Probing the ultrafast gain and refractive index dynamics of a VECSEL
| Autor: | Nathan Giannini, Martin Koch, David J. Hagan, Sepehr Benis, Alexander R. Albrecht, Arash Rahimi-Iman, Mansoor Sheik-Bahae, E. W. Van Stryland, Sanaz Faryadras, Christian Kriso, T. Bergmeier, Gerson Mette |
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| Rok vydání: | 2021 |
| Předmět: | |
| Zdroj: | Applied Physics Letters. 119:191105 |
| ISSN: | 1077-3118 0003-6951 |
| Popis: | Typically, strong gain saturation and gain dynamics play a crucial role in semiconductor laser mode-locking. While there have been several investigations of the ultrafast gain dynamics in vertical-external-cavity surface-emitting lasers (VECSELs), little is known about the associated refractive index changes. Yet, such refractive index changes do not only have a profound impact on the pulse formation process leading to self-phase modulation, which needs to be compensated by dispersion, but they are also of particular relevance for assessing the feasibility of Kerr-lens mode-locking of VECSELs. Here, we measure both refractive index as well as gain dynamics of a VECSEL chip using the ultrafast beam deflection method. We find that, in contrast to the gain dynamics, the refractive index dynamics is dominated by an instantaneous ($\sim$100~fs) and a very slow component ($\sim$100~ps). The time-resolved measurement of nonlinear refraction allows us to predict a pulse-length dependent, effective nonlinear refractive index $n_{2,eff}$, which is shown to be negative and in the order of $10^{-16}$ $m^2/W$ for short pulse lengths ($\sim$100~fs) . It becomes positive for large excitation fluences and large pulse lengths (few ps). These results agree with some previous reports of self-mode-locked VECSELs for which the cavity design and pulse properties determine sign and strength of the nonlinear refractive index when assuming Kerr-lens mode-locking. |
| Databáze: | OpenAIRE |
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