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Thread: Advice Please

  1. #21
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    Quote Originally Posted by Shadow View Post
    Wow that thread is from 2008.
    Hehe... Back then was a totally different era. If you had more than a watt of RGB, you were king shit. These days that's a typical lumia projector! Crazy...

    Does that mean that the 635nm from that time was dpss?
    No. 635 nm red has always been a direct-injection diode. There is a 671 nm red that is DPSS, but it's rather uncommon. (It's also not very good for laser show use, because 671 is such a deep red that you can't see it very well.)

    About the efficiency he states: "Efficiency will be around 98% for the reflected beam, and 96% for the transmitted beam." I don't know much about lab lasers or their optics but I do know that is insanely efficient given that the difference in wavelength is only 15-25nm.
    Yes, the coatings were really good. That's why the dichro was so expensive. To put this in perspective, back then a high-quality dichro from Edmund's Optics cost around $35 in quantities of 1. These special Semrock dichros were over $150 each, and we had to buy 10 of them to get that price. I imagine they're quite a bit more expensive today. Also, those Edmund Dichros had a dead-band of 30 to 40 nm between full-reflect and full-pass. This dichro had a dead-band of less than 12 nm. So, yeah, it was a very precise optic, and it had a price to match.

    As for the issue of buy vs build - you *can* get some very nice stuff on the retail market. But if you go super-cheap, you'll likely be disappointed. Conversely, building your own projector is a great way to learn, and you can usually save money as well, but it isn't the best solution for everyone.

    And regarding A1XD's projector, I'm reasonably certain they used a PBS cube to mix the two reds. A custom dichro would be way too expensive, and so long as you don't need really high power, it's just as easy to use a PBS cube.

    The reason we needed this dichros back then was because many people were using the long open-can 660 nm red diodes. They had fantastic beam specs, but they only made about 200 mw tops. So lots of people used a PBS cube to combine a pair of those diodes to get ~ 400 mw of red. That sounds like a lot of red, but remember that 660 nm is very deep on the spectrum. Our eyes aren't very sensitive to it, so it appears to be less bright. So typically everyone was always looking for ways to get more red.

    However, if you were already using a pair of PBS'ed 660 nm diodes and you still wanted more red (and you didn't want to get into knife-edging multiple beams together), then you needed a second red wavelength in your projector and a dichro to mix it in with the 660 nm red. You couldn't use another PBS cube to mix in the new red wavelength, because the beam from the two 660 nm reds was already randomly polarized after exiting the PBS cube used to combine those two. Also note that in 2008, the 637 / 638 nm red diodes hadn't been released yet, so the best candidate was either 642 nm (which was right at the cut-off point for the dichro), or 635 nm, which was cheaper and easier to find.

    Adam

  2. #22
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    Buffo, that explains why you were running the gb for those dichros. We still today don't have much for red and 405 seems to have stopped forever. Everyone is virtually going digital these days and bluray is a thing of the past.

    Brad yeah you're right. I haven't done much with the hobby in awhile but talking about projectors is giving me that itch again.

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    Quote Originally Posted by Shadow View Post
    Buffo, that explains why you were running the gb for those dichros. We still today don't have much for red and 405 seems to have stopped forever. Everyone is virtually going digital these days and bluray is a thing of the past.

    Brad yeah you're right. I haven't done much with the hobby in awhile but talking about projectors is giving me that itch again.
    Actually dkumpula is doing a lot with 405nm and his glow in the dark paint experiments. Pretty amazing stuff and I suspect some may follow his lead so, there may be a resurgence of 405.
    .
    I may have a proper place to actually work on this stuff in the very near future. So, maybe I can join the ranks of people putting up pictures. I have a host of things that I have had good intentions of working on but, never the time or place.
    PM Sent...

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    Quote Originally Posted by Bradfo69 View Post
    Actually dkumpula is doing a lot with 405nm and his glow in the dark paint experiments. Pretty amazing stuff and I suspect some may follow his lead so, there may be a resurgence of 405.
    Thanks, Brad!

    Yeah, I've built a few dual 405nm projectors recently and scooped up some of the remaining 405nm PBS cubes and 405nm dichros that Rob at StanWax has in his bargain basement. Such cubes and dichros are available elsewhere, but at a significantly higher cost, so anyone considering building a glow-in-the-dark laser projector should consider picking some up. (Side note: Most Fleabay dealers claiming their blue PBS cube can handle 405nm is not being accurate as the losses are atrocious.)

    As I believe it was stated earlier, 405nm is too far into the blue end of the spectrum to be very visible and that combined with the high power single mode diodes out there, makes it a hazard in the wrong hands. Personally, I wouldn't use it for either graphics or beams as 450nm is blue enough. However, for glow in the dark, you get a relatively dim beam for the power level which is exactly what you want for this sort of thing.

    Now if single mode, high power 370-380nm laser diodes were available for a reasonable price, I'd go that route so that your drawing beam would be nearly invisible. That'd be really cool, but high power laser diodes in this range don't appear to exist yet. (Someone please correct me if I'm wrong!)

    -David
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    There's a small science museum that has a dark room with a gitd wall and a light on the other end. It's meant to show your shadow against the wall but it's a great way to play around with a portable.

    Thanks for the heads up on the pbs cubes and dichros. I would have never known that until it was too late. I probably wouldn't have even suspected the cubes were inadequate. I came into the hobby when the 8x diodes were just coming out. I still got the sled it came from actually. When I saw that color I was amazed. It has such a unique glow to it. It really is an amazing wavelength.
    Those 9mm 405 diodes turned out to be multimode didn't they? Song song was selling those on facebook.
    Last edited by Shadow; 02-09-2017 at 16:36.

  6. #26
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    Quote Originally Posted by Shadow View Post
    There's a small science museum that has a dark room with a gitd wall and a light on the other end. It's meant to show your shadow against the wall but it's a great way to play around with a portable.
    Well that's a great idea! My understanding is that these walls are generally painted with strontium aluminate and erased with lots of deep red (~700nm). A big wall of strontium aluminate is pricey. A section of a back wall that I did with small particle strontium aluminate measuring 4 feet by 8 feet cost me more than US$250 in paint to get nice even coverage.

    Thanks for the heads up on the pbs cubes and dichros. I would have never known that until it was too late. I probably wouldn't have even suspected the cubes were inadequate. I came into the hobby when the 8x diodes were just coming out. I still got the sled it came from actually. When I saw that color I was amazed. It has such a unique glow to it. It really is an amazing wavelength.
    Those 9mm 405 diodes turned out to be multimode didn't they? Song song was selling those on facebook.
    I didn't see the diodes that you referred to. I've been using DTR's 16x 405nm diodes which are single mode or very close to it. Those can be run at 750mW each (more over a short duration) which is more than adequate for drawing on GITD paint. Too much power in fact leads to poor drawings as the 'flare' from the beam charges the areas around what you are drawing. I have blown several of these diodes however. I know they are ESD sensitive, but it doesn't appear to be my problem. Either back reflection or just long drawing times at high powers are my current (pun intended ) suspects.

    -David
    Last edited by dkumpula; 02-10-2017 at 04:28.
    "Help, help, I'm being repressed!"

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    Hi Guys :-)

    Photos of the lasers insides.

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    Humm.... anybody else seeing what I'm seeing? Looks like a red wire to 1 red diode, a blue wire to 1 blue diode and a green wire to 1 green diode. I sure don't think this is a combined 650 and 638. I'm kinda thinking the position of that lens pair is a part of his issue.
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  9. #29
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    Yeah, agreed Brad. That appears to be one corrected multimode red diode. Even if the unit had some novel way of combining two diodes (one 650nm and one 638nm) with some kinda tiny cube or odd knife-edging set-up, it doesn't make sense that they were powered by one driver. In addition, they wouldn't likely correct the same as set-up with one set of lenses.

    I suspect that the manufacturer probably was sourcing either a 650nm OR a 638nm, which ever one was cheaper or more readily available at the time.
    "Help, help, I'm being repressed!"

  10. #30
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    Agree...only see three diodes there...multimode capless red expanded with 2 spherical telescope (nice hi-res pics btw!)..so fake PJ specs? one red only.
    Maybe problem on green, can you measure its power?

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