Signature of Wave Chaos in Spectral Characteristics of Microcavity Lasers.

We report an experimental investigation on the spectra of fully chaotic and nonchaotic microcavity lasers under continuous-wave operating conditions. It is found that fully chaotic microcavity lasers operate in single mode, whereas nonchaotic microcavity lasers operate in multimode. The suppression of multimode lasing for fully chaotic microcavity lasers is explained by large spatial overlaps of the resonance wave functions that spread throughout the two-dimensional cavity due to the ergodicity of chaotic ray orbits.

Light propagation in a Penrose unilluminable room.

Using the finite-difference time-domain method, propagation of light waves is studied in a Penrose unilluminable room. Such a room always has dark (unilluminated) regions, regardless of the position of a point source in it. However, in contrast to the predictions of ray dynamical simulations, a small amount of light propagates into the unilluminated regions via diffraction. We conjecture that this diffraction effect becomes more prominent as the size of the room decreases.

Lasing of TM modes in a two-dimensional GaAs microlaser.

We fabricated and tested an unstrained GaAs single-quantum-well microlaser which has a two-dimensional cavity shape known as the Penrose unilluminable room. The cavity exhibits quasi-one-dimensional modes, namely axial, diamond-shaped, and V-shaped modes. In contrast to previous observations of TE-polarized emission in GaAs microlasers, we observed TM-polarized emission. We explain this observation as being the result of lasing of the diamond-shaped modes whose incident angle at the cavity interface is very close to the Brewster angle.

Selective excitation of lowest-order transverse ring modes in a quasi-stadium laser diode.

For a two-dimensional quasi-stadium laser diode, we demonstrate stable excitation of the lowest-order transverse ring modes by optimally designing the confocal end mirrors of the laser cavity based on extended Fox-Li mode calculations. We observe kink-free light output versus injection current characteristics and highly directional single-peak emissions corresponding to the diamond-shaped trajectory in the cavity. These results provide convincing evidence for selective excitation of the lowest-order transverse modes.

Lowest-order axial and ring mode lasing in confocal quasi-stadium laser diodes.

We investigated the lasing modes of quasi-stadium laser diodes that have confocal cavity geometries, with stripe electrode contacts formed either along the cavity axis or a diamond-shaped trajectory. It was clearly demonstrated that by using narrow electrode contact patterns of 2 µm width, the lowest-order axial and ring modes were excited selectively. On the other hand, the second-lowest-order axial and ring modes were excited by using broad electrode patterns of 14 µm width. Experimentally obtained far-field patterns for lasers with broad and narrow electrode contact patterns agree very well with the simulation results obtained using an extended Fox-Li mode calculation method.

Fresnel filtering of Gaussian beams in microcavities.

We study the output from the modes described by the superposition of Gaussian beams confined in the quasi-stadium microcavities. We experimentally observe the deviation from Snell's law in the output when the incident angle of the Gaussian beam at the cavity interface is near the critical angle for total internal reflection, providing direct experimental evidence on the Fresnel filtering. The theory of the Fresnel filtering for a planar interface qualitatively reproduces experimental data, and a discussion is given on small deviation between the measured data and the theory.

Chaos-assisted directional light emission from microcavity lasers.

We study the effect of dynamical tunneling on emission from ray-chaotic microcavities by introducing a suitably designed deformed disk cavity. We focus on its high quality factor modes strongly localized along a stable periodic ray orbit confined by total internal reflection. It is shown that dominant emission originates from the tunneling from the periodic ray orbit to chaotic ones; the latter eventually escape from the cavity refractively, resulting in directional emission that is unexpected from the geometry of the periodic orbit, but fully explained by unstable manifolds of chaotic ray dynamics. Experimentally performing selective excitation of those modes, we succeeded in observing the directional emission in good agreement with theoretical prediction. This provides decisive experimental evidence of dynamical tunneling in a ray-chaotic microcavity.

Dissection of rye chromosome 1R in common wheat.

Rye chromosome 1R contains many agronomically useful genes. Physical dissection of chromosome 1R into segments would be useful in mapping 1R-specific DNA markers and in assembling DNA clones into contig maps. We applied the gametocidal system to produce rearranged 1R chromosomes of Imperial rye (1R(i)) added to common wheat. We identified rearranged 1R(i) chromosomes and established 55 1R(i) dissection lines of common wheat carrying a single rearranged 1R(i) chromosome. Fifty-two of the rearranged 1R(i) chromosomes had single breakpoints and three had double breakpoints. The 58 breakpoints were distributed in the short arm excluding the satellite (12 breakpoints), in the satellite (4), in the long arm (28), and in the centromere (14). Out of the 55 lines, nine were homozygous for the rearranged 1R(i) chromosomes, and the remaining lines were hemizygous. We developed 26 PCR-based EST markers that were specific to the 1R(i) chromosome, and nine of them amplified 1R(i) arm-specific PCR products without restriction-enzyme digestion. Using the nine EST markers and two previously reported 1R-specific markers, we characterized the 55 1R(i) dissection lines, and also proved that we can select critical progeny plants carrying specific rearranged 1R(i) chromosomes by PCR, without cytological screening, in 48 out of the 55 hemizygous dissection lines.

High-quality lowest-loss-mode lasing in GaAs quasi-stadium laser diodes having unstable resonators.

We obtained high-quality lowest-loss-mode lasing in quasi-stadium laser diodes having unstable resonators that consisted of two curved end mirrors and two straight sidewall mirrors. The laser diodes were fabricated by applying a reactive ion etching technique to a metal-organic chemical-vapor deposition-grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The electrode contact area of the laser diodes was formed along unstable periodic orbits, along which the optical beams are localized. Highly directional fan-out beams corresponding to the numerically obtained lowest loss mode were emitted from the end mirrors under CW operation at room temperature.

Classical phase space revealed by coherent light.

We study the far-field characteristics of oval-resonator laser diodes made of an GaAs/Al(x)Ga(1-x)As quantum well. The resonator shapes are various oval geometries, thereby probing chaotic and mixed classical dynamics. The far-field pattern shows a pronounced fine structure that strongly depends on the cavity shape. Comparing the experimental data with ray-model simulations for a Fresnel billiard yields convincing agreement for all geometries and reveals the importance of the underlying classical phase space for the lasing characteristics.

Light beam output from diamond-shaped total-internal reflection modes by using intracavity air gaps.

We propose a novel method for extracting light beams from diamond-shaped total-internal reflection modes in two-dimensional microcavity laser diodes by the use of intracavity air gaps. By fabricating such a laser diode, we experimentally demonstrate that the direction and longitudinal mode spacing of the output beams are in good accordance with theoretical calculations.

Asymmetric stationary lasing patterns in 2D symmetric microcavities.

Locking of two resonance modes of different symmetry classes and different frequencies in 2D resonant microcavity lasers is investigated by using a nonlinear dynamical model. The patterns of stationary lasing states and far fields are asymmetric in spite of the symmetric shape of the resonant microcavity. The corresponding phenomenon is actually observed in the experiment of a 2D semiconductor microcavity laser diode.

Quasi-stadium laser diodes with an unstable resonator condition.

We have observed lasing in a complicated eigenmode of a quasi-stadium laser diode with an unstable resonator consisting of two curved end mirrors obeying an unstable resonator condition and two straight sidewall mirrors. The laser was fabricated by application of a reactive-ion-etching technique to a molecular beam epitaxy-grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The far-field pattern shows that the lasing mode corresponds to the complicated lowest-loss mode obtained numerically by an extended Fox-Li method.

Ring and axis mode lasing in quasi-stadium laser diodes with concentric end mirrors.

We fabricated quasi-stadium laser diodes whose resonators consist of two concentric curved end mirrors and two straight sidewall mirrors. We observed two lasing modes that correspond to different beam propagations along the cavity axis and along a ring trajectory, and different far-field patterns with wide angular separation. The modes can be selected by control of an electrode pattern. We also show that the far-field patterns numerically obtained by the extended Fox-Li mode calculation method are in good agreement with the experimental results.