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Thread: Glow in the Dark Lasering (The Next Generation)

  1. #21
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    David has spent a lot of time researching (and experimenting with) various glow-in-the-dark materials. Originally he was using the Zinc Sulfide based paints, which could be extinguished with red (or even infrared). However, since it didn't glow for very long anyway, the "erasing" wasn't nearly as useful as you might think. (Plus it takes much longer to erase the glow than it does to excite it in the first place.) Some of you may remember his early glow projector that he showed at SELEM a few years ago that used an 808 nm diode for erasing...

    Later, he switched to the Strontium-based paints, which glow for a much longer period of time (but are also *crazy* expensive - up to $800 per gallon!). All the videos you see above were done with the new long-duration paint. The videos look damned good, but it's even more impressive in real life. (SELEM is going to be amazing this year!)

    Anyway, he has been messing around with this stuff for several years, so he's got lots of experience with glow-in-the-dark stuff and has tried multiple commercially-available paints. What he is using now is the best he could find without resorting to a custom-spec paint.

    I chatted with him about the possibility of doing other colors, but he admitted that it would be even more expensive to attempt that. (Custom-milled pigment + fluorescent dyes added to a one-off order of paint isn't going to be cheap, and it could take a half-dozen tries to get something usable.) Given the already high cost of the paint he's using now, I can see why he's not keen to try for RGB.

    Adam

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    DAYGLO is right here in town. I could inquire about whatever you might like. Not sure if I can take it on the plane.

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    DK is going to be tied up through the end of next week, so we may not hear too much from him before then. However, Marc, if they are local it might be worthwhile to stop over there just to sit down with one of their chemists and discuss what might be possible.

    I had a long chat with one of the chemists here at work (even though I work at the wastewater facility, I interface with all the production buildings, and the entire south half of the plant is devoted to dyes, inks, pigments, and cosmetics, so organic chemists are everywhere) and he seemed to think that by adding the proper fluorescent dye you could use the emission from the Strontium-based paint to excite the dye and thus get some red or yellow to mix with the greenish hue and alter the shade a bit... That wouldn't give you RGB, of course, but getting something like yellow might be an improvement over the standard light green.

    I strongly suspect that true RGB (as in variable across the entire image) is going to be nearly impossible unless you do it in a grid/cluster formation like pixels on a CRT, for example. And even then it's going to be pricey. But it might be a fun conversation to have, and if you learn anything interesting you can share it with David at SELEM.

    Adam

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    If I make it to Selem, and I am going to try for two days later in the week, I'll bring some proprietary daylight lasering material for DK to try. Nice long persistence, too, as it turns into a light absorber when hit by UV. I've been setting on it for years. Update rate is slow, think road sign or laser restaurant menu screen.
    ~
    "The Home Laser Disco" with the room lights on might be cool. I don't know if 405 will hit it, it works best at 325... If it works with the diode, it would be P.F.M. to a viewer who has never seen the technology.
    ~
    I'll also bring the proprietary book on phosphor chemistry. The lighting industry had a text made on recipes for Phosphors, with details on the excitation. I have a copy for professional reasons involving two photon microscopy. From memory, you should have no problem finding an orange and green pair. I've made some of them in a low cost lab furnace. There is another one that is orange on excitation, shifts to blue on persistence.

    ~

    If I can't make it,I'll send it with Kecked.
    ~
    It is VERY possible to have a two color system or color on black.



    Steve
    Last edited by mixedgas; 07-26-2018 at 12:40.
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    There is a partly finnished projector I would like to convert to UV. I got frustrated because of the losses.
    What diodes did you use? are all the >100mw diodes still single mode? Is stacking or pbsing multiple diodes worth the effort?
    Which scanner mirrors work well? Did you fit special scanner mirrors, if so where from?
    Did you use a special output window? Some are coated for vis and block uv.
    For mixing with vis, do you know good ‘affordable’ dichro’s ?

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    https://www.ebay.com/itm/420nm-Long-...sid=m570.l1313

    this might work or something similar. might have to move back to 450. Now if you want to spend the money you can get nice edge filters that will work well but be prepared to pay few hundred for them. Why not just use edge combining as you won't use them together and if you do the alignment won't matter much if you are a tiny off as your not mixing colors.

    almost forgot....stock mirrors on galvos leak 405 like a car wreck.

  7. #27
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    Quote Originally Posted by yaddatrance View Post
    Love this!

    Some food for thought... If your glow in the dark material is similar to what I've played with, red lasers should extinguish the glow immediately. I don't know how far in wavelength the behavior extends, but I was using a HeNe laser at the time
    so at the very least the 635nm pointers should be in the ballpark.

    But anyways, if you scan with a red right after you might get really cool effects.
    Thank you! Yes, red light extinguishes the glow from the strontium based paint, but mw for mw the erase effect is too slow to be practical in my experience. There are also some technical issues that add to the challenge of erasing. For the strontium based paint I use, ~700nm is the sweet spot for effective erasing. (A HeNe is pretty close to this, right?) I’m planning on attacking it with high doses of LEDs in the near future as a broader eraser, but the cost of the diodes might become an obstacle.

    On the other hand, the zinc sulfide stuff is easy to erase with the right wavelength of IR, but that paint fades so quickly, it wasn’t necessary. I later repainted with strontium based paint anyhow, so that ship has sailed in my space.

    David
    "Help, help, I'm being repressed!"

  8. #28
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    Oh wow, lots of great posts here that I just saw. Adam was dead-on with his info, of course. I was wondering what adding a layer of day invisible red would look like on top of the green. The red will be much dimmer and fade faster, but it might get you an initial yellow with fade to green which would be interesting. But as Adam pointed out, this stuff is kind of pricey to experiment with on even a small scale. Another thought I had was to subdivide areas into different colors. Light blue will be my next target for experimentation as it is the next brightest color (~30% as bright as green).

    Steve: That info is really exciting. I can’t wait to see what you have on the topic! I’d love to go with a shorter wavelength than 405nm for complete invisibility but I need to find a reasonably priced single mode diode with the power I can get from DTR’s 16x diodes which I set to about 750mw with a G2 lens. Let’s talk further next week!

    Kecked: Spot on regarding most stock mirrors although Pangolin’s stock mirrors do really well with 405nm. I have swapped out CT mirrors for Pangolin mirrors on one occasion, but typically have Pango galvos in my projectors. Getting IR through 405nm required silvered mirrors which Pangolin acquired for me on a set of Compact 506’s although I only did this once before abandoning the whole IR thing as I mentioned earlier.

    Regarding 450nm for drawing, I tested that side by side with 405nm and found it to be very bright/distracting and it doesn’t charge well mw for mw as compared with 405nm.

    Bart: Great questions! Most are covered above, but for dichros, look at EdmundOptics for their near UV dichro. It works great at combining 405nm with a typical 450/520/638/650nm setup. It is relatively cheap at $150 for their tiny round one. Near field alignment is . . . challenging!

    Regarding windows, the best I have found yields 7-8% loss of the 405nm. I’ll have to look up that glass when I get home and post a link.

    I look forward to seeing many of you next week and chatting more!

    David
    "Help, help, I'm being repressed!"

  9. #29
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    These days simple SolGel dip AR coatings are cheap and very effective for near UV.
    I'm checking to see if we have an TEOS around to solve a similar problem at work.
    ~


    http://exoplanets.astro.yale.edu/ins...on/sol-gel.php


    ~
    https://www.allentownoptical.com/services/
    ~
    Steve
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  10. #30
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    Quote Originally Posted by dkumpula View Post
    For the strontium based paint I use, ~700nm is the sweet spot for effective erasing. (A HeNe is pretty close to this, right?)
    Not really - no. The most common line for HeNe is 632.8 nm. There are a few HeNe IR lines, but they are all longer than 1100 nm, so no good for this purpose. The rest of the HeNe lines are shorter than the customary red at 632.8 nm. (And have much lower gain than the red line.)

    More importantly, HeNe lasers have terrible gain in general - even for the most common red line. The highest output I've ever seen on a HeNe was around 35 mw, and that was on a tube that was 6 ft long! Just not bright enough (or small enough) to work with.

    The long, open-can, single mode red diodes at 660 nm might be a good start though. (Remember the old Maxyz modules? That's what they used.) You can get a bit over 200 mw out of one of those diodes, and they're pretty cheap. PBS a pair together and you've got a stew going! They also have a very tight beam, btw.

    If you need to be closer to that 700 nm target, you might consider using DPSS red at 671 nm. Unfortunately, they're a little on the expensive side. But you can also get those in higher power models if you need it. (Several watts on the high end.)

    Another option might be the multi-mode 650 nm diodes. They have a much wider beam, which may or may not pose an issue, but they are readily available up to at least a watt (if not more), and they are quite affordable.

    The important questions are: 1) what power level do you need, and 2) would you want a narrow or wide beam?

    Adam

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