Aqueous sample in an EPR cavity: sensitivity considerations

The radial mode matching (RMM) method has been used to calculate accurately the microwave field distribution of the TE(011) mode in a spherical EPR cavity containing a linear aqueous sample, in order to understand in detail the factors affecting sensitivity in EPR measurements at X band. Specific details of the experiment were included in the calculations, such as the cavity geometry, the presence of a quartz dewar, the size of the aqueous sample, and the sample's dielectric properties. From the field distribution, several key physical parameters were calculated, including cavity Q, filling factor, mean microwave magnetic field at the sample, and cavity efficiency parameter Lambda. The dependence of EPR signal intensity on sample diameter for a cylindrical aqueous sample was calculated and measured experimentally for non-saturated and half-saturated samples. The optimal aqueous sample diameter was determined for both cases. The impact of sample temperature, conductivity, and cavity Q on sensitivity of EPR is discussed.     

Helicoidal distributed-feedback cavity action in a ferroelectric liquid crystal

Second-Harmonic (SH) generation was observed in homeotropically aligned ferroelectric liquid-crystal cells using fundamental light propagating along the helicoidal axis. Relatively strong SH light was observed in the helicoidal structure when the optical pitch was nearly the same as the SH-light wavelength, though, otherwise, the cancellation of the generated SH light by the helicoid results in negligibly weak SH intensity. Because the observed SH light is independent of the cell thickness, the SH light is attributed to the one generated from the surface region and the SH light generated inside the cell is confined and lost by the helicoid. This phenomenon indicates the helicoidal Distributed-FeedBack (DFB) cavity action and suggests the possibility of the helicoidal DFB laser using dye-doped ferroelectric liquid-crystal cells.     

EPR and NMR line shapes in disordered ferroelectric crystals

A theory is developed for the magnetic resonance line shape in disordered ferroelectric crystals. In a study of the random fields responsible for inhomogeneous line broadening, nonlinear and spatial correlation effects are taken into account. It is shown that homogeneous broadening depends on the temperature and on the magnitude and orientation of the external magnetic field, as well as on the nonlinearity parameters of the ferroelectric material. The resonance line shape is calculated as the envelope of homogeneously broadened Lorentzian spin packets. Analytic expressions for I ₂(ω) and I ₃(ω) are introduced to account for nonlinearity and correlation effects of second and third order, respectively. Calculations are done for centrally symmetric crystals, as well as for those without a center of symmetry. It is shown that homogeneous broadening is important near the line peak, while the wings are determined mainly by inhomogeneous broadening. Manifestations of the predicted effects in the spectrum lines of disordered ferroelectric crystals are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 340–347 (February 1998)     

Enhanced chiral response from the Fabry–Perot cavity coupled meta-surfaces

The circular dichroism(CD) signal of a two-dimensional(2D) chiral meta-surface is usually weak, where the difference between the transmitted(or reflected) right and left circular polarization is barely small. We present a general method to enhance the reflective CD spectrum, by adding a layer of reflective film behind the meta-surface. The light passes through the chiral meta-surface and propagates towards the reflector, where it is reflected back and further interacts with the chiral meta-surface. The light is reflected back and forth between these two layers, forming a Fabry–Perot type resonance,which interacts with the localized surface plasmonic resonance(LSPR) mode and greatly enhances the CD signal of the light wave leaving the meta-surface. We numerically calculate the CD enhancing effect of an L-shaped chiral meta-surface on a gold film in the visible range. Compared with the single layer meta-surface, the L-shaped chiral meta-surface has a CD maximum that is dramatically increased to 1. The analysis of reflection efficiency reveals that our design can be used to realize a reflective circular polarizer. Corresponding mode analysis shows that the huge CD originates from the hybrid mode comprised of FP mode and LSPR. Our results provide a general approach to enhancing the CD signal of a chiral meta-surface and can be used in areas like biosensing, circular polarizer, integrated photonics, etc.     

Enhanced sensitivity of a gravitational wave detector

We calculate the change in energy absorbed and the power spectrum in a coherently driven antenna induced by interaction with gravitational radiation. The coherent driving field prepares the antenna in a correlated state which enhances the sensitivity of the detector as proposed in a recent paper by Weber.     

EPR study of the ferroelectric phase transition in chromium-doped DMAAS

X-band electron paramagnetic resonance (EPR) investigations of single crystals of Cr³⁺-doped dimethylammonium aluminium sulphate hexahydrate are presented from 100 K to room temperature. The crystal undergoes a phase transition at 152 K from the ferroelastic to the ferroelectric phase. The spin-Hamiltonian parameters have been determined for both phases. The spin-Hamiltonian parameters in the ferroelectric phase are:g=1.980±0.003,b ₂ ⁰ =(1140±15)·10^?4 cm^?1,b ₂ ² =(214±10)·10^?4 cm^?1. Remarkable EPR line width changes confirm the order-disorder character of the ferroelectric phase transition on a microscopic level and demonstrate that the dimethylammonium reorientation freezing-out is the prime reason for this transition.     

Enhanced photon detection in EPR type experiments

Local realistic models of enhanced photon detection reproducing quantum mechanical predictions for single photons and approximating closely the quantum mechanical predictions for pairs of correlated photons are discussed. It is shown that Einstein-Podolsky-Rosen-type experiments with three polarizers can easily discriminate such models from ordinary quantum theory.     

Raising the sensitivity of the electron-paramagnetic-resonance spectrometer using a ferroelectric resonator

In order to raise the sensitivity of microwave electron-paramagnetic-resonance (EPR) spectrometers, it is proposed to use a piece of ferroelectric material as an additional resonator. The method has been tested using the RE-1307 microwave EPR spectrometer and a pulsed microwave spectrometer. The possibility of raising the signal-to-noise ratio when using ferroelectric resonators of rectangular-parallelepiped and spherical shape has been considered. For a potassium-tantalate ferroelectric resonator of rectangular-parallelepiped shape, the signal-to-noise ratio has been raised by a factor of 16 at 331 K and by a factor of 10 at 292 K. In the pulse experiment, the presence of the ferroelectric resonator permits a reduction in microwave power, required for sample saturation, by a factor of 50 at 50 K.     

Enhanced electrical properties in bilayered ferroelectric thin films

Sr2Bi4Ti5O18(SBTi) single layered and Sr2Bi4Ti5O18 /Pb(Zr0.53Ti0.47)O3(SBTi/PZT) bilayered thin films have been prepared on Pt/TiO2/SiO2/Si substrates by pulsed-laser deposition(PLD).The related structural characterizations and electrical properties have been comparatively investigated.X-ray diffraction reveals that both films have crystallized into perovskite phases and scanning electron microscopy shows the sharp interfaces.Both films show well-saturated ferroelectric hysteresis loops,however,compared with the single layered SBTi films,the SBTi/PZT bilayered films have significantly increased remnant polarization(Pr) and decreased coercive field(Ec),with the applied field of 260 kV/cm.The measured Pr and Ec of SBTi and SBTi/PZT films were 7.9 C/cm 2,88.1 kV/cm and 13.0 C/cm 2,51.2 kV/cm,respectively.In addition,both films showed good fatigue-free characteristics,the switchable polarization decreased by 9% and 11% of the initial values after 2.2 10 9 switching cycles for the SBTi single layered films and the SBTi/PZT bilayered films,respectively.Our results may provide some guidelines for further optimization of multilayered ferroelectric thin films.     

Teleportation of a two-atom entangled state using a single EPR pair in cavity QED

We propose a scheme for teleporting a two-atom entangled state in cavity quantum electrodynamics (QED). In the scheme, we choose a single Einstein--Podolsky--Rosen (EPR) pair as the quantum channel which is shared by the sender and the receiver. By using the atom--cavity-field interaction and introducing an additional atom, we can teleport the two-atom entangled state successfully with a probability of 1.0. Moreover, we show that the scheme is insensitive to cavity decay and thermal field.     

Enhanced entanglement and asymmetric EPR steering between magnons

The generation and manipulation of strong entanglement and Einstein-Podolsky-Rosen(EPR)steering in macroscopic systems are outstanding challenges in modern physics.Especially,the observation of asymmetric EPR steering is important for both its fundamental role in interpreting the nature of quantum mechanics and its application as resource for the tasks where the levels of trust at different parties are highly asymmetric.Here,we study the entanglement and EPR steering between two macroscopic magnons in a hybrid ferrimagnet—light system.In the absence of light,the two types of magnons on the two sublattices can be entangled,but no quantum steering occurs when they are damped with the same rates.In the presence of the cavity field,the entanglement can be significantly enhanced,and strong two-way asymmetric quantum steering appears between two magnons with equal dissipation.This is very different from the conventional protocols to produce asymmetric steering by imposing additional unbalanced losses or noises on the two parties at the cost of reducing steerability.The essential physics is well understood by the unbalanced population of acoustic and optical magnons under the cooling effect of cavity photons.Our finding may provide a novel platform to manipulate the quantum steering and the detection of bi-party steering provides a knob to probe the magnetic damping on each sublattice of a magnet.     

Enhanced resolution for EPR imaging by two-step deblurring

The broad spectrum of spin probes used for electron paramagnetic resonance imaging (EPRI) result in poor spatial resolution of the reconstructed images. Conventional deconvolution procedures can enhance the resolution to some extent but obtaining high resolution EPR images is still a challenge. In this work, we have implemented and analyzed the performance of a postacquisition deblurring technique to enhance the spatial resolution of the EPR images. The technique consists of two steps; noniterative deconvolution followed by iterative deconvolution of the acquired projections which are then projected back using filtered backprojection (FBP) to reconstruct a high resolution image. Further, we have proposed an analogous technique for iterative reconstruction algorithms such as multiplicative simultaneous iterative reconstruction technique (MSIRT) which can be a method of choice for many applications. The performance of the suggested deblurring approach is evaluated using computer simulations and EPRI experiments. Results suggest that the proposed procedure is superior to the standard FBP and standard iterative reconstruction algorithms in terms of mean-square-error (MSE), spatial resolution, and visual judgment. Although the procedure is described for 2D imaging, it can be readily extended to 3D imaging.     

Enhanced ferroelectric and piezoelectric properties in La-modified PZT ceramics

The effect of lanthanum (La) doping on ferroelectric and piezoelectric properties of lead zirconate titanate (PZT) sample has been investigated. Pb_1?x La _x Zr_0.52Ti_0.48O₃ ceramics with x = 0.00, 0.02, 0.04, 0.06 and 0.10 were prepared by the sol–gel technique. Raman and Fourier transforms infrared spectroscopy have been employed to understand the structural modification due to ionic size mismatch. Raman spectra show the existence of both rhombohedral and tetragonal crystal symmetries. It also shows the dielectric relaxation with increase in La concentration in the sample. The increase in lattice strain due to La doping increases the remnant polarization and coercive field. The linear piezoelectric coefficient increases with the increase in La concentration. It reveals that La-substituted PZT is a better candidate for piezoelectric sensor applications as compared to that of PZT.     

Enhanced surface plasmon interference lithography from cavity resonance in the grating slits

Surface plasmon interference lithography based on grating diffraction has been studied both theoretically and experimentally in recent years. In this paper, we demonstrate that the cavity resonance in the grating slits can improve the subwavelength interference, not only the intensity but also the uniformity of the pattern. Both the typical lithography structure which merely consists of periodic metallic gratings and the modified structure equipped with a reflection layer are studied. The finite element method has been performed to study the interference pattern. Numerical simulations show that the property of the interference pattern is the optimum when cavity resonance happens. This enhancement can be applied to all the lithography structures which are based on the grating diffraction.     

Enhanced spontaneous emission into the mode of a cavity QED system

We study the light generated by spontaneous emission into a mode of a cavity QED system under weak excitation of the orthogonally polarized mode. Operating in the intermediate regime of cavity QED with comparable coherent and decoherent coupling constants, we find an enhancement of the emission into the undriven cavity mode by more than a factor of 18.5 over that expected by the solid angle subtended by the mode. A model that incorporates three atomic levels and two polarization modes quantitatively explains the observations.     

Enhanced cooling of a V-type three-level atom in an optical cavity

We have studied theoretically and numerically the enhanced cooling of a V-type three-level atom in a high-finesse optical cavity and shown that the cooling rate can be increased by one order of magnitude over that of a two-level atom, and the momentum amplitude tends to a stationary state much smaller than that of a two-level atom. We have further shown that the cooling rate can be significantly improved by using feedback and a time-dependent pump.     

Multibore sample cell increases EPR sensitivity for aqueous samples

We have performed calculations, verified by experiment, to explain why the sensitivity of biological EPR can be dramatically increased by dividing the aqueous sample into separate compartments. In biological EPR, the major factor affecting sensitivity is the number of spins in the sample. For an aqueous sample at ambient temperature, this is limited by the requirement for a small volume, due to strong non-resonant absorption of microwaves by water. However, recent empirical studies have shown that this volume limitation can be greatly relieved by dividing the aqueous sample into separate volumes, which allows much more aqueous sample to be loaded into a resonant cavity without significant degradation of the cavity quality factor. Calculations, based on the Bruggeman mixing rule, show quantitatively that the composite aqueous sample has a permittivity much less than that of bulk water, depending on the aqueous volume fraction f. Analysis for X-band EPR spectroscopy shows that the optimal volume fraction of an aqueous composite sample, producing maximum sensitivity, is f=0.15, increasing the sensitivity by a factor of 8.7, compared with an aqueous sample in a single tube.     

Enhanced photomultiplier sensitivity in spectroscopy systems

A fiber-ribbon-based coupling method is presented as a practical way to enhance light sensitivity in spectroscopic and similar systems employing a multialkali photomultiplier tube as a detector. The sensitivity enhancement is achieved by an increase in absorption in the photocathode through multiple total internal reflection in the photomultiplier entrance window. Improvements by factors of ~2 (blue-green) to more than 10 (near infrared) have been measured. Implications for spectroscopic applications are discussed.