No abstract

We examine fluidically tunable periodic structures acting as highly-selective frequency selective surfaces (FSSs) or spatial phase shifters (SPSs) capable of providing phase shifts in the range of 0 -360 . These devices are multi-layer periodic structures composed of non-resonant unit cells. The tuning mechanism is based on integrating small, movable liquid metal droplets with the unit cells of the periodic structure. By moving these liquid metal droplets by small distances within the unit cell, the structure's frequency response can be tuned continuously. Using this technique, a fluidically tunable FSS with a fifth-order bandpass response is designed and its tuning performance is examined for various incidence angles and polarizations of the incident EM wave. Additionally, electronically tunable counterparts of the same structure are also designed and their tuning performances are examined under short-duration high-power excitation conditions. It is demonstrated that such electronically tunable FSSs/PSSs demonstrate extremely nonlinear responses. Since the fluidically tunable structure examined in this work does not use any nonlinear devices, its response is expected to remain linear for such short-duration high-power excitation conditions. The tuning performances of these fluidically tunable periodic structures are also experimentally demonstrated by fabricating three prototypes and characterizing their responses in a waveguide environment.

No abstract

The quantum yield is a critically important parameter in the development of lanthanide-based upconverting nanoparticles (UCNPs) for use as novel contrast agents in biological imaging and optical reporters in assays. The present work focuses on the influence of the beam profile in measuring the quantum yield (ϕ) of nonscattering dispersions of nonlinear upconverting probes, by establishing a relation between ϕ and excitation light power density from a rate equation analysis. A resulting 60% correction in the measured ϕ due to the beam profile utilized for excitation underlines the significance of the beam profile in such measurements, and its impact when comparing results from different setups and groups across the world.

Forestry is raising concern about the outbreaks of European spruce bark beetle, Ips typographus, causing extensive damage to the spruce forest and timber values. Precise monitoring of these beetles is a necessary step towards preventing outbreaks. Current commercial monitoring methods are catch‐based and lack in both temporal and spatial resolution. In this work, light scattering from beetles is characterized, and the feasibility of entomological lidar as a tool for long‐term monitoring of bark beetles is explored. Laboratory optical properties, wing thickness, and wingbeat frequency of bark beetles are reported, and these parameters can infer target identity in lidar data. Lidar results from a Swedish forest with controlled bark beetle release event are presented. The capability of lidar to simultaneously monitor both insects and a pheromone plume mixed with chemical smoke governing the dispersal of many insects is demonstrated. In conclusion, entomological lidar is a promising tool for monitoring bark beetles.