Multi-frequency focusing of microjets generated by polygonal prisms

We systematically investigate the power distribution characteristics of microjets generated by prismatic scatterers with different shapes at sub-THz region (lambda = 8.57 mm). Among these prismatic scatterers, the hexagonal-type one shows better focusing feature than the others. Aiming at the hexagonal-type one, we propose a double-layer scatterer composed of a Teflon hexagonal prism as an outer layer and a semiconductor cuboid as an inner layer. Aiming at the double-layer scatterer, we further study the effects of refractive index, size, and shape of the inner cuboid on microjet's features. The study allows us to present an optimized double-layer scatterer, which has a side length lambda/2 (lambda) and a refractive index 2.0 (1.4) for the inner (outer) layer. We show that the optimized scatterer can produce an ultra-strong, ultra-narrow microjet with a power enhancement of similar to 30 and a full width at half maximum (FWHM) of similar to 0.26 lambda, and the microjet is just located at the output face. The microjet keeps compact within the distance range of lambda from the output face. These features and effects are explained from the viewpoint of ray optics theory. According to the optimized double-layer scatterer, we further study the multi-frequency focusing features of the microjets, and find that the microjet remains good features at harmonic frequencies 2f (0) and 3f (0). In addition, we investigate the effect of an Au sphere presence in the center of the microjet on the power distribution. The results show that a spherical dark spot with a size similar to that of the Au sphere emerges in the area where the Au sphere is placed. The feature can be used to measure the size of a metallic particle.

Automated summary

In this paper, we systematically investigate the power distribution characteristics of microjets in the sub-THz region. We propose a double-layer scatterer composed of a Teflon hexagonal prism and a semiconductor cuboid to optimize the microjet's features. The optimized scatterer produces an ultra-strong, ultra-narrow microjet with excellent focusing capabilities.