unfocused laser light

[Cheryl]

I'm pretty sure this is an extraordinarily dumb question but I'm a complete laser-ludite and could really do with some help, so here goes...

The Royal Greenwich Observatory in London uses a laser to mark the Meridian Line (0° longitude) each evening - sending a green beam across the London skyline. Although I love seeing the beam overhead, what fascinates me more is that when you enter the room that houses the laser, behind the laser is a miasma of unfocused green light. I am assuming that this is unfocused radiation spilling out of the laser housing and bouncing off any moats of dust in the air? It is visually befuddling and not a little spectacular and as a visual artist and I would dearly love to be able to recreate this unfocused effect in a room-sized installation. So... my questions to the forum are...

1. what is it that I'm looking at when I see this fuzzy green light?
2. is it possible to recreate the phenomenon? If yes, how?
3. would it be safe to do so?

Many thanks in advance for any help, Cheryl

 

[lasersbee]

I've never been there so I don't know what you are
actually looking at.
It is difficult to suggest a way of producing the same
effect.

I sometimes use a 50mW 523nm Laser at night to illuminate
the room to find the door buy just shinning the beam onto
the ceiling...
The light reflected diffused laser light is dispersed enough
that is using the Laser I mentioned is safe..
It is important NOT to look down into the Laser or at the
ceiling where the Laser Dot hits the ceiling without appropriate
Laser Safety Goggles/Glasses.
I my example I am in a dark room with my pupils very dilated
letting in even more light of any kind.

Perhaps that's the effect you are looking for...



Jerry

 

[DrSid]

Or you could unfocus the laser and shine it on the ceiling. Spot 10x10cm won't be dangerous even for 400mW laser, and it's ability to light up the room would be the same. it just would be wise to mount the laser high enough, so people can insert objects (or eyes) into the path of the direct beam.

 

[Ghostchrome]

Is this the room you're talking about?

 

[DrSid]

Hmm .. pretty ! Easy to do, quite safe, as long as nobody can reach there. Though to get enough light from beam alone would require some serious power, and it would depend on moisture/dust/smoke amount in the air, which can vary a lot. What can be dim in clean air, can be blindingly bright with just a bit smoke.

 

[Cheryl]

Jerry - thanks for that, yes, I suspect the effect you describe illuminating your room is probably similar to what I am looking for.

 

[Cheryl]

DrSid - that sounds like a cunning plan. Having never handled a 400mW laser, is it pretty obvious how to unfocus it (i.e. is there a lens that I could remove or fiddle with or would I just play about with?) And do you have any suggestions where I could get a really cheap 400mW laser to experiment with?

 

[Cheryl]

Ghostchrome - yes, that looks like it could be the room (if it's not, it is very similar) and the effect I am trying to replicate is the green fuzz rather than the focused beam of light. The weird fuzziness isn't obvious from the photo (not surprisingly).

 

[Cheryl]

DrSid - I think I need to do a fair bit of playing around, so if I can do a cheap & dirty experiment and then look to scale it up, that would probably be the best for me. I'm looking for a fairly subtle effect in all honesty - so clean air, probably with ambient light (i.e. not a darkroom situation). In my head I have the fantasy that it will look like the scene out of the original 1971 Willy Wonka & The Chocolate Factory movie, when Mike TV is disintegrated and the 'molecules' looked like white noise along the ceiling. Having written that down, I am now aware of quite how bonkers that sounds !

 

[Cheryl]

....many thanks all three of you for getting back to me, and apologies it has taken a while to reply (offline and on holiday!) Cheers, Cheryl

 

[DrSid]

I got my 400mW from o-like.com. Make sure to get good goggles too ! Or get some 50mW first, we here generally want people to start with weaker lasers and 'work up' toward stronger ones. It will a lot cheaper and for testing the effect it will be perfectly fine.
PS: We here also don't like this style of replying .. use multiquote button next time !

 

[Cheryl]

I got my 400mW from o-like.com. Make sure to get good goggles too ! Or get some 50mW first, we here generally want people to start with weaker lasers and 'work up' toward stronger ones. It will a lot cheaper and for testing the effect it will be perfectly fine.
PS: We here also don't like this style of replying .. use multiquote button next time !

Many thanks DrSid - and apologies for not using the appropriate forum etiquette... first time ever on any forum... takes a bit of getting used to.