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Thread: Laserscope 808 q-switched runs up to 20 watts then starts to power backwards

  1. #1
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    Question Laserscope 808 q-switched runs up to 20 watts then starts to power backwards

    Hello, just wondering what anyone may think is happening with this KTP Laserscope 808 - with the Q-switch on, the laser will rise to 20 watts exact or 50 to 100Mw more but then goes backwards if you try to raise above the 20 watt range. The lamp current continues to rise like normal but the Laser power drops?? Is the Doubler bad? the Crystal inside looks normal at 20 Watts, when you try to re-align as I thought is was out of alignment. it still may be out of alignment but with a 20 watt loss that seems unlikly. dirty optics (little bit) but still 20 watts?? I checked all the systems throughout the unit all seems normal, even the temp. I have been tring the walk though the alignment one step at a time from the C.W. at 1 watt and aligning up to the Q-switch stage aligned it at 15 watts. Still the laser stops at 20 watts. I know this laser has a max at 39.5 Watts on a good day.

    Any help Please, DSL Jon or any Scope masters??

    P.S. very sorry for the spelling errors due to my tiredness...zzzz

    Thanks again,
    Marcus Chapman

  2. #2
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    Not a z-fold pro, but here's what I'd do, after my DIY expirience.
    Assuming You haven't been moving/removing any optics recently - I'd:

    -try fine tuning the SAM optic (dead end of the short arm). If You're watching the spot position on crystal (532nm/1,06 goggles!), this can be done with q-sw gated, other tuning better proceed at CW operation.

    -if max power cannot be pushed up higher SAM way - remove the KTP crystal (remember the arrow position on it's side) and inspect crystal faces under low power microscope. I suppose the power limit comes from to some extent degraded AR coatings, so there's little You can do without replacement. One could try moving the spot on the crystal to a side or up/down (done using SAM and RAM optics).
    If You have good 532nm/1,06 goggles You can notice brighter dots on crystal face during high power q-sw operation. These are the craters in crystal surface killing lasing in this spot area.

    If You suspect that LAM optics may have been moved recently, I'd try to walk the laser with LAM / SAM pair. But remember to keep the spot on the crystal!
    I woudn't recommend rough re-aligning the z-fold, as it's easy to loose lasing. If You've haven't been replacing any optics the chances it's misaligned seriously is low.

    How's the lamp hours ?

    Piotr.K
    Last edited by LesioQ; 09-07-2008 at 22:20.

  3. #3
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    Quote Originally Posted by LesioQ View Post
    Not a z-fold pro, but here's what I'd do, after my DIY expirience.
    Assuming You haven't been moving/removing any optics recently - I'd:

    -try fine tuning the SAM optic (dead end of the short arm). If You're watching the spot position on crystal (532nm/1,06 goggles!), this can be done with q-sw gated, other tuning better proceed at CW operation.

    -if max power cannot be pushed up higher SAM way - remove the KTP crystal (remember the arrow position on it's side) and inspect crystal faces under low power microscope. I suppose the power limit comes from to some extent degraded AR coatings, so there's little You can do without replacement. One could try moving the spot on the crystal to a side or up/down (done using SAM and RAM optics).
    If You have good 532nm/1,06 goggles You can notice brighter dots on crystal face during high power q-sw operation. These are the craters in crystal surface killing lasing in this spot area.

    If You suspect that LAM optics may have been moved recently, I'd try to walk the laser with LAM / SAM pair. But remember to keep the spot on the crystal!
    I woudn't recommend rough re-aligning the z-fold, as it's easy to loose lasing. If You've haven't been replacing any optics the chances it's misaligned seriously is low.

    How's the lamp hours ?

    Piotr.K
    Lamp is about half life, no optics have been removed, the laser has traveled alot(smacked around a little and vibration).
    the laser is lasing very well though in C.W. and Q-switched(a good sign) but still the 20 Watt loss is there??. I will take a closer look at the crystal as you recommended(big thanks for that)

    Thanks again,
    Marcus Chapman

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    have you tested KTP absorbtion? Set the laser to operate at say 20 watts (of green). Close the shutter wait 1 minute, measure your oven temperature should be 750 ohms, open the shutter measure the ohms if it is +/- 10 ohms your KTP is absorbing. COuld be a frap, dirty, or grey tracking phenon. What is the history of the xtal, new, used, litton, raycol??? too many variables with your limited description without knowing what your vag burner is all about...it could be anything but I suspect bleached optics or grey tracking. You can measure absorbtion with q-switch on or off...beter data is acheived with q-sw on and switching at 25 khz. There is also the very possibliity of thermal lensing in the rod which can be caused by many things.

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    Quote Originally Posted by Laserman532 View Post
    have you tested KTP absorbtion? Set the laser to operate at say 20 watts (of green). Close the shutter wait 1 minute, measure your oven temperature should be 750 ohms, open the shutter measure the ohms if it is +/- 10 ohms your KTP is absorbing. COuld be a frap, dirty, or grey tracking phenon. What is the history of the xtal, new, used, litton, raycol??? too many variables with your limited description without knowing what your vag burner is all about...it could be anything but I suspect bleached optics or grey tracking. You can measure absorbtion with q-switch on or off...beter data is acheived with q-sw on and switching at 25 khz. There is also the very possibliity of thermal lensing in the rod which can be caused by many things.
    forgot to add that water temp could also cause this...anyway, basically anything can cause this. I am of course assuming you are peaking the laser correctly.

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    Gold ? Isn't Laserscope's pump built with ceramic reflector ?
    Piotr.K

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    Quote Originally Posted by Tribal Existance Prod. View Post
    Hello, just wondering what anyone may think is happening with this KTP Laserscope 808 - with the Q-switch on, the laser will rise to 20 watts exact or 50 to 100Mw more but then goes backwards if you try to raise above the 20 watt range. The lamp current continues to rise like normal but the Laser power drops?? Is the Doubler bad? the Crystal inside looks normal at 20 Watts, when you try to re-align as I thought is was out of alignment. it still may be out of alignment but with a 20 watt loss that seems unlikly. dirty optics (little bit) but still 20 watts?? I checked all the systems throughout the unit all seems normal, even the temp. I have been tring the walk though the alignment one step at a time from the C.W. at 1 watt and aligning up to the Q-switch stage aligned it at 15 watts. Still the laser stops at 20 watts. I know this laser has a max at 39.5 Watts on a good day.

    Any help Please, DSL Jon or any Scope masters??

    P.S. very sorry for the spelling errors due to my tiredness...zzzz

    Thanks again,
    Marcus Chapman
    And what's Your today 20 Watt lamp current ? Do You know what it was before the problem ? These answers would clearly show whether the effeciency has dropped or it's just a foldback above halfway in power/lamp current.
    Piotr.K

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    I'M very blessed to be among folks who understand our World in the Laser Light Show Industry, I have gotten a few great idea's from all of you so I will go through the entire unit with a fine tooth comb. The Current seems higher than normal(the lamp) its showing 7-10 amps off from the normal operation(the lamp has low hours of use). I am very tired again and the key board letters seem to look like they are moving. I'VE got installations and rental bookings slamming me around the universe so i'm dead tired. The Laserscope sits waiting for me to continue trouble shooting it. I'm getting on it right away....

    I will come back with a better picture of whats happening and would request a tiny bit more help from anyone who has a second....

    The laser did take a little smack on its side, as it did tip over half way. A stupid mistake but it never fell over as we were tranporting it at the time of dumbness when the harnests broke on a turn. The temp of the water seems very normal but I need to check the temp. of the KTP crystal cavity and check the doubler crystal. I have checked all optics and all are correct.

    Thank you all so very much,
    Marcus Chapman

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    Quote Originally Posted by Laserman532 View Post
    have you tested KTP absorbtion? Set the laser to operate at say 20 watts (of green). Close the shutter wait 1 minute, measure your oven temperature should be 750 ohms, open the shutter measure the ohms if it is +/- 10 ohms your KTP is absorbing. COuld be a frap, dirty, or grey tracking phenon. What is the history of the xtal, new, used, litton, raycol??? too many variables with your limited description without knowing what your vag burner is all about...it could be anything but I suspect bleached optics or grey tracking. You can measure absorbtion with q-switch on or off...beter data is acheived with q-sw on and switching at 25 khz. There is also the very possibliity of thermal lensing in the rod which can be caused by many things.

    I wanted to focus on the KTP absorbtion if I may for a second as I'm checking a few other things as well. I'm checking the Crystal first to see if it's bleached or grey tracking(Fried Crystal in short) BUT I'm going to look into the KTP absorbtion and measurement of the oven temp. I would like to know at what points do you measure the ohms? I did'nt build the oven I just designed the rest of the unit, like the projector, the water cooling system and the control panel that operates the unit with lamp current ect. Kinda like Jon from Day Star's systems and Kevin's systems. So may I be Duh and ask at what points the ohms are measured at? Please with sugar.
    I'm getting the Microscope ready for the crystal inspection. at least the laser still works.

    Advice from Photon lexicon = PRICELESS........

    Cheers and thanks again so very much,
    Marcus Chapman

  10. #10
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    surface defects, fraps, films, chips & cracks can be inspected under a microscope. Absorbtion, grey tracking or outgassing must be checked by checking oven thermister. On normal laserscope boards it is TP9 & TP 10 on the BI8 and LCB PCBS. On Vag burners that people have modified it is usually the red bananna jacks on the oven industries control module. If you have a home made oven control module...then you would know where to test it. Point is if the shutter is closed the oven is at equilibrium or at rest. When you interject laser light into the crystal it will start to absorbe which is a measurement of the thermister. In normal laserscopes, if the crystal ohms reading vary more than about 10 to 14 ohms you are with in reason (high but with in reason) if your oven can not track the absorbtion it is usually grey tracking wihch will be a steady decrease in power and if you close the shutter wait a minute and then open it up and it does the same thing than i suspect a bad coating (film) or grey tracking. If the output beam looks good quality (no real bad spurious reflections) it is probably absorption. If beam looks crappy it is probably a surface frap or dog eye bugar on the surface. Clean and inspect under a microscope. It is all trial and error and being able to exchange parts with known good parts, which is why I gave up on the entertainment laser yags...no one would spend money on good replacement parts...always looking for the deal, dont care about quality...your other option is to call your 20 watt laser a 40 watt laser like everyone else does. (note sarcasm and sour grapes) Fold back can be many things, even reflectors, rods, water...and more. If your PS goes up to 40 amps (and it really does...) it is not the power supply. You can look at the pin outs that are called CURRENT RECEIVE on what ever PS you have and 1v equals 10 amps and 4v=40 amps and that is the real current feedback...not to be confused with CURRENT SEND...anyway...my fingers are tired.

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