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Thread: Repair and Redesign of a 110W surgical laser unit to operational functionality.

  1. #21
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    Quote Originally Posted by NobleGas View Post
    You may want to make the effort to get up to Lincolnshire on the weekend of the 17 /18th Sept for UKLEM. Lots of knowledgeable people there and Dan Briggs is likely to be there; look for the UKLEM thread on here.
    I may be going over to Barcelona on a business trip to one of our drives suppliers around that time, I will have to check, however if not. I certainly have every intention off! It'd be nice to do such a trip.

    EDIT:
    looking grim there... just calculating it out, Trains = 100 plus the last 2 days remaining of my holidays this year, along with hotel, food and 40 entry.
    If someone going there lived down towards Dorset I'd happily fuel share with them if they'd be willing, but it's a little much to go out of pocket until I have a car (I used a moped for transportation currently due to cost and fuel efficiency)

    Quote Originally Posted by mixedgas View Post
    I'm hesitant to mention the miscreant, reading and seeing pictures about his exploits, alleged and actual, gave many of us headaches from fear. Some people here might have felt a duty to arrange an introduction for him with the Federal authorities. Including his plans to scan his audience with 35 watts of green light point blank. I'm told he has straightened up after a few years in college and having to be self employed.
    That is.... fairly understandable from what you are saying. After all, a bad apple like that causing such an incident would bring major scrutiny on our forum and this hobby in like.
    Scanning an audience with 35Watts? Bloody hell, intimidate thoughts are unsafe / faildangerous Galvo failure, someone ducking down / jumping while looking in the wrong direction. I wonder if a suitable slow scan could cut neck veins... This is getting more scary by the second.
    It is good to hear he has straightened out however....


    Quote Originally Posted by mixedgas View Post
    Especially about his statements that it was up to his unskilled audience to decide if they wanted to walk past his "Danger" sign on the door to public facilities. In other words, his free will to have fun was possibly more important then the safety of others who are un-aware of what they are walking into.
    And like that, he has no right to ever touch anything more dangerous then a wired mains socket. I do hope he has came around from such thoughts...

    Quote Originally Posted by mixedgas View Post
    That lead to self enforced rules on PL about discussing how to bypass the controller on a common, cheap, big, green, medical laser.
    !
    My point is this, mentoring people on PL has been a pleasure for me in most cases. I've arranged graduate school interviews, and helped some PLers get scholarships based on a healthy interest in lasers. There have been a few bad apples, and two or three very dangerous ones. So now I screen whom I help. Usually the discussion on high power goes off list. Fair Enough?
    I'm glad to hear you have helped many people like that. I understand where you are coming from there. Please, screen me all you want. I'd think myself as a responsible, careful person person?


    Quote Originally Posted by Diachi View Post
    Actually yeah, ~50W (possibly more, I'm not caught up on recent developments...) Q-switched, frequency doubled YAGs have been used in public shows for years - decades really - nothing wrong with that if you know what you're doing. Things go very wrong, very fast, when you don't know what you're doing.

    Not a YAG laser, IIRC it was a CuBr (Copper Bromide laser) but still 10s of watts and pulsed, much like the YAG lasers we're talking of: http://www.telegraph.co.uk/news/worl...blinds-30.html
    Yeah.... I'm feeling a lot less safe at such shows from now on... though I suppose they secure them well enough so they can't miss aim at people / failsafe galvos so the risk would be as high as getting stabbed, possibly lower, providing our recently discussed DJ isn't manning the stage.

    Quote Originally Posted by Diachi View Post
    I remember being pretty much flash blinded by a beam at 20W(Or was it Dan's larger 40W...?) scanning briefly over a light post about 50 yards down the car park at one LEM.
    Not sure how I feel about knowing that...
    Last edited by TCWilliamson; 07-28-2016 at 14:52.

  2. #22
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    Food for thought, the AEL for a Class IIA laser is .95 mW into a 7 mm eye pupil. AEL = Accessable Emission Limits. Class IIA basically means the blink reflex of your eye will protect you 99.9999 percent of the time. Most of us here can tell you that 1 millwatt in the eye hurts like a bitch.
    !
    For industrial and certain public use the license free limit pops up to 4.95 mW. Prolonged eye exposure to a non-moving, high quality, 5 mW beam hurts like a half kick in the balls, can be very dis-orienting, and you wont do it very often.
    !
    Some place around 15-20-25 mW CW, temporary scarring of the retina can happen for a very high quality beam, in some individuals. Ten mW of Qswitched light with its very high peak power would be more then enough to scare me. I'd have to look at a chart and do some math, but lets call just 10-20 mW of what you could have as being very damaging with a small beam diameter. I may be way off, but that is the number that sticks in my head for a Q-Switched Yag...
    !
    We've seen video cameras get dead pixels with 5-10 Milliwatts of CW light, if they have a decent lens.
    !
    So it does not take much. The exact threshold for retinal damage is difficult to assess in a single post.
    !
    That Q-Switch in your laser lets it discharge the laser rod in a quick spike or series of spikes. Think capacitor discharge into a shorted load. ND:Yag has a storage time constant of about 250 microseconds, and a huge storage depth per unit volume. For yours, a guess would be a 40 to 150 nanosecond pulse if the Q-switch is active. Which makes the pulsed laser a whole new ballgame in terms of safety! When the Acoustic Q-Switch is active, it causes a loss in the cavity, preventing lasing. Energy gets stored in the rod, waiting to be dumped. When the Q-Switch opens, that rod will lase again in a pulse with very high peak power. If your laser is what I think it is, an optimal rate would be between 6,000 and 15,000 fast pulses per second.
    Yet it can also lase CW, and will at greatly reduced power.
    !
    If your working with VFDs for motors, I'm starting to be encouraged.

    Steve
    Last edited by mixedgas; 07-28-2016 at 15:27.
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  3. #23
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    Quote Originally Posted by mixedgas View Post
    Food for thought, the AEL for a Class IIA laser is .95 mW into a 7 mm eye pupil. AEL = Accessable Emission Limits. Class IIA basically means the blink reflex of your eye will protect you 99.9999 percent of the time. Most of us here can tell you that 1 millwatt in the eye hurts like a bitch.
    !
    For industrial and certain public use the license free limit pops up to 4.95 mW. Prolonged eye exposure to a non-moving, high quality, 5 mW beam hurts like a half kick in the balls, can be very dis-orienting, and you wont do it very often.
    !
    Some place around 15-20-25 mW, temporary scarring of the retina can happen for a very high quality beam, in some individuals.
    !
    We've seen video cameras get dead pixels with 5-10 Milliwatts of light, if they have a decent lens.
    !
    So it does not take much. The exact threshold for retinal damage is difficult to assess in a single post.
    !
    If your working with VFDs for motors, I'm starting to be encouraged.

    Steve
    Yes, my full time job is with Servo drives primarily (Controlled VFDs)
    I also do a lot of experimental / power electronics work in my spare time


    Bare in mind this was a year ago, I was 18, I have moved on with bigger stuff now and I'm doing safer / more 'rigid' designs (actual PCB designed controllers)
    That video pretty much got me my job. I've changed a lot since then in terms of 'adult knowledge / understanding' now I'm in a work place for over a year and a half now.

    I'm more interested in the concept of not allowing any laser light to hit my eyes then a 'small amount'


    EDIT:

    Oh, another application I just got reminded of... I've wanted to do trials of a laser soldering system for certain concept that has viable commercial potential.
    Last edited by TCWilliamson; 07-28-2016 at 15:23.

  4. #24
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    Go back and see what I added with an edit to the last post.


    Steve
    Last edited by mixedgas; 07-28-2016 at 15:39.
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  5. #25
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    A tad expensive, but here you go:

    http://www.abebooks.com/servlet/Book...6n%3D100121503

    Steve
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    Quote Originally Posted by mixedgas View Post
    Go back and see what I added with an edit to the last post.

    Steve
    Now, that's right up my street. I just need to learn more about the Q-switcher etc. I will remove the black cover again tomorrow and take some detailed pictures for you guys to see what I'm working with there. From what it's looking like most of the drive electronics can be redone, the control board will have to be replaced anyway simply due to the fact it will not work as the HMI is broken.

    Would you advise I do a careful, documented tear-down of the drive / control gear and document it all up so we know what we are working with here, or would it be better to leave it complete for now?


    I'm getting really quite excited now. This will be a really interesting learning experience and certainly a project to document up and add to my Projects CV.


    Quote Originally Posted by mixedgas View Post
    A tad expensive, but here you go:

    http://www.abebooks.com/servlet/Book...6n%3D100121503

    Steve

    Brought

    Found 'SOLID-STATE LASER ENGINEERING, 6TH REVISED AND UPDATED EDITION Paperback – 2011 by KOECHNER W.' for 22 on Amazon
    Last edited by TCWilliamson; 07-28-2016 at 15:57.

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    Quote Originally Posted by TCWilliamson View Post
    I'm more interested in the concept of not allowing any laser light to hit my eyes then a 'small amount'
    It's the laser output that ISN'T visible light that's even more scary.
    .
    You're in good hands with Steve and I think you're demonstrating a favorable level of budding competency in pursuing this should you want to take it all the way. I'm hoping you're able to find a way to get to the laser enthusiast meet. I think it will be very rewarding for you and worth whatever sacrifice it takes to get there. Great bunch of very knowledgeable guys over there to help you with this.
    PM Sent...

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    Quote Originally Posted by Bradfo69 View Post
    It's the laser output that ISN'T visible light that's even more scary. ]
    Indeed, but did I specify which wavelength?

    Quote Originally Posted by Bradfo69 View Post
    You're in good hands with Steve and I think you're demonstrating a favorable level of budding competency in pursuing this should you want to take it all the way. I'm hoping you're able to find a way to get to the laser enthusiast meet. I think it will be very rewarding for you and worth whatever sacrifice it takes to get there. Great bunch of very knowledgeable guys over there to help you with this.
    Thank you. Yes I really want to go to that meeting, I'll start putting my 'beer money' aside into a vase, I shall probibly be able to go then, It's in nearly two months time anyway..
    (do you guys know anyone in the south I could carpool with?)

  9. #29
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    Just got some more pictures of the unit, under the black cover.....


    I'm not sure what the second side is to, they arn't optically linked at all and there is no output port, it seems blocked into that specific area... any idea what is going on there?

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  10. #30
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    That is the green light generation side, and it will be coupled to the IR side.
    !
    Now you have a problem, if you scrap the mother board, you need to control and tune the KTP temperature to +/- 0.2 C, precisely set the pulse repetition rate to a region that makes the KTP happy, generate giant pulse suppression to protect the KTP crystal, and prevent any lamp overcurrent excursion, so you do not damage the KTP. The PRF rate may be set inside the NEOS RF Driver for the Q-Switch, and NEOS is part of Gooch and Housego LTD, so their UK office may give you some data on the Q-Switch Driver. Makers of Green systems usually default to the internal pulse clock on the NEOS Q-switch driver, which produces a few tens of Watts of RF to drive the acousto-optic Q-Switch crystal. The Q-Switch crystal will be water cooled. So it needs water. Because you have a green system, there probably will be an internal 20-30 watt beam dump for the computer to calibrate the crystal with. Now you need 24 VDC at beaucoup amps to drive the RF amp in the Driver. Running the RF driver without a controlled impedance load on its output will likely kill it.
    !
    Also, since you have a KTP, you need to seal up the laser head to prevent ANY entry of dust or moisture onto the KTP Crystal, which are difficult to clean and you need specialized solvents to do so. We try to NEVER have to clean them. The intracavity light comes to a focus inside that crystal, and so the power density is enormous, in order to create the conditions for frequency doubling to green. Thus any dust results in degradation of the crystal because of a massive electric field from the focused light. The optical faces of the crystal are AR coated, but the sides are sensitive to moisture and solvents. So place a new, VERY clean plastic bag over the KTP mount and get a packaged, dust free, desiccant near it. Then button it back up.
    !
    Because you have a KTP, some of the IR optics may leak laser light to aid in tuning. So this thing will have some stray beams inside that may or may not get terminated. The temptation to peak the cavity alignment with just a single power measuring device must now be avoided, because the crystal is angle sensitive, very angle sensitive and as you move any one mirror, the beam path will rotate/translate inside the crystal and rod. Thus two meters and two or more mirror adjustments are used to preserve centering. Thus V and Z fold KTP based systems are tuned with two power detectors, one using leakage from a high reflector optic, and one on the output.
    !

    I'd urge you to replace the display at this point. Or at least try to find an equivalent. One thing, in the US a replacement arc lamp would be between 150-250$, so keep in mind you have only one, and find Dan Briggs.
    !
    is this an Aurora or Orion by AMS / Laserscope / Boston Scientific ? If not, it is certainly a clone of the design. Your in over your head, and this just became a very long term project. especially with the need of two thermal laser power meters for tuning. Most medical lasers are scrapped because the local Biomed does not have the training to tune it back to power, or because the doctor who owns it/uses it moves on or upgrades. Given you have NHS, there may be other reasons. Find Sir Briggs!
    !
    (Expecting Inbound from Jon about the KTP rules any minute)
    !



    Steve
    Attached Thumbnails Attached Thumbnails UK-KTP-CHAV1.jpg  

    Last edited by mixedgas; 07-29-2016 at 06:48.
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