Presently, among the most demanding applications for highly sensitive magnetometers are Magnetocardiography (MCG) and Magnetoencephalography (MEG), where sensitivities of around 1pT.Hz-1/2 and 1fT.Hz-1/2 are required. Cryogenic Superconducting Quantum Interference Devices (SQUIDs) are currently used as the magnetometers. However, there has been some recent work on replacing these devices with magnetometers based on atomic spectroscopy and operating at room temperature. There are demonstrations of MCG and MEG signals measured using atomic spectroscopy These atomic magnetometers are based on chip-scale microfabricated components. In this paper we discuss the prospects of using photonic crystal optical fibres or hollow core fibres (HCFs) loaded with Rb vapour in atomic magnetometer systems. We also consider new components for magnetometers based on mode-locked semiconductor lasers for measuring magnetic field via coherent population trapping (CPT) in Rb loaded HCFs.
Presently, among the most demanding applications for highly sensitive magnetometers are Magnetocardiography (MCG) and Magnetoencephalography (MEG), where sensitivities of around 1pT.Hz-1/2 and 1fT.Hz-1/2 are required. Cryogenic Superconducting Quantum Interference Devices (SQUIDs) are currently used as the magnetometers. However, there has been some recent work on replacing these devices with magnetometers based on atomic spectroscopy and operating at room temperature. There are demonstrations of MCG and MEG signals measured using atomic spectroscopy These atomic magnetometers are based on chip-scale microfabricated components. In this paper we discuss the prospects of using photonic crystal optical fibres or hollow core fibres (HCFs) loaded with Rb vapour in atomic magnetometer systems. We also consider new components for magnetometers based on mode-locked semiconductor lasers for measuring magnetic field via coherent population trapping (CPT) in Rb loaded HCFs.
Abstract The chip-scale hybrid optical pumping spin-exchange relaxation-free (SERF) atomic magnetometer with a single-beam arrangement has prominent applications in biomagnetic measurements because of its outstanding features, including ultrahigh sensitivity, an enhanced signal-to-noise ratio, homogeneous spin polarization and a much simpler optical configuration than other devices. In this work, a miniaturized single-beam hybrid optical pumping SERF atomic magnetometer based on a microfabricated atomic vapor cell is demonstrated. Although the optically thin Cs atoms are spin-polarized, the dense Rb atoms determine the experimental results. The enhanced signal strength and narrowed resonance linewidth are experimentally proven, which shows the superiority of the proposed magnetometer scheme. By using a differential detection scheme, we effectively suppress optical noise with an approximate five-fold improvement. Moreover, the cell temperature markedly affects the performance of the magnetometer. We systematically investigate the effects of temperature on the magnetometer parameters. The theoretical basis for these effects is explained in detail. The developed miniaturized magnetometer has an optimal magnetic sensitivity of 20 fT/Hz 1/2 . The presented work provides a foundation for the chip-scale integration of ultrahighly sensitive quantum magnetometers that can be used for forward-looking magnetocardiography (MCG) and magnetoencephalography (MEG) applications.
There has been permanent interest in investigations of new magnetic sensors and their various applications (Edelstein, 2007). Last years there is a rapid progress in development of magneto-optical sensors because of their sensitivity and potential for miniaturization. Magnetometers, based on magneto-optical sensors have high sensitivity comparable to, or even surpassing this of the SQUIDs (Superconducting Quantum Interference Devices) (Kominis et al., 2003; Dang et al., 2010; Savukov, 2010; Knappe, 2010). Microfabrication of components using the techniques of Micro-Electro-Mechanical Systems (MEMS) developed for atomic clocks (Knappe, 2004) gives the opportunity for building small, low consuming, low cost and non-cryogenic (as SQUIDs) sensors (Griffith et al., 2010). Coherent optical effects can be applied for magnetic field detection and offer perspectives for development of high-precision optical magnetometers (Cox et al., 2011; Kitching et al., 2011). These magnetometers are appropriate for geomagnetic, space, nuclear and biological magnetic field measurements (cardio and brain magnetic field imaging), environmental monitoring, magnetic microscopy, investigations of fundamental physics, etc. Coherent magneto-optical resonances have many applications not only in magnetometry, but in high-resolution spectroscopy, lasing without inversion, laser cooling, ultraslow group velocity propagation of light, etc. (Gao, 2009).
Advances in Optical and Photonic Devices 330 integration into microfabricated packages.Such packages will be not only inexpensive and easy to batch produce they will also have lower power consumption, light weight and unimpeded mobility (Knappe et al., 2006).Sensitive magnetic field measurements, for which AMs can be used, are important owing to many existing and potential applications.Magnetometers have been in wide use, for example, in geology, military, biomagnetism, space magnetic field measurements.AMs have been used because they are both relatively sensitive compared to conventional inexpensive magnetometers, such as fluxgates, and more convenient compared to SQUIDs that require cryogenic cooling.For a long time low-T c SQUIDs had been by far the most sensitive magnetometers at low frequency.However, this has changed with the demonstration with AMs of record 0.5 fT/Hz 1/2 sensitivity (Kominis et al., 2003).High-sensitivity AMs are based on spin-polarized atomic gases or vapors, and AM research is closely related to the atomic physics subfield dedicated to the investigation of spin interactions in such media.This subfield includes the research on optical pumping and related topics such as atomic clocks, masers, hyperpolarized gases, spin-based spectroscopy, and some others.A comprehensive review of optical pumping experiments before 1972 and theory of optical pumping and various relaxation mechanisms are given by William Happer (Happer, 1972).This theory, which still stands the test of time, includes the formulation of density matrix equations, which can be directly applied to the analysis of magnetic resonances of vapors on which atomic magnetometers are based.Atomic magnetometers find many applications as other magnetometers, but they are most useful when high sensitivity and non-cryogenic operation are required.For example, AMs have been developed for submarine detection, and many other military applications are possible on similar principles.Some applications of Rb-vapor or 3 He magnetometers in geophysics and space physics were mentioned as early as in 1961 by Bloom (Bloom, 1961) who did some pioneering work on the high-sensitivity measurements of magnetic fields and theory for the operation of atomic magnetometers.Theoretical analysis of early atomic magnetometers was also done by Dehmelt (Dehmelt, 1957) and by Bell and Bloom (Bell & Bloom, 1957).Although the history of atomic magnetometers is quite fascinating and they played an important role in applications where simpler and less expensive methods did not provide sufficient sensitivity, the atomic magnetometers of the past were much less sensitive than the modern ones.Most exciting results appeared only recently with the various demonstrations of performance of high-density AMs, which we would like to focus on in this chapter. How to referenceIn order to correctly reference this scholarly work, feel free to copy and paste the following: Igor Savukov (2010).Ultra-Sensitive Optical Atomic Magnetometers and Their Applications, Advances in Optical and Photonic Devices, Ki Young Kim (Ed.),
This thesis describes developments in atomic vapour loading in hollow core photonic crystal fibre (HC-PCF) for fabrication of atomic vapour loaded photonic microcells (PMC). These developments have been targeted at addressing some of the issues associated with loading atomic vapours in confined waveguiding geometries such as increased dephasing and physio-chemical wall absorptions. Atomic vapour loaded HC-PCF and PMC’s have applications in laser metrology, coherent optics and magneto optical spectroscopy. State of the art HC-PCF have been fabricated for loading with atomic vapour including both photonic bandgap (PBG) guiding and inhibited coupling (IC) hypocycloidal core shape Kagome HC-PCF. Record loss of 70 dB/km has been achieved in IC hypocycloid core shape Kagome HC-PCF in the spectral region centred at 800 nm. This fibre retains excellent single mode propagation combined with large core and increased optical bandwidth in comparison with specialist PBG HC-PCF optimised for operation around 800 nm. Aluminosilicate sol-gel coatings have been developed and successfully applied to the inner core wall of HC-PCF’s to reduce the atomic vapour surface interaction. Confining atomic vapours in micron scaled HC-PCF results in increased dephasing rates because of the frequent atom wall collisions. Anti relaxation coating materials have been applied to the inner core wall and the longitudinal relaxation time has been measured in coated and uncoated fibres utilising a magneto optical technique. Additionally sub Doppler transparencies are investigated in anti relaxation coated and uncoated HC-PCF.
Atomic magnetometers with magnetic field modulation have emerged as pivotal sensors for biomagnetic measurements. However, challenges such as crosstalk between adjacent modulation fields and the complexity of signal circuitry become increasingly serious in the development of array-based equipment with the magnetometers, especially in the miniaturized atomic magnetometer. This paper proposes an all-optical, fully integrated fiber-coupled atomic magnetometer that employs pump beam modulation. A miniaturized atomic magnetometer with a volume of 10 cm³ has been designed, incorporating an active measurement area of 3 × 3 × 3 mm3. The magnetometer operates in the spinexchange relaxation-free (SERF) regime with an 87Rb vapor cell. An amplitude-modulated pump beam directly modulates the rubidium atomic ensembles, rather than the magnetic field modulation. The optical rotation angle is detected by an unmodulated probe beam oriented orthogonally to the pump beam. In light of the discontinuous pumping characteristics, we developed a modified theoretical model to clarify the output response of the proposed atomic magnetometer. The experimental results demonstrate that the new design achieves the same sensitivity as conventional magnetometer configurations with a smaller volume and without crosstalk of the magnetic field. This research highlights the significant potential for advancing the development of highly sensitive, miniaturized atomic magnetometers, making them particularly suitable for applications in magnetocardiography (MCG) and magnetoencephalography (MEG).
Abstract The magnetic field is one of the most fundamental and ubiquitous physical observables, carrying information about all electromagnetic phenomena. For the past 30 years, superconducting quantum interference devices (SQUIDs) operating at 4 K have been unchallenged as ultrahigh-sensitivity magnetic field detectors1, with a sensitivity reaching down to 1 fT Hz-1/2 (1 fT = 10-15 T). They have enabled, for example, mapping of the magnetic fields produced by the brain, and localization of the underlying electrical activity (magnetoencephalography). Atomic magnetometers, based on detection of Larmor spin precession of optically pumped atoms, have approached similar levels of sensitivity using large measurement volumes2, 3, but have much lower sensitivity in the more compact designs required for magnetic imaging applications4. Higher sensitivity and spatial resolution combined with non-cryogenic operation of atomic magnetometers would enable new applications, including the possibility of mapping non-invasively the cortical modules in the brain. Here we describe a new spin-exchange relaxation-free (SERF) atomic magnetometer, and demonstrate magnetic field sensitivity of 0.54 fT Hz-1/2 with a measurement volume of only 0.3 cm3. Theoretical analysis shows that fundamental sensitivity limits of this device are below 0.01 fT Hz-1/2. We also demonstrate simple multichannel operation of the magnetometer, and localization of magnetic field sources with a resolution of 2 mm.