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The time-domain thermoreflectance metrology is applied to evaluate the thermal conductivities of filler particles embedded in a composite matrix. Specifically, a system of glass and ceramic microspheres with a diameter of 100 to 150 μm embedded in an epoxy matrix was used as a representation of a typical composite thermal interface material (TIM) suitable for microelectronics applications. These measurements provide a direct characterization of the thermal properties of filler materials. The measured thermal conductivities of both borosilicate glass and yttria stabilized zirconia microspheres agree well with literature values for bulk materials, whereas the thermal conductivity of the alumina microspheres is nearly 50% lower than that of bulk crystals. The reduction in thermal conductivity of the alumina microspheres highlights how important this level of understanding is for TIM development and is attributed to enhanced phonon scattering due to structural heterogeneity, such as defects induced by phase mixing and microvoids. Combining sample preparation, structural characterization, and direct thermal measurements, our study reveals the structure–thermal property relationship for individual microspheres. The results of this work can facilitate the design and engineering of composite-based thermally conductive materials for thermal management applications.

Optically coupled semiconductor laser arrays are described by coupled rate equations. The coupled mode equations and carrier densities are included in the analysis, which inherently incorporate the carrier-induced nonlinearities including gain saturation and amplitude-phase coupling. We solve the steady-state coupled rate equations and consider the cavity frequency detuning and the individual laser pump rates as the experimentally controlled variables. We show that the carrier-induced nonlinearities play a critical role in the mode control, and we identify gain contrast induced by cavity frequency detuning as a unique mechanism for mode control. Photon-mediated energy transfer between cavities is also discussed. Parity-time symmetry and exceptional points in this system are studied. Unbroken parity-time symmetry can be achieved by judiciously combining cavity detuning and unequal pump rates, while broken symmetry lies on the boundary of the optical locking region. Exceptional points are identified at the intersection between broken symmetry and unbroken parity-time symmetry.

Coherently coupled vertical-cavity surface-emitting laser arrays offer unique advantages for nonmechanical beam steering applications. We have applied dynamic coupled mode theory to show that the observed temporal phase shift between vertical-cavity surface-emitting array elements is caused by the detuning of their resonant wavelengths. Hence, a complete theoretical connection between the differential current injection into array elements and the beam steering direction has been established. It is found to be a fundamentally unique beam-steering mechanism with distinct advantages in efficiency, compactness, speed, and phase-sensitivity to current.

The relative coherence and phase are extracted from two-element, coherently coupled, vertical cavity surface emitting laser arrays. The array elements are defined optically by a photonic crystal pattern and electrically by ion implantation. We obtain the near and far fields experimentally under varying current injection. The Fraunhofer approximation is used to simulate propagation from the near to far field. The phase and coherence are extracted as fitting parameters to match the experimental and propagated far field patterns. The phase and coherence will aid in future array designs and in elucidating the phase-shifting mechanism.