RESUMO
A simple and robust method is presented for the construction of 3-dimensional crystals from silica and polystyrene microspheres. The crystals are suitable for use as templates in the production of three-dimensional photonic band gap (PBG) materials. Manipulation of the microspheres was achieved using a dynamic holographic assembler (DHA) consisting of computer controlled holographic optical tweezers. Attachment of the microspheres was achieved by adjusting their colloidal interactions during assembly. The method is demonstrated by constructing a variety of 3-dimensional crystals using spheres ranging in size from 3 microm down to 800 nm. A major advantage of the technique is that it may be used to build structures that cannot be made using self-assembly. This is illustrated through the construction of crystals in which line defects have been deliberately included, and by building simple cubic structures.
Assuntos
Cristalização/métodos , Holografia/métodos , Pinças Ópticas , Óptica e Fotônica/instrumentação , Poliestirenos/química , Dióxido de Silício/química , Desenho de Equipamento , Análise de Falha de Equipamento , Teste de Materiais , FótonsRESUMO
Charts to assist in linear accelerator bunker design have been produced using the Monte Carlo framework, Geant4. These charts assess the amount of forward scatter produced at different angles to the beam axis by concrete and steel barriers irradiated by 6 MV and 10 MV photon beams at normal incidence. These new charts complement existing charts of broad-beam transmission through walls. This is because the existing charts give no indication of the amount of scatter emerging at large angles from the beam axis, for example, towards the maze entrance.
