Experimentally verified pulse formation model for high-power femtosecond VECSELs

Abstract

Optically pumped vertical-external-cavity surface-emitting lasers (OP-VECSELs), passively modelocked with a semiconductor saturable absorber mirror (SESAM), have generated the highest average output power from any sub-picosecond semiconductor laser. Many applications, including frequency comb synthesis and coherent supercontinuum generation, require pulses in the sub-300-fs regime. A quantitative understanding of the pulse formation mechanism is required in order to reach this regime while maintaining stable, high-average-power performance. We present a numerical model with which we have obtained excellent quantitative agreement with two recent experiments in the femtosecond regime, and we have been able to correctly predict both the observed pulse duration and the output power for the first time. Our numerical model not only confirms the soliton-like pulse formation in the femtosecond regime, but also allows us to develop several clear guidelines to scale the performance toward shorter pulses and higher average output power. In particular, we show that a key VECSEL design parameter is a high gain saturation fluence. By optimizing this parameter, 200-fs pulses with an average output power of more than 1 W should be possible.

Non-equilibrium ultrashort pulse generation strategies in VECSELs

“…As yet another important aspect, one has to be able to manage the cavity group delay dispersion (GDD) to generate ultrashort pulses [5,15,16,22]. When a pulse is propagating through a dispersive media, the group velocity will be frequency dependent, and consequently, different frequency components of the pulse will travel at separate velocities.…”

“…When a pulse is propagating through a dispersive media, the group velocity will be frequency dependent, and consequently, different frequency components of the pulse will travel at separate velocities. This will cause the pulse to elongate and, thus, an ideal configuration is designed such that the GDD is minimized in a wide spectral range to produce ultrashort pulses [16,22]. The total GDD in a gain structure is comprised of the dispersion from the material layers as well as the electronic contribution from the active QWs.…”

“…In particular, a rate-equation type approach that corresponds to an adiabatic eliminating of the microscopic QW polarizations has become popular [16]. One has to fit about a dozen parameters to reproduce experimental observations with such a model.…”

Influence of microscopic many-body scattering on the performance of ultrashort pulsed and CW multi-wavelength VECSEL lasing

“…A possibility is to derive rate equations, where the microscopic QW polarization dynamics is adiabatically eliminated by assuming that carriers are in equilibrium Fermi distributions. 18,19 Thus reducing the nonlinear QW carrier dynamics to many fit parameters that are experimentally approximated e.g. the amplitude of the QW gain that is assumed to have a parabolic shape.…”

“…the amplitude of the QW gain that is assumed to have a parabolic shape. 18 However, a VECSEL configured for high-power or ultrashort pulse generation will naturally generate intracavity fields that drive the QW carriers far from equilibrium, which will result in significant gain deformation and a departure from equilibrium dynamics. In these situations, a quantitative microscopic model is required in order to study the influence of the microscopic dynamics on the cavity field.…”