The absorption and excitation spectra of a strong photoinduced band found in samples of ZnS:Mn at 6 and 77K are reported. The process involves first the population of a metastable level and subsequently excitation to a higher level, which shows the induced absorption. The centre responsible is not identified.
Studies the competition between absorption and stimulated emission induced by two laser fields at low intensities interacting on a two-photon resonance with a three-level atom. The induced spectrum into the ground state consists of a peak whose height and asymmetry depend strongly on the detuning. The spectra arising from the emission of a laser photon by the excited state consists of two peaks describing stimulated emission and induced absorption, respectively, where the former dominates the latter for small values of the Rabi frequencies but for higher ones, they cancel each other out.
We have considered the induced processes that occur in a driven two-level atom, where a laser photon is absorbed and emitted by the ground and by the excited states of the atom, respectively. In the low-intensity limit of the laser field, the induced spectra arising when a laser photon is absorbed by the ground state of the atom consist of two peaks describing induced-absorption and stimulated-emission processes, respectively, where the former prevails over the latter. Asymmetry of the spectral lines occurs at off-resonance and its extent depends on the detuning of the laser field. The physical, process where a laser photon is emitted by the excited state is the reverse of that arising from the absorption of a laser photon by the ground state of the atom. The former differs from the latter in that the emission of a laser photon by the excited state occurs in the low-frequency regime and that the stimulated-emission process prevails over that of the induced absorption. In this case, amplification of ultrashort pulses is likely to occur without the need of population inversion between the optical transitions. The computed spectra are graphically presented and discussed.
The excitonic nonlinearities in II-VI wide gap semiconductors have recently become an interesting research topic. Andersen et al.1 studied the saturating absorption of excitonic resonance in ZnSe single crystal films and (Zn, Mn)Se superlattices, which they attributed to Coulombic screening for the case of ZnSe film or a wide-well (Zn,Mn)Se quantum well structure at 77 K, and the Coulombic screening and phase space filling for a narrow-well structure. Gribkovskii et al.2 have observed the increase of excitonic absorption optical bistability in ZnSe film and attributed it to excitonic broadening and gap renormalization for the nonlinear mechanism. We report the first observation of optical bistability in ZnSe/ZnS MQWs grown by MOCVD on CaF2 substrates.