Session 07 – Laser Beam Safety

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The Concise RDWorks Learning Lab with Russ Sadler. Session 7: Laser Beam Safety.

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Well, it’s six years since I bought my first laser machine,

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and we’re at a point now in this short series where we’re going to talk about laser safety.

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Now, remember, I said I’ve been using these machines for six years. Am I dead?

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Am I blind? I know I’m ugly and gray, and fact, and old, but that’s just something that God has given me.

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It’s not self-inflicted. I want to talk today about the safety aspects of this laser machine and particularly the laser beam itself.

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Now, I have another series running which documents my six years of learning with this machine.

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It’s a bit like watching grass grow, so it’s not for the faint hearted.

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And it’s called RDWorks Learning Lab. Just recently I did a video about laser safety.

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And so I’m not going to bother to remake that video.

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So what we’re going to do now is let my cardboard clone take you through the next part of this safety session.

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Well, welcome to this unplanned session of RDWorks Learning Lab, now two things.

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First of all, unplanned. Every session I do is unplanned.

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But what I really mean is this was not intended to be part of the sequence of my thought processes.

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As far as RDWorks Learning Lab is concerned, we’re in the middle of doing something with lenses at the moment.

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And hey, this is just a major interruption, but. Oh, what do you mean?

Transcript for Laser Beam Safety (Cont…)

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I’ve got a screw loose. Yeah, I know that. that’s what happens when you buy cheap Pound Shop glasses. But,

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I am wearing these for very good reason. And will go on to explain that in a minute.

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Today, this unplanned session is all about laser safety.

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Now I know you see me using this machine all the time, you think, without glasses on.

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But of course, out of camera. I’ve always got my my reading glasses on.

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Yeah, there’s another very expensive pair of glasses there as well. Newcomers to this hobby are continuously asking me when they see my videos.

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Why are you working the machine with the lid open? Surely, that’s dangerous?

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What sort of safety glasses can you recommend that I buy?

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I’ve seen you can get safety glasses from sort of something like about twenty dollars up to maybe two hundred dollars, which are the best ones to buy.

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Well, I hope by the end of this session you won’t need to ask me those questions.

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I’m not just going to give you a quick, glib answer which says, yes, this machine is safe or this machine is not safe.

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Therefore, you know, you need all your earmuffs and your eyeglasses and all the rest of the gear on.

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You need to understand how dangerous this machine is, so that you can make your own assessment.

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Fear of the unknown gives the opportunity for those people that want to sell you 200 pound glasses a great opportunity.

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They’re preying on your fear. Now you can make up your own mind about the risks after you watch this video.

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So let’s dive in and we’ll start off at the beginning.

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Now, I’m going to go into some of the physics behind the laser technology.

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Don’t get too concerned because this is not anything complicated that requires a master’s degree or anything like that.

Transcript for Laser Beam Safety (Cont…)

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But I’m only going to give you a few basic facts enough for you to build a picture and assess what the safety issues are.

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OK, here we are looking at the laser tube and it’s just about to switch on.

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And there we go. And if you listen carefully, you’ll hear something going on at the front of the machine, which I’ll explain in a minute.

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But what you see there in the laser tube is a pink beam.

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Now that pink beam is not and I repeat not the laser, that is just basically lightning in a bottle. That’s ionized nitrogen,

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which is part of the chemistry that creates a laser beam.

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Now what’s coming out of the end just here where my finger is.

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This brass thing, is the laser beam. It’s invisible.

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If that pink beam was the laser beam, then you’d expect to see a pink beam around the front of the machine.

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But you can’t, because the laser beam is invisible.

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OK, so this beam bounces off mirrors.

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Here’s one of them here.

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So over here, we’ve got a second mirror where the beam bounces off of and then there’s another mirror and that directs the beam down. In here,

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you’ve got a lens made of this strange yellow material.

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And that lens does exactly the same as a magnifying glass.

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It amplifies the laser beam into something that is very, very, very dangerous as opposed to just dangerous.

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Laser beams have got different classifications.

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The silly thing is this machine has got all these labels on it and it says it’s a Class 1 laser product.

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Ha ha. No, it’s not. It’s only a class one laser product.

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If you keep the lid closed. When you look at this specification. Class 1 says

Transcript for Laser Beam Safety (Cont…)

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It’s safe for viewing directly with the naked eye. Well, provided we got the lid down, that is true.

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In reality, it’s a Class 4 product and a Class 4 says;

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This is the highest class of laser radiation. Radiation in this class is very dangerous.

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And viewing of the diffused reflection may be dangerous.

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It says may. Class 4 laser beams are capable of setting fire to materials onto which they are projected.

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There we go, now the laser beam is running. Can you see a laser beam across there?

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You can’t because I told you it’s invisible. But trust me, it is there.

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And what did it do? It set fire to things. So this is a Class 4 laser, and on that basis, everybody’s going to try and sell you safety equipment.

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I will explain what’s going on here in a little while. But at the moment, you can see I’m trying to boil myself up some water for a new cup of coffee.

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OK, so you’re watching this because you’re a newcomer to the hobby.

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Now, old timers will know and they will recognize my colored pins and this piece of paper.

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I’m pretty good at dodgy diagrams. And as I’ve commented many times, I always remember my art teacher at school telling me, take up plumbing boy.

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There are a few pieces of basic science associated with laser cutting, laser engraving, the laser beam.

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The first thing is, it’s a beam of light. It’s not a beam of heat, which many people seem to be confused by.

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Now, you’ll recognize this as a wave.

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Now, if this was sound, you could hear it and it would go on your ear drums and it would make them do this vibrate.

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That would be a frequency of round about anything from five to maybe 20000 cycles

Transcript for Laser Beam Safety (Cont…)

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a second. Light is exactly like this, but it’s in a different league. Instead of 20000 cycles

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a second maximum, which is what you can hear when you’re young. We’re talking about a thousand billion cycles per second,

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a completely different league of frequency. Now whether they’re sound vibrations or light vibrations, at a completely different frequency makes no difference.

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Let me give you a silly example of what I’m going to start to talk about.

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If we have a table and we put a jelly or jello, depends on which part of the world you’re from, on the table.

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You know, the sort of thing you have at birthday parties and a cake. And then you grab hold of the table and you start shaking it.

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What happens? You shake it at a certain frequency and the jelly goes bonkers.

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What does the cake do? Nothing, the reason being the material structure itself is completely different.

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The jelly responds to your shaking and the cake doesn’t. Now,

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if you shake the table fast enough and hard enough, you will have an effect on the cake as well.

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But the cake responds at a different frequency. So there is a very good example of two different materials.

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Different materials react differently to frequencies.

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Now, everything in this world, my pens, the paper, the metal, everything that you can see around me,

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including your skin, is made up of molecules and atoms and all atoms and molecules are always doing this.

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They’re vibrating. They’re shaking.

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Now, it’s a physics principle that they don’t teach you about at school because it’s too complex for young kids to think about.

Transcript for Laser Beam Safety (Cont…)

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The vibration level of a molecule is its temperature, the more it vibrates, the hotter it is.

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And that’s what temperature is, the amount of vibration in a molecule or atom.

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Let’s turn this whole thing around again and come back to these frequencies and our jelly and our cake, which is material.

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And even they are shaking like this. But of course, light at several thousand billion cycles a second, which is totally unimaginable,

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just happens to be the frequency range at which molecules and atoms are shaking.

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So if we can excite the molecules and atoms with light frequency, we can make them shake faster.

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And if they shake faster, they get hotter.

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And if they keep heating up, they will get to a point where, as you saw with that paper, it heats up so much and bursts into flames.

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So that is the mechanism by which light waves convert into something else.

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There is no heat in the beam itself. You are using the light energy, the frequency of the light to stimulate the molecules to move faster.

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The faster they move, the hotter they get, the hotter they get,

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there is a point beyond which if you shake them too hard, they will literally just destroy themselves.

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How this laser machine works, is it takes this frequency and it amplifies it through this lens.

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It doesn’t change the frequency. What it does, it changes invisible but bright light into very, very, very bright light.

Transcript for Laser Beam Safety (Cont…)

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Just like when you focus the sun with a magnifying glass onto a piece of paper and it burns or scorches the paper.

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That’s exactly the same principle that we’re using here. OK, so here’s our laser beam and we’re now going to send that laser beam through a lens and

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that lens is going to focus the laser beam like this to something called a focal point.

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Now you’ve seen how dangerous that beam is before we even send it through this lens.

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But look what happens here? We’re compressing it down to an incredibly small point and it becomes very, very, very,

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very dangerous at this point because the intensity of the light is so high at that point, that

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it doesn’t just go up and shake the molecules a little bit. Because the intensity is so high,

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it shakes them incredibly fast and incredibly quickly. It can’t shake them any faster than it’s breakdown point, its destruction point.

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Once it gets to that temperature, it will burst into flames.

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The only thing about concentrating the light is it happens quicker.

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So that’s the whole point of the lens in this setup, is to make the intensity of the light so great that things happen very, very quickly.

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Obviously, light rays only travel in straight lines. It’s relatively not dangerous before it hits the lens.

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And after the focal point, it’s relatively not dangerous.

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Again, down here, relatively.

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I still wouldn’t want to put my hand in the way of either that beam there or this beam here.

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I’m going to give you a demonstration of what I mean about the intensity of the light having different effect.

Transcript for Laser Beam Safety (Cont…)

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The focal point here is about 20 millimeters away from the end of this nozzle.

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Now the beam is starting to fire down into that water and nothing is happening.

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Get the idea, as I move closer to the focal point.

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The energy concentration is so high, it immediately creates steam.

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I purposely used water here, because you think of water as being transparent in the same way that you think

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of glass as being transparent or my glasses as being transparent because you can see light through them.

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This is one of the strange properties of light. Not all laser beams are exactly the same.

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What I’m going to talk about in this session, this specifically applies to this CO2 laser light.

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Now, this has got a very special wavelength. Ten point six microns, that’s ten point six millionths of a meter.

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Now, just to put that into some sort of perspective. Oh, dear, I’ve just pulled two or three hairs out of my head.

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Those hairs are approximately 50 microns.

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So those hairs are five times thicker than the wavelength of this light.

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Those wavelengths are in a part of the electromagnetic spectrum, which your eyes are not sensitive to.

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Your eyes are not vibrating at that frequency. That’s, that’s the reason why they are invisible.

Transcript for Laser Beam Safety (Cont…)

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Remember, back to the jelly and the cake example. Every material has got its own vibration frequency.

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And this frequency here at ten point six microns wavelength is a very broad spectrum vibration.

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This light, it can only see three things.

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Let me just tell you what those three things are. One of them is metal.

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Any type of metal, raw, bare metal reflects, becomes a mirror.

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Look, even this mild steel here, which is mucky and badly scraped on the surface with scratches,

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this will still reflect something like about maybe 70 or 80 percent of the light,

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that’s fired at it. Put a piece of aluminum down and it will probably reflect 99 percent.

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So we use metals on this machine to act as mirrors, to send the light around the machine.

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Group Two, I’m going to use the word salt.

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No, it’s not salt in the condiment style of salt.

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This is a special group of materials, salt like materials, which are crystalline.

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Now, this might look like yellow glass to you, but it’s not.

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It’s a material called zinc selenide, and it is a salt like material.

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It’s harder than salt crystals. But believe me, if you drop this very far, it will shatter.

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So treat your lenses very carefully. And as you can see through it.

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Yeah. So the laser beam can see through it. That’s just one of these salts.

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There is another one in the group, which is called gallium arsenide.

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Can you see anything through it? No, you can’t. This frequency passes right through this unaffected.

Transcript for Laser Beam Safety (Cont…)

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This is transparent to this frequency of light, and that’s one of the weird properties of light. Here we’ve got our

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salt like materials, which is group two. And then we’ve got group three, the third thing in the ten point six micron Wavelength Universe.

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And there it is. So are your eyes made of this material?

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Are your eyes made of that material?

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Your eyes are in this group and that means that this frequency of light will shake your jelly, it will shake your cake.

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It will have an effect on everything else. And remember, as I shake things and make them shake faster, they get hotter.

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If these waves hit your eyeball, what they will do,

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they will vibrate the front face of your eyeball because that’s the first thing that they’re going to come into contact with.

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And you get this lovely smell of frying bacon. You won’t be able to see it, but you could smell it.

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OK, I’m being rather rude and crude there, but that’s a fact.

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If you put your eye and it’s an impossibility virtually to get your eye in the way of a laser beam,

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the laser beam, regard it like a bullet that somebody fired at you.

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If it misses you by half a millimeter, it’s not dangerous.

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It is only dangerous if it hits you. And that’s exactly the same as this laser beam.

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You can stand here and it’s not going to jump out at you.

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It’s not got any sideways ray that are flying out and are going to affect your eyes.

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When the laser beam comes out of the laser tube, it starts off at this diameter.

Transcript for Laser Beam Safety (Cont…)

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And technically and if you want to imagine it this way, that laser beam looks like this.

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It doesn’t spread out, it doesn’t send rays out that are going to bite you. No, it stays just like that, a continuous stick of light.

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It’s a special form of light which remains bound together.

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It doesn’t need an outer casing. In reality, it’s not quite as simple as that.

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But nearly, this beam will gradually grow like this.

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And the amount of growth is very small. For a CO2 laser tube, the growth is something like about three millirads.

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What the hell is a millirad? Well, very simply, what that means is three millimeters

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of beam growth per meter.

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So if that beam length is a meter long and it started off at seven millimeters, it will finish up at 10 millimeters.

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But that’s as much as that beam is going to distort. It’s certainly not going to jump at you and be dangerous.

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So the only danger that you’re going to get, is if you put your eye in front of the beam somehow,

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or you have to be stupid enough to put a piece of metal underneath the laser beam in some way,

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shape or form, accidentally or otherwise, so that the beam reflects off there like a pool ball coming off a cushion and flies out at you.

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So never put metal in front of the beam, especially down here.

Transcript for Laser Beam Safety (Cont…)

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OK, I know we’ve got a table. And trust me, if you fire that laser beam at the table and I put my hand up here,

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it could be dangerous depending on how much power I’m firing down at the table,

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because remember, 70 percent of that power is going to get reflected back up.

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OK, so it’s going to be slightly diffused and you may well find it hot on your hand.

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And I mean hot. All right, you’ll be able to feel it because it is infrared radiation and, you know what

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infrared radiation is. It’s that stuff that comes from the sun, from radiators, from fires.

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It’s things that you can feel it’s hot. It’s not hot at all.

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All it is is energy, which is heating up the molecules in your skin.

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There is no heat in that light, I keep reinforcing that, the light is busy affecting the molecules that it impacts and that’s why you feel heat.

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So I think that’s probably about as much science as we need to talk about.

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Now, let’s talk about those guys that want to sell you expensive safety glasses.

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What do they know?

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Well, they know that you’re frightened of a laser beam. As you rightly should be, because I’ve already shown you what it could do to your eyes.

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Yeah, it won’t set fire to your eyes, but it will certainly turn them into lovely fried bacon.

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I purposely raise this up so that you could see steam being produced.

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OK, now you therefore know that energy is passing through that mirror.

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There, going down through the lens and heating up the water. What happens if I put my eye in front of that?

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Yes, but look what’s happened. Now

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I’m going to completely destroy these glasses. I want you to watch the steam.

Transcript for Laser Beam Safety (Cont…)

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Steam, no steam, no steam. Now,

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I think you probably can imagine that if you happen to put your eye in front of the laser beam and you saw flames in front of your eyes,

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you would jump out the way pretty damn quickly. OK, now, if we take a look at this side of the glasses, they’re completely undamaged.

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This side, yeah, we’ve done a lot of damage to that material, because that is not metal,

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that is not one of these special salts, that is a polycarbonate material which they use to make these lenses with.

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And that has absorbed all the light energy that’s been fired at it. It’s vibrated the molecules on the surface of this material and made it disappear.

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It’s burnt it.

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Now, exactly the same thing will happen to glass because, look, this is transparent and therefore you would think that light would pass through it.

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There’s a demonstration that the light does not pass through it.

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OK, it’s absolutely undamaged on this side.

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This is unlike the visible light where certain types of laser will pass right

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through this material and right through to the back of your eyeball and the retina,

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and it will damage the back of your eyeball and make you blind.

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This is a different sort of light. I’m not saying it’s any safer, but that’s why I’m saying you need to understand the differences between the

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way in which light, different frequencies of light affect different materials.

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This is not just I’ll wear a pair of glasses and you’re safe.

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So I always have to wear some sort of reading glasses. So I’ve always got these cheap glasses on.

Transcript for Laser Beam Safety (Cont…)

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You don’t need anything expensive, right, to protect your eyes, just industrial safety glasses.

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These are polycarbonate. I’m not going to destroy these because I use these for people that come in and visit me.

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And are a little bit frightened of the laser machine, especially when I’ve got the lid open.

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I haven’t got time to tell them that it’s not particularly dangerous. For something like about two dollars,

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you can go on to eBay, and you can get some rather nice looking Rayburn style ski glasses almost, safety glasses.

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So you don’t have to look like an idiot. Spend two dollars. Don’t spend the twenty or the two hundred dollars on these special safety glasses.

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There is no danger other than those I’ve explained to you here.

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That’s why I can operate this with my camera. And the lens is not at risk.

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I can operate this with the lid open and my eyes are not risk either with or without glasses.

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But I always wear glasses anyway, so I know that my eyes are protected.

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But you protect your eyes, but it doesn’t stop you burning your skin around the outside of your eyes if you happen to get a flash.

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Remember, everything is a group three material, including your skin and your clothes.

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So nothing is safe, but everything effectively is safe if you don’t put anything in the way of the laser beam.

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Remember the bullet passing by you, missing you by a millimeter. That’s the level of danger

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That you’re in. OK now, when you come to cut organic materials.

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This is a piece of MDF and here we’ve got a piece of plywood or wood, leather card, something like that.

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When you’re in engraving or cutting, what I want you to do is to watch this surface here and you will see a bright white light.

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Now, that bright white light is very, very intense.

Transcript for Laser Beam Safety (Cont…)

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That’s effectively a carbon arc. It’s just like looking at an arc welder or looking at the sun.

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It’s not incredibly intense because it’s so small.

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But what it is doing, it’s sending out UVB radiation. Within that very bright white light,

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there are nasty spikes of dangerous light. Now, you know what UVB is?

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It’s the stuff that gives you sunburn. It’s the stuff that can affect the cells in your body. That is a far more insidious

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form of damage that you can do to your eyes than the laser beam itself.

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It looks harmless, but that is what you need to be really careful about.

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You could look at it for a few seconds. If you close your eyes and you see white spots before your eyes, then you know,

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you’ve overstressed the cells in the retina at the back of your eye, just like looking at the sun. For a few moments,

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it’s not a problem, but don’t spend time looking at the laser beam as it works.

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It’s a fascinating thing to do and it’s almost hypnotic. Ten, fifteen seconds at a time,

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not a problem. Look away. Give yourself, give your eyes a few moments to relax.

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Go back and look again. OK, now I’ve closed the lid of my machine. Now this machine is very well made and it has glass, real glass for windows.

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You will find the screen, or windows on your laser machine could be made of two other types of materials.

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So this is glass. You can look at UVB light through this glass because UVB light does not pass through glass.

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You can sit behind a sheet of glass with bright sunlight outside.

Transcript for Laser Beam Safety (Cont…)

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You will turn into a lobster, but you will not get sunburnt, you will feel the heat, but the UVB light is filtered by glass.

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This is the strange properties of different light frequencies.

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UVB is a shorter wavelength light and it does not pass through glass.

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However, it does pass through acrylic.

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So if you’ve got an acrylic cover on your machine and that’s what most covers will be,

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the UVB light will pass through and your eyes are still at risk.

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Even when you close the lid, put a pair of sunglasses on and it’s just like looking at the sun with sunglasses.

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It will filter those UVB rays out. Don’t get overstressed about it because it’s not highly dangerous.

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It’s just something you shouldn’t spend time looking at. If you’ve got glass, the rays get filtered out.

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But the one thing that isn’t filtered out is the intensity of the light.

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OK, so there are two dangers with that bright light. One is its intensity.

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And because it’s a fairly small white light, but it’s a very intense beam of light, it will have a long term effect on your eyes.

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If you spend a lot of time studying it, staring at it and looking at it 20, 30 seconds at a time, is not going to damage your eyes.

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The UVB is not going to damage your eyes, only if you keep doing that over the long term.

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So the other thing is polycarbonate like my glasses here, they do also filter out the UVB rays.

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So when I wear my glasses, I’m immediately protected against the direct effects of being hit by that bullet.

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And I’m also being protected against the UVB light rays that are generated when I cut or engrave organic materials.

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Yes, this is a dangerous piece of equipment and you’ve seen how dangerous it can be.

Transcript for Laser Beam Safety (Cont…)

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OK, so now you’ve got all the science facts which allows you to, first of all, understand how your machine works.

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How it may or may not fry your eyeballs and C. why you should or shouldn’t spend a huge amount of money on safety glasses.

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Please do not fear this technology. It’s fantastic. Just understand it.

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Thanks for your time and your patience. And all I can say to you is enjoy the hobby and cut and engrave safely. Catch up with you in another session.

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Bye for now.

Transcript for Laser Beam Safety