From billbeskimo.com Tue Jun 23 09:42:08 1998 Date: Mon, 22 Jun 1998 13:30:49 -0700 (PDT) From: William Beaty Reply-To: freenrg-l@eskimo.com To: "'freenrg-l@eskimo.com'" Subject: Re: Ring laser gyro Resent-Date: Mon, 22 Jun 1998 13:30:49 -0700 Resent-From: freenrg-l@eskimo.com On Sun, 21 Jun 1998, Kyle R. Mcallister wrote: > Hello all: > > Anyone here know how I can set up a ring laser gyro? I've never tried it, but here's what I would do. First rig up a photocell and amplifier so you can hear the laser beat frequenciess from physical motion. This is pretty easy: amplify the output from a small photocell and apply it to loudspeakers, shine the laser at the photocell, then turn the photocell so the reflected beam goes back into the laser. Hold everything very still, and then push very slightly on the surface where the laser and photocell are resting. You will hear loud squeals and chirps (they sound much like the sounds of tuning a shortware radio past certain CW stations.) This occurs because the distance between the laser and the photocell is changing, and as it changes it causes a linear interference pattern to move along the laser beam. Each "click" of the squealing sound is one node or antinode of the interference pattern going past the photocell. Having accomplished this, you'll know how much audio amplification is required in order to hear the beat frequencies in the light. Now for the gyro. Shine the laser on the end of a pair of single fiber optical fibers each a couple of feet long. Wrap the two fibers around a circle with each fiber going in the opposite direction (one wraps CCW, the other wraps CW). Aim the far ends of the fibers at your photocell so the laser light combines. If anything should now alter the "optical length" of the fibers, you should hear a squeal from your loudspeaker. Extremely slow rotation of the entire laser/fibers/photocell assembly should create a loud squeal. I would first try all of the above with a HeNe laser. Laser pointers have terrible coherence. If one fiber was a tiny bit longer than the other, the whole thing might fail to work if a Laser pointer is used, while it might be fine if a HeNe tube-laser is used. In the above, I am unsure of the size of the interference fringes which the fibers will project onto the photocell. If several fringes are on the surface of the photocell at one time, then the sound of moving fringes will be very low in amplitude. Perhaps you'll have to glue the fibers parallel to each other so their ends are very very close, and then hold them at quite a distance from the photocell. Perhaps use a lens near the fiber ends to beam the spreading light towards the photocell. All this is intended to set up a "double slit diffraction" system where the light-emitting ends of the optical fibers are the "slits". The diffraction pattern projected onto the photocell should be large enough that just one "fringe" hits the photocell at a time. The photocell probably needs to be masked, so that it has a "slit" shape which can grab one single fringe of the diffraction pattern. When the entire assembly is rotated, the fringe pattern will zoom wildly across the photocell, and a high-freq signal will come out of the loudspeaker. The end result is a sort of "digital potentiometer" device which has many "clicks" per rotation. If you managed to count the number of clicks digitally (and also detect the direction of motion of the dirifting interference pattern?) then you'll have a compass which can detect incredibly tiny rotary motions, like hundred thousandths of a degree. The down side: I hear that these things are sensitive to fiber motion and fiber thermal expansion. Simply walking on the floor near the lab bench would cause squealing sounds in the output. Once you had it working, you'd want to cast the fibers into solid plastic, and imbed the plastic block inside a very thick layer of styrofoam (or perhaps make a little one which could fit inside a thermos bottle. Without thermal protection, I bet the fibers would respond to small amounts of IR radiation. While listening to the loudspeaker output, maybe you can wave your warm hands near the bare fibers and make them squeal. Is this the laser-powered relativistic thermosensitive version of the Theremin? :) ((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billbeskimo.com amasci.com EE/programmer/sci-exhibits science projects, tesla, weird science Seattle, WA 206-762-3818 freenrg-L taoshum-L vortex-L webhead-L