Hee-Jong Moon

Observation of scarred modes in asymmetrically deformed microcylinder lasers.

We report observation of lasing in the scarred modes in an asymmetrically deformed microcavity made of liquid jet. The observed scarred modes correspond to morphology-dependent resonance of radial mode order 3 with their Q values in the range of 10(6). Emission directionality is also observed, corresponding to a hexagonal unstable periodic orbit.

Cavity-Q-driven spectral shift in a cylindrical whispering-gallery-mode microcavity laser

Cavity-Q-driven spectral shift of lasing was observed in a cylindrical microcavity formed by rhodamine6G-doped quinoline in a capillary. The envelope of lasing spectrum showed a blueshift induced by the decreasing cavity Q of whispering gallery modes as the pump fluence increases. The thermally induced refractive index changes were measured from the shifts of individual lasing modes. The observed cavity-Q-driven spectral shift was well described by a simple dye laser model, which accounts for the dependence of cavity Q on the thermally induced refractive index change.

Waveguide mode lasing via evanescent-wave-coupled gain from a thin cylindrical shell resonator

We reported waveguide mode lasing in a thin dielectric cylindrical shell made on the inner wall of a circular capillary, in which the laser oscillation was achieved through the evanescent-wave-coupled gain from the interior dye-doped liquid. Periodically peaked spectra of waveguide modes showed blueshift when the refractive index of interior liquid was decreased. We could quantitatively estimate the occupation factor of inner evanescent-wave portion from the dependence of blueshift, which allowed the spectral analysis on the effective cavity quality factor Q. Typical Q of the lasing waveguide modes was about 2×10 6 .

Interferential coupling effect on the whispering-gallery mode lasing in a double-layered microcylinder

Enhanced mode selection through a strong interferential coupling effect was observed in a double-layered cylindrical microcavity laser. The coupling was induced by partial reflection and recombination with refracted light on the internal circular boundary of the fused silica capillary tube, filled with a dye-doped liquid having lower reflective index than that of fused silica. The observed interference period agreed well with the prediction by a ray-optic model.

Single spatial mode selection in a layered square microcavity laser

We propose a scheme for mode selection in a square-shaped two-dimensional layered microcavity laser. By using a fused-silica square-shaped capillary containing a dye-doped liquid as a layered microcavity, whose refractive index was smaller than that of the fused silica, we could realize our idea for single spatial-mode lasing. By analyzing the amount of peak shift induced by varying the refractive index of inner liquid, we could confirm that the lasing modes originate by the free-running trajectories that are constrained on the outer layer by the presence of the inner boundary in such a way that only the ray having a refraction angle of 45° in the inner gain layer could be selected.

Laser oscillations with pumping-independent ultrahigh cavity quality factors in evanescent-wave-coupled-gain microsphere dye lasers

We report laser oscillations in whispering-gallery modes (WGMs) of a microsphere with its cavity quality factor Q unchanged for varied optical pumping intensities well above the laser threshold. La...

Efficient diffusive reflector-type diode side-pumped Nd:YAG rod laser with an optical slope efficiency of 55%

We fabricated a compact diode side-pumped Nd:YAG laser with a diffusive reflector, in which the diode laser power is transferred directly into the threefold symmetric diffusive cavity through long narrow slits. With a 7.5% output coupler in a linear resonator, we obtained 62.4-W multimode output power with an optical slope efficiency of 53.4% at a diode power of 182 W, which corresponds to an optical-to-optical efficiency of 34.3%. The optical slope efficiency increased to 55.5% when we used an 11% output coupler. From the leakage power analysis method, the pumping efficiency was measured to be approximately 82%. We discuss the thermal lens and the slope efficiency with respect to absorbed power that is derived from the measured pumping efficiency.

Whispering gallery mode lasing in a gain-coated square microcavity with round corners

We investigated the lasing property of the whispering gallery modes in a square microcavity with round corners. A thin gain layer was coated only on the outer boundary of cavity. With the corner radius of ~40 µm and the coating thickness of about 3 µm, we observed three distinct groups of lasing spectrum with the spacing of 0.18 nm, which was consistent with the prediction by a ray tracing analysis. By decreasing the corner radius to ~10 µm, we could reduce the number of lasing groups and obtained even a single spatial mode lasing with a thin coating thickness.

Guided mode lasing in a double-layered square microcavity

We investigated the lasing characteristics of guided modes in a double-layered square microcavity made of a fused-silica hollow square capillary, in which the modes were formed by the total internal reflections off the inner and outer boundaries. Periodically peaked spectra of guided modes were observed when a dye-doped dielectric was coated on the outer boundary for a laser gain. By reducing the distance between the outer and the inner boundaries, we could achieve even a lasing of single closed guided modes with multiple reflections at each side of the inner boundary. Our double-layered square cavity can be adapted for various applications, particularly in the photonic integrated circuits.

Intracavity frequency doubling of a slab Nd:YAG laser pumped by high power diode laser array

A high power diode-array-pumped slab Nd:YAG laser is described. The resonator consists of three mirrors in folded geometry. The laser is operated in acousto-optic Q-switching mode and intracavity frequency doubling is tried. We demonstrate that the laser exhibits frequency doubling efficiency of ∼60% with a type I LBO crystal.