Light propagation and emission in complex photonic media

We provide an introduction to complex photonic media, that is, composite materials with spatial inhomogeneities that are distributed over length scales comparable to or smaller than the wavelength of light. This blossoming field is firmly rooted in condensed matter physics, in optics, and in materials science. Many stimulating analogies exist with other wave phenomena such as sound and seismology, X-rays, neutrons. The field has a rich history, which has led to many applications in lighting, novel lasers, light harvesting, microscopy, and bio optics. We provide a brief overview of complex photonic media with different classes of spatial order, varying from completely random to long-periodically ordered structures, quasi crystalline and aperiodic structures, and arrays of cavities. In addition to shaping optical waves by suitable photonic nanostructures, the realization is quickly arising that the spatial shaping of optical wavefronts with spatial light modulators dramatically increases the number of control parameters. As a result, it is becoming possible for instance to literally see through completely opaque complex media. We discuss a unified view of complex photonic media by means of a photonic interaction strength parameter. This parameter gauges the interaction of light with any complex photonic medium, and allows to compare complex media from different classes for similar applications.Comment: 8 pages, 2 figures, Light Localisation and Lasing: Random and Quasi-Random Photonic Structures, Eds. M. Ghulinyan and L. Pavesi, (Cambridge Univ. Press, Cambridge, 2015) Ch. 1, p.

Local density of optical states in the band gap of a finite photonic crystal

We study the local density of states (LDOS) in a finite photonic crystal, in particular in the frequency range of the band gap. We propose a new point of view on the band gap, which we consider to be the result of vacuum fluctuations in free space that tunnel in the forbidden range in the crystal. As a result, we arrive at a model for the LDOS that is in two major items modified compared to the well-known expression for infinite crystals. Firstly, we modify the Dirac delta functions to become Lorentzians with a width set by the crystal size. Secondly, building on characterization of the fields versus frequency and position we calculated the fields in the band gap. We start from the fields at the band edges, interpolated in space and position, and incorporating the exponential damping in the band gap. We compare our proposed model to exact calculations in one dimension using the transfer matrix method and find very good agreement. Notably, we find that in finite crystals, the LDOS depends on frequency, on position, and on crystal size, in stark contrast to the well-known results for infinite crystals.Comment: 22 pages, 8 figure

Intrinsic fluctuations in random lasers

We present a quantitative experimental and theoretical study of shot-to-shot intensity fluctuations in the emitted light of a random laser. A model that clarifies these intrinsic fluctuations is developed. We describe the output versus input power graphs of the random laser with an effective spontaneous emission factor (beta factor).Comment: accepted by Phys. Rev. A. submitted; 7 pages, 5 figure

Critical Quantum Fluctuations and Localization of the Small Polaron

The first quantitative evidence of critical quantum fluctuations and superlocalization of the small polaron model in one, two, and three dimensions is presented. Starting from a discrete version of the Feynman path-integral representation of the partition function, the boson field is eliminated analytically and the polaron contribution is calculated by means of the standard Monte Carlo Method.

β factor in a random laser

We develop a definition for the β factor, the fraction of spontaneous emission that seeds the laser process, for a random laser. With the wavelength-dependence of the gain (and potentially scattering) being the only possible criterion in the competition between gain and loss, our concept of β is based on the spectral properties of the spontaneous emission and laser light. We find β≈0.1. We discuss the apparent similarities and differences between the β for a cavity and a random laser

Observation of spatial quantum correlations induced by multiple scattering of non-classical light

We present the experimental realization of spatial quantum correlations of photons that are induced by multiple scattering of squeezed light. The quantum correlation relates photons propagating along two different light trajectories through the random medium and is infinite in range. Both positive and negative spatial quantum correlations are observed when varying the quantum state incident to the multiple scattering medium, and the magnitude of the correlations is controlled by the number of photons. The experimental results are in excellent agreement with recent theoretical proposals by implementing the full quantum model of multiple scattering