arXiv subjects

Ad Lagendijk

Publications and source records attributed to Ad Lagendijk.

47 records · Page 3Linked to original sources

arXiv2009

Experimental observation of second-harmonic generation and diffusion inside random media

We have experimentally measured the distribution of the second-harmonic intensity that is generated inside a highly-scattering slab of porous gallium phosphide. Two complementary techniques for determining the distribution are used. First, the spatial distribution of second-harmonic light intensity at the side of a cleaved slab has been recorded. Second, the total second-harmonic radiation at each side of the slab has been measured for several samples at various wavelengths. By combining these measurements with a diffusion model for second-harmonic generation that incorporates extrapolated boundary conditions, we present a consistent picture of the distribution of the second-harmonic intensity inside the slab. We find that the ratio $\ell_{2ω}/L_c$ of the mean free path at the second-harmonic frequency to the coherence length, which was suggested by some earlier calculations, cannot describe the second-harmonic yield in our samples. For describing the total second-harmonic yield, our experiments show that the scattering parameter at the fundamental frequency $\k_{1ω}\ell_{1ω}$ is the most relevant parameter in our type of samples.

physics.optics↗

arXiv2008

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.

quant-ph↗

arXiv2007

Light scattering from three-level systems: The T-matrix of a point-dipole with gain

We present an extension of the T-matrix approach to scattering of light by a three-level system, using a description based on a Master equation. More particularly, we apply our formalism to calculate the T-matrix of a pumped three-level atom, providing an exact and analytical expression describing the influence of a pump on the light scattering properties of an atomic three-level system.

cond-mat.dis-nn↗

arXiv2007

Relaxation oscillations in long-pulsed random lasers

We have measured the evolution of the light intensity of a random laser during a nanosecond pump pulse. Relaxation oscillations in a titania random laser were observed in the time trace of the total emitted intensity. We compare our experimental results with a simple model, based on the four-level rate equations for a single mode laser.

physics.optics↗

arXiv2007

Spatial Extent of Random Laser Modes

We have experimentally studied the distribution of the spatial extent of modes, and the crossover from essentially single-mode to distinctly multi-mode behavior inside a porous gallium phosphide random laser. This system serves as a paragon for random lasers due to its exemplary high index contrast. In the multi-mode regime we observed mode competition. We have measured the distribution of spectral mode spacings in our emission spectra, and found level repulsion that is well described by the Gaussian orthogonal ensemble of random-matrix theory.

cond-mat.dis-nn↗

arXiv2006

Quantitative analysis of several random lasers

We prescribe the minimal set of experimental data and parameters that should be reported for random-laser experiments and models. This prescript allows for a quantitative comparison between different experiments, and for a criterion whether a model predicts the outcome of an experiment correctly. In none of more than 150 papers on random lasers that we found these requirements were fulfilled. We have nevertheless been able to analyze a number of published experimental results and recent experiments of our own. Using our method we determined that the most intriguing property of the random laser (spikes) is in fact remarkably similar for different random lasers.

cond-mat.dis-nn↗

arXiv2006

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).

cond-mat.dis-nn↗

arXiv2006

Gain narrowing in few-atom systems

Using a density matrix approach, we study the simplest systems that display both gain and feedback: clusters of 2 to 5 atoms, one of which is pumped. The other atoms supply feedback through multiple scattering of light. We show that, if the atoms are in each other's near-field, the system exhibits large gain narrowing and spectral mode redistribution. The observed phenomena are more pronounced if the feedback is enhanced. Our system is to our knowledge the simplest exactly solvable microscopic system which shows the approach to laser oscillation.

quant-ph↗

arXiv2005

Optical extinction due to intrinsic structural variations of photonic crystals

Unavoidable variations in size and position of the building blocks of photonic crystals cause light scattering and extinction of coherent beams. We present a new model for both 2 and 3-dimensional photonic crystals that relates the extinction length to the magnitude of the variations. The predicted lengths agree well with our new experiments on high-quality opals and inverse opals, and with literature data analyzed by us. As a result, control over photons is limited to distances up to 50 lattice parameters ($\sim 15 μ$m) in state-of-the-art structures, thereby impeding large-scale applications such as integrated circuits. Conversely, scattering in photonic crystals may lead to novel physics such as Anderson localization and non-classical diffusion.

physics.optics↗

arXiv2005

The independent scattering approximation in the saturated regime

We show that a saturable single-frequency elastic T-matrix approach to scattering of light by atoms agrees remarkably well with a master equation description in the regime of unsaturated atoms, or for large separation between the atoms. If the atoms are in each other's near-field and the saturation of the atoms is high enough, the two approaches yield different results.

cond-mat.dis-nn↗

arXiv2005

Dynamics of a two-level system in a broadband light field

We provide analytic solutions of the optical Bloch equations for a two-level system interacting with a broadband light field. We will focus on two special examples: incident light with a Lorentzian spectral density and the limit of incident monochromatic light. The results are used to obtain an expression for the nonlinear polarizability of a two-level atom irradiated by a wave with a Lorentzian spectral density.

cond-mat.dis-nn↗