A.F. Koenderink

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

Broadband coherent backscattering spectroscopy of the interplay between order and disorder in three-dimensional opal photonic crystals

We present an investigation of coherent backscattering of light that is multiple scattered by a photonic crystal by using a broadband technique. The results significantly extend on previous backscattering measurements on photonic crystals by simultaneously accessing a large frequency and angular range. Backscatter cones around the stop gap are successfully modeled with diffusion theory for a random medium. Strong variations of the apparent mean free path and the cone enhancement are observed around the stop band. The variations of the mean free path are described by a semiempirical three-gap model including band structure effects on the internal reflection and penetration depth. A good match between theory and experiment is obtained without the need of additional contributions of group velocity or density of states. It is found that the internal reflection contribution does not improve the semiempirical fits. We argue that the cone enhancement reveals additional information on directional transport properties that are otherwise averaged out in diffuse multiple scattering.

Experimental probes of the optical properties of photonic crystals

The propagation of electromagnetic radiation in three-dimensional periodic dielectric structures is strongly modified if the wavelength of the radiation is on the order of the lattice spacing.1–5 Such structures are called photonic crystals. Their periodicity gives rise to photonic band structures in a way that is analogous to electronic band structures.6 Much of the recent interest in photonic crystals stems from the possibility of making lattices for which there exists a range of frequencies in which waves cannot propagate in any direction in the crystal.1–4 Such a photonic band gap occurs if the coupling between light and lattice is sufficiently strong. The coupling is conveniently gauged by the polarizability per volume of the scatters.7 If a lattice could be constructed with a photonic band gap at optical frequencies, this would result in spectacular effects such as the inhibition of spontaneous emission,3 and localization of light.4