Abstract Biomagnetic sensing is a powerful non-invasive tool for sensing the extremely small magnetic signals of living organisms. In recent years, the efforts to achieve higher resolution has brought about a demand for novel methods of increasing this tool’s sensitivity and further its miniaturization. In this paper, we present our studies on the optical control of the atomic vapor density in antirelaxation coated cells for application in optical magnetometry. A special system for homogeneous illumination of the cell walls is used to increase the atomic density, avoid the deposition of alkali atoms on the cell walls and reduce the coating deterioration.
Abstract Biomagnetic sensing is a powerful non-invasive tool for sensing the extremely small magnetic signals of living organisms. In recent years, the efforts to achieve higher resolution has brought about a demand for novel methods of increasing this tool’s sensitivity and further its miniaturization. In this paper, we present our studies on the optical control of the atomic vapor density in antirelaxation coated cells for application in optical magnetometry. A special system for homogeneous illumination of the cell walls is used to increase the atomic density, avoid the deposition of alkali atoms on the cell walls and reduce the coating deterioration.
Antirelaxation coatings (ARC) are used in optical cells containing alkali metal vapor to reduce the depolarization of alkali atoms after collisions with the cell walls. The long-lived ground state polarization is a basis for development of atomic clocks, magnetometers, quantum memory, slow light experiments, precision measurements of fundamental symmetries etc. Another application of ARC is with Light-Induced Atomic Desorption (LIAD) for implementation optical dispensers for loading atomic devices as atomic magnetometers, atomic clocks, magneto-optical traps and their miniaturization. In this work, the Rb atomic density and the spin randomization (the number of collisions without spin depolarization) are investigated in PDMS coated vacuum cell when the density is controlled by LIAD, and compared with the results when the density is controlled by temperature. A simple method for measurement of the number of collisions without spin-randomization is used, which comprises recording of the time dependence of the fluorescence intensity of alkali atoms during exposure of the cell to resonant radiation pulses. The obtained results are discussed from point of view of LIAD applications for density control in spectroscopy investigations.
Abstract In this work, we report on our investigations on LIAD (Light Induced Atomic Desorption) aimed at achieving high density of alkali atoms vapor in a coated cell at room temperature. The experimental results show the possibility to reach a density up to the limit when the medium becomes optically thick by applying highly efficient homogeneous illumination. The photon reabsorption mechanism prevents the precise evaluation of the density by measuring the absorption of a probe laser beam, but there is clear evidence that densities can be achieved higher by two orders of magnitude than the thermodynamic equilibrium value.
Sensitive and accurate magnetic-field measurements are essential in many applications, including geophysical studies, biomagnetic signal detection, navigation, event monitoring, and magnetic anomaly detection. In this context, atomic magnetometers are a particularly promising approach, combining high sensitivity and accuracy, and able to rival superconducting quantum interference devices (SQUIDs) without requiring cryogenic cooling. While the best sensitivity levels are achieved in the zero-field regime within magnetic shielding, scalar magnetometers operating in ambient fields also demonstrated remarkable sensitivities. Initiated in the 2000s, the miniaturization of atomic devices, and in particular alkali-vapor cells, paves the way for magnetometers that are both sensitive and compact, well suited to embedded measurements and field applications.This thesis contributes to the development of microfabricated vapor cells for atomic magnetometry. We propose a new filling and sealing method that overcomes some limitations of conventional approaches and could enable the fabrication of purer cells compatible with a wider range of chemical species. This strategy could also facilitate the integration of anti-relaxation coatings, which reduce relaxation caused by collisions with the cell walls. To date, no long-lasting anti-relaxation effects have been demonstrated in microfabricated cells, as traditional methods rely on high temperatures that are incompatible with these coatings.A cell design suited to the deposition of anti-relaxation coatings is presented. We then describe the fabrication and characterization of a multi-axis microfabricated cell, designed for compact atomic devices using multiple optical beams. This multi-axis cell was experimentally validated in a dual-beam magnetometry configuration using an experimental setup developed as part of this thesis.
Introduction and history Paraffin films and other surface coatings have played a decisive role in the emergence and development of optical magnetometry. When alkali atoms in the vapor phase collide with the bare surface of a glass container, they disappear inside the glass and are replaced in the vapor phase by another atom with random spin orientation. With a mean free path of the dimensions of the cell (typically on the order of 1 to several cm), the collision frequency is much too high, 10 4 s −1 , to maintain the substantial spin polarization required for practical applications. In order to prevent this detrimental effect, vapor cells include either an inert buffer gas [1–3] or an antirelaxation surface coating [4]. In the presence of a noble gas at a pressure from 10 −2 to a few atmospheres, the alkali atoms diffuse very slowly from the center of the cell to the glass walls, and their orientation is only very slightly affected by gas collisions. However, there are several advantages to the use of a surface coating instead of buffer gas. If the static magnetic field is not homogeneous, then resonance lines suffer from inhomogeneous broadening in the presence of the gas [5–7]. In addition, the optical pumping process is perturbed by the buffer gas [8, 9]: (i) it is more efficient at the center of the cell than near the uncoated walls, so that the atomic orientation is inhomogeneous inside the cell; (ii) the pump beam absorption line is broadened, and its profile varies with the distance from the entrance window. These effects are unfavorable for the production of alignment in the ground state.
An investigation of the influence of light-induced atomic desorption (LIAD) on the transmission spectra from point of view of LIAD application for miniaturization of magneto-optical sensors and anti-relaxation coatings diagnostics is reported. With reduction of the dimensions of the cells, the amplitude of the signals decreases and it can be compensated by increasing the atomic density with temperature using special high temperature anti-relaxation coatings, or by LIAD. LIAD is a non-thermal process in which atoms adsorbed at a surface are released under illumination. It is investigated in various papers and has different applications - vapor density stabilization, MOT loading, surface nanostructuring etc. In this work the dependence of the shape of the absorption spectra on the laser power and blue light power is measured and analysis of the influence of different factors is done. All measurements are performed on the Rb D2 line in 3 different vacuum cells (uncoated, paraffin coated and SC-77 coated) with a 460 nm light emitting diode illumination. The good knowledge of the factors influencing the alkali atom spectra will be useful not only for the development of new alloptical sensors, but for study atom-dielectric surface interactions and development of new all-optical methods for surface and coating diagnostics.
Antirelaxation coatings (ARC) are used in optical cells containing alkali metal vapor to reduce the depolarization of alkali atoms after collisions with the cell walls. The long-lived ground state polarization is a basis for development of atomic clocks, magnetometers, quantum memory, slow light experiments, precision measurements of fundamental symmetries etc. In this work, a simple method for measuring the number of collisions of the alkali atoms with the cell walls without atomic spin randomization (Nasyrov et al., Proc. SPIE (2015)) was applied to characterize the AR properties of two PDMS coatings prepared from different solutions in ether (PDMS 2% and PDMS 5%). We observed influence of the light-induced atomic desorption (LIAD) on the AR properties of coatings.