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

  1. #31
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    Do you sense a recurring suggested theme here involving talking to Dan Briggs? You want to make the effort, trust us. Great guy and truly knows these beasts in and out.
    PM Sent...

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    Well, this thread has progressed rapidly!

    TC: To expound a bit on what others have been saying - the reason everyone is harping on safety is because this laser really should scare you. I owned one similar to yours for about 2 years, and I finally sold it because I wasn't comfortable working with it, even after spending a weekend tearing it apart and putting it back together with the assistance of two experts.

    The danger with a Q-switched laser (as Steve has already pointed out) is that they act a bit like a capacitor for light. They can store up a tremendous amount of energy and then release it all in a short pulse. Even if the average visible output of your laser is only 60 watts (which is already a shitload of power!), the peak pulse power in the IR section of that laser is several 10's of killowatts.

    Think about that for a moment: 10's of KW. If that doesn't give you serious pause, then you're not thinking clearly. (And we haven't even talked about the high-voltage next to flowing water hazard yet!)

    A first-pulse / giant-pulse suppression circuit is a must if you don't want to destroy your optics and your KTP every time you fire it. Likewise, good water purity is a must if you don't want to blow up your power supply and/or destroy your lamp each time you fire it. (Or worse, get the shit shocked out of you!) These topics are not well-documented, at least not in the traditional materials you'll find on-line. This is why having a mentor is key.

    I'll second the suggestion to attend the UKLEM, at any cost! You will meet an amazing bunch of people, have a great time, and learn a ton about lasers and laser safety. And in all likelihood, you'll leave the event with a mentor who can help you get your laser operating safely.

    Lasers are an expensive hobby, and big lasers are even more expensive. You have one of the largest (in terms of power output) lasers that is easily available to the general public. About the only thing that tops your unit is a high-power copper-vapor laser, and they also produce a pulsed output and thus have many of the same risks. This point can't be over-stressed: pulsed lasers are the most dangerous lasers you will ever work with - period.

    If it sounds like we are beating a dead horse, please understand that it is due to years of experience (and healthy respect) that has lead us here. (Not to mention some of the incredibly stupid things we've seen done with these monsters in the hands of the inexperienced.) We don't want an incident to happen, both to protect you *AND* to protect us, indirectly. Because every time someone does something stupid with a laser, the repercussions affect all of us. And your laser, in the hands of an idiot, is well and truly dangerous.

    We're not saying you are an idiot (quite the opposite, actually), but we still need to be certain that you fully understand what you're dealing with.

    Adam

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    Up until now, I was contemplating that 110W was the Warning Label Power. Now that I've seen test sheet photos, well, I think it is something else, like an early Greenlight...
    !
    Boy, I'd shoot the QC Manager, there is very little useful data on the test sheet. I can't see it being 110W green, due to the lack of beam enclosure tubes and air filters... 50 A lamp???? If its what I think it might be, that is one dangerous beast, but without intra-cavity tubes the lifetime would be short.
    !
    Well into the VERY DANGEROUS zone...
    !
    Not to mention the system while robust, is fragile. I'm also NOT seeing a 50 amp lamp PSU or cooling system in any of those pictures...
    !
    TC, Your really in over your head if you pursue this. I work with this sort of stuff on a daily basis, and these beasts scare me, just like they scare Buffo.
    !
    What I've given you so far is guidance on where to start learning. There is no where near enough info in my posts to get you going. Were it me, based on your manufacturing interests, I'd keep the rod assembly, the cooling assembly, some of the parts and the lamp PSU, and make myself a two mirror cavity IR industrial laser. That alone is a significant, but dangerous, technical challenge.
    !
    The green systems are not known for their beam quality, in fact, far from it. The beams wander in the cavity, and mode hop, and the fiber launch accommodates that. However, as built, they are a very poor laser for adapting to manufacturing use due to the beam position problem,,and beam cross section constantly shifting. I have helped to place a 35 watt unit in materials processing service, and the client has constant problems with beam wander at the target. He doesn't care, because his alternative was tens of thousands of dollars per year in knife blades to cut thin brass sheet.
    !

    Steve
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    When I still could have...

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    Quote Originally Posted by mixedgas View Post
    That is the green light generation side, and it will be coupled to the IR side.
    I didn't see it well, it's hard to see where the beams connect but I think I have an idea there now.

    Quote Originally Posted by mixedgas View Post
    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.
    Well shit that is a lot of work / risks. I think the motherboard is a no-go still, The screen is cracked and I have no useful error messages from it too, the manual doesn't contain any needed information meaning I can't fix it unless I get help from LaserScope... which I have a feeling is unlikely.

    Quote Originally Posted by mixedgas View Post
    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.
    I have not done this, what I did is I opened the unit up, took the pictures and closed it once more. I figure it would be better to leave it closed now rather then risk opening it once more? Or should I open it and toss a few of those desiccant bags in there through the gap and re-seal it?

    Quote Originally Posted by mixedgas View Post
    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.
    Okay, no-pokey unless I want to completely rebuild it, I got it.

    Quote Originally Posted by mixedgas View Post
    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.
    I shall send him a message now. Worst comes to worst, a lamp isn't out of the question if I know the rest works.


    Quote Originally Posted by mixedgas View Post
    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!
    The unit is a Laserscope Greenlight!

    Steve[/QUOTE]

    ------------------------------------------------------------------------

    ------------------------------------------------------------------------

    Quote Originally Posted by buffo View Post
    Well, this thread has progressed rapidly!

    TC: To expound a bit on what others have been saying - the reason everyone is harping on safety is because this laser really should scare you. I owned one similar to yours for about 2 years, and I finally sold it because I wasn't comfortable working with it, even after spending a weekend tearing it apart and putting it back together with the assistance of two experts.

    The danger with a Q-switched laser (as Steve has already pointed out) is that they act a bit like a capacitor for light. They can store up a tremendous amount of energy and then release it all in a short pulse. Even if the average visible output of your laser is only 60 watts (which is already a shitload of power!), the peak pulse power in the IR section of that laser is several 10's of killowatts.

    Think about that for a moment: 10's of KW. If that doesn't give you serious pause, then you're not thinking clearly. (And we haven't even talked about the high-voltage next to flowing water hazard yet!)
    I'm getting this now. I swear with each post it's getting more dangerous... am I going to find out that it is abomb pumped laser from the military next?

    Quote Originally Posted by buffo View Post
    A first-pulse / giant-pulse suppression circuit is a must if you don't want to destroy your optics and your KTP every time you fire it. Likewise, good water purity is a must if you don't want to blow up your power supply and/or destroy your lamp each time you fire it. (Or worse, get the shit shocked out of you!) These topics are not well-documented, at least not in the traditional materials you'll find on-line. This is why having a mentor is key.
    Well, I'm not probing further yet until I have one to guide me through what I should do and uh... mentor me.

    Quote Originally Posted by buffo View Post
    I'll second the suggestion to attend the UKLEM, at any cost! You will meet an amazing bunch of people, have a great time, and learn a ton about lasers and laser safety. And in all likelihood, you'll leave the event with a mentor who can help you get your laser operating safely.
    Alright then, I will. I should be able to squeeze it in without having to cut my payment for the Turbo-molecular pump I'm buying off my friend. Could make myself an awesome sputter chamber with that to make a cavity for a future project (or even one of you guys, think there would be interest in that?)


    Quote Originally Posted by buffo View Post
    Lasers are an expensive hobby, and big lasers are even more expensive. You have one of the largest (in terms of power output) lasers that is easily available to the general public. About the only thing that tops your unit is a high-power copper-vapor laser, and they also produce a pulsed output and thus have many of the same risks. This point can't be over-stressed: pulsed lasers are the most dangerous lasers you will ever work with - period.

    If it sounds like we are beating a dead horse, please understand that it is due to years of experience (and healthy respect) that has lead us here. (Not to mention some of the incredibly stupid things we've seen done with these monsters in the hands of the inexperienced.) We don't want an incident to happen, both to protect you *AND* to protect us, indirectly. Because every time someone does something stupid with a laser, the repercussions affect all of us. And your laser, in the hands of an idiot, is well and truly dangerous.

    We're not saying you are an idiot (quite the opposite, actually), but we still need to be certain that you fully understand what you're dealing with.

    Adam
    I'm going to repeat myself once more. I ain't turning that damn thing on until you say I have no chance of blinding myself with it during operation. Even if that means building an enclosure for tests that I can close during operation with interlocks. I get that.

    ----------------------------------------------------------------------

    ----------------------------------------------------------------------

    Quote Originally Posted by mixedgas View Post
    Up until now, I was contemplating that 110W was the Warning Label Power. Now that I've seen test sheet photos, well, I think it is something else, like an early Greenlight...
    Sounds right considering it's called the Laserscope Greenlight.

    Quote Originally Posted by mixedgas View Post
    Boy, I'd shoot the QC Manager, there is very little useful data on the test sheet. I can't see it being 110W green, due to the lack of beam enclosure tubes and air filters... 50 A lamp???? If its what I think it might be, that is one dangerous beast, but without intra-cavity tubes the lifetime would be short.
    I can't disagree there.


    Quote Originally Posted by mixedgas View Post
    Well into the VERY DANGEROUS zone...
    I think I recall that being mentioned... At this rate I'll be building a de-militarized zone around it.
    Safety is paramount.


    Quote Originally Posted by mixedgas View Post
    Not to mention the system while robust, is fragile. I'm also NOT seeing a 50 amp lamp PSU or cooling system in any of those pictures...
    I think it's just a well designed one. I've seen some impressive 50A power supplies in my time in very compact spaces. Either way, it's got to be there somewhere.

    Quote Originally Posted by mixedgas View Post
    TC, Your really in over your head if you pursue this. I work with this sort of stuff on a daily basis, and these beasts scare me, just like they scare Buffo.
    I'm starting to feel this too, but I'm not backing down, even if I have to go at the longhaul with this, redesign it into a 'simple' non q-switched unit. I want to do something with this.


    Quote Originally Posted by mixedgas View Post
    What I've given you so far is guidance on where to start learning. There is no where near enough info in my posts to get you going. Were it me, based on your manufacturing interests, I'd keep the rod assembly, the cooling assembly, some of the parts and the lamp PSU, and make myself a two mirror cavity IR industrial laser. That alone is a significant, but dangerous, technical challenge.
    Alright then. I do hesitate to take the unit apart at all. I suppose it also makes sense to keep it whole until I have exactly what I want to do planned out... I feel it's a waste to throw the Q-Switch and doubling crystal. I want to do something with them.


    Quote Originally Posted by mixedgas View Post
    The green systems are not known for their beam quality, in fact, far from it. The beams wander in the cavity, and mode hop, and the fiber launch accommodates that. However, as built, they are a very poor laser for adapting to manufacturing use due to the beam position problem,,and beam cross section constantly shifting. I have helped to place a 35 watt unit in materials processing service, and the client has constant problems with beam wander at the target. He doesn't care, because his alternative was tens of thousands of dollars per year in knife blades to cut thin brass sheet.
    Steve
    Interesting...



    -------------------------------------------------------------------

    So, over all, beyond the book I am eagerly waiting to arrive, and going to that show in a couple of month's time.... what should I do? To be honest I'm very excited with this project as I have some clever people who are willing to teach me (from what I can see) and plenty of things to learn. I can bide my time on this and be patient still, I'd rather do that then jump in head first with such a unit, to the same way I started off with a microwave transformer before moving towards a Potential transformer then my big 70kV XRT in my high-voltage 'experiments'




    EDIT:

    Would I be correct in thinking I could remove the complex and tricky frequency doubler, but keep the Q-Switch in the unit so I can still do Q-switched sharp pulses if I want to in the future? (could allow me to do laser welding as a project?)
    Last edited by TCWilliamson; 07-29-2016 at 13:34.

  5. #35
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    Oh, get some experience at the 1-2 Watt class of laser... Go to the regional big library with lots of books and find old laser books. Do the same at a serious university science library.
    !
    MIT OPEN COURSEWARE "Laser Fundamentals" with Dr. Shaoul Ezekiel. All Eight or more hours of Youtube. Yes, he speaks slowly. Yes its old. Yes, he knows what he is doing and his hardware demos are first class. Be glad its free, I once had to check out one videotape every two weeks and could not wait for the next installment. The tape set cost 250$ when I was a kid.
    !
    Find a copy of Laser Fundamentals, second edition, by Silfvast. The correct version has a photo of PLs own Laserman532 on the cover, with lots of colored beams from a pair of Ion Lasers.
    !
    Download and learn to use the cavity modeling part of PSST! Laser Software.
    !
    Find a University laser lab with serious science lasers locally and carefully make friends. Although if you walked in mine and said you want to get 110 watts going, that would cause some fear until I know you better. However a discussion about your qualifications to attend our college, a campus tour, and an evaluation of your math skills would be probably be forthcoming. Dress conservative, and speak slowly and carefully when making contact. If a Prof or Post-doc tells you it might be 30 days before they can see you, its not uncommon. They are very busy. There are two ways in, Cold Calls, and going thru recruiting/admissions. The later is usually not successful.
    What might be more successful is visiting the departmental office in person, and asking for an introduction. Emailing for a tour rarely works.
    !
    One of my favorite questions to perspective trainees is "What do you want to be when you grow up?" It throws young adults for a loop, as they think its an odd question. Students who immediately say "I am grown up" usually get a far more careful evaluation as to why they want this career choice.. This is because one should never stop learning! Engineers and Academics will question you to death during your visit. A good answer is often "I don't know" or "I have not thought about that yet, Sir."
    !
    If your host blows a hole in a business card for you, you might just be in the right place. If he/she declines because it gets his expensive pulsed optics dirty, you might be in an even better place. If the laser is not lit during your visit, probably wrong place. (Let them suggest the business card thing, its part of the standard tour, but not something to ask for!)
    !
    So just say, in better English then this, " I received a big Nd:YAG and the serious laser engineers on line said I should make friends and learn before messing with it." Talk your way into a university grade laser safety course, those are free for enrolled students using lasers on most campuses and take 4-8 hours. Start with the university safety office for the course. There are some good on-line materials, find and read. I like the US Army and University of Chicago Materials.
    !

    Tour a local laser machining job shop or stereolithography facility.
    !

    Start figuring out how to make metal beam tunnels that can take a 120 watt hit without serious back reflections or burning out.... That will require a serious wall thickness. Then design a tunnel with fold mirrors, and figure out how to align at low power so you never hit the wall.
    !
    Learn how to use a milling machine, Manual AND CNC.
    !
    Learn what Class I is, learn what class IIIA is, Class IIIB is, Learn what Class 4 is. Bonus points if you learn about the long extinct Class V laser safety designation. Learn how to calculate safe levels of laser light from direct and diffuse reflections. Hint, always measure what is there, but the math is a good start. Learn that for CW laser light(Easy) , then go find the pulse duration and wavelength tables and thus learn how to do it for pulsed laser light (Hard!)
    !
    Keep your grades up, and keep your employer happy.
    !
    The laser is a third of the equation, the application of the laser is a third, and the supporting electronics, power, cooling, lab, and safety is a third.
    !
    See if any of the Laser Factories in the UK still exist, there were/are a few that make industrial YAGs.
    Go Visit them!
    !
    Figure out why most of us do not want you to post schematics or blog about EXACTLY how this thing works.
    !
    Figure out how a three point kinematic mirror mount works. (Hint, Ball, Cone, and Flat)
    !
    Procedures, Procedures, Procedures. Make written procdures..
    !
    Find a copy of the Perkin Elmer or Heraeus long arc lamp /flashlamp brochures . The correct ones are 40 pages or more long and spell out how not to kill a lamp. Figure out what lamp you have.
    !
    Understand that the circulating power in the cavity is far more then what comes out the output coupler. Given a certain output power, and the OC mirror transmission, calculate the circulating power.
    !
    Learn how to calculate pulsed laser math. Given a pulse duration, repetition rate and average power, calculate the peak power per pulse. Be able to do it backwards.
    !
    Locate a 100-200 Mhz oscilloscope with a 50 Ohm input, and learn how to make a fast photodiode to detect your beam shape. Hint, 100 Mhz or faster PD is what you need.

    !
    Learn math, and as much high order math as you can learn while your young. Then practice and retain it.
    !
    I can keep you busy for weeks...
    ~
    Steve
    Last edited by mixedgas; 07-29-2016 at 16:50.
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    When I still could have...

  6. #36
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    Quote Originally Posted by mixedgas View Post
    Oh, get some experience at the 1-2 Watt class of laser... Go to the regional big library with lots of books and find old laser books. Do the same at a serious university science library.

    !
    Find a University laser lab with serious science lasers locally and carefully make friends. Although if you walked in mine and said you want to get 110 watts going, that would cause some fear until I know you better. However a discussion about your qualifications to attend our college, a campus tour, and an evaluation of your math skills would be probably be forthcoming. Dress conservative, and speak slowly and carefully when making contact. If a Prof or Post-doc tells you it might be 30 days before they can see you, its not uncommon. They are very busy. There are two ways in, Cold Calls, and going thru recruiting/admissions. The later is usually not successful.
    What might be more successful is visiting the departmental office in person, and asking for an introduction. Emailing for a tour rarely works.
    !
    One of my favorite questions to perspective trainees is "What do you want to be when you grow up?" It throws young adults for a loop, as they think its an odd question. Students who immediately say "I am grown up" usually get a far more careful evaluation as to why they want this career choice.. This is because one should never stop learning! Engineers and Academics will question you to death during your visit. A good answer is often "I don't know" or "I have not thought about that yet, Sir."
    !
    If your host blows a hole in a business card for you, you might just be in the right place. If he/she declines because it gets his expensive pulsed optics dirty, you might be in an even better place. If the laser is not lit during your visit, probably wrong place. (Let them suggest the business card thing, its part of the standard tour, but not something to ask for!)
    !
    So just say, in better English then this, " I received a big Nd:YAG and the serious laser engineers on line said I should make friends and learn before messing with it." Talk your way into a university grade laser safety course, those are free for students using lasers on most campuses and take 4-8 hours. Start with the university safety office for the course. There are some good on-line materials.
    This is a lot more tricky in the UK, possibly impossible, from what I know UK universities are a lot more closed compared to US universities. Over here you have to be a student to access the library, everyone has campus badges etc. I'll have to discuss with one of my cousins who is at the Southampton university medical side of things. Southampton have a pretty massive laser lab from what I can see, along with a -massive- high voltage lab.

    Quote Originally Posted by mixedgas View Post
    Tour a local laser machining job shop or stereolithography facility.
    That would be really interesting. I'll have to hunt about to see regarding that.

    Quote Originally Posted by mixedgas View Post
    Start figuring out how to make metal beam tunnels that can take a 120 watt hit without serious back reflections or burning out.... That will require a serious wall thickness. Then design a tunnel with fold mirrors, and figure out how to align at low power so you never hit the wall.
    metal beam tunnel? ... right well the first thing to making it is knowing what it even is! Time to research.

    Quote Originally Posted by mixedgas View Post
    Learn how to use a milling machine, Manual AND CNC.
    I lack practical access but I am familiar with the workings enough to operate one with a G-Code manual.
    Looking to get a home miniature mill / lathe.


    Learn what Class I is, learn what class IIIA is, Class IIIB is, Learn what Class 4 is. Bonus points if you learn about the long extinct Class V laser safety designation. Learn how to calculate safe levels of laser light from direct and diffuse reflections. Hint, always measure what is there, but the math is a good start.
    !
    Keep your grades up, and keep your employer happy.
    !
    The laser is a third of the equation, the application of the laser is a third, and the supporting electronics, power, cooling, lab, and safety is a third.

    Quote Originally Posted by mixedgas View Post
    See if any of the Laser Factories in the UK still exist, there were/are a few that make industrial YAGs.
    Go Visit them!
    Now that's something to do next year when my work holidays are free (I am full time employed...)

    Quote Originally Posted by mixedgas View Post
    Figure out why most of us do not want you to post schematics or blog about EXACTLY how this thing works.
    I think I have enough of an idea on that now.

    Quote Originally Posted by mixedgas View Post
    Understand that the circulating power in the cavity is far more then what comes out the output coupler. Given a certain output power, and the OC mirror transmission, calculate the circulating power.
    !
    Learn how to calculate pulsed laser math. Given a pulse duration, repetition rate and average power, calculate the peak power per pulse. Be able to do it backwards.
    Right-ho! I take it a good bit of that is in the book?

    Quote Originally Posted by mixedgas View Post
    Locate a 100-200 Mhz oscilloscope with a 50 Ohm input, and learn how to make a fast photodiode to detect your beam shape. Hint, 100 Mhz or faster PD is what you need.
    I have a 4 channel RIGOL DS1104Z at home, and a 400MHz beautiful beast of a LeCroy at work.
    How can you detect a beamshape with a single photodiode... have you got any good references for me to read on that?

    Quote Originally Posted by mixedgas View Post
    Learn math, and as much high order math as you can learn while your young. Then practice and retain it.
    Time to contact my math's tutor once more. I can pick up where I left off (calculus) (He has a PhD in Acoustic Engineering, I'd say I'm in good hands.)

    Quote Originally Posted by mixedgas View Post
    I can keep you busy for weeks...
    Steve
    Seems so...


    I've been talking with Dan Briggs, he seems to have actually opened up, tested and sold a unit very similar to mine.
    (slightly lower power it seems, but in exactly the same case / format interestingly enough, some optical differences and cooling differences only.)

    We have organized a phone call for Sunday.

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    My bet is that with care, you can approach a librarian and gain access. My librarian friends tell me they are pretty much bored now that most people use the internet. Public librarians find themselves being just computer help desk operators who maintain printers. People who ask for actual books are rare. Thus librarians long for the old days.. UK might have something like our free or low cost "Interlibrary Loan" too.
    !
    I like the DET-10A from Thorlabs.. Rumor has it they sell the bare photodiode for ~15$ and the schematic may be in the marketing literature for the DET-10A. For a person with your skills, creating a "Bias Tee" and putting the PD at the end of a 50 Ohm impedance RF Stripline cut from a scrap PCB with an exacto knife might be easy. The guys at EEVBLOG forums might enjoy helping you. I buy them for work, its worth investing, rather then building when using them at work. One can do an educated guess which PD it is, on their bare detector page.
    !
    There are circuits for simple "Avalanche Transistor" led pulse drivers on the web. Mine hits 750 picoseconds with 20 dollars worth of parts. That lets you test your PD.
    !
    Phil Hobbs has published some excellent literature on understanding laser photo diodes, on the web.
    !
    Pulsed photodiode stuff is all over the academic web for free. Its a common problem. Your pulses are slow by modern terms.
    !
    See if your college friends will let you browse "Review of Scientific Instruments" on line.
    !
    Ok, If I had a son, and I had to teach him the family business, these last two posts would be most of what I start with. I'd toss in Navy NEETs, and Art of Electronics Edition Two, but not three. I'd also toss in the US Army and Navy free pdfs on how to machine. Enjoy...
    !
    Steve
    Last edited by mixedgas; 07-29-2016 at 17:15.
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    Quote Originally Posted by mixedgas View Post
    My bet is that with care, you can approach a librarian and gain access. My librarian friends tell me they are pretty much bored now that most people use the internet. Public librarians find themselves being just computer help desk operators who maintain printers. People who ask for actual books are rare. Thus librarians long for the old days.. UK might have something like our free or low cost "Interlibrary Loan" too.
    Good point! I shall see if I can pop over to one of them when I have the time. I do actually have access to one of the university libraries as it's part of the college. I'll have to investigate.

    Quote Originally Posted by mixedgas View Post
    I like the DET-10A from Thorlabs.. Rumor has it they sell the bare photodiode for ~15$ and the schematic may be in the marketing literature for the DET-10A. For a person with your skills, creating a "Bias Tee" and putting the PD at the end of a 50 Ohm impedance RF Stripline cut from a scrap PCB with an exacto knife might be easy. The guys at EEVBLOG forums might enjoy helping you. I buy them for work, its worth investing, rather then building when using them at work. One can do an educated guess which PD it is, on their bare detector page.
    !
    There are circuits for simple "Avalanche Transistor" led pulse drivers on the web. Mine hits 750 picoseconds with 20 dollars worth of parts. That lets you test your PD.
    !
    Phil Hobbs has published some excellent literature on understanding laser photo diodes, on the web.
    !
    Pulsed photodiode stuff is all over the academic web for free. Its a common problem. Your pulses are slow by modern terms.
    Great. I'm going to order two of the photodiodes plus the other components come Monday.
    I imagine this one is suitable: https://www.thorlabs.de/_sd.cfm?path...tnumber=FDS100 ?


    Quote Originally Posted by mixedgas View Post
    See if your college friends will let you browse "Review of Scientific Instruments" on line.
    I'd toss in Navy NEETs, and Art of Electronics Edition Two, but not three.
    Thanks Steve, I'll check that out! Really, thanks for all the information you have provided me with.
    Last edited by TCWilliamson; 07-30-2016 at 09:23.

  9. #39
    Join Date
    Sep 2008
    Location
    Rocklea Brisbane , QLD, Australia
    Posts
    265

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    .... best thread i've read here in ages. I feel i am witnessing the birth of a true laser nut. (or at least a budding electrical engineer)

    I must admit i opened the thread expecting to see some one being educated in the difference between mw w W

    While he states he is not interested in the oooh pretty colours, i am confident we can make a convert of him.

    what happened here .....

    did he attended the LEM
    did he get the unit working with both eyes in working order
    is there a hole burnt in the side of his employees building?
    has he accidentally cut any limbs off

    did this thread get siphoned of to some password protected portion of the site where, only need to know information is disseminated??

    we need updates

  10. #40
    Join Date
    Jul 2016
    Location
    Dorset UK
    Posts
    40

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    Quote Originally Posted by zerowaitstate View Post
    .... best thread i've read here in ages. I feel i am witnessing the birth of a true laser nut. (or at least a budding electrical engineer)

    I must admit i opened the thread expecting to see some one being educated in the difference between mw w W

    While he states he is not interested in the oooh pretty colours, i am confident we can make a convert of him.

    what happened here .....

    did he attended the LEM
    did he get the unit working with both eyes in working order
    is there a hole burnt in the side of his employees building?
    has he accidentally cut any limbs off

    did this thread get siphoned of to some password protected portion of the site where, only need to know information is disseminated??

    we need updates
    The story of TCWilliamson is one wrought of misery and lack of time....

    did he attended the LEM
    -TCWilliamson did indeed make a pilgrimage to LEM, staying for 2 days and one nights.


    did he get the unit working with both eyes in working order
    -He failed to get the blasted thing working.


    is there a hole burnt in the side of his employees building?
    -Nope.


    has he accidentally cut any limbs off
    -He types with both hands.

    did this thread get siphoned of to some password protected portion of the site where, only need to know information is disseminated??
    -We may never know.

    we need updates
    The laser sits with many other things gathering dust, waiting to be awoken once again...

    (TL;DR; Brought unit, realised just how difficult and dangerous this shit is... learnt about danger...
    then learnt that it would be expensive and painfully tricky to work with the existing electrionics)


    ... Still wondering if the bar would be suitable for diode pumping.
    ... Still working out how to fund cost-effective dangerously high power lasering.

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