Inductive imaging of the concealed defects with radio-frequency atomic magnetometers

We explore the capabilities of the radio-frequency atomic magnetometers in the non-destructive detection of concealed defects. We present results from the systematic magnetic inductive measurement of various defect types in an electrically conductive object at different rf field frequencies (0.4–12 kHz) that indicate the presence of an optimum operational frequency of the sensor. The optimum in the frequency dependence of the amplitude/phase contrast for defects under a 0.5–1.5 mm conductive barrier was observed within the 1–2 kHz frequency range. The experiments are performed in the self-compensated configuration that automatically removes the background signal created by the rf field producing object response

Cancellation of the collisional frequency shift in caesium fountain clocks

We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F = 4, mF = 0> atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation. Our results also have implications for test operation of fountains at multiple pi/2 pulse areas

Enhanced material defect imaging with a radio-frequency atomic magnetometer

Imaging of structural defects in a material can be realized with a radio-frequency atomic magnetometer by monitoring the material’s response to a radio-frequency excitation field. We demonstrate two measurement configurations that enable the increase of the amplitude and phase contrast in images that represent a structural defect in electrically conductive and magnetically permeable samples. Both concepts involve the elimination of the excitation field component, orthogonal to the sample surface, from the atomic magnetometer signal. The first method relies on the implementation of a set of coils that directly compensates the excitation field component in the magnetometer signal. The second takes advantage of the fact that the radio-frequency magnetometer is not sensitive to the magnetic field oscillating along one of its axes. Results from simple modelling confirm the experimental observation and are discussed in detail

Generation of atomic spin orientation with a linearly polarized beam in room-temperature alkali-metal vapor

Traditionally, atomic spin orientation is achieved by the transfer of angular momentum from polarized light to an atomic system. We demonstrate the mechanism of orientation generation in room-temperature caesium vapors that combines three elements: optical pumping, nonlinear spin dynamics, and spin-exchange collisions. Through the variation of the spin-exchange relaxation rate, the transition between an aligned and an oriented atomic sample is presented. The observation is performed by monitoring the atomic radio-frequency spectra. The measurement configuration discussed paves the way to simple and robust radio-frequency atomic magnetometers that are based on a single low-power laser diode that approach the performance of multilaser pump-probe systems

Spin noise spectroscopy of a noise-squeezed atomic state

Spin noise spectroscopy is emerging as a powerful technique for studying the dynamics of various spin systems also beyond their thermal equilibrium and linear response. Here, we study spin fluctuations of room-temperature neutral atoms in a Bell-Bloom type magnetometer. Driven by indirect pumping and undergoing a parametric excitation, this system is known to produce noise-squeezing. Our measurements not only reveal a strong asymmetry in the noise distribution of the atomic signal quadratures at the magnetic resonance, but also provide insight into the mechanism behind its generation and evolution. In particular, a structure in the spectrum is identified which allows to investigate the main dependencies and the characteristic timescales of the noise process. The results obtained are compatible with parametrically induced noise squeezing. Notably, the noise spectrum provides information on the spin dynamics even in regimes where the macroscopic atomic coherence is lost, effectively enhancing the sensitivity of the measurements. Our work promotes spin noise spectroscopy as a versatile technique for the study of noise squeezing in a wide range of spin based magnetic sensors

Parametric amplification and noise-squeezing in room temperature atomic vapours

We report on the use of parametric excitation to coherently manipulate the collective spin state of an atomic vapour at room temperature. Signatures of the parametric excitation are detected in the ground-state spin evolution. These include the excitation spectrum of the atomic coherences, which contains resonances at frequencies characteristic of the parametric process. The amplitudes of the signal quadratures show amplification and attenuation, and their noise distribution is characterized by a strong asymmetry, similarly to those observed in mechanical oscillators. The parametric excitation is produced by periodic modulation of the pumping beam, exploiting a Bell-Bloom-like technique widely used in atomic magnetometry. Notably, we find that the noise-squeezing obtained by this technique enhances the signal-to-noise ratio of the measurements up to a factor of 10, and improves the performance of a Bell-Bloom magnetometer by a factor of 3

Imaging of material defects with a radio-frequency atomic magnetometer

Non-destructive inductive testing of defects in metal plates using the magnetic resonance signal of a radio-frequency atomic magnetometer is demonstrated. The shape and amplitude of the spatial profile of the signal features, which represent structural defects, are explored. By comparing numerical and experimental results on a series of benchmark aluminium plates, we show correspondence between the properties of the secondary field and those of the magnetometer signal. In particular, we show that two components of the secondary field are mapped onto the amplitude and phase of the atomic magnetometer signal. Hence, a magnetic field measurement with the atomic magnetometer, although scalar in its nature, provides semi-vectorial information on the secondary field. Moreover, we demonstrate a robust process for determining defect dimensions, which is not limited by the size of the sensor. We prove that the amplitude and phase contrast of the observed profiles enables us to reliably measure defect depth

Dual-frequency cesium spin maser

Comagnetometers have been validated as valuable components of the atomic physics toolbox in fundamental and applied physics. So far, the explorations have been focused on systems involving nuclear spins. Presented here is a demonstration of an active alkali-metal (electronic) system, i.e., a dual-frequency spin maser operating with the collective cesium F=3 and F=4 spins. The experiments have been conducted in both magnetically shielded and unshielded environments. In addition to the discussion of the system's positive-feedback mechanism, the implementation of the dual-frequency spin maser for industrial nondestructive testing is shown. The stability of the F=3 and F=4 spin precession frequency ratio measurement is limited at the 3×10-8 level by the laser frequency drift, corresponding to a frequency stability of 1.2mHz for 104 s integration time. We discuss measurement strategies that could improve this stability to nHz, enabling measurements with sensitivities to the axion-nucleon and axion-electron interactions at the levels of fa/CN∼109 and fa/Ce∼108 GeV, respectively

Non-destructive structural imaging of steelwork with atomic magnetometers

We demonstrate the imaging of ferromagnetic carbon steel samples and we detect the thinning of their profile with a sensitivity of 0.1 mm using a Cs radio-frequency atomic magnetometer. Images are obtained at room temperature, in magnetically unscreened environments. By using a dedicated arrangement of the setup and active compensation of background fields, the magnetic disturbance created by the samples’ magnetization is compensated. Proof-of-concept demonstrations of non-destructive structural evaluation in the presence of concealing conductive barriers are also provided. The relevant impact for steelwork inspection and health and usage monitoring without disruption of operation is envisaged, with direct benefit for industry, from welding in construction to pipeline inspection and corrosion under insulation in the energy sector. Published by AIP Publishing. https://doi.org/10.1063/1.504203

Non-destructive structural imaging of steelwork with atomic magnetometers

We demonstrate the imaging of ferromagnetic carbon steel samples and we detect the thinning of their profile with a sensitivity of 0.1 mm using a Cs radio-frequency atomic magnetometer. Images are obtained at room temperature, in magnetically unscreened environments. By using a dedicated arrangement of the setup and active compensation of background fields, the magnetic disturbance created by the samples' magnetization is compensated. Proof-of-concept demonstrations of non-destructive structural evaluation in the presence of concealing conductive barriers are also provided. The relevant impact for steelwork inspection and health and usage monitoring without disruption of operation is envisaged, with direct benefit for industry, from welding in construction to pipeline inspection and corrosion under insulation in the energy sector