Vertical external cavity semiconductor lasers (VECSELs) have shown a promise of becoming efficient sources of high power and high beam quality coherent radiation. In order to live up to their true potential potential, the VECSELs must be thermally managed in order to avoid thermal damage as thermal lensing and filamentation causing preventing it from operating in a single mode regime. For optically pumped VECSELs optical cooling presents an elegant solution for thermal management as it does not require electrical or thermal conduction. The goal of optical refrigeration is to achieve radiation balance lasing (RBL) when the active medium is maintained at the steady uniform temperature. In this work we investigate the active medium characteritics and operating conditions that can lead to RBL in semiconductor medium and show that in order to achieve RBL the gain medium should be engineered to create the density of states that simultaneously allows gain and strong Anti-Stokes Luminescence. Such media may incorporate bandtail states, impurities or quantum dots. We provide the recepee for optimization of such bandstructure-engineered materials to achieve the lowest threshold and highest output power.
Radiation balanced lasing (RBL) is an attractive pathway towards development of high power and good beam quality lasers because heat removal via anti-Stokes luminescence (optical refrigeration) does not require additional connections and components and the heat is dissipated away from the active medium. Optical refrigeration had been demonstrated in rare-earth doped laser medium, but is far more difficult to achieve it in semiconductors laser medium. The main obstacle to RBL in semiconductors that the most efficient cooling occurs at relatively low carrier densities, while the gain required to sustain laser operation requires much higher densities. In this talk we explore the means of resolving this conundrum by separating the optical refrigeration and lasing in temporal, spatial, and/or spectral domains. Time multiplexing involves modulating the pump and operating the laser in pulse modes with lasing and cooling intervals. Space multiplexing involves having separate regions (quantum wells and dots) for lasing and cooling. The spectral multiplexing involves operating with two separate pumps – one for lasing and one for cooling. This methods will be compared in the talk with the goal of selecting the optimal path towards radiation balanced semiconductor lasers.
A tunable slow light thermal modulator using 2D semiconductor metamaterial is presented and investigated. We have designed and simulated a terahertz (THz) semiconductor metamaterial (MM) waveguide system; The simulation results show the spectral properties and the group delay of the proposed 2D metamaterial can be tuned by adjusting temperature and the semiconductor used in the waveguide. Our calculations exhibit a significant slow-light effect, based on electromagnetically induced transparency (EIT) effect. By appropriately adjusting the distance between the sub radiant and supper radiant modes, a flat band corresponding to nearly constant group delay (of order of 71) over a narrow bandwidth of THz regime can be achieved. Our analytical results show that the group velocity dispersion (GVD) parameter can reach zero. The simulation results show the incident pulse can be slowed down without distortion owing to the low group velocity dispersion (LGVD). The outstanding result is that, the 2D semiconductor metamaterial is in a high decrease of the group velocity and therefore slow light applications. The proposed compact slow light thermal modulator can avoid the distortion of signal pulse, and thus may find potential applications in slow-light and thermal modulator devices and thermal applications.