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Radiative emission experienced by a subwavelength particle near a resonant cavity is typically characterized by the well-known Purcell factor figure of merit. In recent work, we presented a generalization of Purcell enhancement that applies to situations involving exceptional points (EP)---spectral singularities in non-Hermitian systems where two or more eigenvectors and their corresponding complex eigenvalues coalesce, leading to a non-diagonalizable, defective Hamiltonian. EPs are attended by many intriguing physical effects and have been studied in various contexts, including lasers, atomic and molecular systems, photonic crystals, parity-time symmetric lattices, and optomechanical resonators. Thus far, the main focus of these works has been on analyzing the impact of second-order exceptional points on scattering from eternally incident light, e.g. for unidirectional transmission. An important but little explored property of EPs related to light-matter interactions is their ability to modify and enhance the local density of states (LDOS). Recently, we showed that EPs can modify the spontaneous emission rate or Purcell factor of narrow-band emitters embedded in resonant cavities. In this talk, we show that EPs can have an even greater impact on nonlinear optical processes like frequency conversion. In particular, we derive a general formula quantifying radiative emission from a subwavelength emitter in the vicinity of a triply resonant χ(2) cavity that supports an EP near the emission frequency and a bright mode at the second harmonic. We show that the resulting frequency up-conversion process can be enhanced by up to two orders of magnitude compared to nondegenerate scenarios and that, in contrast to the recently predicted spontaneous-emission enhancements, nonlinear EP enhancements can persist even when considering spatial distributions of broadband emitters, provided that the cavity satisfies special nonlinear selection rules. This is demonstrated via a two-dimensional proof-of-concept PhC designed to partially fulfill the various criteria needed to approach the derived bounds on the maximum achievable up-conversion efficiencies. Along these lines, we show that similar enhancements can arise in quantum systems consisting of single and multi-level atoms embedded in photonic cavities. Our predictions suggest an indirect but practically relevant route to experimentally observe the impact of EPs on spontaneous emission and related light–matter interactions, with implications to quantum information science.

Van der Waals (vdW) forces play an integral role in the binding and interaction energies of molecules in condensed phases; their long-range, many-body nature can modify phonons in molecular crystals and thereby impact thermodynamic stability. Typical macroscopic descriptions of such optical forces tend to ignore important atomistic effects arising at short (nanometric) scales, while microscopic treatments tend to ignore long-range, geometry-dependent electromagnetic effects. We describe an ab-initio approach to model such fluctuation-induced forces in mesoscopic systems comprising large molecules in the vicinity of macroscopic bodies, conjoining atomistic treatments of electronic and vibrational fluctuations derived from density functional theory in the former, with continuum descriptions of electromagnetic response in the latter, thereby accounting for many-body and multiple scattering effects to all orders. Such long-range electromagnetic effects become particularly important in situations where the finite sizes and shapes of the molecules and continuum bodies combine to create phonon polaritons with highly delocalized (nonlocal) charge distributions. We find that even in small molecules, but especially in elongated low-dimensional molecular systems, these effects modify van der Waals forces by orders of magnitude and produce qualitatively different behavior compared to predictions based on simple dipolar or pairwise approximations, valid only in atomically small or dilute molecular systems. In particular, we focus on the interactions of fullerenes, carbyne wires, and graphene sheets with one another and with a gold surface. We compare forces with and without phonon and at multiple temperatures, and compare our predictions to those obtained from commonly used dipolar and continuum treatments. In particular, we show that phonons can delocalize molecular charge distributions from a few angstroms to several nanometers, in ways that depend strongly on the shape of the molecules and their proximity to the surface. Even for small fullerenes, phonons can lead to force deviations at tens of nanometer separations from the surface compared to treatments lacking phononic effects, while for higher dimensional molecules such as elongated carbyne wires and graphene sheets, the nonlocality of these interactions produces nonmonotonic power laws that cannot be qualitatively captured by dipolar and/or continuum models.

For 75 years it has been known that radiative heat transfer can exceed far-field blackbody rates when two bodies are separated by less than a thermal wavelength. Yet an open question has remained: what is the maximum achievable radiative transfer rate? Here we describe basic energy-conservation principles that answer this question, yielding upper bounds that depend on the temperatures, material susceptibilities, and separation distance, but which encompass all geometries. The simple structures studied to date fall far short of the bounds, offering the possibility for significant future enhancement, with ramifications for experimental studies as well as thermophotovoltaic applications.

Photonic crystals provide superb opportunities for tailoring of the photonic density of states. This ability can in turn be explored to control radiation into far-field, enhance fluorescent light emission, as well as optimize laser emission. In order to make these phenomena useful for large macroscopic devices, large-area nano-fabrication techniques have to be successfully implemented. In this talk, I will present some of our recent theoretical and experimental progress in exploring these opportunities.

Quantum dot (QD) luminescent solar concentrator (LSC) uses a sheet of highly transparent materials doped with luminescent QDs materials. Sunlight is absorbed by these quantum dots and emitted through down conversion process. The emitted light is trapped in the sheet and travels to the edges where it can be collected by photovoltaic solar cells. In this study, we investigate the performance of LSCs fabricated with near infrared QDs (lead sulfide) and compared with the performance of LSCs containing normal visible QDs (CdSe/ZnS), and LSCs containing organic dye (Rhodamine B). Effects of materials concentrations (related to re-absorption) on the power conversion efficiency are also analyzed. The results show that near infrared QDs LSCs can generate nearly twice as much as the output current from normal QDs and organic dye LSCs. This is due to their broad absorption spectra. If stability of QDs is further improved, the near infrared QDs will dramatically improve the efficiency of LSCs for solar energy conversion with lower cost per Wp.

We present two photonic crystal enabled platforms, exhibiting novel active optical phenomena. First, using a detailed theoretical and numerical analysis, we show how a Purcell-effect inspired nonlinear nanophotonic scheme could enable optimal and compact THz sources via optical difference frequency generation. Second, we show how electromagnetic one-way edge modes analogous to quantum Hall edge states, originally predicted by Raghu and Haldane in gyroelectric photonic crystals, can appear in more general settings. In gyromagnetic YIG photonic crystals operating at microwave frequencies, time-reversal breaking is strong enough that the effect is readily observable. We present our experimental results on this novel phenomenon.

In terrestrial free-space laser communication, aside from pointing issues, the major problem that have to be dealt with is the turbulent atmosphere that produces irradiance fluctuations in the received signal, greatly reducing the link performance. Aperture averaging is the standard method used to mitigate these irradiance fluctuations consisting in increasing the area of the detector, or effectively increasing it by using a collecting lens with a diameter as large as possible. Prediction of the aperture averaging factor for Gaussian beam with currently available theory is compared with data collected experimentally and simulations based in the beam propagation method, where the atmospheric turbulence is represented by linearly spaced random phase screens. Experiments were carried out using a collecting lens with two simultaneous detectors, one of them with a small aperture to emulate an effective point detector, while the other one was mounted with interchangeable diaphragms, hence measurements for different aperture diameters could be made. The testbed for the experiments consists of a nearly horizontal path of 1.2 km with the transmitter and receiver on either side of the optical link. The analysis of the experimental data is used to characterize the aperture averaging factor when different values of laser divergence are selected.

Free-space optical communications have distinct advantages over conventional RF and microwave systems by virtue of their high carrier frequencies that permit high modulation bandwidth, enhanced security, freedom from interference, and low power. However, the turbulent atmosphere causes phase variations along the path that are manifested in intensity variations (scintillation) and beam profile distortion and boresight wander. These variations manifest as a multiplicative noise source that reduces the ability of the receiver to determine the information contained in the modulation. For many years, the emphasis throughout this area has been on elucidating those implications of the atmospheric propagation problem that bear on the design and performance of optical communication systems. In this work, it is our intention to elucidate how the addition of adaptive optics to the transmitter or receiver can reduce the effects of atmospheric propagation and, in so doing, to quantify the improvement on the performance of optical communications systems regarding coherent detection.

The European Aerosol Research Lidar Network (EARLINET) was established in 2000 to derive a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on the European scale. At present, EARLINET consists of 25 stations: 16 Raman lidar stations, including 8 multi-wavelength Raman lidar stations which are used to retrieve aerosol microphysical properties. EARLINET performs a rigorous quality assurance program for instruments and evaluation algorithms. All stations measure simultaneously on a predefined schedule at three dates per week to obtain unbiased data for climatological studies. Since June 2006 the first backscatter lidar is operational aboard the CALIPSO satellite. EARLINET represents an excellent tool to validate CALIPSO lidar data on a continental scale. Aerosol extinction and lidar ratio measurements provided by the network will be particularly important for that validation. The measurement strategy of EARLINET is as follows: Measurements are performed at all stations within 80 km from the overpasses and additionally at the lidar station which is closest to the actually overpassed site. If a multi-wavelength Raman lidar station is overpassed then also the next closest 3+2 station performs a measurement. Altogether we performed more than 1000 correlative observations for CALIPSO between June 2006 and June 2007. Direct intercomparisons between CALIPSO profiles and attenuated backscatter profiles obtained by EARLINET lidars look very promising. Two measurement examples are used to discuss the potential of multi-wavelength Raman lidar observations for the validation and optimization of the CALIOP Scene Classification Algorithm. Correlative observations with multi-wavelength Raman lidars provide also the data base for a harmonization of the CALIPSO aerosol data and the data collected in future ESA lidar-in-space missions.

Finite-difference time-domain (FDTD) methods suffer from reduced accuracy when modeling discontinuous dielectric materials, due to the inhererent discretization (“pixellization”). We show that accuracy can be significantly improved by using a sub-pixel smoothing of the dielectric function, but only if the smoothing scheme is properly designed. We develop such a scheme based on a simple criterion taken from perturbation theory, and compare it to other published FDTD smoothing methods. In addition to consistently achieving the smallest errors, our scheme is the only one that attains quadratic convergence with resolution for arbitrarily sloped interfaces. Finally, we discuss additional difficulties that arise for sharp dielectric corners.

The combination of molecular exclusion chromatography and laser polarimetric detection has turned into a carbohydrate separation and quantification system for plant fluids of industrial value, making it possible the evaluation of the quality of sugarcane juices, agave juices and many other plant extracts. Some previous papers described a system where liquid chromatography separation and polarimetric detection using a LASERPOL 101M polarimeter with He-Ne light source allowed the collection and quantification of discrete samples for analytical purposes. In this paper, the authors are introducing a new improved system which accomplishes polarimetric measurements in a continuous flux. Chromatograms of several carbohydrates standard solutions were obtained as useful references to study juice quality of several sugarcane varieties under different physiological conditions. Results by either discrete or continuous flux systems were compared in order to test the validation of the new system. An application of the system to the diagnostics of scalded foliar is described. A computer program allowing the output of the chromatograms to a display on line and the possibility of digital storing, maxima detections, zone integration, and some other possibilities make this system very competitive and self-convincing.

Since the European Space Agency (ESA) geostationary data-relay satellite ARTEMIS started its operation in February 2003, ESA and the Instituto de Astrofisica de Canarias (IAC) have carried out routinely bidirectional optical link experiments between ARTEMIS and the Optical Ground Station (OGS), installed in the Teide Observatory of the IAC in the Canary Islands, Spain. The experiments aimed at characterizing statically and dynamically the performance of the optical downlinks and uplinks in different atmospheric turbulence conditions, together with the development and testing of appropriate theoretical models to predict the link performance. An overview of the OGS and additional facilities on top the IAC Teide Observatory is given, as well as a summary of the statistical results on propagation and communication for different experimental configurations, including different number of transmitting subapertures and divergence in the uplink. Key parameters, like scintillation and fade and surge statistics, are correlated with theoretical predictions and an analysis of the far field pattern is included. The results of the deep space uplink experiments between the OGS and ESA satellite SMART-1 are also presented. Finally ESA free space optical communication programs are summarised, including optical payloads on board different satellites.

As a support for the experimental activities related to the operation of bi-directional optical links between the European Space Agency (ESA) ARTEMIS geostationary satellite and the Optical Ground Station (OGS) in Teide Observatory (Tenerife island, Canary Islands, Spain), carried out by ESA and Instituto de Astrofisica de Canarias (IAC), calculations on the behavior of a multi-beam ground-to-satellite link have been performed. The goal is to assess the impact of refractive turbulence on the uplink (deemed to be more critical than the downlink because of beam-wander effects) and the mitigation effect on the power fluctuations in the satellite receiver achievable with such a space diversity approach, that involves several mutually time-incoherent beams in the uplink. Results from the multiple-beam uplink model and comparison with experiments are presented.

The European Space Agency (ESA) has launched the geostationary data-relay satellite ARTEMIS with one of its payloads being a laser communication terminal (LCT). The LCT is used within the semiconductor-laser intersatellite link experiment (SILEX) to receive Earth observation data transmitted from a similar LCT onboard the SPOT-4 satellite. To support SILEX, ESA has also reached an agreement with the Instituto de Astrofisica de Canarias (JAC) to build the Optical Ground Station (OGS), in the Teide Observatory ofthe IAC. ARTEMIS and the OGS are an ideal and unique test-bed to study and characterise laser beam propagation through atmospheric turbulence. Theoretical models of laser beam propagation through atmospheric turbulence have been reviewed and developed, to predict the performance of the optical links from the propagation and communication point of view. Special effort has been invested in modelling the uplink effects. Optical link experiments have been planned in detail, to gather the necessary data required to be statistically representative, to compare the results with theoretical predictions and to validate and adjust the theoretical models. This comparison will pave the way towards the implementation of deep-space laser communication links. The first results ofthese experiments, presenting the theoretical models, analysing separately downlink and uplink measurements, and comparing the data with the theoretical predictions, are presented.

This article is aimed at describing the technology, system architecture and specifications of a new 3D Nd:YAG scanning lidar. Main features of the system are interspersed low-range and far-range exploration, open user-configuration scanning tools and a specific architectural design based on parallel CPU control, a LabView user interface and a digitally controlled optoelectronic receiver. The latter provides key advantages to the whole system architecture such as calibration of lidar returns in terms of absolute power and repeatability. Issues concerning system responsivity calibration, receiver gain self-calibration, automatic gain control and synchronization offset-drift zeroing and the like, all of which are of prime importance for the lidarist, are presented. As far as we know, these contributions are new to the state-of-the-art of the community of optical and electronic lidar system designers.

Results presented in this contribution correspond to the first measurements made with the transportable lidar system developed by the Universitat Politecnica de Catalunya, which were collected during the eyra 2000 in the city of Barcelona. The system uses a Nd:YAG laser at 1064 nm wavelength and 0.35 J pulse energy at a 20 Hz pulse repetition rate, has a 20 cm diameter telescope and a scanning range of 120 degrees in elevation and 300 degrees in azimuth. In this study only vertical profiles of atmospheric extinction will be shown. Data were acquired under several meteorological situations, showing the influence that this factor has in the arrangement of aerosols in the vertical dimension, and the distributions of backscatter extinction coefficients obtained from the lidar. Data have also been compared to radiosonde profiles acquired in Barcelona at a near time and have shown how the vertical arrangement of aerosols is correlated with changes in atmospheric stability condition, water content and wind direction.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A novel configuration for a reference-beam, continuous-wave, heterodyne low-power radar prototype is presented. It measures both magnitude and sign of the radial component of the displacement velocity. The basic set-up includes a low power (~10 mW) commercial HeNe laser, a beam-splitter, an acousto-optic modulator, and a two-lens system that both focuses the transmitted beam on the target surface and collects the scattered light. Both the reference beam and the radiation collected are focused onto a Si avalanche photo-detector. The self-aligned configuration of the receiver makes possible, theoretically, to perform optimal mixing between the received scattered radiation and the reference beam. The resulting electrical signal is fed to a transimpedance amplifier and displayed on a spectrum analyzer. Laboratory experiments employing as a target the rim of a 50 cm-diameter rotating wheel placed at several distances have been performed. Results concerning detected signal-to-noise ratio, detected- signal spectral width, accuracy of the radial component of the velocity under measurement, system working range, and system tolerance in focus-adjustment distance will be presented and discussed. Compared to a previous homodyne prototype presented by the authors, the present system shows a shorter working range (~12 m compared to nearly ~16 m in the homodyne prototype). We attribute this smaller range to the additional losses in the acousto-optic modulator.