Two-beam linear magneto-optical spectroscopy of atomic transitions between short lived states

Two-beam, linear magneto-optical spectroscopy is a powerful tool for studying short-lived states. We present both measurements and a quantitative theoretical analysis of magneto-rotation observed in the forward scattering of a linearly polarised laser beam passing through an amplifying atomic medium placed in a longitudinal magnetic field. The probed transition connects two short-lived, excited atomic levels, the upper state (here the 7S _1/2 level of cesium) being prepared initially via another transition from ground state, excited by a linearly polarised pump beam. The probe polarisation undergoes three different magneto-optical processes: optical rotation, with separate contributions from the two transitions, and linear dichroism due to Hanle precession of the upper state alignment. Complete resolution of the hyperfine structures and ninety degree switching of the probe polarisation enable us to isolate all of these processes. To lowest order in optical thickness the relative intensities and lineshapes are well interpreted.     

Communication: Manipulating the singlet-triplet equilibrium in organic biradical materials

We investigated the tunability of the singlet-triplet equilibrium population in the organic biradical 1,4-phenylenedinitrene via magneto-optical spectroscopy. A rich magnetochromic response occurs because applied field increases the concentration of the triplet state species, which has a unique optical signature by comparison with the singlet biradical and the precursor molecule. A Curie-like analysis of the magneto-optical properties allows us to extract the spin gap, which is smaller than previously supposed. These measurements establish the value of local-probe photophysical techniques for magnetic property determination in open-shell systems such as biradicals where a traditional electron paramagnetic resonance Curie law analysis has intrinsic limitations.     

Magneto-Optical Properties of Silica Gel Containing Magnetite Fine Particles

The magnetic composite materials that consist of transparent matrix and magnetic fine particles are expected to have large residual magnetization and coercive force because of their fine magnetic domain structure, and also to show magneto-optical effects. Silica gels containing magnetite (Fe₃O₄) fine particles were prepared by sol-gel method. The magnetic, optical and magneto-optical properties of the composites were investigated by measurements of magnetization curves, UV-visible spectra and Faraday rotation in visible range. The saturation magnetization of the composite was almost as same as that expected from the amount of magnetite fine particles in it. Although the composites had large and broad absorption at around 400 nm, they still maintained their transparency. The origins of decrement of transparency attributed to the optical absorption of magnetite and scattering due to magnetite fine particles. The whole composites showed positive Faraday rotation under external static magnetic field due to the large contribution of diamagnetic silica gel matrix. Magnetite contributed negative Faraday rotation with maximum at around 470–480 nm to the magneto-optical spectra of the composites.     

Magnetless Optical Circulator Based on an Iron Garnet with Reduced Magnetization Saturation

A three-port circulator for optical communication systems comprising a photonic crystal slab made of a magneto-optical material in which an magnetizing element is not required to keep its magnetic domains aligned is suggested for the first time. By maximizing the incorporation of europium to its molecular formula, the magneto-optical material can remain in the saturated magnetic state even in the absence of an external DC magnetic field. Two- and three-dimensional simulations of the device performed with full-wave electromagnetic solvers based on the finite element method demonstrate that, at the 1550 nm wavelength, the insertion loss, isolation, and reflection levels are equal to or better than −1 dB, −14 dB, and −20 dB, respectively. Since its operation does not require an electromagnet or a permanent magnet, the suggested circulator is much more compact, being able to reach footprints in the range of three orders of magnitude smaller, when compared to other circulator designs referred to in the literature and the presented results can be useful for the design of other nonreciprocal devices with reduced dimensions for optical communication systems.     

Analytical and spectral features of atomic magneto-optical rotation spectroscopy (the atomic Faraday effect) of Sb,Bi, Ag and Cu with a hollow cathode lamp operated in a pulse mode

In order to increase source intensity, hollow cathode lamps were operated in a pulse mode and combined with instrumentation for Faraday or atomic magneto-optical rotation spectroscopy. The analytical and spectral features of this method were studied for the trace determination of elements Sb, Bi, Ag and Cu. Novel line crossings between the σ^±-components in the analytical line Bi I 306.772 nm were found from the dependence of the transmitted intensity on the magnetic field strength. This is related to the theoretically calculated Zeeman splitting pattern. The enhancement in the source radiance by the pulse mode gave an increase in the detection power by a factor of ten.     

Iron-dextran complex: geometrical structure and magneto-optical features

Molecular mass of the iron-dextran complex (M(w)=1133 kDa), diameter of its particles (～8.3 nm) and the content of iron ions in the complex core (N(Fe)=6360) were determined by static light scattering, measurements of refractive index increment and the Cotton-Mouton effect in solution. The known number of iron ions permitted the calculation of the permanent magnetic dipole moment value to be μ(Fe)=3.17×10(-18) erg Oe(-1) and the determination of anisotropy of linear magneto-optical polarizabilities components as Δχ=9.2×10(-21) cm(3). Knowing both values and the value of the mean linear optical polarizability α=7.3×10(-20) cm(3), it was possible to show that the total measured CM effect was due to the reorientation of the permanent and the induced magnetic dipole moments of the complex. Analysis of the measured magneto-optical birefringence indicated very small optical anisotropy of linear optical polarizability components, κ(α), which suggested a homogeneous structure of particles of spherical symmetry.     

Magneto-optics of Ferritin

Measurements of Rayleigh light scattering, nonlinear light scattering in DC magnetic fields, and the Cotton-Mouton effect were carried out for 15 mM NaCl and water solutions of ferritin at room temperature. The spherical geometry of the molecule implies that it is optically isotropic. Such a macromolecule should not manifest magnetic anisotropy; however, in solution it shows induced magnetic birefringence (Cotton-Mouton effect) and changes in the intensity of the scattered light components. The analysis of the obtained results indicates the deformation of linear optical polarizability induced in the ferritin by a magnetic field as the main source of the magneto-optical phenomena observed. Light scattering and the CM effects theoretically depend on the linear magneto-optical polarizability, chi, and the nonlinear magneto-optical polarizability, eta. Using the theory describing the phenomena as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizability components, chi(parallel) - chi(perpendicular) = -(1.3 +/- 0.7) x 10(-22) [cm3] (in SI units chi(parallel) - chi(perpendicular) = -(2.0 +/- 1.2) x 10(-33) [m3]), the linear optical polarizability, alpha = (alpha(parallel) + 2alpha(perpendicular))/3 = (3.9 +/- 1.0) x 10(-20) [cm3] (in SI units alpha = (3.52 +/- 0.09)x10(-4) [Cm2 V(-1)]), and its anisotropy, kappa(alpha) = (alpha(parallel) - alpha(perpendicular))/3alpha = -(0.06+/-0.03), nonlinear magneto-optical polarizability, eta = (eta(parallel) + 2eta(perpendicular))/3 = -(4.7 +/- 0.9) x 10(-30) [cm3 Oe(-2)] (in SI units eta = -(6.7 +/- 1.3) x 10(-18) [Cm4 V(-1) A(-2)]) and its anisotropy, kappa(eta) = (eta[parallel) - eta(perpendicular))/3eta = -(0.15 +/- 0.10), were deduced. Here alpha(parallel), eta(parallel), alpha(perpendicular), eta(perpendicular) are the optical and magneto-optical polarizability components along the parallel and the perpendicular axes of the axially symmetric molecule, respectively.     

Magneto-Optical Effects in Colloidal Solutions of Barium Hexaferrite

Hydrothermal synthesis was used to obtain lamellar magnetic particles of barium hexaferrite, and colloidal solutions were prepared on their basis. Magneto-optical effects in colloid solutions of barium hexaferrite were examined. It was found that the aqueous colloidal solution of coarse planar particles of barium hexaferrite is a magneto-optical medium that is nearly two orders of magnitude more effective than the colloid formed from isometric cobalt ferrite particles. It was shown that measuring the frequency dependence of the magneto-optical effects and approximating the experimental data with the Debye function makes it possible to find the frequency f₀ characteristic of the given colloid and to calculate the characteristic size of particles (or aggregates) creating the optical anisotropy in the colloid under the action of a magnetic field. A dichroism is observed in the aqueous colloid formed by coarse planar barium hexaferrite particles. This phenomenon is due to the change in the light scattering on coarse particles upon their orientation by a magnetic field.     

Spectral features of atomic magneto-optical rotation spectroscopy (the atomic Faraday effect) and Zeeman splittings of various elements

Spectral features of atomic magneto-optical rotation spectroscopy (AMORS) or the atomic Faraday effect of various elements are described. As a stable atomizer, an air-hydrogen flame is located between the pole pieces of the electromagnet. The dependence of the transmitted intensity on the magnetic field strength was recorded on an X-Y recorder by scanning the magnetic field. For most of the analytical lines of elements, the maximum energy was transmitted through the optical system in the Faraday configuration at magnetic field strengths of up to a few kilogauss. The theoretically calculated Zeeman splitting patterns are successfully related to the experimental results.     

Universal on-line detector for high-performance liquid chromatography via magneto-optical rotation

Detecting changes in magneto-optical rotation is useful as a universal on-line detector for high-performance liquid chromatography. Such apparatus is similar to a polarimeter except for the external magnetic field on a flow cell. Two modulation modes suitable for the magneto-optical rotation detector are discussed. Use of a semiconductor laser provides better sensitivity than a He-Ne laser. The detection limit is 0.006% (w/w) for polyethylene glycol 20000 in a 20-mul injection.     

Optical fibre sensor for hydrogen sulphide monitoring in mouth air

A reversible optical fibre chemical sensor for hydrogen sulphide monitoring in mouth air based on reflectance measurements has been developed. The active sensing phase has been prepared by immobilising the colorimetric reagent 2,6-dichlorophenolindophenol (DCPI) in a silica gel support. The principle of the determination is based on the increase of reflectance of such solid sensing phase when hydrogen sulphide reduces the colorimetric reagent with the subsequent decolouration process. The addition of 1.26 μg of Cu(II) per gram of solid support improved the response time and reversibility of the sensing phase.The detection limit is 10 ppb (v/v) of hydrogen sulphide. The linear range using the Kubelka-Munk function extends at least up to 1000 ppb (v/v). The sensor exhibits a response time of less than 2 min for hydrogen sulphide concentrations in the linear range and the signal is reversible.The optical sensor has been successfully tested for human malodour monitoring and the results validated by comparison with those obtained for the same individuals using a commercially available electrochemical instrument.     

Ultrafast Auger Spectroscopy of Quantum Well Excitons in Strong Magnetic Fields

We study theoretically the ultrafast nonlinear optical response of quantum well excitons in a perpendicular magnetic field. We address the role of many-body correlations originating from the electron scattering between Landau levels (LL). In the linear optical response, the processes involving inter-LL transitions are suppressed provided that the magnetic field is sufficiently strong. However, in the nonlinear response, the Auger processes involving inter-LL scattering of two photoexcited electrons remain unsuppressed. We show that Auger scattering plays a dominant role in the coherent exciton dynamics in strong magnetic fields. We perform numerical calculations for the third-order four-wave-mixing (FWM) polarization, which incorporate the Auger processes nonperturbatively. We find that inter-LL scattering leads to a strong enhancement of FWM signal and to oscillations at negative time delays. These oscillations represent quantum beats between optically inactive two-exciton states related to each other via Auger processes.     

Magnetic circular dichroism analysis of crude oil

Optical and magneto-optical properties of solutions of crude oil of different origin (i.e., taken from different fields) are studied in the visible and near-UV region of optical emission. Magnetic circular dichroism (MCD) spectra of oil are obtained in the vicinity of wavelengths of ~410 nm, 533 nm, and 576 nm. It is demonstrated that the intensity of the MCD signal depends on the origin of crude oil, and it is proportional to the oil concentration in the solution. The comparison of the magneto-optical spectroscopy data with the chemical composition of samples allows us to conclude that the observed magneto-optical activity is determined by the presence of VO²⁺ complexes in the oil samples studied. The revealed magneto-optical activity of conventional oil can form a basis of a new method for the analysis of the composition and properties of oil of different origin.     

Light-rewritable geometric phase and reflectance modulations enabled by pattern-aligned photoresponsive liquid crystal superstructures

ABSTRACT

We propose a universal method of fabricating and operating a multifunctional diffractive optical element (DOE) with light-rewritable geometric phase and reflectance modulations enabled by pattern-aligned photoresponsive liquid crystal superstructures via manipulating the photoalignment layers as well as the phototunable helical pitch of the cholesteric liquid crystal (CLC) under different light stimuli, i.e. ultraviolet and visible (green) lights. The diffractive behaviour of the fabricated CLC DOE is simultaneously governed by the geometric phase induced by the pattern-aligned CLC and the reflectance (amplitude) modulation attributed to the helical pitch manipulation, endowing the proposed DOE with versatile practical light-controllable characteristics and outstanding performance.     

Electrical resistivity, optical and magnetic properties of the layered oxyselenide SmCuOSe

The electrical and magnetic properties of the tetragonal phase SmCuOSe are reported as a function of the temperature. The optical properties were studied by means of diffuse reflectance spectrum in the UV-Vis range. The electrical resistivity measurements as well as diffuse reflectance spectrum show that SmCuOSe is a semiconductor with an optical band gap (E_g) of 2.6 eV. In this phase, Cu is at its monovalent oxidation state and, as such, it does not contribute to the total magnetic moment, whereas Sm is in its 3+ oxidation state, with a large VanVleck contribution due to the admixture of the fundamental state with higher energy levels.     

Fiber-optic fluorometer signal enhancement and application to biosensor design

Fiber-optic fluorescence spectroscopy is currently the focus of active research because of the high sensitivity of fluorimetry and capacity for remote analysis with optical fibers. It is shown here that a further increase in sensitivity can be achieved by placing a mirror within a few fiber diameters of the distal end of the optical fiber in a solution of flourophore. A potentially four-fold signal enhancement results which is due to an increase in the excitation intensity as well as the reflection of the collected emitted light. The enhancement is shown to be dependent on the pathlength and concentration of the fluorophore, as well as the numerical aperture and core diameter of the optical fiber. The limit of detection of the fluorometer, which incorporates a mirror, is nanomolar dye concentrations, with the maximum response in path lengths of dye that are in the order of 6 fiber diameters. This principle can be applied to the design of optical sensors for continuously monitoring the concentration of specific biochemicals, and a conceptual design for such a sensor is described. A mathematical model is presented which describes the fluorescence output signal of a fiber-optic flourometer which incorporates a mirror.     

Magneto-chiral Nonlinear Optical Effect with Large Anisotropic Response in Two-Dimensional Halide Perovskite

The chiral organic–inorganic halide perovskites (OIHPs) are vital candidates for superior nonlinear optical (NLO) effects associated with circularly polarized (CP) light. NLO in chiral materials often couples with magnetic dipole (MD) transition, as well as the conventional electric dipole (ED) transition. However, the importance of MD transition in NLO process of chiral OIHPs has not yet been well recognized. Here, the circular polarized probe analysis of second harmonic generation circular dichroism (SHG-CD) provides the direct evidence that the contribution of MD leads to a large anisotropic response to CP lights in chiral OIHPs, (R-/S-MBACl)₂PbI₄. The thin films exhibit great sensitivity to CP lights over a wide wavelength range, and the g-value reaches up to 1.57 at the wavelength where the contribution of MD is maximized. Furthermore, it is also effective as CP light generator, outputting CP-SHG with maximum g-factor of 1.76 upon the stimulation of linearly polarized light. This study deepens the understanding of relation between chirality and magneto-optical effect, and such an efficient discrimination and generation of CP light signal is highly applicable for chirality-based sensor and optical communication devices.     

On the anisotropic optical response of Al(1 1 0)

In a recent paper, good agreement was reported between the results of an ab initio full-potential linear augmented plane wave (FP-LAPW) calculation of the linear optical response of Al(1 1 0) and experimental measurements of the reflectance anisotropy. In the present work, our FP-LAPW calculations are extended to develop a microscopic picture of the anisotropic optical response at the Al(1 1 0) surface. Evidence for an anisotropic intraband transition (Drude) contribution in the infrared is presented, and the anisotropy is explained by considering the redistribution of charge that occurs when an Al(1 1 0) surface is created. The interband transitions that make the dominant contribution to the reflectance anisotropy at higher energy are identified, and the symmetries and the surface or bulk character of the initial and final states are determined. Changes in the relative energies and occupations of electronic states due to surface charge redistribution are a possible mechanism for the interband contribution to the reflectance anisotropy.     

Fluorous materials in microbubble engineering science and technology—Design and development of new bubble preparation and sizing technologies

Microbubbles are being used in ultrasound diagnosis imaging, could serve as contrast agents for multiple imaging modalities and for parenteral oxygen delivery, and have potential in materials science as new multi-scale materials for magnetic, optical and magneto-optical devices. We designed new procedures for the preparation of narrowly size-distributed, monomodal microbubble populations, as well as a new multifrequency acoustical device for microbubble sizing. Methods for microbubble stabilization using fluorinated gases and surfactants are also discussed. Prospects include further use of fluorinated amphiphiles for bubble stabilization and size control, and decoration of bubble surface with functional particles (e.g. magnetic iron oxide nanoparticles).     

Luminescent Single-Molecule Magnets as Dual Magneto-Optical Molecular Thermometers

Luminescent thermometry allows the remote detection of the temperature and holds great potential in future technological applications in which conventional systems could not operate. Complementary approaches to measuring the temperature aiming to enhance the thermal sensitivity would however represent a decisive step forward. For the first time, we demonstrate the proof-of-concept that luminescence thermometry could be associated with a complementary temperature readout related to a different property. Namely, we propose to take advantage of the temperature dependence of both magnetic (canonical susceptibility and relaxation time) and luminescence features (emission intensity) found in Single-Molecule Magnets (SMM) to develop original dual magneto-optical molecular thermometers to conciliate high-performance SMM and Boltzmann-type luminescence thermometry. We highlight this integrative approach to concurrent luminescent and magnetic thermometry using an air-stable benchmark SMM [Dy(bbpen)Cl] (H₂bbpen=N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)ethyl-enediamine)) exhibiting Dy³⁺ luminescence. The synergy between multiparametric magneto-optical readouts and multiple linear regression makes possible a 10-fold improvement in the relative thermal sensitivity of the thermometer over the whole temperature range, compared with the values obtained with the single optical or magnetic devices.