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Thread: Need some advice from experienced laser operators

  1. #11
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    Quote Originally Posted by ZeroPoint View Post
    Another test you could try which would eliminate the florescent theory is to briefly place the glasses in the beam path to see how much light passes through.
    Thanks for that good suggestion. I just drank a beer, so no more lasers tonight! I wish I had two pairs of glasses so I could wear one while holding the others in front of the beam.

    When I look through the glasses at the ambient light in the room, all I see is amber color. I am wondering how much of that is because the glasses are that color, or if it is because amber is approximately the color of white light with blue removed? When I looked at my power supply with its strong red and green LED light sources, the colors were as if I didn't have the glasses on. It is a pretty weird sight because everything is amber except for the LEDs. So it has me thinking that because the color of the laser through the glasses is amber, I am thinking that what I am seeing is either white light or amber light. If it were blue, I don't think I would see it. If it was any other specific color, I think I would see that. But more tests like the one you suggested are needed to narrow this down. Ideally I just need to find someone with a wavelength meter to measure it. I'll have to ask around and maybe I'll find someone that has access to such test equipment. I just did a quick search for information on making your own spectrometer. Leave it to the pot heads to show how to do it:

    https://www.420magazine.com/forums/d...-give-out.html

    When I have some time I'll have to look into that more. I'll probably use my camera to take a picture of it rather than look at it without safety glasses.

    Thanks,

    Greg

  2. #12
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    Quote Originally Posted by VDX View Post
    Hi Viktor,

    I just realized that that post was from you! I didn't take the time to look at the other forum thread until now, because you had conveniently posted the pictures of interest in this thread. Do you know what the optical density is of the shielding you used? What do you see if you turned the power as low as you can go, so that no burning takes place? Do you see any light?

    Thanks,

    Greg

  3. #13
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    Hi Greg,

    the "official" shielding material is stated as "L5" -- it's a pretty high blocking/shielding value, but don't know the relation to OD5.

    Found a much cheaper "UV-protect" window in a local tool-store, what's a bit more transparent, but seems to block the 445nm in the same manor ... so using this type at home.

    When thesting with beaming through both of the window a nonfocussed beam with 1W optical power ist totally blocked -- see the images of the full beam, partially and totally blocked:

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    This are the two acrylic materials - on the left the "random find", on the right the "official" laser shielding window:

    Click image for larger version. 

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    But when focussing through the material, a faint "orange-yellow" beam is visible - maybe some sort of wavelength-shifting inside the windows?

    But again - nearly no difference with the expensive "official" shield:

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    ...and the cheaper UV-window

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    When focussing onto the window material, then I can engrave or cut it ...

    Viktor

  4. #14
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    Thank you Viktor for posting all of those pictures. I will need to find some of that material you found. I'll look at our local hardware stores for material that blocks UV rays.

    I was thinking about that cheap DIY spectrometer using a CD as a prism. Why not get a real prism? So I looked on eBay and found one that is 7.8" (198 mm) long and about $10 USD. I might be able to get a definitive answer about which wavelength(s) are present in this laser beam. I suppose I will then have concerns about whether the prism is working properly .

    http://www.ebay.com/itm/Neewer-7-8-O...-/311383136793

    If I find any good deals on shielding material I will post it here. Thanks again for the pictures and information.

    Greg

  5. #15
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    I received the prism a few days ago and just got a chance to try it out. It was a sunny day today and so I put it in the sunlight and took a picture:

    Click image for larger version. 

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    It is kind of tricky to get the angle just right, but it does refract white light into its component colors. Of the three sides of the prism, I found one side to be better than the other two. The other two had some distortions, making me think these prisms are either cheaply made or are factory seconds from a quality manufacturer.

    I placed a piece of cardboard over the prism and laser in case the laser was reflected up towards my eyes. I was able to move the laser back and forth and observe the light on a white background. Since it was hard to position the prism just right to get a nice spectrum from sunlight, I decided to spend a fair amount of time with the laser trying to create colors other than blue. I wasn't able to see any other colors. I tried it with the laser focused fairly well and with it very unfocused.

    I decided it was probably safe to shine the laser on the glasses and see if any light shined through. I unfocused the laser so that the spot was about 2" x 1", and waved the glasses in front of the beam. I couldn't see any light illuminating on the white background behind. I don't think that was a definitive experiment, though it was pretty good. I don't think it was definitive because it might be that shining the laser on the white background and viewing the reflection through the glasses might be much brighter than viewing the reflection off of a white background when shining the laser through the glasses. To prove this I would need to put the glasses on and stare at the laser, which I'm not going to do.

    I need to do a little more research to find an explanation.

    I found some inexpensive safety plastic, though I haven't purchased any yet. Here is the link:

    https://jtechphotonics.com/?product_cat=safety-gear

    If I figure out anything more I'll post my results.

    Greg

  6. #16
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    Hi Viktor,

    I read your last post again and I have some questions. I think I understood everything you said.

    Quote Originally Posted by VDX View Post
    When thesting with beaming through both of the window a nonfocussed beam with 1W optical power ist totally blocked -- see the images of the full beam, partially and totally blocked:
    I think this test was similar to the one I just did when I shined the laser through the glasses. You were shining the light through the safety window and you couldn't see any light on the background. You were using a higher power than I was. I am guessing my laser was at about 0.075W, which less than 1/10th of yours. I should order some safety plastic and perform the same test you did. I would use a much higher power if I was shining it on the safety plastic rather than the glasses.

    Quote Originally Posted by VDX View Post
    But when focussing through the material, a faint "orange-yellow" beam is visible - maybe some sort of wavelength-shifting inside the windows?

    But again - nearly no difference with the expensive "official" shield:
    It is interesting that the light was not blue. I see red and green light through my glasses as red and green. Perhaps the answer is the same as the answer to my question about viewing reflections of the laser through the glasses. What do you see when you shine the unfocused laser on a white background while viewing it through the safety window? Do you see an orange-yellow color?

    Quote Originally Posted by VDX View Post
    When focussing onto the window material, then I can engrave or cut it ...

    Viktor
    It makes sense that you could engrave or cut it, because the window material absorbs the light. That would make it heat up and melt.

    Thank you again for helping me figure this out.

    Regards,

    Greg

  7. #17
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    Hi Greg,

    Quote Originally Posted by electronherder View Post
    ... What do you see when you shine the unfocused laser on a white background while viewing it through the safety window? Do you see an orange-yellow color?
    yes, a faint orange-yellow "image" of the emitter -- it's nearly the same "image", how it would be visible much brighter and in blue, when beamed without shielding.

    Viktor

  8. #18
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    Thanks Viktor. That is very similar to what I see. I see the same "image", which is a rectangular shape, which I am guessing is due to the shape of the laser diode or possibly the optics. Comparing the brightness to an incandescent light bulb, the light bulb is much brighter. But that might have to do with the fact that my safety glasses do not block hardly any yellow-green, yellow, orange, or red light.

    I think your very first reply contains the answer to my question. I'm sorry that I wasn't completely convinced. I suspected you were right about the ""secondary emission" from fluorescency", but I wanted to be sure (I knew you were definitely right about the plasma emitting light). I think I was less convinced because the people at Thor Labs suggested I purchase the "VRC1" card, which fluoresces when blue light hits it. There is absolutely no need for that card because an ordinary piece of paper will do just fine. I am going to call them again and discuss this further. You don't need to read the rest of this post unless you're interested. I am very convinced of what is going on, though I'll still be looking for more information on the subject.

    I made a new interesting observation. When looking at different colored objects in the room through the glasses, I see blue objects as black, deep green objects as dark green, and every other longer wavelength comes through without any color change (yellow-green, yellow, orange, and red). However, white objects appear yellowish-orange. This is completely consistent with the transmission curve of my safety glasses. I found the following interesting YouTube video that you might enjoy watching:

    https://www.youtube.com/watch?v=53-g1Oa0ReI

    At 50 seconds into the video, they show a banana, and explain that it is yellow because all hues except for yellow are absorbed. The yellow light reflects to our eyes and we see yellow. But then they say "In other words bananas are every color except yellow. And what is everything but yellow? It's complementary color, blue! A banana is theoretically blue!". When I look at my glasses as I hold them in my hand, the lenses are orange in color. If the glasses only absorb blue light, I would expect them to look yellow. But since they also absorb some green and all of violet in addition to blue, perhaps that is why they look orange. I think that is why white objects appear yellowish-orange through the glasses when viewed in ambient white light.

    Since blue objects appear black through the glasses, I thought I would see what a blue object would look like if I shined the laser on it. I just did that, and the reflected light is faint. Then I thought about shining the laser at different objects in the room. When I did that I could see a faint reflected glow through the glasses. But surprisingly, I saw a flash of light as it hit two different objects. I turned off the laser and turned the lights on, and those two objects happened to be labels on boxes that were fluorescent orange and fluorescent green. I tried it again, and looked at it without the glasses as well. I took a few pictures:

    Here is a cropped picture from across the room. The label is fluorescent orange and says "PACKING LIST ENCLOSED" in black lettering. You can see the blue light around the label, and the label is white because of the high ISO level. Notice the reflection of the light on the metal shelving near by. You can see the blue and orange light.

    Click image for larger version. 

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    Here is a close up picture of the whole label, with the ISO setting at "auto", which means it was automatically turned up high because the camera was trying to take a picture in the dark. This picture doesn't really show much. I only included it so that you could see the whole label.

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    Here is a picture with the ISO level set as low as possible, which is ISO 50. Now you can see the colors and letters distinctly.

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    What I see through the glasses is the same thing except that the blue is very dim and appears as a faint orange glow.

    So it is quite clear to me that paper can fluoresce, and your answer was correct. I did a search for something on fluorescent colors and found an interesting answer on Yahoo:

    https://answers.yahoo.com/question/i...4155253AAlgR22

    Knowing exactly what words to look for makes Internet searches more fruitful. I'm not sure why I didn't find these pages before (I really did look after I read your post), and here is another interesting Wikipedia page:

    https://en.wikipedia.org/wiki/Optical_brightener

    That page doesn't explain why I see the reflection, because it says optical brightening agents (OBA) "absorb light in the ultraviolet and violet region (usually 340-370 nm), and re-emit light in the blue region (typically 420-470 nm) by fluorescence". Under those conditions I wouldn't expect to see either wavelength through the glasses. I suspect the extreme intensity of a single wavelength of light hitting the paper is causing a similar effect with the same or different compounds. After a few more searches I think I hit upon the best words to search for. They are "Laser-induced fluorescence". Lots of interesting links for me to look through on another day.

    If I find anything more definitive on this subject I'll post it here, but it might be a while because I'm feeling comfortable about it.

    Thank you very much for your help!

    Greg

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