Stefka Cartaleva

Bio: Stefka Cartaleva is an academic researcher from Bulgarian Academy of Sciences. The author has contributed to research in topics: Resonance & Laser. The author has an hindex of 18, co-authored 118 publications receiving 1037 citations. Previous affiliations of Stefka Cartaleva include University of Siena & University of Pisa.

Cesium coherent population trapping magnetometer for cardiosignal detection in an unshielded environment

Abstract: We present encouraging results obtained with an experimental apparatus based on coherent population trapping and aimed at detecting a biological (cardiac) magnetic field in a magnetically compensated but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection to cancel common mode magnetic noise. Synchronous data acquisition with a reference (electrocardiographic or pulse-oximetric) signal makes possible improvement of the signal-to-noise ratio in off-line averaging. The setup has the significant advantages of working at room temperature with a small-size head, and the possibility of fast adjustments of the dc bias magnetic field, which makes the sensor suitable for detecting a biomagnetic signal at any orientation with respect to the axis of the head and in any position on the patient's chest, which is not the case with other kinds of magnetometers.

Coherent spectroscopy of degenerate two-level systems in Cs

Abstract: Coherent spectroscopy of degenerate two-level systems of the Doppler-broadened ${D}_{2}$ cesium line has been performed in vacuum and in buffer gas cells Subnatural-width (SNW) electromagnetically induced transparency and electromagnetically induced absorption (EIA) resonances have been observed with single-frequency laser excitation for different light polarizations and collision regimes SNW-EIA resonances with linearly polarized excitation of the ${F}_{g}=4$ level are observed, and they increase their contrast with power density increase and reach a contrast of 20% at $200 \mathrm{mW}{\mathrm{cm}}^{\ensuremath{-}2}$ A theoretical model has been elaborated, taking into account the Doppler broadening of the transitions, the linewidth of the laser light, and the experimental conditions for observation of the fluorescence Here the theoretical results are in agreement with those of the experiment In a buffer gas cell, the SNW resonances in the fluorescence, in degenerate two-level systems are observed for the first time and they are only obtained with circularly polarized light A theoretical explanation of this result is proposed At the expense of contrast, in the presence of a buffer gas the coherent resonances are significantly narrower than in a vacuum cell for the same power density The observation of SNW resonances in buffer gas is significantly less sensitive to the laser frequency drift than in a vacuum cell, which could be advantageous for applications in metrology and in the measurement of weak magnetic fields

Enhanced absorption Hanle effect in the configuration of crossed laser beam and magnetic field

Abstract: We have analyzed the Hanle effect on the closed ${F}_{\mathrm{g}}=\stackrel{\ensuremath{\rightarrow}}{3}{F}_{\mathrm{e}}=4$ ${D}_{2}$-line transition of ${}^{85}\mathrm{Rb}.$ Exciting the rubidium atoms by circularly polarized laser light, and scanning an applied transverse magnetic field, a bright resonance Hanle signal is obtained at different values of an applied longitudinal magnetic field. We report experimental and numerical evidence of this bright resonance.

Saturation effects in the sub-Doppler spectroscopy of Cesium vapor confined in an Extremely Thin Cell

Abstract: Saturation effects affecting absorption and fluorescence spectra of an atomic vapor confined in an extremely thin cell (cell thickness $Ll1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$) are investigated experimentally and theoretically. The study is performed on the ${D}_{2}$ line $(\ensuremath{\lambda}=852\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ of Cs and concentrates on the two situations $L=\ensuremath{\lambda}∕2$ and $L=\ensuremath{\lambda}$, the most contrasted ones with respect to the length dependence of the coherent Dicke narrowing. For $L=\ensuremath{\lambda}∕2$, the Dicke-narrowed absorption profile simply broadens and saturates in amplitude when increasing the light intensity, while for $L=\ensuremath{\lambda}$, sub-Doppler dips of reduced absorption at the line-center appear on the broad absorption profile. For a fluorescence detection at $L=\ensuremath{\lambda}$, saturation induces narrow dips, but only for hyperfine components undergoing a population loss through optical pumping. These experimental results are interpreted with the help of the various existing models and are compared with numerical calculations based upon a two-level modeling that considers both a closed and an open system.

Optical magnetometry - eScholarship

Abstract: Some of the most sensitive methods of measuring magnetic fields use interactions of resonant light with atomic vapour. Recent developments in this vibrant field have led to improvements in sensitivity and other characteristics of atomic magnetometers, benefiting their traditional applications for measurements of geomagnetic anomalies and magnetic fields in space, and opening many new areas previously accessible only to magnetometers based on superconducting quantum interference devices. We review basic principles of modern optical magnetometers, discuss fundamental limitations on their performance, and describe recently explored applications for dynamical measurements of biomagnetic fields, detecting signals in NMR and MRI, inertial rotation sensing, magnetic microscopy with cold atoms, and tests of fundamental symmetries of nature.

Resonant nonlinear magneto-optical effects in atoms

Abstract: The authors review the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors. They begin by describing the pioneering work of Macaluso and Corbino over a century ago on linear magneto-optical effects (in which the properties of the medium do not depend on the light power) in the vicinity of atomic resonances. These effects are then contrasted with various nonlinear magneto-optical phenomena that have been studied both theoretically and experimentally since the late 1960s. In recent years, the field of nonlinear magneto-optics has experienced a revival of interest that has led to a number of developments, including the observation of ultranarrow (1-Hz) magneto-optical resonances, applications in sensitive magnetometry, nonlinear magneto-optical tomography, and the possibility of a search for parity- and time-reversal-invariance violation in atoms.

Observation of Electromagnetically Induced Transparency in Collisionally Broadened Lead Vapor

Abstract: As stated in the text, Figs. 3 and 4 (transmission versus probe laser detuning) were taken at an energy of 10 nJ in a 0.5-mm-diam beam. We should have noted that when the probe energy is increased to 150 n3 (— 10" W/cm ) the absorption cross section at the transmission maximum increases by a factor of approximately 2. At this energy density, with or without the coupling laser present, transmitted probe energy is no longer linear with incident probe energy.

Photocatalytic synthesis of silver nanoparticles stabilized by TiO2 nanorods: a semiconductor/metal nanocomposite in homogeneous nonpolar solution.

Abstract: A novel colloidal approach toward semiconductor/metal nanocomposites is presented. Organic-soluble anatase TiO2 nanorods are used for the first time to stabilize Ag nanoparticles in optically clear nonpolar solutions in the absence of specific ligands for silver. Metallic silver is generated upon UV illumination of deaerated TiO2 solutions containing AgNO3. The Ag nanoparticles can be obtained in different size-morphological regimes as a function of the irradiation time, due to light-induced photofragmentation and ripening processes. A mechanism for the colloidal stabilization of the silver nanoparticles is tentatively suggested, which regards the TiO2 nanorods as inorganic stabilizers, thus acting in the same manner as conventional surfactant molecules. The proposed photocatalytic approach offers a convenient method for producing TiO2/Ag nanocomposite systems with a certain control over the metal particle size without the use of surfactants and/or additives. Stable colloidal TiO2-nanorod-stabilized Ag na...

Developments in alkali -metal atomic magnetometry

Abstract: Alkali-metal magnetometers use the coherent precession of polarized atomic spins to detect and measure magnetic fields. Recent advances have enabled magnetometers to become competitive with SQUIDs as the most sensitive magnetic field detectors, and they now find use in a variety of areas ranging from medicine and NMR to explosives detection and fundamental physics research. In this thesis we discuss several developments in alkali-metal atomic magnetometry for both practical and fundamental applications. We present a new method of polarizing the alkali atoms by modulating the optical pumping rate at both the linear and quadratic Zeeman resonance frequencies. We demonstrate experimentally that this method enhances the sensitivity of a potassium magnetometer operating in the Earth’s field by a factor of 4, and we calculate that it can reduce the orientation-dependent heading error to less than 0.1 nT. We discuss a radio-frequency magnetometer for detection of oscillating magnetic fields with sensitivity better than 0.2 fT/ √ Hz, which we apply to the observation of nuclear magnetic resonance (NMR) signals from polarized water, as well as nuclear quadrupole resonance (NQR) signals from ammonium nitrate. We demonstrate that a spin-exchange relaxation-free (SERF) magnetometer can measure all three vector components of the magnetic field in an unshielded environment with comparable sensitivity to other devices. We find that octadecyltrichlorosilane (OTS) acts as an anti-relaxation coating for alkali atoms at temperatures below 170◦C, allowing them to collide with a glass surface up to 2,000 times before depolarizing, and we present the first demonstration of high-temperature magnetometry with a coated cell. We also describe a reusable alkali vapor cell intended for the study of interactions between alkali atoms and surface coatings. Finally, we explore the use of a cesium-xenon SERF comagnetometer for a proposed measurement of the permanent electric dipole moments (EDMs) of the electron and the 129Xe atom, with projected sensitivity of δde=9×10−30 e-cm and δdXe=4×10−31 e-cm after 100 days of integration; both bounds are more than two orders of magnitude better than the existing experimental limits on the EDMs of the electron and of any diamagnetic atom.