Nonlinear Optical Rotation Research Articles

Second-Harmonic Generation Optical Rotation Solely Attributable to Chirality in Plasmonic Metasurfaces.

Chiral plasmonic nanostructures, those lacking mirror symmetry, can be designed to manipulate the polarization of incident light resulting in chiroptical (chiral optical) effects such as circular dichroism (CD) and optical rotation (OR). Due to high symmetry sensitivity, corresponding effects in second-harmonic generation (SHG-CD and SHG-OR) are typically much stronger in comparison. These nonlinear effects have long been used for chiral molecular analysis and characterization; however both linear and nonlinear optical rotation can occur even in achiral structures, if the structure is birefringent due to anisotropy. Crucially, chiroptical effects resulting from anisotropy typically exhibit a strong dependence on structural orientation. Here we report a large second-harmonic generation optical rotation of ±45°, due to intrinsic chirality in a highly anisotropic helical metamaterial. The SHG intensity is found to strongly relate to the structural anisotropy; however, the angle of SHG-OR is invariant under sample rotation. We show that by tuning the geometry of anisotropic nanostructures, the interaction between anisotropy, chirality, and experimental geometry can allow even greater control over the chiroptical properties of plasmonic metamaterials.

Nonlinear and anisotropic polarization rotation in two-dimensional Dirac materials

We predict nonlinear optical polarization rotation in two dimensional massless Dirac systems including graphene and 8-$Pmmn$ borophene. When illuminated, a continuous wave optical field leads to a nonlinear steady state of photo-excited carriers in the medium. The photo-excited population inversion and the inter-band coherence gives rise to a finite transverse optical conductivity, $\sigma_{xy} (\omega)$. This in turn leads to definitive signatures in associated Kerr and Faraday polarization rotation, which are measurable in a realistic experimental scenario.

Intensity-dependent modulation of optically active signals in a chiral metamaterial

Chiral media exhibit optical phenomena that provide distinctive responses from opposite circular polarizations. The disparity between these responses can be optimized by structurally engineering absorptive materials into chiral nanopatterns to form metamaterials that provide gigantic chiroptical resonances. To fully leverage the innate duality of chiral metamaterials for future optical technologies, it is essential to make such chiroptical responses tunable via external means. Here we report an optical metamaterial with tailored chiroptical effects in the nonlinear regime, which exhibits a pronounced shift in its circular dichroism spectrum under a modest level of excitation power. Strong nonlinear optical rotation is observed at key spectral locations, with an intensity-induced change of 14° in the polarization rotation from a metamaterial thickness of less than λ/7. The modulation of chiroptical responses by manipulation of input powers incident on chiral metamaterials offers potential for active optics such as all-optical switching and light modulation.

Pulse Propagation with Self-Phase Modulation in Nonlinear Chiral Fiber and Its Applications**Supported by the National Natural Science Foundation of China under Grant No 60977032, and the Program for Innovation Research of Science of Harbin Institute of Technology (PIRS-HIT) under Grant No T201407.

From Maxwell's equations and Post's formalism, a generalized chiral nonlinear Schrödinger equation (CNLSE) is obtained for the nonlinear chiral fiber. This equation governs light transmission through a dispersive nonlinear chiral fiber with joint action of chirality in linear and nonlinear ways. The generalized CNLSE shows a modulation of chirality to the effect of attenuation and nonlinearity compared with the case for a conventional fiber. Simulations based on the split-step beam propagation method reveal the role of nonlinearity with cooperation to chirality playing in the pulse evolution. By adjusting its strength the role of chirality in forming solitons is demonstrated for a given circularly polarized component. The application of nonlinear optical rotation is also discussed in an all-optical switch.

Phase-controlled optical Faraday rotation in a closed-loop atomic system

We investigate the nonlinear optical Faraday rotation (OFR) of a probe field passing through a double V–type closed-loop atomic system in the absence of an external static magnetic field. Enhancement OFR is obtained by applying the control fields to establish the closed-loop configuration. It is shown that the scattering of both control fields into the probe field mode via wave mixing induce an OFR enhancement. We find that the rotation of the polarization plane in the nonlinear OFR depends on the intensity and relative phase of applied fields and can be controlled by these parameters. It is demonstrated that applying a microwave field to the system has a constructive role in enhancement of phase-controlled nonlinear OFR.

CLUSTERIZATION OF FULLERENE C70 MOLECULES IN SOLUTIONS AND ITS INFLUENCE TO OPTICAL AND NONLINEAR OPTICAL PROPERTIES OF SOLUTIONS

Nonlinear optical rotation of elliptically polarized laser pulses (λ = 532 nm, τFWHM ~ 12 ns) in benzene, toluene and binary (toluene+acetonitrile) solutions of fullerene C 70–D5h(6) has been investigated experimentally. High-resolution transmission electron microscope studies of C 70-solutions showed stable ball-shaped C 70-clusters formation in toluene+acetonitrile mixtures. It has been demonstrated, that the C 70-clusters sizes depend on initial concentration of C 70, as well as volume fraction of acetonitrile in solvent mixture. The most probable model of C 70-clusterization in solutions was proposed. Correlations between the processes of nonlinear rotation of polarization ellipse, change of electronic absorption spectra and C 70-clusters formation in solutions have been demonstrated. Physical mechanisms of laser-induced optical activity in C 70-solutions have been discussed. The values of the nonlinear Kerr coefficient (n2) and nonlinear susceptibility component [Formula: see text] of C 70-solutions in: toluene, benzene with various polarization ellipticity (θ = 0.2-0.8), and toluene+acetonitrile at different concentrations of C 70 for various volume fractions of acetonitrile have been determined.

Enhancement of optical effects in zero-reflection metal slabs based on light-tunneling mechanism in metamaterials

Metals have many extraordinary optical properties. However, thick metals are nice mirrors, which prevent light penetrating deep into them. Since the skin depth is very thin, most optical properties of bulk metals are unavailable. In this paper, we review the way of reducing reflections in thick metal slabs by coating dielectric photonic crystals, based on the light-tunneling mechanism in metamaterials. Owing to the boost of local fields in the metals, many optical effects such as nonlinear effects, optical extinction (absorption) and optical rotation are greatly enhanced in these simple structures. The enhancement of optical effects in thick metals may be very useful in some optical devices including optical switches and diodes, absorbers, insulators and so on.

Development of NMOR magnetometer for spin-maser EDM experiment

We have been developing a high sensitivity atomic magnetometer for atomic EDM experiments using a lowfrequency nuclear spin maser. In the developed nuclear spin maser of 129Xe, suppression of drift and fluctuation in the magnetic field is one of the important issues. The magnetometer being developed for spin maser EDM experiments utilizes the nonlinear magneto optical rotation (NMOR) e_ect in Rb atomic vapor. The enhancement of the optical rotation in a small magnetic field relies on the long spin-coherence time of Rb atoms in a vapor cell. The NMOR spectrum was measured by using fabricated Rb cells coated with an anti-relaxation material. The NMOR spectrum dependence on laser frequency, cell coating, and laser beam diameter were investigated. The magnetic sensitivity at present is 0:2μG/√Hz from observed NMOR and noise spectra.

Magnetometric sensitivity optimization for nonlinear optical rotation with frequency-modulated light: Rubidium D2 line

Atomic spin polarization of alkali atoms in the ground-state can survive thousands of collisions with paraffin-coated cell walls. The resulting long spin-relaxation times achieved in evacuated, paraffin-coated cells enable precise measurement of atomic spin precession and energy shifts of ground-state Zeeman sublevels. In the present work, nonlinear magneto-optical rotation with frequency-modulated light (FM NMOR) is used to measure magnetic field-induced spin precession for rubidium atoms contained in a paraffin-coated cell. The magnetometric sensitivity of FM NMOR for the rubidium D2 line is studied as a function of light power, detuning, frequency-modulation amplitude, and rubidium vapor density. For a 5-cm-diameter cell at temperature T≈35 °C, the optimal shot-noise-projected magnetometric sensitivity is found to be 2×10−11 G/Hz (corresponding to a sensitivity to spin precession frequency of ≈10 μHz/Hz or a sensitivity to Zeeman sublevel shifts of ≈4×10−20 eV/Hz).

Mechanisms of holographic recording in rubidium vapor close to resonance

We investigate the nonlinear refraction and absorption related to holographic writing in rubidium vapor at resonance with 87Rb D2 transition. The numerical model based on time-dependent density matrix formalism is used. The theory adequately describes nonlinear optical rotation and absorption at light intensities in the 0.1-30 mW/cm2 range. The basic configurations for obtaining amplitude and phase gratings for nearly equal frequencies of writing beams are investigated experimentally, and the writing time is estimated.

Theory, calculation and observation of nonlinear optical activity in chiral molecules

Since the late 1960s theories have appeared which address nonlinear optical activity, that is, optical rotation and circular dichroism effects which depend on the intensity of the light incident on the sample. Only recently have there been efforts based on these theories to compute the relevant molecular parameters and experimental attempts to measure the predicted phenomena. This Report reviews the field with emphasis on progress made in the last ten years for isotropic media.

Magneto Optical Rotation in the Doppler- broadened Spectrum of Rb atoms in Intermediate fields

Doppler-broadened absorption spectrum of rubidium (87Rb and 85Rb) D2 line has been studied in the presence of a magnetic field of intermediate strength i.e. up to 5mT. Resonant non - linear magneto optical rotation is measured in the Doppler broadened spectrum of rubidium atomic vapour. Low light intensity approximation in the intermediate field region has been made to calculate the magneto optical rotation and to compare with experimental data. The enhancement of non-linear magneto optical rotation is discussed taking into account hole burning and circular birefringence in the intermediate field region.

Characterization of intensity-dependent optical rotation phenomena in chiral molecules in solution

The rotation of the plane of polarization of linearly polarized light by chiral molecules in solution is due to a forward scattering event. Ordinary optical rotation, a single-photon effect, is independent of intensity. As the light intensity is increased, other effects can appear, such as two-photon scattering or alignment of the molecule by one photon and scattering with a change of polarization by another. Both of these effects result in intensity-dependent (or nonlinear) optical rotation. A polarimeter was used to measure the nonlinear optical rotation of solutions in a heterodyne experiment. No nonlinear optical rotation was found in molecules lacking an absorption band near the laser frequency. In the three pyrimidine nucleosides studied, which do have such an absorption band, a nonlinear optical rotation was identified that was cumulative with each laser pulse. The effect persisted with a time constant that was on the order of seconds and characteristic of the molecule.

Ab initio calculations of nonlinear optical rotation by several small chiral molecules and by uridine stereoisomers

Expressions for nonlinear optical rotation are presented based on the quantum theory of optical birefringence of Atkins and Barron [Proc. R. Soc. London, Ser. A 304, 303 (1968); 306, 119 (1968)]. As concrete examples, the ordinary and nonlinear optical rotations are calculated with density functional theory (DFT) methodology for some simple single-ring molecules, namely, oxaziridine, diaziridine, and their derivatives, and for two, somewhat more complicated, conformations of uridine. For the single-ring molecules, (1) the angles of the ordinary optical rotation are mostly positive and (2) the contributions of the nonlinear effect to the total optical rotation depend both on the nature of the substituted species and of the host atom located on the ring. For the two conformations of uridine, (1) the signs of nonlinear optical rotation differ even though their ordinary optical rotations have the same sign and (2) whether the molecular structures are geometrically optimized with Hartree-Fock or DFT methodologies has no significant effect on the calculated nonlinear optical rotation when gauge-including atomic orbitals were used, even though the basis sets are small. These studies are expected to be helpful for interpretation of experimental results on nonlinear optical rotation by molecules underway in our research group.

Nonlinear optical spectroscopy of chiral molecules

We review nonlinear optical processes that are specific to chiral molecules in solution and on surfaces. In contrast to conventional natural optical activity phenomena, which depend linearly on the electric field strength of the optical field, we discuss how optical processes that are nonlinear (quadratic, cubic, and quartic) functions of the electromagnetic field strength may probe optically active centers and chiral vibrations. We show that nonlinear techniques open entirely new ways of exploring chirality in chemical and biological systems: The cubic processes give rise to nonlinear circular dichroism and nonlinear optical rotation and make it possible to observe dynamic chiral processes at ultrafast time scales. The quadratic second-harmonic and sum-frequency-generation phenomena and the quartic processes may arise entirely in the electric-dipole approximation and do not require the use of circularly polarized light to detect chirality. They provide surface selectivity and their observables can be relatively much larger than in linear optical activity. These processes also give rise to the generation of light at a new color, and in liquids this frequency conversion only occurs if the solution is optically active. We survey recent chiral nonlinear optical experiments and give examples of their application to problems of biophysical interest.

Influence of transverse magnetic fields and depletion of working levels on the nonlinear resonance Faraday effect

The nonlinear resonance Faraday effect is studied under the condition of coherent population trapping in 87Rb vapor at the D1-line F=2→F′=1 transition. The influence of transverse magnetic fields on the nonlinear optical Faraday rotation is studied. For the transverse fields perpendicular to the electromagnetic-wave polarization, a simple theoretical model is proposed, which is in good agreement with experimental data. The optimal intensity providing the maximum sensitivity is found based on the results obtained. The influence of working-level depletion on the parameters of Faraday rotation in open systems is studied experimentally and theoretically. The system was closed in the experiment by using an additional laser to increase the sensitivity and extend the dynamic range of measured fields. The importance of compensating for the depletion in the presence of spurious magnetic fields is shown; in particular, the sensitivity was enhanced by a factor of 50 in experiments with a buffer gas.

Nonlinear resonant polarization rotation under conditions of coherent population trapping

Nonlinear resonant optical rotation was studied over a wide range of experimental parameters at the Rb D1F = 2→F′ = 1 transition in the 87Rb vapor under conditions of coherent population trapping. The angle of rotation was found to depend nonmonotonically on the laser intensity and applied magnetic field. The effect of optical pumping out to the level F = 1 is discussed. It is demonstrated experimentally that the Faraday rotation angle increases twofold upon the compensation for pumping.

Nonlinear electro- and magneto-optical effects related to Bennett structures

Optical pumping of an atomic sample with narrow-band light can create sub-Doppler features, known as Bennett structures, in the velocity distribution of state populations. In the presence of static magnetic or electric fields, the corresponding sub-Doppler features in the index of refraction can cause nonlinear optical rotation and induced ellipticity of resonant light propagating through the atomic medium. Physical mechanisms causing Bennett-structure-related nonlinear electro- and magneto-optical effects are discussed in detail for transitions involving states with low angular momenta. Measurements of Bennett-structure-related nonlinear magneto-optical rotation and electric-field-induced ellipticity for the Rb D2 line are performed and compared to density-matrix calculations. The latter effect can he used for measuring electric fields applied to atoms.

Nonlinear magneto-optical rotation via alignment-to-orientation conversion

Nonlinear magneto-optical rotation is investigated at high light powers where the rotation is significantly modified by ac Stark shifts. These shifts are shown to change the overall sign of rotation for closed F-->F+1 transitions compared to the low light power limit. The effect is demonstrated by measurements in rubidium and density matrix calculations. The results are important for applications of nonlinear optical rotation such as sensitive magnetometry.

Polarization flip–flop operation and dissipative structure generation with nonlinear gyrotropic resonators

We investigate the influence of nonlinear optical Faraday rotation on polarization multistability and modulational instabilities in nonlinear resonators. The potential use of gyrotropic cavities for implementing a light polarization-controlled set–reset flip–flop element and a high-repetition-rate pulse train generator is analysed.