A diode laser is powered by a function generator so that the laser intensity is fluctuating sinusoidally at 3 MHz. The laser beam is reflected off a concave mirror mounted on a tripod to a light intensity meter. The output of the meter is shown on the oscilloscope. The 3MHz signal that causes the laser to pulse also triggers the oscilloscope. Moving the mirror changes the path length of one of the signals thus causing the signal displayed on the oscilloscope to also move. Thus, the distance the mirror is moved can be correlated with the displacement of the sine wave on the oscilloscope.