We fabricated two dimensional photonic crystal structures in zinc oxide films with focused ion beam etching. Lasing is realized in the near ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in either localized or extended defect modes near the dielectric edge of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process. Fine tuning of lasing wavelength across 20nm range has been realized by varying the lattice constant of PhCS structure. A qualitative explanation for these PhCS lasers with self optimization of laser cavity quality factor has been proposed.
We demonstrate lasing in a cavity formed by two Mie scatterers in a dye colloidal solution. Like a Fabry-Perot cavity, the feedback mechanism for lasing is based on back scattering from each particle. Strong light amplification in between the scatterer pair not only compensate its large diffraction loss, but also help to choose the particular pair out of many scatterers in the suspension to form the laser cavity. Such cavity selection is facilitated by a careful designed cone shaped excitation geometry. Detailed experimental studies on the threshold behavior, spectral characteristic of lasing emission, and output directionality are presented. A simple theoretical model provides qualitative explanation for this lasing phenomenon.
We investigate the lasing modes in diffusive random media with local pumping. The reabsorption of emitter light suppresses the feedback from the unpumped part of the sample and effectively reduces the system size. The lasing modes are dramatically different from the quasimodes of the passive system (without gain or absorption). Even if all the quasimodes of a passive diffusive system are extended across the entire sample, the lasing modes are still confined in the pumped volume with an exponential tail outside it. The reduction of effective system volume by absoption broadens the distribution of decay rates of quasimodes and facilitates the occurrence of discrete lasing peaks.