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G. G. Kozlov

Publications and source records attributed to G. G. Kozlov.

At least 37 records · Page 2Linked to original sources
arXiv2019

Stimulated spin noise in an activated crystal

In the spin noise spectroscopy, the magnetic susceptibility spectrum is known to be provided by the spin-system untouched by any external perturbation, or, better to say, disturbed only by its thermal bath. We propose a new version of the spin noise spectroscopy, with the detected magnetization (Faraday-rotation) noise being stimulated by an external fluctuating magnetic field with a quasi-white spectrum. Experimental study of the stimulated spin noise performed on a $\text{BaF}_2 : \text{U}^{3+}$ crystal in a longitudinal magnetic field has revealed specific features of this approach and allowed us to identify the Van-Vleck and population-related contributions to the AC susceptibility of the system and to discover unusual magnetic-field dependence of the longitudinal spin relaxation rate in low magnetic fields. It is shown that spectra of the stimulated and spontaneous spin noise, being both closely related to the spin-system magnetic susceptibility, are still essentially different. Distinctions between the two types of the spin-noise spectra and two approaches to the spin noise spectroscopy are discussed.

cond-mat.mes-hall↗
arXiv2017

Homogenization of Doppler broadening in spin noise spectroscopy

The spin noise of cesium atoms vapor with admixture of buffer gas is experimentally investigated by measuring the spin induced Faraday rotation fluctuations in the vicinity of D 2 line. The line, under these conditions, is known to be strongly inhomogeneously broadened due to the Doppler effect. Despite that, optical spectrum of the spin noise power, as we have found, has the characteristic shape of the homogeneously broadened line with the dip at the line center. This fact is in stark contrast with the results of previous studies of inhomogeneous quantum dot ensembles. In addition, the two-color experiments, where correlations of the Faraday rotation fluctuations for two probe wavelengths were measured, have shown, in a highly spectacular way, that these fluctuations are either correlated, or anticorrelated depending on whether the two wavelengths lie on the same side, or on different sides of the resonance. The experimental data are explained within the developed theoretical model which takes into account both kinetics and spin dynamics of Cs atoms. It is shown that the unexpected behavior of the optical Faraday rotation noise spectra and effective homogenization of the optical transition in the spin-noise measurements are related to smallness of the momentum relaxation time of the atoms as compared with their spin relaxation time.

physics.atom-ph↗
arXiv2017

Spin noise spectroscopy of randomly moving spins in the model of light scattering: Two-beam arrangement

A strict analytical solution of the problem of spin-noise signal formation in a volume medium with randomly moving spin carriers is presented. The treatment is performed in the model of light scattering in a medium with fluctuating inhomogeneity. Along with conventional single-beam, geometry, we consider the two-beam arrangement, with the scattering field of the auxiliary ("tilted") beam heterodyned on the photodetector illuminated by the main beam. It is shown that the spin noise signal detected in the two-beam arrangement is highly sensitive to motion (diffusion) of the spin carriers within the illuminated volume and thus can provide additional information about spin dynamics and spatial correlations of spin polarization in volume media. Our quantitative estimates show that, under real experimental conditions, spin diffusion may strongly suppress the spin-noise signal in the two-beam geometry. Mechanism of this suppression is similar to that of the time-of-flight broadening with the critical distance determined by the period of spatial interference of the two beams rather than by the beam diameter.

physics.optics↗
arXiv2017

Heterodyne detection of scattered light: Application to mapping and tomography of optically inhomogeneous media

The signal registered by a plane photodetector placed behind an optically inhomogeneous object irradiated by two coherent Gaussian beams intersecting inside the object at small angle to each other is calculated in the single-scattering approximation. In the considered arrangement, only one of the beams hits the detector and serves as local oscillator for heterodyning the field scattered by the other beam (not hitting the detector). The results of analytical calculation show that the signal detected in this way is contributed only by the region of the inhomogeneous object where the two beams overlap. By moving the scatterer with respect to the overlap region and monitoring the heterodyned signal, with the aid of the derived expression, one can reconstruct the refractive-index relief of the scatterer. We also propose a simple method of spatial mapping of the sample that allows one to estimate the magnitude and characteristic dimensions of the inhomogeneities.

physics.optics↗
arXiv2017

Spin temperature concept verified by optical magnetometry of nuclear spins

We develop a method of non-perturbative optical control over adiabatic remagnetisation of the nuclear spin system and apply it to verify the spin temperature concept in GaAs microcavities. The nuclear spin system is shown to exactly follow the predictions of the spin-temperature theory, despite the quadrupole interaction that was earlier reported to disrupt nuclear spin thermalisation. These findings open a way to deep cooling of nuclear spins in semiconductor structures, with a prospect of realisation of nuclear spin-ordered statesfor high fidelity spin-photon interfaces.

cond-mat.other↗
arXiv2017

Light scattering in the medium with fluctuating gyrotropy: application to spin noise spectroscopy

The spin noise signal in the Faraday-rotation-based detection technique can be considered equally correctly either as a manifestation of the spin-flip Raman effect or as a result of light scattering in the medium with fluctuating gyrotropy. In this paper, we present rigorous description of the signal formation process upon heterodyning of the field scattered due to fluctuating gyrotropy. Along with conventional single-beam experimental arrangement, we consider here a more complicated, but more informative, two-beam configuration that implies the use of an auxiliary light beam passing through the same scattering volume and delivering additional scattered field to the detector. We show that the signal in the spin noise spectroscopy arising due to heterodyning of the scattered field is formed only by the scattered field components whose wave vectors coincide with those of the probe beam. Therefore, in principle, the detected signal in spin noise spectroscopy can be increased by increasing overlap of the two fields in the momentum space. We also show that, in the two-beam geometry, contribution of the auxiliary (tilted) beam to the detected signal is represented by Fourier transform of the gyrotropy relief at the difference of two wave vectors. This effect can be used to study spin correlations by means of noise spectroscopy.

physics.optics↗
arXiv2016

Nuclear spin relaxation in n-GaAs: from insulating to metallic regime

Nuclear spin relaxation is studied in n-GaAs thick layers and microcavity samples with different electron densities. We reveal that both in metallic samples where electrons are free and mobile, and in insulating samples, where electrons are localized, nuclear spin relaxation is strongly enhanced at low magnetic field. The origin of this effect could reside in the quadrupole interaction between nuclei and fluctuating electron charges, that has been proposed to drive nuclear spin dynamics at low magnetic fields in the insulating samples. The characteristic values of these magnetic fields are given by dipole-dipole interaction between nuclei in bulk samples, and are greatly enhanced in microcavities, presumably due to additional strain, inherent to micro and nanostructures.

cond-mat.mes-hall↗
arXiv2016

Spin noise of a polariton laser

We report on experimental study of the exciton-polariton emission (PE) polarization noise below and above the polariton lasing threshold under continuous wave nonresonant excitation. The experiments were performed with a high-Q graded 5λ/2 GaAs/AlGaAs microcavity with three quantum wells in the strong coupling regime. The PE polarization noise substantially exceeded in magnitude the shot noise level and, in the studied frequency range (up to 650 MHz), had a flat spectrum. We have found that the PE polarization noise magnitude dependence on the pump intensity showed specific features that had no analogy in power dependences of the PE intensity and intensity noise. Particularly, the linear polarization fluctuations normalized by the emission intensity showed a remarkably non-monotonic dependence on the pump power. A theoretical model describing the observed peculiarity of the PE polarization noise is proposed.

cond-mat.mes-hall↗
arXiv2015

Spin-noise-based magnetometry of an $n$-doped GaAs microcavity in the field of elliptically polarized light

Recently reported optical nuclear orientation in the $n$-doped GaAs microcavity under pumping in nominal transparency region of the crystal [Appl. Phys. Lett. $\mathbf{106}$, 242405 (2015)] has arisen a number of questions, the main of them concerning mechanisms of angular momentum transfer from the light to the nuclear spin system and the nature of the light-related magnetic fields accompanying the optical nuclear polarization. In this paper, we use the spin noise spectroscopy for magnetometric purposes, particularly, to study effective fields acting upon electron spin system of an $n$-GaAs layer inside a high-Q microcavity in the presence of elliptically polarized probe beam. In addition to the external magnetic field applied to the sample in the Voigt geometry and the Overhauser field created by optically oriented nuclei, the spin noise spectrum reveals an additional effective, "optical," magnetic field produced by elliptically polarized probe itself. This field is directed along the light propagation axis, with its sign being determined by the sign of the probe helicity and its magnitude depending on degree of circular polarization and intensity of the probe beam. We analyze properties of this optical magnetic field and suggest that it results from the optical Stark effect in the field of the elliptically polarized electromagnetic wave.

cond-mat.mes-hall↗
arXiv2015

Single-shot measurement of transient nuclear magnetization with spin-noise spectroscopy in n-GaAs microcavities

We exploit spin noise spectroscopy (SNS) to directly observe build-up of dynamic nuclear polarization and relaxation of a perturbed nuclear spin-system to its equilibrium state in a single-shot experiment. The SNS experiments were performed on a layer of bulk $n$-type GaAs embedded into a high-finesse microcavity with negative detuning. The dynamic nuclear spin polarization is observed as a shift of the peak in the electron spin noise spectrum due to the build-up of the Overhauser field acting on the electron spin. The relaxation dynamics of nuclear spin system was revealed in the time-resolved SNS experiments where the exponential decay of the Overhauser field with characteristic timescale of hundreds of seconds was detected. We show that elliptically polarized laser beam tuned in resonance with the cavity mode, whose energy corresponds to nominal transparency of the semiconductor, can nevertheless produce a sizable nuclear polarization.

cond-mat.mes-hall↗
arXiv2014

Noise spectroscopy of the optical microcavity: nonlinear amplification of the spin noise signal and giant noise

The spin-fluctuations-related Kerr rotation noise of the optical beam reflected from a microcavity with a quantum well in the intermirror gap is studied. In the regime of anti-crossing of the cavity polariton branches, the several hundred times enhancement of the noise signal, or giant noise, is observed. The effect of the amplification of the noise signal is explained by the nonlinear instability of the microcavity. In the frame of the developed model of built-in amplifier, the non-trivial properties of the noise signal in the regime of the negative detuning of microcavity are described.

cond-mat.mes-hall↗
arXiv2014

Anti-mirror reflection of a bounded plane optical waveguide: string model

The effect of anti-mirror reflection from a bounded plane optical waveguide used earlier for observation of slow light in a Bragg waveguide is considered. A theory of the effect is proposed that allowed us to interpret the observed spectral (Gaussian lineshape) and angular (Lorentzian angular profile) properties of the light scattered by the bounded waveguide in the anti-specular direction.

cond-mat.mes-hall↗
arXiv2014

The Correlated Lloyd model: exact solution

Exactly solvable model of disordered system representing the generalized Lloyd model with correlated random potential is described. It is shown, that for the model under consideration, the averaged Green's function does not depend on random potential correlation radius and, similarly to the classical Lloyd model, has the form of Green's function of a crystal system, with energy argument supplied by an imaginary part which depends on degree of disorder.

cond-mat.dis-nn↗
arXiv2014

Optics of spin-noise-induced gyrotropy of asymmetric microcavity

The optical gyrotropy noise of a high-finesse semiconductor Bragg microcavity with an embedded quantum well (QW) is studied at different detunings of the photon mode and the QW exciton resonances. A strong suppression of the noise magnitude for the photon mode frequencies lying above exciton resonances is found. We show that such a critical behavior of the observed optical noise power is specific of asymmetric Fabry-Perot resonators. As follows from our analysis, at a certain level of intracavity loss, the reflectivity of the asymmetric resonator vanishes, while the polarimetric sensitivity to the gyrotropy changes dramatically when moving across the critical point. The results of model calculations are in a good agreement with our experimental data on the spin noise in a single-quantum-well microcavity and are confirmed also by the spectra of the photo-induced Kerr rotation in the pump-probe experiments.

cond-mat.mes-hall↗
arXiv2014

Spin noise spectroscopy of a single-quantum-well microcavity

We report on the first experimental observation of spin noise in a single semiconductor quantum well embedded into a microcavity. The great cavity-enhanced sensitivity to fluctuations of optical anisotropy has allowed us to measure the Kerr rotation and ellipticity noise spectra in the strong coupling regime. The spin noise spectra clearly show two resonant features: a conventional magneto-resonant component shifting towards higher frequencies with magnetic field and an unusual "nonmagnetic" component centered at zero frequency and getting suppressed with increasing magnetic field. We attribute the first of them to the Larmor precession of free electron spins, while the second one being presumably due to hyperfine electron-nuclei spin interactions.

cond-mat.mes-hall↗
arXiv2013

Resources of polarimetric sensitivity in spin noise spectroscopy

We attract attention to the fact that the ultimate (shot-noise-limited) polarimetric sensitivity can be enhanced by orders of magnitude leaving the photon flux incident onto the photodetector on the same low level. This opportunity is of crucial importance for present-day spin noise spectroscopy, where a direct increase of sensitivity by increasing the probe beam power is strongly restricted by the admissible input power of the broadband photodetectors. The gain in sensitivity is achieved by replacing the 45-deg polarization geometry commonly used in conventional schemes with balanced detectors by geometries with stronger polarization extinction. The efficiency of these high-extinction polarization geometries with enhancement of the detected signal by more than an order of magnitude is demonstrated by measurements of the spin noise spectra of bulk n:GaAs in the spectral range 835-918 nm. It is shown that the inevitable growth of the probe beam power with the sensitivity gain makes spin noise spectroscopy much more perturbative, but, at the same time, opens up fresh opportunities for studying nonlinear interactions of strong light fields with spin ensembles.

cond-mat.mes-hall↗