The paper Two laser interference visible to the naked eye has been published on-line in European Journal of Physics in November 2011:
Eur. J. Phys. 33 (2012) 85-90
One can also find there two short movies as supplementary data.
An experimental setup allowing the observation of two-laser interference by the naked eye is described. The key concept is the use of an electronic phase lock between two external cavity diode lasers and the shift of the frequency of one of the beams in such a way that the interfering beams are of the same frequency.
The relative stabilization of the laser frequencies is realized with a PLL circuit, which stabilizes the frequency and phase of the beat note signal to an external reference. The shift of the frequency of one of the beams is realized in a common way with an acousto-optical modulator.
