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Thread: 520nm diodes - Beam shape? Bias current? Cooling?

  1. #1
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    Laser Warning 520nm diodes - Beam shape? Bias current? Cooling?

    I'm currently looking into adding a 1W 520nm green diode to my projector, in place of the existing 1W 532nm DPSS unit, and have a few questions. Firstly, beam shape - I've looked at the beam pictures on DTR's website, https://sites.google.com/site/dtrlpf...s/ndg-1w-520nm and the pics of the beam shape aren't ideal - other than the G2 lens, what other optics would be needed to get a more symmetrical (circular or square, rather than rectangular) beam? Or should I just use it as-is and let the galvo mirrors cut out the overspill?
    Secondly, I've been considering using a Flexmod P3 driver - this needs to have the bias current setting before the diode is connected, any idea what that current should be?
    Finally, cooling - I'm proposing to mount the diode + lens housing in an aluminium block, with a heatsink on top and a 60w Peltier plate sandwiched between the block and the heatsink, and a thermostatic control with the sensor in the ally block. What's the optimum temperature to run the diode at, and will this arrangement provide enough cooling? I intend to use a 12v 10A psu to run the diode and the cooling plate.
    Any and all advice appreciated! TIA.

  2. #2
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    I do not have one of these diodes but here is what I can tell you. DTR has a nice set of pictures on his page showing current verses output. I think it was 1.5A or so for a watt. As for bias, every diode is different. Just turn the pot. All diodes like it cool. Cooler is better so long as you keep moisture out from condensation. DTR also shows the diode matches well with the 445/450nm diodes. Red is your problem not blue and green.

  3. #3
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    I already have red and blue Kvant modules - I'm happy with them, however, I'm not going to dismantle them to see what's inside!
    What beam shaping is currently recommended for 445 diodes? and if you use a Flexmod P3, what bias are you setting, with what diode? (just to give me an approximate starting point?)

  4. #4
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    depends on what beam size and divergence you want ?
    olike lens and a prism pair should get you a 5mm beam @ <1mrad depending on how far you adjust prism angle had mine as low as 0.65mrad the trade off is steeper angle on the prisms you will lose a little power .also note not a great idea for the green diode as olike lens will clip the beam a bit so you would start with a power loss anyway,this is not a problem as the blues bang out way more than a watt
    or use a g2 lens and a 3x cylinder lens set gets you around 3mm beam @ 1mrad no power loss but a little more work to set up cylinder lens properly



    Quote Originally Posted by greenalien View Post
    I already have red and blue Kvant modules - I'm happy with them, however, I'm not going to dismantle them to see what's inside!
    What beam shaping is currently recommended for 445 diodes? and if you use a Flexmod P3, what bias are you setting, with what diode? (just to give me an approximate starting point?)
    When God said “Let there be light” he surely must have meant perfectly coherent light.

  5. #5
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    Why does the bias need setting before you connect the diode?
    Surely the best way to set the bias is to wind it all the way down, then connect the diode and adjust the bias until it is just before the point the diode lases.
    Then disconnect the diode, apply 5v to the mod lines and set your max current as per the manual.
    Job done.
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  6. #6
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    @Badger 1666 - thanks for that - my current DPSS green is about 3mm with 1mrad divergence, so it looks like the G2 plus 3-lens set would be the way to go. I notice that DTR has 3-lens sets on his site, but they are AR coated for either blue or red - can you recommend a suitable lens set?
    @Norty303 - much appreciated - just trying to be careful as it's an expensive diode to break, and the Flexmod P3 manual only suggests setting the bias current 'to the required value' using a multimeter across the driver output and the mod input shorted, then setting max current value with 5v mod voltage - but both settings to be done with no diode connected, only finally connecting the diode once all the settings have been done. However, I've now found the datasheet for the diode, and it gives a typical threshold value of 300mA which will do nicely as a starting point.

  7. #7
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    the three element lens set is the same as the olike lens , it will clip the beam a bit
    you will just need the g2 from jordan and cylinder lens set from dave
    you might have trouble getting hold of a p3 driver,
    When God said “Let there be light” he surely must have meant perfectly coherent light.

  8. #8
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    I personally would no longer bother with a P3 driver; Alex's drivers from LaserTack are better:
    http://www.lasertack.com/en/laser-diode-drivers

    Also... While Norty is right, you don't necessarily want to set your bias current to a hair under threshold, (such that you get laser output at "1%" brightness in software.
    Most drivers won't hit lasing until around the rather meaningless 10% on the software power level.
    I would look at what level your red and blue stop lasing on the software power slider, and adjust your new green to come on at the same point.
    It's not wrong to do either, both can be corrected by setting colour pallets, but should you plug the projector into a controller that doesn't have your colour pallet set, colour rendition will be better by having the thresholds all at the same point.
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  9. #9
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    Thanks Daniel - As it looks like P3 drivers arer in short supply, the LaserTack drivers look good, I like the fact that they can run a TEC cooling plate as well. I'm now wondering if I can get away with just a G2 long-focus lens on its own - might get that and try it first, with the option of adding a cylinder lens afterwards. I also noticed that several threads are predicting an imminent price drop on the 520 diodes - anyone have any further info on that?

  10. #10
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    If anyone wants a P3 driver shoot me a PM, I have a few in my spares stock hanging around. Sorry don't want to highjack the the thread, just posted in case I can help someone out

    Cheers

    Steve

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