Nathan B. Rex

Stimulated emission and lasing in whispering-gallery modes of GaN microdisk cavities

We report optically pumped, pulsed lasing action in whispering-gallery modes of GaN microdisk cavities at room temperature. The microdisk structure was fabricated by reactive-ion etching a 2-μm-thick GaN epitaxial layer grown via metalorganic chemical vapor deposition. Below the lasing threshold, stimulated emission with superlinear pump-intensity dependence is observed. Spontaneous-to-stimulated emission transition occurs at a pump intensity that is 10× lower than that for a GaN sample without a cavity structure. Above the lasing threshold, the pump-intensity dependence is almost linear and gain pinning is observed. In addition, whispering-gallery modes are observed with the linewidth of individual peaks being as narrow as 0.1 nm.

Threshold lowering in GaN micropillar lasers by means of spatially selective optical pumping

A new optical pumping method is demonstrated for creating a population inversion in GaN micropillar cavities with circular symmetry. This approach employs an axicon lens to produce a ring-shaped optical beam and provides for independent control of ring thickness and diameter. By bringing the pump beam into coincidence with whispering gallery modes confined near the outer rim of the cavity, we achieve a significant reduction in the threshold pump intensity for room-temperature operation of GaN micropillar lasers.

Threshold minimization and directional laser emission from GaN microdisks

2-micrometers thick GaN microdisks with the following shapes: circular; square; and quadrupolar with various deformation amplitudes have been investigated by optical pumping. For circular microdisks, the minimum laser threshold was found when the pump is a ring-shaped 355 nm laser beam. An imaging technique is used to photograph (with a CCD camera) the sidewall of the microdisk at various angles in the horizontal plane. From the imaging results as a function of observation angle, it is possible to extract information about the laser output location along the sidewall and its far-field angular pattern. Image results for the quadrupoles (with optical pumping of the top face) suggest that the directionality of laser emission is associated with chaotic- orbits that emerge just outside the highest curvature edges. With focused pumping of the same quadrupole structures at the middle of the top face, only Fabry-Perot modes involving the two lowest curvature interfaces are observed.

GaN near-UV microdisk lasers: efficient pumping configuration and low lasing threshold

Summary form only given. Shape deformation of a whispering gallery mode (WGM) microdisk laser was recently proposed and demonstrated to achieve high-power directional emission. Here, we demonstrate the first optically pumped, near-UV microdisk gallium nitride (GaN) laser. By using judicious pumping geometry, the lasing threshold was reduced to 60 kW/cm/sup 2/, which is an order of magnitude lower than previously reported for a conventional Fabry-Perot cavity structure. The pumping configuration is as important as the cavity structure in the design of low threshold lasers.

Directional stimulated emission from deformed GaN micropillar cavities

Whispering gallery mode (WGM) lasers hold promise because of their high Q and low thresholds. Their drawback, however, is the lack of directional emission. Deformed cavities support both regular and chaotic orbits that have emission directionality. Recent work with deformed WGM cavities has shown that regular orbit modes (bow-ties) can provide both higher output and directional emission. Here, we report the first directional stimulated emission from a deformed GaN micropillar cavity. By imaging the micropillar, we show emission due to regular bow-tie orbits, as in previous work, and due to chaotic orbits, the latter have higher intensity emission and lower threshold for stimulated emission.

Erratum: “Stimulated emission and lasing in whispering gallery modes of GaN microdisk cavities” [Appl. Phys. Lett. 75, 166 (1999)]

Seongsik Chang, Nathan B. Rex, Richard K. Chang, Gabel Chong, and Louis J. Guido Citation: Appl. Phys. Lett. 75, 3719 (1999); doi: 10.1063/1.125392 View online: http://dx.doi.org/10.1063/1.125392 View Table of Contents: http://apl.aip.org/resource/1/APPLAB/v75/i23 Published by the AIP Publishing LLC.

Lasing in GaN micro-pillar cavities: whispering gallery modes and polygonal modes

We report stimulated emission (SE) and lasing at blue wavelength from GaN micro-pillar cavities with various cross sections (circle, and polygons) at room temperature. For a circular shape, whispering gallery modes are observed, and for n-polygonal shapes, period-n modes are observed.