Past Events

Abstract:

The quantum cascade (QC) laser is based on artificial potentials made of a sequence of nanometric semiconductor layers. The electronic and optical properties of this device are independent from the constituent materials and can be tailored by choosing the appropriate layer sequence.

In these lasers there is no electron-hole recombination across the band-gap as the laser transition occurs between conduction band states arising from size quantisation in quantum wells. A direct consequence is that the emission wavelength does not depend on the band-gap and can be tuned by tailoring the thickness of the quantum wells.

In recent years the performance of these devices has improved markedly and this semiconductor technology is now an attractive choice for the fabrication of infrared lasers for spectroscopic and security applications. Presently, the best performances are obtained in the 4 – 12μm wavelength range, where continuous-wave room temperature operation is routinely achieved with Watt level optical power. Conversely, in the far infrared (λ > 70μm) quantum cascade lasers operate only at cryogenic temperatures.

After an introductory part on the principles of operation, I will present the state-of-the-art and performances of these devices. I will then comment on the fundamental physical challenges that still hold in this domain, pointing out some of our recent results on integrated laser-modulator devices. I will conclude with a perspective on applications.

Coffee and tea will be served 20 minutes prior to the seminar.