Experimental stability diagram of a diode laser subject to weak phase-conjugate feedback from a rubidium vapor cell

We report on a systematic experimental investigation of the dynamical behav ior of a diode laser subject to delayed feedback from a phase-conjugating m irror based on nearly-degenerate four-wave mixing in rubidium vapor. We pre sent the first experimental stability diagram for this system. In the weak feedback regime, with feedback levels up to -30 dB, we demonstrate locking to the pump frequency with a reduced linewidth smaller than 8 MHz. In contr ast to a laser with external injection, and contrary to predictions made fo r phase-conjugate feedback, the extent of this locking region is found to b e limited. For increased feedback rates, the laser leaves the locking regio n and enters an unstable region through a series of multiple sidebands spec tra, This is associated with self-excitation of the relaxation oscillation, and the observed scenario suggests a series of period-doublings after an i nitial Hopf bifurcation.