Quantum cascade disk lasers

The fabrication and characterization of quantum cascade (QC) disk lasers at 5 mu m wavelength is reported. The QC scheme yields several advantages for the disk geometry: an inherently transverse magnetic polarization, tailorable wavelength, and unipolar carrier transport. The low loss whispering gallery resonator allows small devices, 17-125 mu m in diameter, and low threshold currents (2.85 mA for a 17 mu m diameter disk) with a size independent pulsed threshold current density of 1.2 kAcm(-2) at 15 K. From the threshold current density the quality factor of the disks is estimated at Q similar to 3500. The emission spectra show single and multiple whispering gallery modes. (C) 1996 American Institute of Physics.