B.H. Husken

Focused ion beam milling of nanocavities in single colloidal particles and self-assembled opals

We present a new method of realizing single nanocavities in individual colloidal particles on the surface of silicon dioxide artificial opals using a focused ion beam milling technique. We show that both the radius and the position of the nanocavity can be controlled with nanometre precision, to radii as small as 40 nm. The relation between the defect size and the milling time has been established. We confirmed that milling not only occurs on the surface of the spheres, but into and through them as well. We also show that an array of nanocavities can be fashioned. Structurally modified colloids have interesting potential applications in nanolithography, as well as in chemical sensing and solar cells, and as photonic crystal cavities.

Angular redistribution of near-infrared emission from quantum dots in 3D photonic crystals

We study the angle-resolved spontaneous emission of near-infrared light sources in three-dimensional photonic crystals over a wavelength range 1200–1550 nm. To this end, PbSe quantum dots are used as light sources inside titania inverse opal photonic crystals. Strong deviations from the Lambertian emission profile are observed. An attenuation of 60% is observed in the angle-dependent radiant flux emitted due to photonic stop bands. At angles that correspond to the edges of the stop band, the emitted flux is increased by up to 34%. This increase is explained by the redistribution of Bragg-diffracted light over the available escape angles. The results are quantitatively explained by an expanded escape-function model. This model is based on diffusion theory and adapted to photonic crystals using band structure calculations. We identify the need to separately consider the transport mean free path of both the emitted light and the light used for excitation. Here, the model is applied to describe emission in the regime where samples are optically thick for the excitation light, yet relatively thin for the photoluminesence light

Method to deterministically study photonic nanostructures in different experimental instruments.

We describe an experimental method to recover a single, deterministically fabricated nanostructure in various experimental instruments without the use of artificially fabricated markers, with the aim to study photonic structures. Therefore, a detailed map of the spatial surroundings of the nanostructure is made during the fabrication of the structure. These maps are made using a series of micrographs with successively decreasing magnifications. The graphs reveal intrinsic and characteristic geometric features that can subsequently be used in different setups to act as markers. As an illustration, we probe surface cavities with radii of 65 nm on a silica opal photonic crystal with various setups: a focused ion beam workstation; a scanning electron microscope (SEM); a wide field optical microscope and a confocal microscope. We use cross‐correlation techniques to recover a small area imaged with the SEM in a large area photographed with the optical microscope, which provides a possible avenue to automatic searching. We show how both structural and optical reflectivity data can be obtained from one and the same nanostructure. Since our approach does not use artificial grids or markers, it is of particular interest for samples whose structure is not known a priori, like samples created solely by self‐assembly. In addition, our method is not restricted to conducting samples.

Spontaneous emission lifetimes of infrared quantum dots controlled with photonic crystals

The spontaneous emission decay rate of light sources is determined both by intrinsic properties of the emitter, and by the Local Density of Optical States (LDOS) [1]. Spontaneous emission control is relevant for lightmatter interaction studies, vacuum field engineering, in the areas of telecommunication and quantum computing. Control over the spontaneous emission decay rate can be used to make efficient light sources, solar cells, and low-threshold lasers. Photonic crystals can control emission over large volumes, as apposed to cavities.