Coherent Optical Interactions Research Articles

Quantum Mechanical Comparison between Lithiated and Sodiated Silicon Nanowires

This computational research study will compare the specific charge capacity (SCC) between lithium ions inserted into crystallized silicon (c-Si) nanowires with that of sodium ions inserted into amorphous silicon (a-Si) nanowires. It will be demonstrated that the potential energy V(r) within a lithium–silicon nanowire supports a coherent energy state model with discrete electron particles, while the potential energy of a sodium–silicon nanowire will be discovered to be essentially zero, and, thus, the electron current that travels through a sodiated silicon nanowire will be modeled as a free electron with wave-like characteristics. This is due to the vast differences in the electric fields of lithiated and sodiated silicon nanowires, where the electric fields are of the order of 1010 V/m and 10−15 V/m, respectively. The main reason for the great disparity in electric fields is the presence of optical amplification within lithium ions and the absence of this process within sodium ions. It will be shown that optical amplification develops coherent optical interactions, which is the primary reason for the surge of specific charge capacity in the lithiated silicon nanowire. Conversely, the lack of optical amplification is the reason for the incoherent optical interactions within sodium ions, which is the reason for the low presence of SCC in sodiated silicon nanowires.

Ultrafast valley-selective coherent optical manipulation with excitons in WSe2 and MoS2 monolayers

Increasing the speed limits of conventional electronics requires innovative approaches to manipulate other quantum properties of electrons besides their charge. An alternative approach utilizes the valley degree of freedom in low-dimensional semiconductors. Here we demonstrate that the valley degeneracy of exciton energies in transition metal dichalcogenide monolayers may be lifted by coherent optical interactions on timescales corresponding to few tens of femtoseconds. The optical Stark and Bloch-Siegert effects generated by strong nonresonant circularly-polarized light induce valley-selective blue shifts of exciton quantum levels by more than 30 meV. We show these phenomena by studying the two most intensive exciton resonances in transiton metal dichalcogenide monolayers and compare the results to a theoretical model, which properly includes the Coulomb interaction and exciton dispersion. These results open the door for ultrafast valleytronics working at multiterahertz frequencies.

Coherent optical interaction between plasmonic nanoparticles and small organic dye molecules in microcavities

We investigate the lasing performance of different composite gain materials consisting of small organic molecules, gold nanoparticles, and a polymer matrix mixed on a nanoscale within a spin-coated thin film. We experimentally demonstrate that the localized surface plasmon resonances of randomly distributed gold nanoparticles can oscillate in phase with the standing wave of the surrounding microcavity resonator and contribute to a lower lasing threshold.

Photonic coherence effects from dual-waveguide coupled pair of co-resonant microring resonators.

We theoretically describe photonic manifestations of electromagnetically induced transparency (EIT) and absorption (EIA) using co-resonant coupled microresonators (CMRs) as opposed to detuned CMRs explored previously. Here the coherent optical interactions between the two resonators are mediated via two adjacent waveguides and the photonic EIT and EIA are achieved by coupling two identical resonators to the waveguides with equal strength, although this coupling is distinct for each waveguide. Using co-resonant CMRs based on either identical or distinct intrinsic quality factor (Q) resonators, these effects may be obtained in both transmission and reflection. We elucidate origin of the sharp features in the spectra of co-resonant CMRs. Furthermore, we demonstrate tunability of these features using Q-tunable resonators, which may lead to tunable slow and fast light effects. The theoretical model described here greatly simplifies accurate numerical studies of coupled-resonator effects, as no additional calculations are required to account for the waveguide dispersion.

Single Quantum Dot Nonlinear Optical Spectroscopy

We report a study of the coherent nonlinear optical response of individual excitons localized in GaAs quantum dots. Our data show that the nonlinear response is comprised of an incoherent contribution dominated by saturation of the oscillator strength and a coherent contribution giving rise to population pulsations. The results compare well with present theory and show the similarities with atoms and quantum dots in their coherent optical interaction with light. The measured energy relaxation and dephasing rates are comparable, reflecting the absence of significant pure dephasing at low temperatures. In addition, we use nonlinear spectroscopy to investigate quantum dot coupling showing the presence of an incoherent coupling leading to fast energy relaxation. The polarization properties as well as the fine structure splitting are also discussed.

Nonlinear Nano-Optics: Probing One Exciton at a Time

Abstract : Coherent nonlinear optical spectroscopy of individual excitons in GaAs quantum dots is demonstrated and shows strong similarities with atoms in their coherent optical interaction, unlike higher dimensional heterostructures. The nonlinear response is dominated by an incoherent contribution (saturation) and a coherent contribution (population pulsations) of the single dot and compares well with present theory. The data shows that energy relaxation and dephasing rates are comparable, reflecting the absence of significant pure dephasing, and also demonstrate the presence of interdot energy transfer.

Introduction

This focus issue of Optics Express is concerned with coherent optical interactions in condensed matter. This field has shown tremendous growth over the past few years - a phenomenon at least partly due to the remarkable progress in ultrafast lasers and measurement techniques which has been a prerequisite to observing coherent transient phenomena on the short time scales required in condensed matter systems. There are many kinds of coherence which can be generated by short optical pulses in solids, including electronic interband and intraband coherence, and coherent phonon fields. The four papers in this issue investigate various aspects of these phenomena.

Coherent optical interaction of a multilevel system with fluctuating laser fields.

The effect of stochastic laser phase fluctuations on nonlinear optical phenomena are investigated within the phase-diffusion model. Averaged equations of motion are derived in the limit of infinitely short correlation times and the results are applied to multiphoton absorption and to four-wave mixing. The effect of the stochastic phase fluctuations is shown to be equivalent to a ${T}_{2}$ dephasing process, and a procedure is described for the inclusion of this equivalence in many nonlinear-optical problems. When a given mode contributes n photons to a multiphoton absorption process, its contribution to the width of the multiphoton transition is ${n}^{2}$ times its own stochastic width. When correlated lasers are used as the excitation sources in four-wave-mixing experiments, (new) stochastic-fluctuation-induced extra resonances in four-wave mixing (SFIER4) will be observed, in complete analogy to the extra resonances induced by collisions [pressure-induced extra resonances in form-wave mixing (PIER4)].