Is this laser really visable?

[tranceport]

http://www.thinkgeek.com/gadgets/lights/657a/



Can this $150 laser really make a beam that is visable at night. They say the beam not just the dot is visable. So could I walk outside at night and point this thing at the sky and get a visable 10,000 ft green beam?


Why would the beam be visable? I had previous thought there had to be something for the light to reflect off of to see the beam. Does "air" work in this situation for this green beam?

10,000 ft of green beam.... You could really scare some airplanes with that


Sorry to post this in HT if it should have went else where...I just wanted some knowledgeable folks for this one.

 

[Mday]

You can only see a laser if:
1 - it is being pointed at your eye, allow for some dispersion
2 - if it is being reflected off of some object

The beam itself can be seen if it reflects off suspensions in the air, such as dust, pollen, etc. Similarly, a ball being thrown in a direction not towards you, cannot hit you unless it bounces off another object.

 

[tranceport]

So they are lying about seeing the green beam?

 

[TuxDave]

Originally posted by: tranceport
So they are lying about seeing the green beam?

Unless it's at some frequency that is readily absorbed and re-emitted by our atmosphere. Then I supposed you would be able to see the beam.

 

[cirthix]

you would see the beam as it is reflected off the billions upon billions of particles floating aroudn in the air, like particulates, water vapor, dust, dirt, little bugs, germs, all sorts of stuff. on a dark night, you can see them with any bright light, a laser would be no different.

 

[Yomicron]

There needs to be something in the air for the light to reflect off of inorder for you to see it. However, your eyes are far more sensitive to green light than red, so it should be easier to see a green beam.

 

[Fencer128]

Hi,

Everyone's right. You'll only see the reflection of the beam. However at ~530nm there's usually plenty of dust in the atmosphere to scatter it. I used a 5W green beam @532nm. You could see it in the pitch dark no problem. I wouldn't think a beam on the order of mW (I'm assuming as I haven't read about it) would be very visable in all but the darkest of conditions.
Cheers,

Andy

EDIT: Just read the link - At 5mW IMHO you're not going to see much of a beam. A bright spot, but not much of a beam at all. I'm not sure about it's "pulsed" operation either. 5mW average power in - say - a Q or gain-switched setup would be very dangerous for the naked eye. I'm guessing it's actually CW.

 

[k1pp3r]

i have seen lasers in fog, that is about the only way that would be safe to your eye

 

[Fencer128]

Originally posted by: k1pp3r
i have seen lasers in fog, that is about the only way that would be safe to your eye

Just to clarify - viewing the beam in fog would be a safe way to do so. Looking directly into the laser source is NEVER a good idea.

Cheers,

Andy

 

[k1pp3r]

Originally posted by: Fencer128

Originally posted by: k1pp3r
i have seen lasers in fog, that is about the only way that would be safe to your eye

Just to clarify - viewing the beam in fog would be a safe way to do so. Looking directly into the laser source is NEVER a good idea.

Cheers,

Andy

yeah, i could have worded that better huh

 

[Rebel Nugget]

Actually, my best friend's mom is an eye surgeon, so she has a pretty good handle on this. She told me that there was a study done at the University of Madison Wisconsin where they determined that the eye can repair itself faster then a normal laser pointer can deal damage. So typical classroom laser pointers are not hazardous.

However, I don't know how that holds up against super-ultra green beams.

Nugget

Edit: I suck at typing

 

[DrPizza]

Originally posted by: Rebel Nugget
Actually, my best friend's mom is an eye surgeon, so she has a pretty good handle on this. She told me that there was a study done at the University of Madison Wisconsin where they determined that the eye can repair itself faster then a normal laser pointer can deal damage. So typical classroom laser pointers are not hazardous.

However, I don't know how that holds up against super-ultra green beams.

Nugget

Edit: I suck at typing

I don't know about the rate the eye repairs itself, but it's correct to say that typical laser pointers do not damage the eye for a typical exposure... ie if someone shines one in your eye for a second or two, it's not going to do any damage.

 

[TuxDave]

Originally posted by: DrPizza

Originally posted by: Rebel Nugget
Actually, my best friend's mom is an eye surgeon, so she has a pretty good handle on this. She told me that there was a study done at the University of Madison Wisconsin where they determined that the eye can repair itself faster then a normal laser pointer can deal damage. So typical classroom laser pointers are not hazardous.

However, I don't know how that holds up against super-ultra green beams.

Nugget

Edit: I suck at typing

I don't know about the rate the eye repairs itself, but it's correct to say that typical laser pointers do not damage the eye for a typical exposure... ie if someone shines one in your eye for a second or two, it's not going to do any damage.

That's reassuring to know. I was doing a demonstration for middle schoolers regarding fiber optics and I had each of them hold a mirror to try to bounce the laser light down a curved path. I couldn't figure out where the laser was going since it obviously wasn't going down the path. Only later did I find out that one kid accidently tilted his mirror in a way such that the laser was flashing all over another kid's face and eyes.

 

[Fencer128]

Originally posted by: TuxDave

Originally posted by: DrPizza

Originally posted by: Rebel Nugget
Actually, my best friend's mom is an eye surgeon, so she has a pretty good handle on this. She told me that there was a study done at the University of Madison Wisconsin where they determined that the eye can repair itself faster then a normal laser pointer can deal damage. So typical classroom laser pointers are not hazardous.

However, I don't know how that holds up against super-ultra green beams.

Nugget

Edit: I suck at typing

I don't know about the rate the eye repairs itself, but it's correct to say that typical laser pointers do not damage the eye for a typical exposure... ie if someone shines one in your eye for a second or two, it's not going to do any damage.

That's reassuring to know. I was doing a demonstration for middle schoolers regarding fiber optics and I had each of them hold a mirror to try to bounce the laser light down a curved path. I couldn't figure out where the laser was going since it obviously wasn't going down the path. Only later did I find out that one kid accidently tilted his mirror in a way such that the laser was flashing all over another kid's face and eyes.

In the UK laser pointers are limited to 3mW, in the US 5mW. The reason for the limitation is the perceived exposure time required (blink of an eye) to cause damage at a particular power/wavelength. I'm inclined to go with the lower number of 3mW - hence why I strongly suggest you never look directly into the pointer - or aim it at anyone's face.

As for the eye "repairing" itself, I've never heard as such. All laser burn damage I've looked at has been irreversable. I would suggest your only defense is your blink reflex and it should not be relied on. For instance if you shine the laser in a dark room and your eyes are dark adjusted then your iris will be dilated. In this instance there is a higher probability of damage to the retina as opposed to be in a brighter background environment.

With regard to the fibre optic experiment outlined above - if that really was a laser pointer (5mW say) and not a bright LED then I'm astounded it could be attempted in a school environment. I not sure what counts as middle school, but I wouldn't use hand held mirrors - especially held by kids! - to direct any laser beam around my lab. If it's ending up pointing at their faces then I think you've had a lucky escape and should not repeat this.

Please be safe.

Cheers,

Andy

 

[TuxDave]

Originally posted by: Fencer128

In the UK laser pointers are limited to 3mW, in the US 5mW. The reason for the limitation is the perceived exposure time required (blink of an eye) to cause damage at a particular power/wavelength. I'm inclined to go with the lower number of 3mW - hence why I strongly suggest you never look directly into the pointer - or aim it at anyone's face.

As for the eye "repairing" itself, I've never heard as such. All laser burn damage I've looked at has been irreversable. I would suggest your only defense is your blink reflex and it should not be relied on. For instance if you shine the laser in a dark room and your eyes are dark adjusted then your iris will be dilated. In this instance there is a higher probability of damage to the retina as opposed to be in a brighter background environment.

With regard to the fibre optic experiment outlined above - if that really was a laser pointer (5mW say) and not a bright LED then I'm astounded it could be attempted in a school environment. I not sure what counts as middle school, but I wouldn't use hand held mirrors - especially held by kids! - to direct any laser beam around my lab. If it's ending up pointing at their faces then I think you've had a lucky escape and should not repeat this.

Please be safe.

Cheers,

Andy

It was 6 years ago and if I recall correctly, the path that the laser was supposed to traverse a short turn totalling a 1 foot distance and terminating against a cardboard sheet. I designed the experiment with a very small low power laser pointer and the kids weren't supposed to touch it at all. It was the teacher's 'innovating idea' to let the kids create the optic path by holding the mirror.

But wow... you guys didn't get to play with lasers in high school? We used them a whole bunch in my physics class when we were describing diffraction gratings and refraction. My high school had a pretty interactive science division. We even made smores using burners in our chemistry lab. Even though it sounds like we should've been some 2nd class science school, we were pretty top notch in the state (NJ) consistant scoring in the top five in state competitions.

Oh... for your reference.
High School = 14-17 years old
Middle School = 13-14 years old (in my district)

 

[Fencer128]

That's reassuring to know. I was doing a demonstration for middle schoolers regarding fiber optics and I had each of them hold a mirror to try to bounce the laser light down a curved path. I couldn't figure out where the laser was going since it obviously wasn't going down the path. Only later did I find out that one kid accidently tilted his mirror in a way such that the laser was flashing all over another kid's face and eyes.

Hi,

We used a wave machine (very wet) to demonstrate diffraction and a light bulb behind a slit to demonstrate refraction through a block of glass! This was about 1990. I guess they have semiconductor lasers now. I also would expect those lasers are bolted down and sealed in an enclosure such that the beam exit is controlled and clearly marked (so it can be pointed towards the experiment and nowhere else). They may even have a filter to take the power down to a mW or so - you don't need anymore really for these tasks. The thing that struck me about your post was the hand held mirrors. That's always a no no. It's just too easy - as you describe - to reflect the beam into your own (looking down at the mirror to try to see the spot) or someone else's eyes. We always use mirrors fimrly attached to a bench to avoid such problems.

Cheers,

Andy

 

[TuxDave]

Originally posted by: Fencer128

That's reassuring to know. I was doing a demonstration for middle schoolers regarding fiber optics and I had each of them hold a mirror to try to bounce the laser light down a curved path. I couldn't figure out where the laser was going since it obviously wasn't going down the path. Only later did I find out that one kid accidently tilted his mirror in a way such that the laser was flashing all over another kid's face and eyes.

Hi,

We used a wave machine (very wet) to demonstrate diffraction and a light bulb behind a slit to demonstrate refraction through a block of glass! This was about 1990. I guess they have semiconductor lasers now. I also would expect those lasers are bolted down and sealed in an enclosure such that the beam exit is controlled and clearly marked (so it can be pointed towards the experiment and nowhere else). They may even have a filter to take the power down to a mW or so - you don't need anymore really for these tasks. The thing that struck me about your post was the hand held mirrors. That's always a no no. It's just too easy - as you describe - to reflect the beam into your own (looking down at the mirror to try to see the spot) or soemone else's eyes. We always use mirrors fimrly attached to a bench. to avoid such problems.

Cheers,

Andy

Hey, it was done a while back, no one got hurt, and I didn't have to repeat the experiment ever again so there's no need to worry about my career as a physics instructor. I would be surprised if you didn't have any 'oops' stories in your lifetime.

Interestingly enough, for the classes that I did take, the lasers were in an enclosure but suprisingly they were not bolted down. So if someone really wanted to, they could blast their eyes away. But given that we all valued our eyes and we were all fairly rational, there was never a problem with using lasers for experimentations.

Actually.. what the heck is a wave machine? I never heard of it. It is some device that directs a beam into a diffraction grating? Regardless, we needed a coherant beam because we needed to measure angles to calculate index of refraction, diffraction grating distances as part of our labs.

 

[Fencer128]

Hey, it was done a while back, no one got hurt, and I didn't have to repeat the experiment ever again so there's no need to worry about my career as a physics instructor. I would be surprised if you didn't have any 'oops' stories in your lifetime.

Interestingly enough, for the classes that I did take, the lasers were in an enclosure but suprisingly they were not bolted down. So if someone really wanted to, they could blast their eyes away. But given that we all valued our eyes and we were all fairly rational, there was never a problem with using lasers for experimentations.

I have lots of "oops" stories (quite a few involving lasers) - I'm sorry if my posts came accross a bit heavy, it's just I've been shown lots of videos of laser eye damage and I've had lots of safety courses as such and I wanted to make sure that you knew where I was coming from and that I wasn't exaggerating risk, etc. I've inadvertantly put my face into an invisable laser beam a couple of times and it's not a nice feeling when you realise. I'm sure you are very responsible in your job.

In my old school I could just about trust everyone not to look into the laser if properly warned, but when the teacher's back was turned I know a couple of the guys would have tried to shine it in the face of other's given half the chance!

Cheers,

Andy

EDIT: The wave machine was a plastic tray filled with water, with a float attached to a motor that moves up and down to make nice plane waves. A sheet with a slit in it is placed in the tray - and if everything is set up correctly - the wave diffracts as it passes through the slit. It's old, wet and not too much fun. You can actually use a light bulb with a slit in front of it as a quasi-point source from which to demonstrate refraction though I admit a nice laser would be better. Snell's law, etc. still holds to a good approximation though if you do the calculations from measurements obtained with such a setup.

 

[TuxDave]

Originally posted by: Fencer128

Hey, it was done a while back, no one got hurt, and I didn't have to repeat the experiment ever again so there's no need to worry about my career as a physics instructor. I would be surprised if you didn't have any 'oops' stories in your lifetime.

Interestingly enough, for the classes that I did take, the lasers were in an enclosure but suprisingly they were not bolted down. So if someone really wanted to, they could blast their eyes away. But given that we all valued our eyes and we were all fairly rational, there was never a problem with using lasers for experimentations.

I have lots of "oops" stories (quite a few involving lasers) - I'm sorry if my posts came accross a bit heavy, it's just I've been shown lots of videos of laser eye damage and I've had lots of safety courses as such and I wanted to make sure that you knew where I was coming from and that I wasn't exaggerating risk, etc. I've inadvertantly put my face into an invisable laser beam a couple of times and it's not a nice feeling when you realise. I'm sure you are very responsible in your job.

In my old school I could just about trust everyone not to look into the laser if properly warned, but when the teacher's back was turned I know a couple of the guys would have tried to shine it in the face of other's given half the chance!

Cheers,

Andy

I did an internship in a fiber optics company and I learned about the dangers of lasers. In fact it was much more dangerous than what I said before because we delt with lasers out of the visible spectrum, operating on the orders of watts. It's kinda scary to suddenly feel this burning sensation and not see where the hell it came from. We were all given goggles to wear in the lab, but our poor hands were usually the ones to suffer. I blame the software because whoever wrote it forgot to include a statement saying that if the program was halted, to turn off everything until it was restarted.

 

[Fencer128]

I did an internship in a fiber optics company and I learned about the dangers of lasers. In fact it was much more dangerous than what I said before because we delt with lasers out of the visible spectrum, operating on the orders of watts. It's kinda scary to suddenly feel this burning sensation and not see where the hell it came from.

It's even worse when you don't feel the burning! I've spent the last few years building and using femtosecond pulsed lasers (~800nm so the near IR just out of the visible) and a couple of times when I've been adjusting the alignment with my head quite low (but not in the beam!) I've scanned a prism in and found the beam deviated more than I thought (probably because I'm not at the correct angle of incidence), which has swept past and quite near to my face. Either that or when I tune the laser into the visible a nice red spot appears somewhere on a wall where it shouldn't be and you realise it was there all along, even when you couldn't see it!

Those were the days! I've recently (this month) moved into IT - a slightly safer profession.

Cheers,

Andy

 

[Mark R]

There have been a couple of instances of minor eye injury with common laser pointers - these were not serious eye injuries, and the main symptom was temporary visual disturbance, with no apparentl long term consequences.

The case that comes to mind involved a couple of young children who were attempting to demonstrate the pupil reflex using a laser pointer as the light source.