200 W. to get a delta T of 50C. Keep the hot side cool. An inexpensive computer style finned heat sink with a fan works well and can be compact and looks nice. As you cool, condensation can guide you to areas that need additional insulation. Finally. A small piece of polystyrene or urethane foam board with a hole to expose the diode/lens and covered with a microscope slide attached RTV adhesive will not experience frost over until the lowest temps. Good luck

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