Safe bright green fatbeam w/TTL recommendation for writing on buildings

[maxcady]

Good, that's a start. We can wait for someone in that area to PM you. If they do, you should take them up on it, really...you'll learn a lot.

Of course I would, that would be awesome to know someone nearby.

You need a power meter. No discussion. No argument. This is the single most important piece of equipment you will use and EVERYTHING else follows from a knowledge of the actual power you are producing. You can calculate divergence with a plastic ruler and paper and pencil. I can ( anyone here can) tell you how to use these to generate energy density/divergence, but you have to have the actual power of your lasers before any of this has meaning. Don't rely on what SOMEONE, some guy, the manufacturer, a partner, a self proclaimed genius said your laser generates...measure it.

What should I buy? also, is there something i can do today without any special tools to get you more information about the green laser i have? like the diameter?

What Steve is recommending with the mask is a fail safe. I have been doing this for some time and just about anything that can go wrong will, really it will. The mirrors for almost all the scanners on the market are GLUED in place and guess what, the glue fails. I had a pair of well regarded commercial scanners on a 20W projector system and a scanner threw one of the mirrors into the safety shutter preventing the aperture from closing, so this is a bad event making itself worse. The mask prevented any of the laser light from going where it could be harmful. I love that mask!

gotcha, my laser is from the side, so if the front end where the beam finally comes out somehow got messed up or a mirror flew off, the laser would not exit the enclosure, it would hit the wall on the other side.

I will admit to ignorance as to the term "fat-beam". I don't think you should depend on it. Measure the power, measure the dimensions of the beam and make a decision.

my engineer told me the lens spreads the beam out to be a larger diameter enough to be safe for talent, whatever that means now.. i will have to find out the specs of my beam myself, i'll need some help and i really appreciate it.

The emails from your engineer are not necessarily right or wrong, but they are of little value here. It is time for you to understand what you are doing and depend less on marketing specs or an engineer who is no longer around.

Yup, thats why I'm glad to have found this forum, and glad that people are helpful (some forums aren't!).

[maxcady]

you're reducing the apparent brightness by changing the duty cycle of the pulse train. it's still TTL.

I don't understand how this can't have an effect on safety like someone else posted above. The thing I'm projecting looks like its falling snowflakes that eventually pile up to create a word, then the word splits into dust again and the thing loops. When its falling snowflakes its hard to get the thing to even hit you in the eye, and if you do, it just flickers past your eye for a split second and then its gone, usually its not at full brightness cuz i'm not using a pulse but a shaped sine or stepped voltage to control the brightness. Doesn't all this help make it safer, compared to the word being full brightness and never blinking?

[mixedgas]

Put the beam on a white paper six foot from the output. Carefully draw a circle around the beam, watching out for reflections from the metal or shiny parts of the pencil. Measure the spot on the paper. DO the same at 12 feet. Report back to us to the nearest 1/16th or preferably in millimeters.

[maxcady]

I was going to wait till I had the diameter numbers, but I'm very much in agreement with Mr. Stewart. I think your "Engineer" needs to show you (and Us) some math and measurements. I think until some one shows you an approved CDRH model report, you are exposing yourself, your clients, and the "talent" to massive liability, and the possibility of an accident. Its not just the possibility of a retinal burn or temporary damage to the retina, but the problem of flash-blinding some one on a elevated stage, resulting in "secondary" hazards, such as falling or tripping. You should discontinue use of these devices.


Steve

I found an email from my "Engineer," he said the beam in the green fatbeam is about 10mm in diameter. That's all the info i could find in my email, i can measure the diameter myself if someone tells me how to do it..

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Put the beam on a white paper six foot from the output. Carefully draw a circle around the beam, watching out for reflections from the metal or shiny parts of the pencil. Measure the spot on the paper. DO the same at 12 feet. Report back to us to the nearest 1/16th or preferably in millimeters.

doing it now. (fifteen characters)

[maxcady]

at 6 feet it was about 0.7 inches, or 17.7mm

at 12 feet it was about 1 inch, or 25.4mm

[planters]

This is a start. If your beam is 10mm in diameter as it exits the laser and increases 7.7mm at 6 feet ( 1829mm) and 7.7mm more at 12 feet (3658mm) then the divergence is 7.7mm/1829mm or 4.2 milliradian. Once you know how much power your laser is generating and you know how far away the CLOSEST eyeball is from the laser you can determine the power/area and there are safe limits that can be referenced.

my engineer told me the lens spreads the beam out to be a larger diameter enough to be safe for talent, whatever that means now.

This all depends on the power. Tonight I have been playing with a dye laser that puts out over 100Wsec into a big, fat low quality "fatbeam". It lights up a field over 100 feet across, but within the building is still so intense you see after images from the reflections. Afterimages are generally a bad thing; yellow zone on the proverbial danger meter. I would not want to be "talent" in line with this thing. Power maters!

gotcha, my laser is from the side, so if the front end where the beam finally comes out somehow got messed up or a mirror flew off, the laser would not exit the enclosure, it would hit the wall on the other side.

If your mirrors stayed on but your scanner motors were given a bad command or rotated to an undesirable angle will the beam always fail to get to a "victim"?

What should I buy? also, is there something i can do today without any special tools to get you more information about the green laser i have? like the diameter?

There is no way around it, you need a power meter. There are some used ones on eBay, there are some threads on this forum that step you through building your own. Maybe someone who sees this thread has a line on a reasonable choice. I need the ones I have.

[JStewart]

As others have said, there is no cheap or quick way around the fact that if you want, or might, be shining laser beams into the faces of people, you will need to measure the beams. You can get a basic calibrated power meter such as the LaserCheck or Thorlabs S120 USB devices for relatively low cost. And if you know the limitations, pitfalls, and how to use a power meter to establish the beam irradiance, then you can make a more informed and defendable judgment about if its safe or not to scan people with. There are several threads on this site covering this topic in more detail.

Listening to hearsay about what some people *think* is safe, is not the way to go; especially when it sounds like the hearsay is wrong.

TTL does not make viewing the laser safer. It can take fractions of second to exceed the MPE. Modulating the light on and off has very little effect, unless of course it is off all the time!

Even making calculations should not be relied upon as the only means of making the safety case. There are a lot of assumptions being made in the calculations that have been discussed so far, and the real life propagation of the beam can vary significantly from what is being assumed. So again always take measurements. Knowing the actual beam irradiance is far more important than thinking you have measured the diameter of the beam, which is meaningless past making an initial estimation.

While on the subject of measuring beam diameters, for the benefit of anyone coming across this thread, I can't really recommend shining a laser at a surface and drawing around it to determine the diameter. This is wrong and hazardous.

1. if is someone this with a higher power laser, there is a strong chance they could cause harm to themselves by viewing a strong diffuse reflection.
2. it's just not the right way to determine the beam diameter of a laser beam. At best it is determining the glow the beam makes. There are defined ways involving measuring apparatus to correctly determine beam diameter, and even then, there are several different ways of expressing this.
3. as previously mentioned, knowing the beam diameter and divergence is only good for estimating the irradiance, which in real life could be quite different to simplifying assumptions made.

So it comes back to needing to make the measurement to determine the irradiance.

Hope this helps.

James

[mixedgas]

James IS correct.

To properly measure the beam diameter would require laboratory equipment. However I cannot mail Maxcady my beam profiler, which requires considerable training to use. Hence a emergency measurement method to quickly prove a point.
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The NOHD numbers in this post are just a quick approximation. They cannot be assumed to have ANY validity and should not be depended on for actual use. As they are at best guesses.
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However they serve to illustrate that the equipment in question is certainly hazardous In a public situation.
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Your actual beam divergence is probably far less then 4.5 milliradian. However at 50 mW and 4.5 mR, the Nominal Ocular Hazard Distance would be at least 40 feet for the green as a estimate.
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A back of the envelope calculation shows that if the Blue laser had similar divergence, and was actually 350 milliwatts, the NOHD would be in excess of 100 feet.
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In reality, no one should set up an audience scanning laser at just beyond the NOHD distance and assume it was eye safe, for there is little margin for error. Besides that, you run a strong risk of secondary effects such as flash-blinding those being scanned.
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Again, this post is to try to help MaxCady understand that his "engineer" who designed this equipment has most likely not done his due diligence in ensuring audience safety.
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Max, the quickest place that I think you could get a friendly power measurement would be at X-Laser in Laurel, Md. Dan and his staff at X-Laser would be quite interested to see what you have, and could offer some good initial advice. Dan also sells legal audience scanning systems, and can help you get a variance for a reasonable fee.
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Max, You MUST stop using this gear in public until you have further training, a valid safety case, test equipment, and the proper permits. It is without a doubt very hazardous for the public.
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Steve

[planters]

Max, You MUST stop using this gear in public until you have further training, a valid safety case, test equipment, and the proper permits. It is without a doubt very hazardous for the public.

I agree with this as well. An issue to keep in mind about your lasers and this applies to all lasers is that the beams are usually not homogeneous. They will have "hot spots" where the intensity is greater than the average. This is why even an accurate power reading can underestimate the safe distance until even these hot spots have diverged sufficiently.

Also, if you have used lasers for years, I am certain you have flashed one across your eyes. There is no way you could not have and the question arises... "so, my vision is OK,right"? Are you sure? Even with lasers in the range commonly available on E Bay, say 10-500mW, these pure light sources are concentrated to a minuscule point on the retina by the lens of the eye. A tiny, welded and permanently blind spot is created and the person with this lesion often compensates during image processing and ignores it, but it's there. Lasers are not just bright, they're different.

Again, I agree with Steve, call X-Laser and see what they can do for you.

JStewart,

While on the subject of measuring beam diameters, for the benefit of anyone coming across this thread, I can't really recommend shining a laser at a surface and drawing around it to determine the diameter. This is wrong and hazardous.

I agree with you here as well. I would like to describe how I evaluate many of my CW beams in the lab. I have dozens of safety goggles. Some are really good and some not so. I will set up a target using a black oxide coated steel plate. I think this material is flatter than anodized aluminum. In any case, I can often find eye ware that attenuates, but still allows enough light through so that the spot can be measured with a machinist's rule. Occasionally, I will pass the beam through a highly (but not perfectly) reflective mirror that sends 99% of the light off to a dump and this allows the dim transmited beam to be evaluated.
Also, placing a convergent lens in the beam allows me to project it at huge magnification onto a surface where its variations can be easily seen.

This is not to suggest that a formal measurement is not the best and sometimes required

[Draco]

The mirror method is currently my way of measuring the power of a laser, my power meter tops out at about 40mw or about that so i reflect the the beam onto a safe target and measure what passes though the mirror, i have a laser i set up on a higher power meter and use that as a reference, it's not as accurate as i would like but does give me an idea of the actual power. I have found that with the Chinese made lasers will often fluctuate in power output over time and in different ambient temperatures. the differences can be quite wide.