Alexander Chen, Yuntian Wang, Md Sadman Sakib Rahman
et al.
Nonlinear computation is essential for various information processing tasks. Optical implementations are attractive because passive light propagation can manipulate high-dimensional signals with extreme throughput and parallelism; yet realizing nonlinear mappings in optical hardware remains challenging due to the weak nonlinearity of optical materials and the large intensities required to induce nonlinear interactions. This challenge is further amplified in many systems that operate with incoherent illumination, motivating a coherence-aware framework for scalable optical nonlinear processing. Here, we show that linear optical systems, in particular, optimized diffractive processors comprising passive surfaces, can perform large-scale nonlinear function approximation under spatially incoherent or partially coherent illumination, when preceded by intensity-only input encoding. We quantify how the accuracy of the nonlinear function approximation varies with the degree of parallelism, the number of diffractive layers, and the number of trainable diffractive features. Numerical results demonstrate snapshot computation of up to one million distinct nonlinear functions in a single forward pass through a diffractive processor, with the function outputs spatially multiplexed and read out using densely packed detectors at the output. We further provide a proof-of-concept experimental demonstration under incoherent illumination from a liquid crystal display (LCD), enabled by a model-free in situ learning strategy that jointly optimizes the diffractive profile and detector readout geometry in the presence of hardware imperfections and misalignments. Our findings establish diffractive processors as a massively parallel universal function approximator for both spatially incoherent and partially coherent illumination.
Elizaveta Gangrskaia, Thomas Schachinger, Christoph Eisenmenger-Sittner
et al.
At optical frequencies, interactions of the electric field component of light with matter are dominating, whereas magnetic dipole transitions are inherently weak and challenging to access independently from electric dipole transitions. However, magnetic dipole transitions are of interest, as they can provide valuable complementary information about the matter under investigation. Here, we present an approach which combines structured light irradiation with tailored sample morphology for enhanced and highcontrast optical magnetic field excitation, and we test this technique on Eu$^{3+}$ ions. We generate spectrally tunable, narrowband, polarization-shaped ultrashort laser pulses, which are specifically optimized for the spectral and the spatial selective excitation of magnetic dipole and electric dipole transitions in Eu$^{3+}$ : Y$_2$O$_3$ nanostructures integrated into a metallic antenna. In the presence of the metallic antenna, the excitation with an azimuthally polarized beam is shown to provide at least a 3.0-4.5-fold enhancement of the magnetic dipole transition as compared to a radially polarized beam or a conventional Gaussian beam. Thus, our setup provides new opportunities for the spectroscopy of forbidden transitions.
As a novel layered noble metal dichalcogenide material, palladium diselenide (PdSe2) has attracted wide interest due to its excellent optical and electronic properties. In this work, a strong third-order nonlinear optical response of 2D PdSe2 films is reported. We conduct both open aperture (OA) and closed-aperture (CA) Z scan measurements with a femtosecond pulsed laser at 800 nm to investigate the nonlinear absorption and nonlinear refraction, respectively. In the OA experiment, we observe optical limiting behaviour originating from large two photo absorption (TPA) in the PdSe2 film of \b{eta} = 3.26 x 10-8 m/W. In the CA experiment, we measure a peak-valley response corresponding to a large and negative Kerr nonlinearity of n2 = -1.33 x 10-15 m2/W, two orders of magnitude larger than bulk silicon. In addition, the variation of n2 as a function of laser intensity is also characterized, with n2 decreasing in magnitude when increasing incident laser intensity, becoming saturated at n2 = -9.96 x 10-16 m2/W at high intensities. Our results show that the extraordinary third order nonlinear optical properties of PdSe2 have strong potential for high-performance nonlinear photonic devices.
This paper presents the optimization of a dual-chirped optical parametric amplification (DC-OPA) scheme for producing an ultrafast intense infrared (IR) pulse. By employing a total energy of 0.77 J Ti:sapphire pump laser and type-I BBO crystals, an IR pulse energy at the center wavelength of 1.7 $μ$m exceeded 0.1 J using the optimized DC-OPA. By adjusting the injected seed spectrum and prism pair compressor with a gross throughput of over 70 \%, the 1.7-$μ$m pulse was compressed to 31 fs, which resulted in a peak power of up to 2.3 TW. Based on the demonstration of the BBO type-I DC-OPA, we propose a novel OPA scheme called the $dual~pump$ DC-OPA for producing a high-energy IR pulse with a two-cycle duration.
Anderson localization is a ubiquitous interference phenomenon in which waves fail to propagate in a disordered medium. Unlike in a classical resonator, satisfying the favorable condition for the interference in a disordered medium is truly a statistical problem in physics. Recent progress in realizing Anderson localization is mainly limited to the iterative method for optimizing the disordered medium. Availability of an in-situ, active control for optimization surely paves the way of realizing the Anderson localization and its applications. In this letter, we have proposed an electro-optic controllable disordered photonic crystal and demonstrated its performance in terms of Anderson localization of light in situ in real time by application of an external electric field. We believe that Anderson localization using this medium is not only expected to address the scientific rigors but also to introduce an extra degree of freedom i.e., the tunability in its technical applications.
Emanuel Peinke, Tobias Sattler, Guilherme Monteiro Torelly
et al.
We report on the generation of few-ps long spontaneous emission pulses by quantum dots (QDs) in a switched optical microcavity. We use a pulsed optical injection of free charge carriers to induce a large frequency shift of the fundamental mode of a GaAs/AlAs micropillar. We track in real time by time-resolved photoluminescence its fundamental mode during its relaxation, using the emission of the QD ensemble as a broadband internal light source. Sub-ensembles of QDs emitting at a given frequency, interact transiently with the mode and emit an ultrashort spontaneous emission pulse into it. By playing with switching parameters and with the emission frequency of the QDs, selected by spectral filtering, pulse durations ranging from 300 ps down to 6 ps have been obtained. These pulses display a very small coherence length, which opens potential applications in the field of ultrafast imaging. The control of QD-mode coupling on ps-time scales establishes also cavity switching as a key resource for quantum photonics.
Ethan R. Avery, Peeyush Sahay, Shirsendu Nanda
et al.
Optical scattering strength of fractal optical disordered media with varying fractal dimension is reported. The diffusion limited aggregation (DLA) technique is used to generate fractal samples in 2D and 3D, and fractal dimensions are calculated using the box-counting method. The degree of structural disorder of these samples are calculated using their light localization strength, using the inverse participation ratio (IPR) analyses of the optical eigenfunctions. Results show non-monotonous behavior of the disorder-induced scattering strength with the fractal dimension, attributed to the competition between increasing structural disorder due to decrease in fractality versus decrease in scattering centers due to decreasing fractality.
In this work, exact mathematical expansions for the intrinsic electromagnetic (EM) or optical cross-sections (i.e., extinction, scattering and absorption) for a pair of perfectly conducting circular cylinders in a homogeneous medium are derived. The incident illuminating field is an axially-polarized electric field composed of plane travelling waves with an arbitrary angle of incidence in the polar plane. The formalism is based on the multipole modal expansion method in cylindrical coordinates and the translational addition theorem applicable to any range of frequencies. An effective EM field, incident on the probed cylinder, is defined first, which includes the initial and re-scattered field from the second cylinder. Subsequently, it is used jointly with the scattered field to derive the mathematical expressions for the intrinsic/local cross-sections based on integrating their corresponding time-averaged intensities over the surface of the probed object by applying the Poynting theorem. Numerical computations for the intrinsic extinction (or scattering) energy efficiencies for a pair of conducting circular cylinders with different radii in a homogeneous medium are considered. Emphasis is given on varying the interparticle distance, the angle of incidence, and the dimensionless sizes of the cylinders. The results computed a priori can be useful in the full characterization of a multiple scattering system of many particles, in conjunction with experimental data for the extrinsic cross-sections.
We studied the excitation dynamics of a finite quantum system with an intense optical near field (ONF) from a perspective of light-dressed states. A simple model consisting of a single electron and a nano-sized short dipole source were employed. By calculating the time-dependent wave function subjected to the ONF, we demonstrated that the optical responses involved not only the first- and third-order but also the second-, fourth-order harmonic generations that were not obtained from conventional spatially homogeneous laser fields. In order to elucidate the origins of the exotic high-order harmonic generations, the dressed states altered by the ONF were explored. The result showed that the spatial distribution of the dressed states were significantly influenced by the ONF, making forbidden optical transitions to be allowed by parity breaking. This was caused by the spatial inhomogeneousness of the ONF, specifically its asymmetry, that was inherited to the dressed states.
Silvia Viciani, Stefano Gherardini, Manuela Lima
et al.
Transport phenomena represent a very interdisciplinary topic with applications in many fields of science, such as physics, chemistry, and biology. In this context, the possibility to design a perfectly controllable experimental setup, where to tune and optimize its dynamics parameters, is a challenging but very relevant task to emulate, for instance, the transmission of energy in light harvesting processes. Here, we experimentally build a scalable and controllable transport emulator based on optical fiber cavity networks where the system noise parameters can be finely tuned while maximizing the transfer efficiency. In particular, we demonstrate that disorder and dephasing noise are two control knobs allowing one to play with constructive and destructive interference to optimize the transport paths towards an exit site. These optical setups, on one side, mimic the transport dynamics in natural photosynthetic organisms and, on the other, are very promising platforms to artificially design optimal nanoscale structures for novel, more efficient, clean energy technologies.
We discuss the prospects for enhancing absorption and scattering of light from a weakly coupled atom in a high-finesse optical cavity by adding a medium with large, positive group index of refraction. The slow-light effect is known to narrow the cavity transmission spectrum and increase the photon lifetime, but the quality factor of the cavity may not be increased in a metrologically useful sense. Specifically, detection of the weakly coupled atom through either cavity ringdown measurements or the Purcell effect fails to improve with the addition of material slow light. A single-atom model of the dispersive medium helps elucidate why this is the case.
The complex nonperturbative color-confining dynamics of QCD is well captured in a semiclassical effective theory based on superconformal quantum mechanics and its extension to the light-front. I describe here how this new approach to hadron physics incorporates confinement, the appearance of nearly massless pseudoscalar particles, and Regge spectroscopy consistent with experiment. It also gives remarkable connections between the meson and baryon spectrum across the light and heavy-light hadron spectrum. I also briefly discuss how higher spin states are consistently described in this framework by the holographic embedding of the superconformal theory in a higher dimensional semiclassical gravity theory.
Agnese Callegari, Mite Mijalkov, A. Burak Gököz
et al.
Optical tweezers have found widespread application in many fields, from physics to biology. Here, we explain in detail how optical forces and torques can be described within the geometrical optics approximation and we show that this approximation provides reliable results in agreement with experiments for particles whose characteristic dimensions are larger than the wavelength of the trapping light. Furthermore, we provide an object-oriented software package implemented in MatLab for the calculation of optical forces and torques in the geometrical optics regime: \texttt{OTGO - Optical Tweezers in Geometrical Optics}. We provide all source codes for \texttt{OTGO} as well as the documentation and code examples -- e.g., standard optical tweezers, optical tweezers with elongated particle, windmill effect, Kramers transitions between two optical traps -- necessary to enable users to effectively employ it in their research and teaching.
MicroBooNE is a neutrino experiment located on axis in the Booster Neutrino Beamline, at Fermi National Accelerator Laboratory, scheduled to begin data collection in 2014. The MicroBooNE detector consists of two main components: a large liquid argon time projection chamber (LArTPC), and a light collection system. Thirty two 8-inch diameter cryogenic photomultiplier tubes (PMTs) will detect the scintillation light generated in the liquid argon. In this article, we describe the basic features of the system and current status of MicroBooNE light collection system.
We investigate the tree level multi-gluon components of the gluon light cone wavefunctions in the light cone gauge keeping the exact kinematics of the gluon emissions. We focus on the components with all helicities identical to the helicity of the incoming gluon. The recurrence relations for the gluon wavefunctions are derived. In the case when the virtuality of the incoming gluon is neglected the exact form of the multi-gluon wavefunction as well as the fragmentation function is obtained. Furthermore we analyze the 2 to N tree-level gluon scattering in the framework of light-front perturbation theory and we demonstrate that the amplitude for this process can be obtained from the 1 to N+1 gluon wavefunction. Finally, we demonstrate that our results for selected helicity configurations are equivalent to the Parke-Taylor amplitudes.
To enable multiple functions of plasmonic nanocircuits, it is of key importance to control the propagation properties and the modal distribution of the guided optical modes such that their impedance matches to that of nearby quantum systems and desired light-matter interaction can be achieved. Here, we present efficient mode converters for manipulating guided modes on a plasmonic two-wire transmission line. The mode conversion is achieved through varying the path length, wire cross section and the surrounding index of refraction. Instead of pure optical interference, strong near-field coupling of surface plasmons results in great momentum splitting and modal profile variation. We theoretically demonstrate control over nanoantenna radiation and discuss the possibility to enhance nanoscale light-matter interaction. The proposed converter may find applications in surface plasmon amplification, index sensing and enhanced nanoscale spectroscopy.
We describe several projects addressing the growth of galaxies and massive black holes, for which adaptive optics is mandatory to reach high spatial resolution but is also a challenge due to the lack of guide stars and long integrations. In each case kinematics of the stars and gas, derived from integral field spectroscopy, plays a key role. We explain why deconvolution is not an option, and that instead the PSF is used to convolve a physical model to the required resolution. We discuss the level of detail with which the PSF needs to be known, and the ways available to derive it. We explain how signal-to-noise can limit the resolution achievable and show there are many science cases that require high, but not necessarily diffraction limited, resolution. Finally, we consider what requirements astrometry and photometry place on adaptive optics performance and design.
A light pulse propagating in a suddenly switched on photonic lattice, when the central frequency lies in the photonic band gap, is an analog of the Rabi model where the two-level system is the two resonant (i.e. Bragg-coupled) Fourier modes of the pulse, while the photonic lattice serves as a monochromatic external field. A simple theory of these Rabi oscillations is given and confirmed by the numerical solution of the corresponding Maxwell equations. This is a direct, i.e. temporal, analog of the Rabi effect, additionally to the spatial analog in optical beam propagation described in Opt. Lett. 32, 1920 (2007). An additional high-frequency modulation of the Rabi oscillations reflects the lattice-induced energy transfer between the electric and magnetic fields of the pulse.