Light-matter Interaction Processes Research Articles

Time-resolved inline digital holography for the study of noncollinear degenerate phase modulation

Recent works demonstrated that digital time-resolved holography is the prospective approach to study nonlinear light-matter interaction processes. In this Letter, we present a straightforward inline holographic approach for studying degenerate phase modulation induced by an inclined collimated pump beam in the isotropic sample. The method is based on a minimization of the difference between experimentally acquired data and simulated inline holograms obtained from a numerical model of pump-probe interaction in optical nonlinear media. A sophisticated experimental data processing algorithm is implemented to provide high sensitivity and a signal-to-noise ratio eligible for soft interaction with a collimated pump beam. The integral phase shift determined by our method can be used to estimate the nonlinear refractive index and the relaxation time for material with a low damage threshold. We validated our approach for the case of soda-lime and BK7 glasses.

Impact of fundamental thermodynamic fluctuations on light propagating in photonic waveguides made of amorphous materials

To improve the detection limit of optical sensors, it is of paramount importance to understand light–matter interaction processes at a fundamental level. At room temperature, the ultimate detection limit is governed amongst others by fundamental thermodynamic fluctuations. Their effect on the properties of light that propagates in amorphous materials is not well understood. Here, we unveil and model for the first time a dominating high-frequency (terahertz-range) noise contribution in the phase of laser light having propagated in optical waveguides, leading to Raman-like sidebands in the optical output spectrum. A salient feature of our approach is to consider a mean relaxation time of the spontaneous random heat flux in the medium, which leads to a spatial correlation of the thermo-refractive noise. The resulting phase noise can be several orders of magnitude larger than what was predicted by earlier models. Our model allows us to explain the origin and specificities of the background that is observed in the Raman optical spectra of silicon nitride waveguides and silica optical fibers. Not only do these findings add a previously unknown dimension to the fundamental knowledge about noise in light–matter interaction, they also need to be taken into account in any optical system in which dynamic fluctuations at the picosecond (ps) or sub-ps level play a role.

Ultrashort Tilted-Pulse-Front Pulses and Nonparaxial Tilted-Phase-Front Beams

Electromagnetic pulses with tilted pulse fronts are instrumental in enhancing the efficiency of many light-matter interaction processes, with prominent examples including terahertz generation by optical rectification, dielectric laser acceleration, ultrafast electron imaging and X-ray generation from free electron lasers. Here, we find closed-form expressions for tilted-pulse-front pulses that capture their exact propagation dynamics even in deeply nonparaxial and sub-single-cycle regimes. By studying the zero-bandwidth counterparts of these pulses, we further obtain classes of nondiffracting wavepackets whose phase fronts are tilted with respect to the direction of travel of the intensity peak. The intensity profile of these nonparaxial nondiffracting wavepackets move at a constant velocity that can be much greater than or much less than the speed of light, and can even travel backwards relative to the direction of phase front propagation.

Granular Permittivity Representation in Extremely Near-Field Light–Matter Interaction Processes

Light-matter interaction processes are significantly affected by surrounding electromagnetic environment. Dielectric materials are usually introduced into an interaction picture via their classical properties, e.g. permittivity, appearing in constitutive relations. While this approach was proven to be applicable in many occasions, it might face limitations when an emitter is situated very close to a material boundary. In this case nonlocal extend of a quantum wave function of an emitter becomes comparable with a distance to a boundary and a lattice constant of a material. Here a semi-classical model, taking into account material's granularity, is developed. In particular, spontaneous emission process in the vicinity of flat boundaries is considered. The material boundary is divided into a pair areas - far zone is modeled as a continuous phase, while the near zone next to a nonlocal emitter is represented with a discrete array of polarizable particles. This array resembles optical properties of the continuous phase under the standard homogenization procedure. Local field effects were shown to lead orders of magnitude corrections to spontaneous emission rates in the case of sub-nanometer emitter-surface separation distances. The developed mesoscopic model enables addressing few aspects of local field corrections in quite complex scenarios, where quantum ab initio techniques yet face challenges owing to involved computational complexity. The developed method could be utilized for designs of quantum sources and networks, enhanced with structured electromagnetic environment.

Vibrational signatures in the THz spectrum of 1,3-DNB: A first-principles and experimental study

Understanding the fundamental processes of light-matter interaction is important for detection of explosives and other energetic materials, which are active in the infrared and terahertz (THz) region. We report a comprehensive study on electronic and vibrational lattice properties of structurally similar 1,3-dinitrobenzene (1,3-DNB) crystals through first-principles electronic structure calculations and THz spectroscopy measurements on polycrystalline samples. Starting from reported x-ray crystal structures, we use density-functional theory (DFT) with periodic boundary conditions to optimize the structures and perform linear response calculations of the vibrational properties at zero phonon momentum. The theoretically identified normal modes agree qualitatively with those obtained experimentally in a frequency range up to 2.5 THz and quantitatively at much higher frequencies. The latter frequencies are set by intra-molecular forces. Our results suggest that van der Waals dispersion forces need to be included to improve the agreement between theory and experiment in the THz region, which is dominated by intermolecular modes and sensitive to details in the DFT calculation. An improved comparison is needed to assess and distinguish between intra- and intermolecular vibrational modes characteristic of energetic materials.

Coherence and resonance effects in the ultra-intense laser-induced ultrafast response of complex atoms.

Both coherent pumping and energy relaxation play important roles in understanding physical processes of ultra-intense coherent light-matter interactions. Here, using a large-scale quantum master equation approach, we describe dynamical processes of practical open quantum systems driven by both coherent and stochastic interactions. As examples, two typical cases of light-matter interactions are studied. First, we investigate coherent dynamics of inner-shell electrons of a neon gas irradiated by a high-intensity X-ray laser along with vast number of decaying channels. In these single-photon dominated processes, we find that, due to coherence-induced Rabi oscillations and power broadening effects, the photon absorptions of a neon gas can be suppressed resulting in differences in ionization processes and final ion-stage distributions. Second, we take helium as an example of multiphoton and multichannel interference dominated electron dynamics, by investigating the transient absorption of an isolated attosecond pulse in the presence of a femtosecond infrared laser pulse.

Optical forces in nanorod metamaterial.

Optomechanical manipulation of micro and nano-scale objects with laser beams finds use in a large span of multidisciplinary applications. Auxiliary nanostructuring could substantially improve performances of classical optical tweezers by means of spatial localization of objects and intensity required for trapping. Here we investigate a three-dimensional nanorod metamaterial platform, serving as an auxiliary tool for the optical manipulation, able to support and control near-field interactions and generate both steep and flat optical potential profiles. It was shown that the ‘topological transition’ from the elliptic to hyperbolic dispersion regime of the metamaterial, usually having a significant impact on various light-matter interaction processes, does not strongly affect the distribution of optical forces in the metamaterial. This effect is explained by the predominant near-fields contributions of the nanostructure to optomechanical interactions. Semi-analytical model, approximating the finite size nanoparticle by a point dipole and neglecting the mutual re-scattering between the particle and nanorod array, was found to be in a good agreement with full-wave numerical simulation. In-plane (perpendicular to the rods) trapping regime, saddle equilibrium points and optical puling forces (directed along the rods towards the light source), acting on a particle situated inside or at the nearby the metamaterial, were found.

ChemInform Abstract: Advances in the Theoretical Understanding of Photon Upconversion in Rare‐Earth Activated Nanophosphors

AbstractReview: 104 refs.

Nanofiber-Mediated Interaction of Light with Cold Atoms

Light-matter interaction processes are extremely attractive for quantum information problems, where one of the main goals consists in a quantum state of light mapping into a collective atomic state. By analogy with the Purcell effect, which exhibits in the presence of a resonator, enhancement of light-matter interaction can be achieved by using a nanofiber [1-2]. In this work we present a theoretical description of light interaction with a cold atomic ensemble mediated the nanofiber, which lies in a base of the experimental realization of a quantum memory protocol [3].

Ultrafast photoinduced linear and circular optical anisotropy in the multiferroic hexagonal manganite YMnO3

Femtosecond laser spectroscopy is an important tool for investigating fundamental processes of light-matter interaction. Here, we report on transient optical anisotropy in the multiferroic hexagonal manganite YMnO${}_{3}$ excited by linearly or circularly polarized laser pulses with $\ensuremath{\sim}$17 fs and $\ensuremath{\sim}$34 fs duration. Spectral dependencies of photoinduced optical rotation and ellipticity at different temperatures are analyzed by considering ultrafast population and relaxation processes near the interband transitions from the hybridized O($2p$)-Mn($3d$) to the Mn($3d$) states at photon energies around 1.6 eV. A Raman coherence time of $\ensuremath{\sim}$10 fs between the excited ${\ensuremath{\Gamma}}_{5}|x\ensuremath{\rangle}$ and ${\ensuremath{\Gamma}}_{5}|y\ensuremath{\rangle}$ states and a relaxation time of $\ensuremath{\sim}$500 fs between the ${\ensuremath{\Gamma}}_{5}|x,y\ensuremath{\rangle}$ and ${\ensuremath{\Gamma}}_{1}|g\ensuremath{\rangle}$ states for the electronic transition ${\ensuremath{\Gamma}}_{1}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{5}$ are determined in that way. The ultrashort Raman coherence time is related to the strong electron Coulomb interaction for the ${\ensuremath{\Gamma}}_{5}|x,y\ensuremath{\rangle}$ states.

Enhancing molecule fluorescence with asymmetrical plasmonic antennas

We propose and justify by the finite-difference time-domain method an efficient strategy to enhance the spontaneous emission of a fluorophore with a multi-resonance plasmonic antenna. The custom-designed asymmetrical antenna consists of two plasmonic nanoparticles with different sizes and is able to couple efficiently to free space light through multiple localized surface plasmon resonances. This design simultaneously permits a large near-field excitation near the antenna as well as a high quantum efficiency, which results in an unusual and significant enhancement of the fluorescence of a single emitter. Such an asymmetrical antenna presents intrinsic advantages over single particle or dimer based antennas made using two identical nanostructures. This promising concept can be exploited in the large domain of light-matter interaction processes involving multiple frequencies.

Directional dependence of the second harmonic response in two-dimensional nonlinear photonic crystals

A two-dimensional periodic arrangement of alternating ferroelectric domains in LiNbO3, with asymmetric domain duty cycle has been used to demonstrate that counterpropagating beams along the polar axis can generate disparate second harmonic patterns, which are nonsymmetrical with respect to the source and the point of observation. These findings provide alternative routes to generate dissimilar light-matter interaction processes in two-dimensional structures assembled onto polar surfaces, including metals for plasmonics or biological compounds.

Finite-Difference Time-Domain Formulation of Stochastic Noise in Macroscopic Atomic Systems

A numerical model based on the finite-difference time-domain method is developed to simulate fluctuations which accompany the dephasing of atomic polarization and the decay of excited state's population. This model is based on the Maxwell-Bloch equations with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -number stochastic noise terms. We successfully apply our method to a numerical simulation of the atomic superfluorescence process. This method opens the door to further studies of the effects of stochastic noise on light-matter interaction and transient processes in complex systems without prior knowledge of modes.

Preface: phys. stat. sol. (b) 244/10

AbstractThe past years have witnessed dramatic progress and interest in the micro‐ and nano‐fabrication techniques of complex photonic systems. These structures are characterized by controlled feature sizes of the order of or even below the wavelength of light. As a consequence, multiple scattering and near field effects have a profound influence on the propagation of light and light–matter interaction in these systems. In turn, this leads to novel regimes for basic research as well as to novel applications in many disciplines. For instance, the modified dispersion relation of photonic crystals and photonic crystal fibers lead to novel nonlinear wave propagation effects such as gap solitons and supercontinuum generation with applications in telecommunication, metrology, medical diagnostics, and many other areas. Similar statements fully apply to linear, nonlinear and quantum optical phenomena in photonic metamaterials and plasmonic systems.Owing to the complex nature of wave interference and light–matter interaction processes, experimental studies of such nano‐photonic systems heavily rely on theoretical guidance both for the design of experiment as well as for the interpretation of the measurements. In almost all cases, a quantitative theoretical description has to be based on advanced computational techniques that solve the corresponding, numerically very demanding linear, nonlinear and coupled partial differential equations.This has led the Wilhelm and Else Heraeus Foundation to devote its 386th Seminar to “Computational Nano‐Photonics”. This seminar has been held in the beautiful setting of the Physikzentrum Bad Honnef, Germany, and has brought together proponents of various computational methods. From 25–28 February 2007, 15 speakers and some 50 participants have summarized and discussed the relative merits and limitations of different methods, and have identified potential future directions. This has sparked a multitude of highly interesting debates many of which, we believe, will continue and will lead to further projects and achievements in this rapidly developing field.This special section provides a (inevitably incomplete) cross‐sectional snapshot of what we feel are some of the most important aspects of the vibrant and highly interdisciplinary field of “Computational Nano‐Photonics”. The contributions range from novel developments on the methodological side all the way to advanced applications of established methods to complex photonic systems and have been written by applied mathematicians, theoretical physicists and electrical engineers. Novel developments in finite element and boundary element methods are, respectively, described in the papers by J. Pomplun et al. and Ch. Hafner. This is followed by the description of the Green’s function integral equation method by T. Søndergaard. E. Popov and N. Bonod report on novel developments of the differential theory of diffraction as applied to photonic micro‐structures. The development of a time‐domain operator‐exponential method using Krylov‐subspace techniques is presented by K. Busch et al. Further developments of the perfectly matched layer open boundary condition for the case of unconditionally stable time‐domain operator‐exponential techniques are given in the paper of H. de Raedt and K. Michielsen. D. Shyroki and A. Lavrinenko discuss how to improve the efficiency of perfectly matched layers using coordinate transformations and the general covariance of Maxwell’s equations in the case of the finite‐difference time‐ and frequency‐domain methods. The last but certainly not least three papers of this special section are devoted to the description of light–matter interaction processes in photonic systems on different levels of sophistication. In the paper of S. Zhukovsky and D. Chigrin, a pedagogical account on the finite‐difference time‐domain and coupled‐mode theory models of simple laser micro‐structures is presented. L. C. Andreani and D. Gerace report on the application of the guided‐mode expansion method to the problem of light propagation and emission in photonic crystal slab structures. Finally, W. Hoyer and co‐workers provide a comprehensive semi‐classical analysis of plasmas in confined geometries.All these contributions to the special section highlight one common theme which summarizes the workshop: A single universal computational method for photonics simply does not exist and a detailed knowledge of different techniques is essential in order to obtain reliable results for any given problem. It is our sincere hope that this special section helps in fostering this point of view and communicates the fascination of today’s computational photonics to a broader audience.

Dynamic nuclear Stark shift in superintense laser fields

The direct interaction of superintense laser fields in the optical frequency domain with nuclei is studied. As main observable, we consider the nuclear dynamic (AC) Stark shift of low-lying nuclear states due to the off-resonant excitation by the laser field. We include the case of accelerated nuclei to be able to control the frequency and the intensity of the laser field in the nuclear rest frame over a wide range of parameters. We find that AC-Stark shifts of the same order as in typical quantum optical systems relative to the respective transition frequencies are feasible with state-of-the-art or near-future laser field intensities and moderate acceleration of the target nuclei. Along with this shift, but only at intensities above the critical field strength, we find laser-induced modifications to the proton root-mean-square radii and to the proton density distribution. We thus expect direct laser-nucleus interaction to become of relevance together with other super-intense light-matter interaction processes such as pair creation.

Entanglement Change in Atomic Photoionization

Photoionization is one of the basic processes of light-matter interaction, which may be used to transfer at least part of quantum information from photons to electrons in the continuum in such a way that the final state electron carries composite information of the initial electron and of the incident photon. We examine how photoionization may change entanglement of electrons. Our result shows that entanglement in one degree of freedom is affected by a transition in another degree of freedom through the coupling of the two degrees of freedom.

Transient nutation in a double resonance configuration: A dressed state description

Nutation occurs when a strong, coherent field is suddenly applied to a transition. It manifests dynamic processes of light-matter interactions and has been extensively studied. In this paper we report the observation of nutation in a double resonance configuration by extending the usual configuration of a two-level system, interacting with a single pulsed field, to that of a three-level system, interacting with two fields simultaneously. The nutation associated with driving one transition is shown to depend on whether the second transition is driven. The Rabi frequency associated with the second driving transition introduces a beating superimposed on the observed nutation. All these observed characteristics can be satisfactorily explained using a dressed state model.