Controlling chaos by negative feedback of subharmonic components

In this paper we present a control technique for stabilizing chaotic motion to periodic orbits in a CO2 laser with electro-optic feedback. The control method is based on negative feedback of subharmonic components of the laser intensity signal. A detailed analysis, performed using the four-level model for the CO2 laser, allows us both to reproduce the experimental features and to compare our method with the time-delayed autosynchronization method introduced by Pyragas [Phys. Lett. A 170, 421 (1992)].