Self-adjustment of a nonlinear lasing mode to a pumped area in a two-dimensional microcavity [Invited]

We numerically performed wave dynamical simulations based on the Maxwell–Bloch(MB) model for a quadrupole-deformed microcavity laser with spatially selective pumping. We demonstrate the appearance of an asymmetric lasing mode whose spatial pattern violates both the x-and y-axes mirror symmetries of the cavity.Dynamical simulations revealed that a lasing mode consisting of a clockwise or counterclockwise rotating-wave component is a stable stationary solution of the MB model. From the results of a passive-cavity mode analysis, we interpret these asymmetric rotating-wave lasing modes by the locking of four nearly degenerate passive-cavity modes. For comparison, we carried out simulations for a uniform pumping case and found a different locking rule for the nearly degenerate modes. Our results demonstrate a nonlinear dynamical mechanism for theformation of a lasing mode that adjusts its pattern to a pumped area.

Optical processes in the formation of stimulated emission from ZnO nanowires

This paper studies power dependent photoluminescence spectra, the stimulated emission occurring at ultraviolet （UV） band instead of the green emission band of ZnO nanowires, which are prepared with a chemical reduction method. The dynamics of the UV emission and green emission is given to demonstrate the reason of stimulated emission occurring at UV band but not the green emission band under high excitation, which indicates that the slow decay rate of trap state makes it easy to be fully filled and saturated, while the fast decay rate of near-band-edge exciton state makes the UV emission dominate the radiative recombination under high excitation. The UV emission, as well as the corresponding stimulated emission, occurs in competition with the green deep-trap emission. In addition, when pump fluence further increases, the multiple lasing modes appear. The dependence of these lasing modes on the pump fluence is first discussed. This diagram should be helpful to understand and design the optical nanodevices of ZnO nanowires.

Threshold Current Characteristics of Intracavity-contacted Vertical-cavity Surface-emitting Laser

Threshold current characteristics of intracavity-contacted oxide-confinedvertical-cavity surface-emitting laser had been investigated in detail. Threshold currentcharacteristics not only were depended on the size of oxide-aperture, but also were also stronglyaffected by the mismatch of its lasing mode and gain peak. For the same degree detuning of the gainpeak and lasing mode at room temperature, the threshold current was approximately proportional tothe square of the oxide-aperture diameter of above 5 μm. For the same oxide-aperture device, thelarger the detuning degree of the lasing mode shifted to the shorter wavelength of the gain peak atroom temperature was, the lower the minimum threshold current was. The wavelengths of the lasingmode and gain peak were ± N X 10 nm detuning at 300 K, The temperature of the minimum thresholdcurrent was changed to be about ± N X 40 K(N real number). The calculated results were consistentwith the experimental ones.

Plasmon enhancement for Vernier coupled single-mode lasing from ZnO/Pt hybrid microcavities

It is essential to develop a single mode operation and improve the performance of lasing in order to ensure practical applicability of microlasers and nanolasers. In this paper, two hexagonal microteeth with varied nanoscaled air-gaps of a ZnO microcomb are used to construct coupled whispering-gallery cavities. This is done to achieve a stable single mode lasing based on Vernier effect without requiring any complicated or sophisticated manipulation to achieve positioning with nanoscale precision. Optical gain and the corresponding ultraviolet lasing performance were improved greatly through coupling with localized surface plasmons of Pt nanoparticles. The ZnO/Pt hybrid microcavities achieved a seven-fold enhancement of intensity of single mode lasing with higher side- mode suppression ratio and lower threshold. The mechanism that led to this enhancement has been described in detail.

Whispering-gallery mode lasing from polymer microsphere for humidity sensing

Microlasers based on high quality （Q） whispering-gallery mode （WGM） resonance are pronfising low threshold laser sources for bio-sensing and imaging applications. In this Letter, dye-doped polymer microspheres were fabricated by a controlling emulsion solvent evaporation method. WGM lasing with low threshold and high Q factors was realized in an individual microsphere under femtosecond laser pumping. The slight change of environmental relative humidity （RH） can be monitored by measuring the shift of the lasing modes at tile ex- posure of water molecules, which dcmonstrates the sensitivity is as high as 6 pm/RH%. The results would offer an insight into employing microlasers as sensors.

Ultraviolet lasing behavior in ZnO optical microcavities

Zinc oxide(ZnO)optical microcavity modulated UV lasers have been attracting a wide range of research interests.As one of the most important materials in developing high quality microcavity and efficient UV evisible optoelectronic devices due to its wide band gap(3.37 eV)and large exciton binding energy(~60 meV).In this review,we summarized the latest development of ZnO optical cavity based microlasers,mainly including Fabry-Perot mode lasers and whispering gallery mode lasers.The synthesis and optical studies of ZnO optical microcavities with different morphologies were discussed in detail.Finally,we also consider that the research focus in the near future would include new nanotechnology and physical effects,such as nano/micro fabrication,surface plasmon enhancement,and quantum dot coupling,which may result in new and interesting physical phenomena.