Non-linear laser-pulse amplification in a medium with single-photon stimulated emission and two-photon absorption

Lawrence L. Hope, Milton O. Vassell

D. Faubert, S. L. Chin, M. Cormier +1 more

We present a rate equation analysis of passive short laser pulse superposition in a fluorescent dye medium, where it is seen that a single dye solution may act as both an absorber and an amplifier. Amplification proceeds via stimulated emission following a population inversion created with the energy the dye gained through absorption. Numerical results are compared with published experimental data. The agreement between the two is qualitative.

Lorenzo M. Narducci, Lambros G. Johnson, E. J. Seibert +1 more

Constantine Mavroyannis

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.

Victor R. Blok

Po Dong, Sing Hai Tang, Weining Man +1 more

We show that amplification without inversion (AWI) can be realized with two coherent driving lasers in a four-level atom. With the help of quantum-jump theory, two transition processes are found to contribute to the absorption or gain behaviour. It is explicitly shown that an asymmetry between the three-photon stimulated emission and the single-photon absorption process leads to AWI. Furthermore, it is demonstrated that AWI can occur in this model with or without quantum interference. The origin of AWI without interference is explained by introducing weights for dressed-state transitions. The asymmetry between the weights for a dressed-state transition in absorption and its counterpart in emission leads to the possibility of AWI.