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Thread: LambdaPro problems, any ideas?

  1. #1
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    Default LambdaPro problems, any ideas?

    Someone I know is having problems with his LambdaPro and has had the same problem since new, now out of warranty

    Laser starts off all happy, strong beam and nice spot like this:





    But then after 30 minutes it goes all dim and yukky:





    Are things moving from where they should be? is something getting too hot? or is earth simply moving closer to the sun?

    Thanks

    Pit.
    A little bit werrrr, a little bit weyyyyyy, a little bit arrrrgggghhh

  2. #2
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    It looks like heat is moving something along the optical path. Like either the crystal or the pump diode. Try mounting it to a heatsink.
    "Gravity its not just a good idea its the law"

  3. #3
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    Quote Originally Posted by Astroguy View Post
    Try mounting it to a heatsink.
    It's already on a sheet of 6mm aluminium as a heatsink.

    Pit.
    A little bit werrrr, a little bit weyyyyyy, a little bit arrrrgggghhh

  4. #4
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    If it is TEC cooled there may be a problem with that.

    Jim

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    Is the fan that is cooling the back of the TEC ok?

    Actually, it looks like a split beam problem perhaps judging from the second pic..
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  6. #6
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    If the problem only occurs after 30 mins. I am 99% sure it is heat related. But may not be overheating, something may have come loose and when it reaches operating temp. it is enugh to move. It only takes a micron to mess it up.
    "Gravity its not just a good idea its the law"

  7. #7
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    How long does it have to "cool" to return to normal ?
    Mike

  8. #8
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    That might be a parting of the KTP and vanadate in a composite crystal, a break in the bonding. Even a very tiny one would do this. By tiny, I mean tiny. It couldn't be seen by eye even if it was enough to stop the cavity working.
    It might be caused by the laser being overdriven too hard for the crystal to bear. One possible fix might be to reduce the drive and accept reduced power, if it's still good and doesn't cause this problem. I have an old 200 mW UGA (with LPS-100 PSU) that goes funny if I try to get the full power out, the beam doesn't change shape but the power falls badly, and the highest it can now give safely is about 160 mW, but the beam is so fine that I keep it. And because I can't trust it to stay stable enough for long enough to try to sell it...

    The power control in there will be called either RwI or RwL, I don't know which, or which direction to turn it in. RwT is the TEC control, you might get some good out of tiny tweaks of that. Like an 8th of a turn, and wait plenty of time between tweaks too, it's almost impossible to observe, let alone predict, the effect of changing it. Don't be tempted to make large changes if it looks pointless, just set it where you found it and forget it. Unless you can get far better guidance than any I ever got.
    Last edited by The_Doctor; 03-07-2007 at 23:44.

  9. #9
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    Update:
    Zoof was discussing with me some LambdaPro stuff in the blue laser thread.
    http://www.photonlexicon.com/forums/...4&postcount=52

    It looks like we have some clarity on the LambdaPro controls. This is my best guess, and it still doesn't make clear whether pot increase is clockwise or anticlockwise.

    RwT = TEC
    Zoof mentions two TEC pots, I've not seen more than one in any PSU I've had though. I think this pot turns ANTIclockwise for cooler TEC, but take care to check heatsink for temperature change as cooling current load increases, to confirm or deny that.

    RwI = LD Current
    I is symbol for current, so this makes sense, but there are other possible interpretations, more on that later...

    RwL = LD Current LIMIT
    Between Zoof's observations and my experience with tweaking, I think this fits. In his case, apparently, the current could never exceed the pump diode's spec anyway, and in my early UGA 200 I never managed to destroy the pump diode with extremes of these controls, so I guess mine is safe too.

    NOTE: The pump diode might not be killed even by extremes of RwI and RwL settings, so we must assume there is another reason for that limiter, and my guess is that the diodes are generously over-rated, and are NOT the weak link in a LambdaPro laser. (Adrian Feudale said years ago that the diodes are over-specified, and it seems this has always been true). The weak link is probably the bonding in the composite crystal, which is what appears to have failed in the laser the OP posted about here.

    I think both of these controls have their low-current end of scale ANTIclockwise, but I think Zoof can help confirm or deny this point. If you lower the RwI control slightly to allow the power to be strong, but not strong enough to cause the collapse of beam strength and quality after initial warmup, follw that by adjusting RwL downwards till you see the RED LED flicker (not the bi-colour LED, as I wrongly suggested in that other thread), then back up just enough to make sure that LED does not flicker.

    Note 2: One other interpretation of RwI and RwL was Incremental and Large, for coarse/fine tuning of LD current. That idea can now be ruled out, it's definitely not that.
    Last edited by The_Doctor; 03-08-2007 at 21:20.

  10. #10
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    Asked the guy for more info & got this back, if it helps:

    The length of time it takes to fail varies, but when it changes the change is instant. The laser also flickers occasionally prior to failing. I have not left the laser on after a failure, was worried I would do more damage. However the laser and PSU are both incredibly cool at the time it fails. Shutting down and restarting clears the fault, but then in re-occurs within a shorter time period.

    Cheers for the thoughts so far

    Pit.
    A little bit werrrr, a little bit weyyyyyy, a little bit arrrrgggghhh

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