Modal analysis of polarization self-modulated lasers

The eigenstate spectrum of polarization self-modulated lasers is theoretically and experimentally investigated. The polarizations and frequencies of the eigenstates of such lasers are theoretically derived in the framework of the Jones matrix formalism by assuming the self-consistency of the field after one round trip through the cavity. The resulting predictions are successfully checked experimentally as well in the case of a polarization self-modulated multimode gas laser as in the case of a polarization self-modulated external-cavity semiconductor laser. In particular, it is shown experimentally that the pulses at a frequency equal to half the free spectral range observed in such lasers can be interpreted as a beat between the two eigenstates that oscillate in a single round trip in the cavity. This behavior is shown to be in agreement with a one round trip operation of the laser. Then, the temporal properties of such lasers are suggested to be due to the self-mode-locking between the different eigenstates.