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.

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Optical magnetometry - eScholarship

This monograph is devoted to the description and interpretation of interference between quantum states of an atom, as manifested in the angular distribution and polarization of spontaneous emission and absorption The basic phenomena are first introduced and explained in terms of the simple classical dipole model A more quantitative description follows, making use of the density matrix formalism and the statistical tensor The theoretical sections are complemented by detailed accounts of experimental methods and results, such that the monograph as a whole gives a comprehensive picture of this field

Interference of atomic states

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.

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

We report an experimental investigation of the effect of electromagnetically induced transparency (EIT) using bichromatic laser radiation and an extremely thin cell filled with pure Rb with smoothly controllable thickness $L$ of the atomic vapor layer in the range $\ensuremath{\sim}780--1600\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, for which $L$ is comparable to the laser wavelength $\ensuremath{\lambda}$ resonant with the ${D}_{2}$ line $(780\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$. It is revealed that the transmission spectrum of the probe laser contains two sub-Doppler peaks that have different linewidths. The narrow peak corresponds to EIT, whereas the broader one results from velocity-selective optical pumping (VSOP) and repumping processes. It is demonstrated that in the case of nonzero detuning of the coupling laser, the EIT resonance and VSOP are shifted with respect to each other on the frequency scale, which makes it possible to observe a competition between the two effects (this is not possible to realize in an ordinary cell). Also, the Dicke-type coherent narrowing effect depending on the ratio $L∕\ensuremath{\lambda}$ influences the absorption spectrum of the probe laser. Formation of an EIT resonance is substantially favored for the atoms with slow normal velocity, caused by their longer interaction time with the bichromatic laser field. As a result of the predominant contribution of these atoms, the observed linewidth of the EIT resonance is only $\ensuremath{\sim}9\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, which is more than ten times narrower than the inverse window-to-window flight time. In an external magnetic field, three and five EIT resonances have been observed for the vapor thickness of $L=2\ensuremath{\lambda}$, on $^{87}\mathrm{Rb}$ and $^{85}\mathrm{Rb}$, respectively.

Dark-line atomic resonances in a submicron-thin Rb vapor layer

We report an experimental investigation of the effect of electromagnetically induced transparency (EIT) using bichromatic laser radiation and an extremely thin cell filled with pure Rb with smoothly controllable thickness $L$ of the atomic vapor layer in the range $\ensuremath{\sim}780\char21{}1600\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, for which $L$ is comparable to the laser wavelength $\ensuremath{\lambda}$ resonant with the ${D}_{2}$ line $(780\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$. It is revealed that the transmission spectrum of the probe laser contains two sub-Doppler peaks that have different linewidths. The narrow peak corresponds to EIT, whereas the broader one results from velocity-selective optical pumping (VSOP) and repumping processes. It is demonstrated that in the case of nonzero detuning of the coupling laser, the EIT resonance and VSOP are shifted with respect to each other on the frequency scale, which makes it possible to observe a competition between the two effects (this is not possible to realize in an ordinary cell). Also, the Dicke-type coherent narrowing effect depending on the ratio $L∕\ensuremath{\lambda}$ influences the absorption spectrum of the probe laser. Formation of an EIT resonance is substantially favored for the atoms with slow normal velocity, caused by their longer interaction time with the bichromatic laser field. As a result of the predominant contribution of these atoms, the observed linewidth of the EIT resonance is only $\ensuremath{\sim}9\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, which is more than ten times narrower than the inverse window-to-window flight time. In an external magnetic field, three and five EIT resonances have been observed for the vapor thickness of $L=2\ensuremath{\lambda}$, on $^{87}\mathrm{Rb}$ and $^{85}\mathrm{Rb}$, respectively.

Dark-line atomic resonances in a submicron-thin Rb vapor layer (7 pages)

Coherent-population-trapping resonances within the degenerate two-level system of the F=2-->F′=1 transition of the 87Rb D1 line were investigated in an uncoated Rb vapor cell by means of level-crossing-type experiments. Tuning over the two-photon resonance is achieved sweeping a magnetic field around zero value. The influence of transverse magnetic fields on the amplitude and the width of the resonances, recorded in fluorescence and absorption, were investigated in the cases of excitation with linear, circular, and elliptical laser light polarization. A theoretical analysis was performed for the case of linearly polarized excitation, the results of which are in good agreement with the experiment.

Polarization-dependent sensitivity of level-crossing, coherent-population-trapping resonances to stray magnetic fields

The shape of the coherent-population-trapping (CPT) resonances was investigated theoretically and experimentally at different laser powers. The CPT resonances were observed in fluorescence on the degenerate two-level system of the $({F}_{\ensuremath{\varphi}}=2\ensuremath{\rightarrow}{F}_{f}=1)$ transition of the $^{87}\mathrm{Rb}$ ${D}_{1}$ line by means of a Hanle effect configuration in an uncoated vacuum cell. Numerical simulations based on the density matrix formalism, which take into account the high-rank polarization moment (HRPMs) influence and the velocity distribution of the atoms, were used to calculate the shape of the nonlinear magnetic resonances. The comparison of the theoretical and experimental shapes of the CPT resonances demonstrated that the HRPMs influence the shape at all laser excitation powers, and this influence can be used to explain some peculiarities at the center of the CPT resonance shape.

Shape of the coherent-population-trapping resonances and high-rank polarization moments

https://iopscience.iop.org/article/10.1088/1361-6455/aa9c36/pdf

Peculiarities of the coherent population trapping resonance in the fluorescence obtained in a coated 87 Rb cell in the presence of transverse magnetic field: theory and experiment

The fast development of CPT applications and the need of g ood magnetooptical sensors result in an increased interest in the Coherent Population Trapping (CPT) resonances and the processes that determine their shape. In this work the shape and width of the CPT resonances are investigated in two different paraffin-coated Rb vapor cells from point of view of understanding the processes influencing the shape of the reso nances and building of miniature and sensitive detector. The dependence of the shape of the resonances on the laser power is measured. Narrow resonances on three hyperfine transitions of the D 1 87 Rb line are registered. For explanat ion of the bright structure in th e resonance shapes at low laser powers analysis of the influence of different processes is made. Keywords: coherent population trapping, line shapes and line widths, coated cell, magnetometry 1. INTRODUCTION During the last decade many applications of Coherent Population Trapping (CPT) resonances in high-resolution spectroscopy, quantum information storage and processing, metrology (atomic clocks), magnetometry, lasing without inversion, laser cooling, ultraslow group velocity propagation of light etc. have been demonstrated

Coherent population trapping resonance structure in paraffin-coated Rb vacuum cells

A model for description of the shapes of the coherent population trapping (CPT) resonances at different geometries of
excitation and observation is developed. The numerical calculations, based on the irreducible tensor operator formalism,
take into account the experimental geometry, the velocity distribution of the atoms, the Gaussian distribution of the laser
beam intensity and the high rank polarization moments (HRPM). The results for different laser beam diameters, aperture
of the detection, position of the photodetector etc. are compared with the experimental data. A method for description of
the experimental shapes is proposed.

G. Todorov

Papers

Polarization-dependent sensitivity of level-crossing, coherent-population-trapping resonances to stray magnetic fields

Shape of the coherent-population-trapping resonances and high-rank polarization moments

Peculiarities of the coherent population trapping resonance in the fluorescence obtained in a coated 87 Rb cell in the presence of transverse magnetic field: theory and experiment

Coherent population trapping resonance structure in paraffin-coated Rb vacuum cells

Shape of the coherent-population-trapping resonances registered in fluorescence at different experimental geometries