Here is a video of my first interference ring.  It is a 10 for $4.99 mini laser diode at 650 nm, two AA batteries taped together with a brass nail taped on one end and the laser diode wires to the +/- on the other end. The diode is laying on a book.  I have two 2" round mirrors (50 for $10.99).  The laser hits the edge of the first one,  bounced back and hits the one closer to the laser, then goes off and hits a piece of white paper about a foot away,  The two mirrors are about 5 cm apart. I have a $39.99 1600x1200x30 fps Crosstour sports cam that can be plugged in as a webcam, sitting a few inches from the screen.  The first dark ring is about 1 centimeter (cm) across.  I am using APowerSoft Screen Pro to record the video.  [ For the next video, I have Javascript/html program that I wrote to read the camera frames and collect statistics, display various pictures of the camera stream, and try to determine what all this wonderful data can be used for.  I have to try to use if for monitoring the pendulum, but I just love the statistics for their own right.]

  Oh, I have four 1 inch round magnets for a dollar, and a pack of 12 for a dollar half inch paper binding clips.  I clip the clip on the mirror, squeeze the wires and remove them, stick the mirror and clip on the magnet.  My table happens to be a wrought iron outdoor table so they stick, but they are heavy enough to sit on a table.  I had to learn to touch the mirror and only move the magnets carefully.  I will measure the angles and restrictions for getting this image because it took me a couple of hours to wrap my head around what it was doing.  Finally, I have a stack of sticky notes blocking the laser beams from hitting the screen, so the camera is not washed out.   The lights are out, except for the computer screens.  Looking forward to seeing what I can do with the data stream.  Will put a picture and diagram. Will record some data and play a bit.  I have other things I am doing, but will try to do more later today or tonight.