Suppression of transverse and longitudinal instabilities in high-power MFA-MOPA semiconductor devices

Summary form only given. Modern devices such as monolithically integrated flared amplifier master oscillator power amplifiers (MFA-MOPAs) have generated high-power, near-diffraction limited, spatially coherent outputs. However, they are subject to transverse instabilities (filamentation, transverse mode beating) as well as longitudinal instabilities (self-pulsing, mode beating). We show theoretically how these difficulties can be minimized by shaping the power amplifier flare to overlap the forward propagating field. The onset of longitudinal and transverse effects is postponed by this improvement, allowing three times as much coherent power to be drawn from the laser. We also indicate that the virtual source movement with drive current is considerably less in the trumpet flared MOPA, offering considerable advantages to systems designers. We present detailed theoretical analyses of MFA-MOPAs comparable with those described in the literature. We use realistic carrier-dependent gain and index spectra, which may be obtained directly from experimental data, but is normally calculated using a detailed microscopic theory including nonlinear (saturable) gain and the influence of many-body effects. The field amplitudes and the carrier density are calculated using effective Bloch equations.