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Instabilities in a coherently pumped laser

N. M. Lawandy, Jonathan C. Ryan

Published Apr 26, 1987• 1 citation
OpenAlex

Abstract

We solved in steady state in the rotating wave limit a five-level model which is fully coherent on the coupled pump–laser transition and includes relaxation of diagonal elements through, two rotational reservoirs connected by vibrational relaxation. The equations were solved in steady state for χ P ″ and χ S ″, the imaginary susceptibilities on the pump and laser transitions. These results were velocity integrated to generate susceptibilities for the inhomogeneously broadened system with arbitrary field strengths and relaxation rates.1 The effects of pump absorption were included by numerically integrating the spatial differential equation for the pump intensity down the laser axis.

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Michael Shaw, John K. Crane

We wish to use atomic group-velocity dispersion to compress energetic copper-vapor laser- pumped dye-laser pulses from 40 ns to approximately 300 ps. This talk focuses on numerical results that illustrate coherent atomic effects on the process. Traditionally, analysis has been based on linear dispersion theory (LDT). This model represents the atoms as a static susceptibility. This susceptibility gives rise to the differential group delay required for compression of frequency-swept pulses. However, LDT is inadequate in analyzing compression in a regime in which the coherent transition rate (Rabi frequency) is comparable to the laser detuning. Here population transfer becomes significant, thus invalidating the concept of a steady-state dipole. An adequate representation of the atomic system requires solution of the coupled Maxwell-Bloch equations. We have developed a code to model near-resonant coherent propagation through inhomogeneously broadened two-level atoms.

Quantum Electronics and Laser Science Conference•May 12, 1991•0 citations
We solved in steady state in the rotating wave limit a five-level model which is fully coherent on the coupled pump–laser transition and includes relaxation of diagonal elements through, two rotational reservoirs connected by vibrational relaxation. The equations were solved in steady state for χ P ″ and χ S ″, the imaginary susceptibilities on the pump and laser transitions. These results were velocity integrated to generate susceptibilities for the inhomogeneously broadened system with arbitrary field strengths and relaxation rates.1 The effects of pump absorption were included by numerically integrating the spatial differential equation for the pump intensity down the laser axis.
We study theoretically the dynamic behavior of a J′=1→J″=0 laser (J is the angular momentum quantum number) optically pumped by means of a linearly polarized coherent field (coupled to an adjacent transition J=0→J′=1) when the pump field polarization is rotated at a constant angular velocity Ω and the laser field polarization either is fixed by the cavity or is free (isotropic cavity). Because of a strong pump-induced gain anisotropy, the dynamic behavior is completely different in each case. In the case of fixed laser field polarization, rich amplitude dynamics, which depend on the pump field strength, are found. At slow modulation frequencies (with respect to the molecular and the cavity relaxation rates), the system does not always follow the sequence of stationary and dynamic solutions that correspond to the autonomous laser as a function of the relative orientation angle between the polarizations of the pump and the laser fields. Phenomena such as delayed switching and suppression of chaos and stabilization of unstable steady states are found. In the case of an isotropic cavity, the pump field vector rotation is transferred to the laser field vector and amplitude unstable regimes are also strongly inhibited.
Abstract The optical properties of the CdSe/ZnS spherical core/shell quantum dot (CSQD), related to the laser-driven transitions 1 s → 1 p − 1 and 1 s → 2 p − 1 , are the subject of this study. We investigate in detail how transition energies, oscillator strengths, imaginary and real parts of the total, linear and third-order susceptibilities change with the variation of the model parameters, such as CSQD radius, core radius, relaxation rates and laser intensity. The energy levels and wave functions, needed for the calculations of the model parameters, were obtained by solving the radial Schrödinger equation in the effective mass approximation with the corresponding boundary conditions. The interaction of CSQD with laser light was studied in a density matrix approach using a two-level model and, for the first time, a five-level model. Optical Bloch equations were derived under dipole and rotating wave approximations and solved in the steady-state regime to obtain an analytic expression for susceptibility. Special attention was paid to the cases in which nonlinear susceptibility prevailed over linear susceptibility, leading to the appearance of the window in the absorption peak. It was found that susceptibility is more sensitive to the change in the core radius than to the change in the CSQD radius and that a greater laser intensity is needed to change the nature of the absorption and dispersion curves for 1 s → 2 p − 1 then for 1 s → 1 p − 1 transition.
We report electromagnetically induced gain in a highly degenerate two-level rotational vibrational molecular system. Using two photon (Raman-type) interaction with right and left circularly polarized pump and probe waves, the Zeeman coherence is established within the manifold of degenerate sublevels belonging to a rotational vibrational eigenstate. We analytically and numerically calculate the third-order nonlinear optical susceptibility for a Doppler-broadened molecular transition for an arbitrary high rotational angular momentum $(J\ensuremath{\ge}20)$. It is shown that for a QQQ-type open transition, a weak probe will experience an electromagnetically induced gain in presence of a strong copropagating pump wave. The inversionless gain originates due to cancellation of absorption from the interference of the coupled $\ensuremath{\Lambda}$- and V-type excitation channels in an NNN-type configuration. A detailed analysis of the optical susceptibility as a function of Doppler detuning explains how the gain bands are generated in a narrow transparency window from the overlapping contributions of different velocity groups. It is shown that the orientation dependent coherent interaction in presence of a strong pump induces narrow resonances for the probe susceptibility. The locations, intensity, and sign (positive or negative susceptibility) of these resonances are decided by the frequency detuning of the Doppler group and the strength of the coupling field. The availability of high power tunable quantum cascade lasers covering a spectral region from about 4 to $12\text{ }\ensuremath{\mu}\text{m}$ opens up the possibility of investigating the molecular vibrational rotational transitions for a variety of coherent effects.
We wish to use atomic group-velocity dispersion to compress energetic copper-vapor laser- pumped dye-laser pulses from 40 ns to approximately 300 ps. This talk focuses on numerical results that illustrate coherent atomic effects on the process. Traditionally, analysis has been based on linear dispersion theory (LDT). This model represents the atoms as a static susceptibility. This susceptibility gives rise to the differential group delay required for compression of frequency-swept pulses. However, LDT is inadequate in analyzing compression in a regime in which the coherent transition rate (Rabi frequency) is comparable to the laser detuning. Here population transfer becomes significant, thus invalidating the concept of a steady-state dipole. An adequate representation of the atomic system requires solution of the coupled Maxwell-Bloch equations. We have developed a code to model near-resonant coherent propagation through inhomogeneously broadened two-level atoms.