I want to commission a tunnel gun for Arctic

Please help. I need to create an illusion of a powerful revolving lighthouse beam for a theatrical production. I have seen videos of blue lasers with tunnel guns, and I think this could work. I imagine using a model lighthouse, replacing the motorized revolving light with an angled mirror, and inserting something like a Wicked Spyder Arctic in the base, pointing up at the mirror.

The beam would be used on a very darkened stage, and we could add a smoke/haze machine to make it more effective. I imagine the beam would need to be about 12" tall at a distance of 10ft.

Not being an expert, I have several questions, and once the design is done, perhaps someone in this community can build a device for our production? We would of course pay you for your time and expertise--but bear in mind it has to be (a) very reliable and robust as it will taken on the road (b) fast to set set up (c) safe, so zero risk of damaging the eyesight of the performers or the audience.

-I've seen the homemade devices on here using PC fans--do those mirrors need to be spinning to create a solid tunnel, or is that just to get additional spirograph effects?

-how do you control the diameter of the tunnel?

-is the risk of burning stuff and damaging eyesight less than with a focused beam?

-what's the minimum power laser I need to make a beam that's visible on stage with no smoke/haze?

-how about with smoke/haze machine--could I get away with a 5mw laser pointer?

-what would happen if I shone a laser through a fresnel lens, such as the kind in the glass of a lantern or boat light?

Thanks a lot for your help!

Thomas Dolby
thomas@floatingcity.com

What your looking for can definitely be done, an issue I'm seeing though is that most any beam that's strong enough to be seen w/o smoke will be too powerful to point into a crowd. The FDA guidlines for a "safe" laser is 5mw and an arctic can be in excess of 1000mw. BTW wicked lasers are very overpriced and many people here don't like them since we can build stronger lasers for cheaper.

Your budget will determine the quality of the prop. A cheap RGB unit and 10X beam expander could get the job done safely but could cost a few hundred, which isn't expensive really compared to other options.

IMO your better suited using a focused flashlight.

Hello, and welcome. First I wonder if for your purposes you could simply unfocus the beam of the laser so that the beam diverges from the mirror. This would create a cone of light, albeit a solid cone. The Mirror and motor trick you speak of would create a hollow cone of light.

1. To make a beam turn into a tunnel you WILL need a motor to spin the mirror.
2. The mirror is supposed to lie on the fan at an angle slightly off from parallel to the ground. The greater the angle, the larger the cone's diameter.
3. With the tunnel effect, the beam is still somewhat focused, you are merely projecting it at a spinning, wobbling mirror to direct the beam at angles. Risk of burning stuff is low, but the risk of damaging eyesight is high, especially with such a high powered 445nm laser.
4. If it is dark on stage you might could do it with a 50-100mW 532nm(green) laser. If you took a 50mW green laser and added a little bit of fog, you would have something very visible and MOSTLY eyesafe. (mostly eyesafe because at the low power, plus having the laser moving rapidly, any exposure time would be low. This doesn't mean don't take precautions though....don't project the tunnel into the audience.)
5. A 5mW laser pointer would probably work with fog, but it may be a bit underwhelming. I would recommend trying it yourself to see what 5mW pointer plus fog looks like to you.
6. I am not sure. I would need to look up how those lenses are shaped, but my guess would be that it won't have much effect. Since the beam is already collimated, I don't think much would happen.


Hope that helps!
-Isaac