I arranged two mirror galvanometers to give two dimensional control of a 10mW HeNe laser beam. “Continue reading” for further information and another 9 photos.
A galvanometer converts a voltage into a rotation of a certain arc of a circle. These have a response to about 100 Hz but can still be used to about 200 Hz. I fed one with 50 Hz and the other from a frequency generator.

If you have 2 at right angles, it gives smoothly rotating complex patterns that vary with the ratios of the two frequencies. These are Lissajous curves.
So 50 Hz + 50 Hz gives a circle, 50 + 100 Hz gives a figure 8 etc.

Above: The two galvanometers and the laser set-up. The two galvanometers are mounted with rotational axes at right angles. The centre photo shows the set-up with the diode laser.

Above: These pictures above show the full set-up with associated drivers. To the right is my (sort of) optical bench to simplify beam paths and to allow connection to the power supply.

The pictures above show some of the many patterns produced. These are constantly moving due to the varying phase relationships and only “slow down” near an exact ratio.

The galvanometers can be connected to the output of a stereo amplifier with resulting scribbly patterns in time with the music.

These are Lissajous (pronounced LEE-suh-zhoo) figures.

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Photo Date: July 2, 2006