Abstract

Time-resolved transmission spectroscopy of a mid-infrared quantum cascade laser emitting at $11.7\mu \mathrm{m}$ allows us to iteratively retrieve the effective refractive index and the extinction coefficient of the gain medium in a broad spectral range with an accuracy of $\pm 7\times {10}^{-3}$. Besides a 3% slowdown of the group velocity we find a large induced group-velocity dispersion with changing signs in the vicinity of the gain maximum, disclosing implications for self-pulse formation in quantum-cascade lasers. Additionally we measured the temperature in the active region by exploiting the thermo-optic effect. A linear behavior with respect to the current and the duty cycle was observed.

© 2009 Optical Society of America

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