Intersubband gain-induced dispersion.

Time-resolved transmission spectroscopy of a mid-infrared quantum cascade laser emitting at 11.7 mum 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 +/-7x10(-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.

Whispering gallery modes inside asymmetric resonant cavities.

Two dimensional resonators with a smooth strictly convex boundary are known to possess a whispering gallery region supporting modes concentrated near the boundary. A new class of asymmetric resonant cavities is introduced, where a whispering gallery-like region is found deep inside the resonator. The construction of such resonators is a novel application of the geometric control methods.

Few-cycle terahertz generation and spectroscopy of nanostructures.

We report on new schemes for terahertz (THz) generation. The THz efficiency of photoconducting antennas can be increased by using a cavity effect for the near-infrared pump beam. The cavity is formed by a molecular beam epitaxy grown semiconductor Bragg mirror below the photoconducting layer.