Paraffin-coated Cell Research Articles

Optimized detection modality for radio-frequency sensing with a double-resonance alignment magnetometer

In this work, we present a comprehensive and comparative analysis of two detection modalities, i.e., polarization rotation and absorption measurement of light, for a double-resonance alignment magnetometer (DRAM). We derive algebraic expressions for magnetometry signals based on the description of multipole moments. Experiments are carried out using a room-temperature paraffin-coated cesium-vapor cell and measuring either the polarization rotation or absorption of the transmitted laser light. A detailed experimental analysis of the resonance spectra is performed to validate the theoretical findings for various input parameters. The results signify the use of a single isotropic relaxation rate, thus simplifying the data analysis for optimization of the DRAM. The sensitivity measurements are performed and reveal that the polarization-rotation detection mode yields larger signals and better sensitivity than absorption measurement of light. Published by the American Physical Society 2024

Light narrowing over broad temperature range with paraffin-coated vapor cells

This study reports light narrowing in paraffin-coated vapor cells from room temperature 27 to 59 °C, where spin-exchange relaxation is suppressed. By means of a coating lock and eliminating the reservoir effect, an ultra-narrow magnetic resonance linewidth of 0.36 Hz and an atomic coherence lifetime of T2=0.9 s are achieved. In cells free of buffer gas, the narrow linewidth over this broad temperature range is a result of enhanced spin polarization, which is facilitated by the effective suppression of radiation trapping benefiting from the stability of the vapor density. Using such cells in atomic magnetometers, the photon shot noise limit is estimated as 0.2 fT/Hz1/2 and the spin-projection noise limit is estimated as 1.1 fT/Hz1/2. Also, a magnetometer system with the stable coated cell is identified, which demonstrates the potential for achieving relatively stable magnetometer sensitivity without precisely controlling the cell temperature. The long coherence lifetime and the broad operating temperature range expand the potential applications of quantum memory and other quantum sensors such as atomic clocks.

Observation of spin bistability with paraffin-coated vapor cells

Observation of spin bistability with paraffin-coated vapor cells

Remote detection of the conductivity of current-carrying metallized traces

The weak magnetic fields generated by a current-carrying metallized traces are detected in view of their applications in bionic systems and neural-electrode interface technologies. The traces are formed by femtosecond laser processing of the surface of polydimethylsiloxane polymer substrate and further functionalization by electroless metallization. The measurements are performed by means of magneto-optical spectroscopy involving two optical beams, serving as pump and probe, where the magnetic field sensor is 87Rb atoms confined in a paraffin-coated optical cell. The experimental results show the feasibility of remote detection of the conductivity of metallized nickel traces.

SERF-like magnetometry in room-temperature environment.

We demonstrate an atomic magnetometry using amplitude-modulated pumping and hyperfine repumping techniques in a paraffin-coated cell. By exploiting the constructive interference between spins polarized by the pump beam and an additional repump beam, we observe a three-fold increase in the amplitude of magnetic resonance, along with a reduction in linewidth by approximately two times. The implementation of the repump beam effectively narrows the linewidth, demonstrating successful suppression of spin-exchange relaxation. This reduction in relaxation rate, combined with the enhanced signal, significantly improves the sensitivity of the magnetometer. Consequently, our technique offers a promising approach for achieving SERF-like magnetometry with sub-fT-level sensitivity in Earth-field range and room-temperature environment.

Alignment-Based Optically Pumped Magnetometer Using a Buffer-Gas Cell

Alignment-based optically pumped magnetometers (OPMs) are capable of measuring oscillating magnetic fields with high sensitivity in the $\mathrm{fT}/\sqrt{\mathrm{Hz}}$ range. Until now, alignment-based magnetometers have only used paraffin-coated vapour cells to extend the spin relaxation lifetimes of the alkali vapour. The drawback of these cells is that they are hand blown and are therefore time intensive, and somewhat unreliable, to produce. Buffer-gas cells, on the other hand, can be manufactured on a mass scale using microfabrication techniques. In this work we use hand-blown cells, but our methods also apply to microfabricated buffer-gas cells. We present the first demonstration of an alignment-based magnetometer using a buffer-gas vapour cell containing caesium (Cs) alkali vapour and nitrogen (${\mathrm{N}}_{2}$) buffer gas. The OPM is operated at $55{\phantom{\rule{0.1em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ and we achieve a $325\phantom{\rule{0.2em}{0ex}}\mathrm{fT}/\sqrt{\mathrm{Hz}}$ sensitivity to 10 kHz oscillating magnetic fields with an 800 Hz bandwidth. The alignment-based magnetometer uses a single low-power laser beam for optical pumping and probing and could potentially allow for more rapid commercialization of radio-frequency OPMs, due to the robustness of the one-beam geometry.

Coherent optical spectroscopy characterization of the magnetic properties of oriented Fe3O4 nanoparticles

Magnetite (Fe3O4) nanoparticles are widely used in microwave components, such as microwave absorbers and anti-reflection coatings. Their magnetic properties are important for these applications. In this work, the weak magnetic field created by the Fe3O4 nanoparticles was estimated using a coherent-spectroscopy all-optical method for measurement of weak magnetic fields. Both the magnitude and the direction of the magnetic field were evaluated through the position and amplitude of a magneto-optical resonance obtained in a paraffin-coated sensor cell containing Rb vapors. A pump-probe scheme was used to prepare a high-contrast magneto-optical resonance. Different possible geometries related to this concept are discussed, including sensor miniaturization.

Dual-beam electromagnetically-induced absorption resonance in a 87Rb cell with antirelaxation coating

Destruction of the laser-induced coherence in the ground state of alkali atoms manifests itself as an ultra-narrow resonance in the atomic spectrum. Depending on the geometry of irradiation and observation, the coherent spectroscopy studies CPT (coherent population trapping), EIT (electromagnetically-induced transparency) or EIA (electromagnetically-induced absorption). In the present work, we investigated EIA on the D1 87Rb line by applying a counter-propagating dual-beam scheme. The main advantage of this scheme is the high resonance contrast – an important parameter for many applications. In our previous work performed in a paraffin-coated cell we observed that, unlike the resonance in buffer gas cell detected in the same experimental scheme, the EIA signal has a complex form, because it is formed by two atomic sub-ensembles in the vapor cell with different relaxation rates determined by the laser excitation conditions. We focused on the narrow component, since it has a higher amplitude-width ratio, making it preferable for applications. We investigate the influence of the atomic vapor density and the pump laser intensity on the resonance parameters in order to optimize the amplitude ratio of the wide and narrow components and achieve the highest amplitude-width ratio value for the narrow component of the EIA resonance.

Transient evolution of optical magnetic resonance in rubidium vapor.

We observe the transient evolution of the laser pumped magnetic resonance in a paraffin-coated rubidium vapor cell and analyze the phenomena numerically by using the four-level density matrix. With the increased radio frequency (RF) sweep rate, the traditional Lorentz signal turns to an asymmetric shape at low sweep rate and starts to oscillate at a high sweep rate. The transient oscillation's features, including frequency and the decay time, are studied by suddenly turning on the RF field to the resonance Larmor precession frequency under the different RF field and light field parameters. The experimental result reveals the transient signals' strong dependence on the RF field power and light power. Especially, the transient oscillation frequency primarily depends on the RF field's power and whatever power the laser light is. When the laser power is lower, the transient oscillation frequency is proportional to the RF field's amplitude. These transient evolution signals are also confirmed with the numerical calculations based on the density-matrix equation of motion.

Note: Pulsed optically pumped atomic clock based on a paraffin-coated cell

We report on the implementation of a pulsed optically pumped atomic clock based on a paraffin-coated cell. The relaxation times are measured, with the longitudinal relaxation time, T1 = 9.7 ± 0.4 ms, and the transversal relaxation time, T2 = 0.40 ± 0.03 ms. We demonstrated that the measured frequency stability of the clock is 3.9 × 10-13 τ-1/2 (1 s ≤ τ ≤ 100 s) and reaches a value of 3.1 × 10-14 for τ = 1000 s, where τ is the averaging time. This is an unprecedented result for a paraffin-coated vapor cell clock, and it makes significant contributions toward improving the performance of the wall-coated vapor cell atomic clock.

Quantitative study of optical pumping in the presence of spin-exchange relaxation

We have performed quantitative measurements of the variation of the on-resonance absorption coefficients ${\ensuremath{\kappa}}_{0}$ of the four hyperfine components of the Cs ${D}_{1}$ transition as a function of laser power $P$, for pumping with linearly and with circularly polarized light. Sublevel populations derived from rate equations assuming isotropic population relaxation (at a rate ${\ensuremath{\gamma}}_{1}$) yield algebraic ${\ensuremath{\kappa}}_{0}(P)$ dependences that do not reproduce the experimental findings from Cs vapor in a paraffin-coated cell. However, numerical results that consider spin-exchange relaxation (at a rate ${\ensuremath{\gamma}}_{\mathrm{se}}$) and isotropic relaxation fit the experimental data perfectly well. The fit parameters, viz., the absolute value of ${\ensuremath{\kappa}}_{0}$, the optical pumping saturation power ${P}_{\mathrm{sat}}$, and the ratio ${\ensuremath{\gamma}}_{\mathrm{se}}/{\ensuremath{\gamma}}_{1}$, are well described by the experimental conditions and yield absolute values for ${\ensuremath{\gamma}}_{1}$ and ${\ensuremath{\gamma}}_{\mathrm{se}}$. The latter is consistent with the previously published Cs-Cs spin-exchange relaxation cross section.

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

We present an experimental and theoretical investigation of the influence of the transverse magnetic field (TMF) on the coherent population trapping resonances obtained on the Zeeman sublevels of the D1 line of 87Rb in a paraffin-coated vacuum cell. It is shown that a TMF changes the shape and sign of the resonance or destroys it completely. The role of the different rank polarization moments in the integral registered fluorescent signal in the presence of stray magnetic fields is clarified using numerical simulations.

Dynamics of the light-induced atomic desorption at homogeneous illumination

An experimental investigation of Light-Induced Atomic Desorption (LIAD) at homogeneous illumination in uncoated Rb glass cell is reported. The dynamics parameters of LIAD and their dependences on the illumination intensity in uncoated cell are measured and compared with these in paraffin-coated cell and the theoretical dependences for coated cell at homogeneous illumination. The homogeneous illumination not only increases the yield of LIAD, but increases the rates of desorption and adsorption. The results are interesting for the better understanding of the process of LIAD and the atom-surface interaction, for the development of new LIAD-loaded atomic devices, all-optical control of light, optical sensors miniaturization, and new methods for surface and coating diagnostics and nanostructuring.

Subnatural-linewidth biphotons from a Doppler-broadened hot atomic vapour cell.

Entangled photon pairs, termed as biphotons, have been the benchmark tool for experimental quantum optics. The quantum-network protocols based on photon–atom interfaces have stimulated a great demand for single photons with bandwidth comparable to or narrower than the atomic natural linewidth. In the past decade, laser-cooled atoms have often been used for producing such biphotons, but the apparatus is too large and complicated for engineering. Here we report the generation of subnatural-linewidth (<6 MHz) biphotons from a Doppler-broadened (530 MHz) hot atomic vapour cell. We use on-resonance spontaneous four-wave mixing in a hot paraffin-coated 87Rb vapour cell at 63 °C to produce biphotons with controllable bandwidth (1.9–3.2 MHz) and coherence time (47–94 ns). Our backward phase-matching scheme with spatially separated optical pumping is the key to suppress uncorrelated photons from resonance fluorescence. The result may lead towards miniature narrowband biphoton sources.

Vector light shift averaging in paraffin-coated alkali vapor cells.

Light shifts are an important source of noise and systematics in optically pumped magnetometers. We demonstrate that the long spin-coherence time in paraffin-coated cells leads to spatial averaging of the vector light shift over the entire cell volume. This renders the averaged vector light shift independent, under certain approximations, of the light-intensity distribution within the sensor cell. Importantly, the demonstrated averaging mechanism can be extended to other spatially varying phenomena in anti-relaxation-coated cells with long coherence times.

Eddy current imaging with an atomic radio-frequency magnetometer

We use a radio-frequency 85Rb alkali-vapor cell magnetometer based on a paraffin-coated cell with long spin-coherence time and a small, low-inductance driving coil to create highly resolved conductivity maps of different objects. We resolve sub-mm features in conductive objects, we characterize the frequency response of our technique, and by operating at frequencies up to 250 kHz we are able to discriminate between differently conductive materials based on the induced response. The method is suited to cover a wide range of driving frequencies and can potentially be used for detecting non-metallic objects with low DC conductivity.

Non-negligible collisions of alkali atoms with background gas in buffer-gas-free cells coated with paraffin

We measured the rate of velocity-changing collisions (VCCs) between alkali atoms and background gas in buffer-gas-free anti-relaxation-coated cells. The average VCC rate in paraffin-coated rubidium vapor cells prepared in this work was $1 \times 10^{6}$ s$^{-1}$, which corresponds to $\sim 1$ mm in the mean free path of rubidium atoms. This short mean free path indicates that the background gas is not negligible in the sense that alkali atoms do not travel freely between the cell walls. In addition, we found that a heating process known as "ripening" increases the VCC rate, and also confirmed that ripening improves the anti-relaxation performance of the coatings.

Stray magnetic field influence on the CPT resonance in a coated Rb vacuum cell

Interaction of a resonant laser beam with an atomic absorption medium creates population redistribution and interference between atomic levels. This anisotropy of the medium is experimentally observed as coherent population trapping (CPT) or electromagnetically induced transparency (EIT). Due to the small sub-natural width of the CPT and EIT resonances, they find wide applications in metrology, quantum optics, atom cooling. A non-compensated stray magnetic field (SMF) can change the shape and sign of the resonance or destroy it completely. In this work, we present an experimental and theoretical investigation of the influence of a stray magnetic field on the CPT resonances obtained on Zeeman sublevels of the D1 line of 87Rb in a paraffin-coated vacuum cell. The role is clarified of the polarization moments with different rank in creating the integral registered fluorescent signal in the presence of a stray magnetic field. It is shown that a transverse magnetic field plays an important role in changing the shape of the signal.

Large magnetic shielding factor measured by nonlinear magneto-optical rotation

A passive magnetic shield was designed and constructed for magnetometer tests for the future neutron electric dipole moment experiment at TRIUMF. The axial shielding factor of the cylindrical magnetic shield was measured using a magnetometer based on non-linear magneto-optical rotation of the plane of polarized laser light upon passage through a paraffin-coated vapor cell containing natural Rb at room temperature. The laser was tuned to the Rb D1 line, near the 85Rb F=2→2,3 transition. The shielding factor was measured by applying an axial field externally and measuring the magnetic field internally using the magnetometer. The axial shielding factor was determined to be (1.3±0.1)×107, from an applied axial field of 1.45μT in the background of Earth׳s magnetic field.

Transformation of Ramsey electromagnetically induced absorption into magnetic-field induced transparency in a paraffin-coated Rb vapor cell

We report on magnetic-field induced transparency (MIT) based on Ramsey electromagnetically induced absorption (EIA) in a paraffin-coated Rb vapor cell. Changing the laser polarization from linear to circular in the presence of a weak residual transverse magnetic field to the laser propagation, the narrow absorption due to the Ramsey EIA transformed into the transparency due to MIT of the 5S1/2 (F = 2)-5P3/2 (F' = 3) transition of 87Rb in the paraffin-coated Rb vapor cell. The spectral widths of the EIA and MIT in the Hanle configuration were measured to be 0.6 mG (425 Hz) and 1.2 mG, respectively. MIT depended on the long preservation time of the ground-state coherent spin states and the transverse magnetic field. From the numerical results, the crossover between the Ramsey EIA and the MIT could be illustrated as the superposition of both signals.