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Thread: Exporting completed laser shows to other software - PROBLEM!

  1. #61
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    Say Bill...

    I know this is taking up even more of your time, but I'm really curious about this audience scanning system you've gotten approved. Would you mind talking a bit about a few specifics of the projector itself? I'm curious as to how large you ended up expanding the beam to, and where in the optical path you did so. (ie: before or after the galvos) Also, how much power are you running?

    That is, if you are free to discuss the details of the system at this time...

    Adam

  2. #62
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    Hi Adam,

    Sorry about the delay in my response, but I was at the LaserFreak conference this past weekend. Then, a few colleagues and I spent about a half-day at Oktoberfest. I hope to have some pictures of these events on the Pangolin web site soon. Keep an eye on the "What's new at Pangolin" section of our web site if you are interested.

    Regarding the audience scanning system, it is just that -- a system. It is an entire laser projection system, including what you guys call the "scanner safety" (really much more than that), and special diverging optics and other elements. It's also a system of how you go about evaluating shows, and how you to about testing and adjusting the projector to ensure safety. So, you might actually call it several systems.

    As far as how large we expand the beam, well the beam is typically diverged (not expanded) and this is typically done after the scanners using a special lens (although it could be done before the scanners too). When using continuous wave lasers, the safety can be increased by decreasing the power per unit area (also called irradiance). You can decrease the power per unit area either by decreasing the laser power (usually undesirable), or by increasing the beam divergence. Due to the inverse square law, increasing the divergence pays off big time and it also has other benefits. People who watch audience scanning shows with the raw beam will find it offensive if the beam scans past their eyes because (at the very least) it will leave an unpleasant after-image. When the divergence and power level are set correctly, it makes it a pleasant experience -- very fun actually... And of course, no after-image.

    The bottom line is that, to be safe you can either use a 5mW un-diverged laser beam, or perhaps beam powers up to 500mW or more if proper divergence is used. The exact spot size in the audience depends on a few factors, including the beam power and even the beam profile (Gaussian, top-hat, etc.). As part of the variance requirement, we have a test setup that is used each night to verify proper performance before each show. (Technically, you are supposed to do some degree of testing before each show anyway, with any laser projector, regardless of the use.)

    I recommend anyone interested in audience scanning, to review two separate documents. The first is an article that I wrote on manually evaluating audience scanning shows. Our system automates this process to some extent, but still system verification must be done, and it is done in a similar manor to the way I outline here:
    http://www.pangolin.com/resguide09a.htm

    The second is a thesis written by John O'Hagan of the National Radiological Protection Board. It's the most definitive text on the topic of audience scanning. It can be found on our web site here:
    http://www.pangolin.com/resguide09b.htm


    Best regards,

    William Benner

  3. #63
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    Hi Bill;

    I understand about being busy. Hope Oktoberfest was fun for you! (I'm sure the LaserFreak conference was - though I imagine you're pretty tired!)
    Quote Originally Posted by Pangolin
    well the beam is typically diverged (not expanded) and this is typically done after the scanners using a special lens
    This is really the part I was interested in. If I understand you correctly, you're not re-collimating the beam - you're just passing it through a lens which increases the divergence. But then the beam would continue to grow larger as you moved away from the projector. :? I assumed it would be more desirable to expand the beam (using a pair of lenses; a collimator if you will) to the given size that your calculations suggest would be eye-safe. That way the beam would be the same diameter (more or less) everywhere in the display venue. Of course, you'd still need to check it in the field to make sure your calculations are correct, but I don't see why you would prefer to have a continuously diverging beam vs one that had been expanded and re-collimated.
    (although it could be done before the scanners too)
    Assuming that your scanners had large enough mirrors to handle the resulting large beam, yes. Though large mirrors = slower scanning speeds, which I would think you'd be trying to avoid.
    When the divergence and power level are set correctly, it makes it a pleasant experience -- very fun actually... And of course, no after-image.
    I understand. My question is a bit more specific. I'm wondering how large the beam actually is (diameter - in inches, say) for an observer somewhere in the audience.

    I've never seen audience scanning done here in the US. I did attend a Rush concert back in 1983 in Germany where they MAY have done it, but I was only 16 at the time, and to tell you the truth I was so damn drunk I don't remember a whole lot of that concert! (Who says foreign exchange students don't get in trouble? :twisted: ) However, I did see a traveling indoor show here in Charleston about 10 years ago that featured some very large beams that were projected out over the audience. (No audience scanning though - the beams were *way* overhead.) They were obviously expanded though - they appeared to be two to three inches in diameter! (Not so with the beams that were projected at the screen backstage, however.)

    I got a chance (very briefly) to speak to the laserist for that show, and he confirmed that they only had a single white light laser for the whole show. They switched the output between two scan heads - one pointed out towards the audience and one aimed at a screen backstage for graphics. The beams from the graphics projector were quite small, but the beams exiting the beamshow projector were huge! Still, they did not diverge noticeably as they passed overhead. (Some were reflected off two or more strategically-placed bounce mirrors, so that the beams traversed the length of the auditorium several times, and yet they clearly weren't diverging.)

    I didn't get a chance to ask all the questions I had, but I assumed he was expanding the beam for the beamshow projector to make the effects look more impressive. As to whether it was done before or after the scanners, I couldn't begin to guess. I also didn't get a chance to ask him how much optical power he was running, nor could I get a look at the laser or the scan heads. :cry:
    to be safe you can either use a 5mW un-diverged laser beam, or perhaps beam powers up to 500mW or more if proper divergence is used. The exact spot size in the audience depends on a few factors, including the beam power and even the beam profile (Gaussian, top-hat, etc.).
    I'm not trying to reverse-engineer your work, and I promise I won't use your answer as the basis for any audience scanning of my own (I don't do public shows anyway, much less audience scanning shows!), but can you tell me how big (roughly) a 500 mw beam would have to be in order to be eye-safe? I'm thinking it's got to be somewhere around two inches or so. (Actually, assuming the human pupil is 7mm, then the math works out to a beam diameter of around 35 mm if you consider a 7mm wide, 5mw beam to be eye safe. But that doesn't take into account the beam profile, etc...) I'm just trying to get a good visual picture of what the beams from your projector would look like as they move around.
    As part of the variance requirement, we have a test setup that is used each night to verify proper performance before each show. (Technically, you are supposed to do some degree of testing before each show anyway, with any laser projector, regardless of the use.)
    I agree that this is prudent and makes good sense. The last thing you'd want to do is risk a lawsuit. (Which, saddly, is all to great a risk already in this country of ours...)

    Adam

  4. #64
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    Hi Adam,

    Sorry again for the delay in my reply but I was attending the Pangolin User Meeting in Amsterdam. It was a great meeting, but I am glad to be back home for a while. In around a week, I do travel again... This time to China...

    Anyway, regarding the spot size that we typically use, I tend to want to relate sizes and measurements to "human-relatable" things. For example, when doing Stereoscopic 3D work, I used to walk up to the projection screen with a 3.5 inch floppy disk to set "a point at infinity". It just so happens that a 3.5 inch floppy disk is just about the perfect distance edge to edge to represent the distance between your two eyes. Plus, back in those days, we always had a 3.5 inch floppy hanging around.

    In the case of beam diameter, as I said, you can work the numbers given John O'Hagan's thesis and my article, but I would say that the smallest spot size I would be comfortable with is around the size of a golf ball. If powers are higher and the audience is bigger, it might get up to the size of a baseball. We have never tried it before, but I think for a large stadium show, the beam might get up to the size of a basketball, but power would also be scaled accordingly. (Again, using common "balls" as a term that everyone can understand and relate to.)

    When using a small beam, such as what comes directly out of a laser, the visuals are as though the fog is being cut by a knife. It looks pretty cool in the fog, until it flashes past your eyes, where it would certainly be quite bright. When using larger beams, it looks a bit more cloudy, but still not bad. And like I said, you could have the "cuts like a knife" at 5mW, or "a bit cloudy" at perhaps 500mW or more. Higher power and "a bit cloudy" is definitely better

    Bill

  5. #65
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    Bill,

    Is the audience scanning technique you describe the same technology that Neo-laser is deploying as "Fat Beam Technology"?

    Thanks.

    Greg

  6. #66
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    Hi Greg,

    This is a very good question, and I can see how "Fat Beam Technology" can cause some confusion. Our technique has nothing to do with "Fat Beam Technology" or FBT as it is otherwise known.

    Fat Beam Technology is a way of using a 10mW laser, with a 10mm beam diameter, and still try to fall under a classification whereas US users would not need a variance.

    As many of you know, you do not need a variance to operate a laser as long as it is 5mW or less. 5mW lasers are considered "Class 3A". Roughly speaking, with a 5mW laser, your retina can dissipate the focused energy fast enough to protect your vision, especially given the natural aversion response (person turning away or blinking to avoid the light). The idea is that no more than 5mW of laser light would enter the pupil of the eye. (Actually, that's not the idea, but many people misinterpret this to be the case as to why 5mW lasers are allowed to be used without a variance, but that's a different, and far more complicated story...)

    What Fat Beam Technology does, is use a 10mW laser but with a 10mm beam diameter. For classification purposes, the eye is assumed to have a dilated pupil diameter of 7mm. Since the beam is 10mm, you can't get the whole beam into the pupil and thus, onto the retina.

    At first blush, it would seem that 7mm pupil still allows 70% of the original 10mm beam to enter the eye, but this is not really true for the purposes of laser safety calculations, which are most often concerned with "irradiance" -- or, power per unit area. The 7mm pupil allows less than 4mW of the 10mW beam power to enter the eye. At the factory, NEO has a test setup to confirm that the resulting beam is less than 5mW and thus is still "safe". In fact, it can be argued that the FBT lasers are actually safer than 5mW lasers, even though the beam has twice the power.

    The FBT laser is classified as "Class 3R", which basically means that it is as safe as "Class 3A" under certain viewing conditions, and given a certain range of wavelengths. Not too many people in the US know about Class 3R, because it is not part of the US Standard. Class 3R is an international classification, but one of the things that US "Laser Notice 50" did, was allow the use of international standards to be used for US report submissions and compliance.

    HOWEVER!!! One thing to keep in mind is that even though this is a Class 3A laser product (or actually Class 3R), you are still not allowed to point it into the audience in the United States. Class 3A products are covered under what's known as the "2.5 Meter Rule", which means that they should not be installed any closer than 2.5 meters away from where people can touch. If you read the manual for these FBT lasers (and hopefully all Class 3A lasers), you will see that the manual says you can't point it downward into the audience. Of course, I have been to many clubs which don't read the manual, and franky, I think many people who sell these lasers are hoping that the user does not read the manual...

    Our scheme technically results in Class 1 exposure. Only a Class 1 laser is allowed to be directly viewed.

    Bill

  7. #67
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    WOW, Very Informative for sure!! Very Interesting
    CREATIVITY AT THE SPEED OF LIGHT!
    www.laser-ad.com

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