Threshold dynamics in meso- and nanoscale lasers - why Vertical Cavity Surface Emitting Lasers?

The laser's threshold properties gradually evolve from the macroscopic to the nanoscopic scale through the mesoscale, whose best examples are the Vertical Cavity Surface Emitting Lasers (VCSELs). We show how the latter contribute to the understanding of the evolution of laser physics as the cavity volume is reduced thanks to favourable conditions: sufficient photon flux for a complete characterization with current instrumentation, coupled to physical characteristics which already approach those of nanodevices. A further reduction in cavity volume is nowadays possible in VCSELs, bringing within reach the nanoscale on the basis of mature technology. This will speed up both the fundamental investigations on the physics of nanolasers and open up the field for shorter-term applications in terms of nanosources - e.g., for optical chips - thanks to the possibility of coupling the VCSEL output into waveguides. Finally, we present an overview of results we have obtained on the physical characterization of the lasing transition in currently available, electrically-pumped VCSEL devices.