Lasers underwater?

I do quite a bit of diving and I've often thought a laser pointer would be useful for pointing things out to fellow divers who hadn't spotted them - it would be much more accurate than using a finger or a regular lamp. Some years ago I tried to mod a cheap laser pointer to make it waterproof, but the seal failed almost straightaway and I never had a chance to see how good the beam might have been.

I've really only just found this forum and I wonder if anyone of you knows of a laser that would be depth-rated to say 30m (100ft) underwater, and if so, whether they know if this idea works well as a pointer? I'd be very interested to know how far the beam can penetrate (blue/green presumably further than red) or whether backscatter is a serious problem (ie if the beam is too quickly absorbed by particles in the water).

Try a ziplock bag. My buddies and I used to go freediving at the lake at night with our lights in ziplock bags. WE probably never broke 15 feet though. Probly a different story with more water hu?

Yes, they do work as pointers underwater. The two common options would be green (532 nm) or red-orange (635 nm). Green (and higher frequencies in general) will travel further, but you'll get significantly better battery life with the red. The first link below lists the range of the 5mW greenie as 5,000 feet, and the 5mW red as 1,000 feet.

see (good to 200ft):
http://www.greenpointer.com/diver.htm

roithnir laser has 5mW 635(red) pointers good to 60 meters (second from bottom of page) {edit, this is apparently the same as the red one in the first link, just a bit cheaper }
http://roithner-laser.com/Pointer.htm

Here's another 5mW greenie good to 60 meters:
http://www.lasermate.com/ScubaGreenLaserMetal.htm

http://www.leisurepro.com/Prod/AQUULP.html?Search=op%3ddtSearch%26Term%3dlaser%26SearchFlag%3dall%26AdvSrchSortField%3dRelevance%26SortDesc%3d0%26Hit%3d1


$29 underwater laser rated for 50 meters