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Thread: Jellybeaning...

  1. #1
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    Default Jellybeaning...

    Ok, so this is driving me insane... I have a laser thats rated for 300mw, but as soon as i put too much blamking into the thing, its total power drops by visually half i would say... I talked to Bill at pangolin, and he calls it Jellybeaning. Where the laser kinda fluctutates its power level.. ( poor design actually) SO... I Now want a NEW laser.. One that does NOT do this.... I will use this one for beams, and NO Blanking.. Anyone have any suggestions??? I dont mind paying a bit more, but i NEED it to be right..
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  2. #2
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    Default

    I guess the problem is akin to the PWM of some led flashlights, where you pulse the thing so fast that it looks dimmer. It has something to do with the time it takes the diode to lase again after being blanked (rise time I believe it's called). If the blanking actually turns the diode off and then turns it back on, the effect is most noticeable. Some manufacturers use a current slightly below lasing threshold for blanking, so the laser is not really off, just not lasing, and it has a faster response.

    As for possible models you may want, I can't really say. All I said is merely theory and some conjecture thrown in for good meassure, so I may be wrong on some of it or, more than likely, all of it :P
    Remember the future?, That'd today, as you imagined it yesterday.

  3. #3
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    Jkaiser;

    You're dead-on... Though there are also thermal effects at play, the main issue is with the pump diode. And you're right, one of the "solutions" to this problem is to design the power supply so that the pump diode never shuts off completely, but only idles down to just below the lasing threshold... In fact, I think some of the larger units only idle down to a point where the output from the doubling stage is down into the microwatts... (But not completely off!)

    I've never heard of it called "Jellybeaning" though... Blanking-induced power loss is the term I'm familiar with. And yeah, it usually manifests at around 20KHz or so...

    Adam

  4. #4
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    So, Why are they Claiming 30k then if its not true??? I want my Money back....
    Adrien, you listening... :
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  5. #5
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    Well, it probably is true that you can blank it at 30K, so they didn't really lie to you... They just didn't say that the power would fall off as the blanking frequency exceeded 20Khz...

    I agree, it sucks! But it's something you almost have to ask for in writing. I've learned that it's a very common problem.

    Adam

  6. #6
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    Ok , That being said then, What company does NOT have this issue with their lasers??
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  7. #7
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    Carey..You didnt mention which laser had this problem ..
    I am assuming it is the green or blue units.
    A couple of things I have noticed:
    First depending on the laser..

    If its blue CNI ., yes..they only reproduce up to about 10khz analog
    TTL a little faster,. I hear they have or are redesigning the driver boards.

    I have two here that act completely different.
    One CNI BLUE (150mw) works great CW , but when modulated up to 10khz I get 15 percent power out..The other (150) has poor CW output (10mW) but has more output (70mw or so) then the first unit when modulated up to 5khz then drops off to almost nothing at 10khz. ..
    There is some circuit differences but not enough to change its characteristics..so more study here..
    I am blaming it for now on TEC and Diode driver settings for now !!!
    Altho , It could be something todo with the laser cavity as this second laser was a problem child from day one..!!

    Now for DPSS greens , I have seen some of these same characteristics as well but they mostly at least do put out 50 percent with 50 percent duty cycle waveforms...CHEAP ones good to maybe 10 to 15khz with GOOD units going well past 30 to 50khz...

    Red diode lasers are a different animal altogether..
    They should faithfully reproduce the input signal , with cheaper units barely doing 5 to 10khz, and good ones should do well past 30khz..
    And yes, It all matters how big a signal swing is involved..
    The smaller the swing the faster it should operate,hence..operating just below threshold..something akin to ECL logic.

    Also i've noticed is not so much as Lasers not producing full power because of the rate at which they are trying to reproduce is the fact that the signal itself may be the problem..

    What I have witnessed in testing with signal generators and PC ports is the fact that the faster the freq. the faster the rise and fall times producing less ON time because of the amplitude being lower..meaning less light output.

    In analog terms , less voltage getting to the laser driver with increasing freq,.
    To make matters worse is poor design in the driver area as well.

    I have noticed this with both TTL and analog using a 400mhz scope.
    Granted Dpss lasers are an exception because of the different factors involved
    Crystal heating cycles with TEC's trying to make-up the difference.
    What I have also noticed in some Laser show software/hardware designs also have erroneous data in the signal too..which is not seen with some packages..while some will do very well.
    I have seen this noise in poorly laid out software and it shows-up as dots or lines that should be blanked..This is one of the things that fooled me when I first started making blanking circuits.
    I had some really slow circuits that didnt notice this and all seemed well at least up to 20khz. with mediocre software .But when I designed circuits that performed way up past 50 to 100khz, man o man the noise showed up with me thinking I had the problem.
    So., After much probing and redesign I have found that it wasnt my problem at all .
    I changed to a different Lasershow package that was very well known and the problem went away..
    So I went back to my old software that had the problem and added some bypass caps to the blanking line to filter out any manmade or computer rf noise and that helped tremendously..
    But it also could have been the box , cables or anything else causing leakage as well.

    Also, another factor with noise is it can get on the control line easily too..
    Sheilded cable is needed and sometimes some bypassing of several hundred to a few thousand picofarads may be needed.
    This is because a good blanking circuit's input my act as a reciever for radio waves as I have witnessed here with an AM radio station tower located a 2 miles away from me.

    Now this really dont help in determining which lasers for you that pass the test but I hope it helps.
    Best to check all cables, connections , the box , or anything else causing leakage or attenuation as well.
    I am trying to not mention names here as I dont want to offend any other company here either..but most are good about this...so.

    For DPSS lasers , The cure may be as simple as re-adjustment of the laser TEC settings or replacement.
    Enough rant for now..if it doesnt make sense its because its late...
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  8. #8
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    LOL, Not the red! YEs its my Green Lambda Pro 300mw unit... And i Use Pangolin software and Hardware with my system. The 25 Pin cable i use is Shielded and only 8 ft long. I have stated it in the past , where i have an animation sequence and some frames , while stepping through the sequence, will be brighter than others, and the only difference is a few more blanking points. Its like someone grabs a dimmer control and turns it down after a split second, very wierd...... In Audio, we would call it a Compressor.....attack set to about 100 ms and release 2 ms
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  9. #9
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    ah ok I C ...maybe he will trade it out for another that works well...
    "My signature has been taken, so Insert another here"
    http://repairfaq.ece.drexel.edu/sam/laserfaq.htm
    *^_^* aka PhiloUHF

  10. #10
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    The problem is, they drop ship them from China, So getting someone to test each one out for laser show use, would be impossible i think. I talked to adrien and i can send it back, but i have a show that runnign all summer and i would have to buy anothe rone to first put in its place, then send this one back for testign and adjustments..... I guess im gonna have to do that... Its funny, Im running shows 3 nights a week, and im the only one that knows! LOL the peopl im doing the show for think everythign is fine!....
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