Optically pumped non-zero field magnetometric sensor for the magnetoencephalographic systems using intra-cavity contacted VCSELs with rhomboidal oxide current aperture
Mikhail A. Bobrov, Sergey A. Blokhin, Nikolay A. Maleev, Alexey A. Blokhin, A. P. Vasyl’ev, Alexander G. Kuzmenkov, Anatoly S. Pazgalev, Mikhail V. Petrenko, Sergei P. Dmitriev, Anton K. Vershovskii, V. M. Ustinov, I. I. Novikov, Л.Я. Карачинский
Abstract We demonstrate the possibility of using vertical-cavity surface emitting lasers with intracavity contacts and a rhomboidal oxide current aperture for creating compact optically pumped 133Cs atomic magnetometer operating in non-zero magnetic fields, which is promising to use in magnetoencephalographic systems. The magnetic resonance parameters were studied in a two-beam MX optically pumped magnetic field sensor scheme based on the effect of the magnetic resonance line narrowing at high laser pumping and high concentrations of alkali-metal atoms. The ultimate sensitivity of OPM was estimated by the ratio of the magnetic resonance steepness to the probe light shot noise level. It is shown that a magnetic sensor based on the vertical-cavity surface emitting lasers and a compact (0.125 cm3 volume) Cs vapor cell can achieve a shot noise-limited sensitivity better than 15 fT in 1 Hz bandwidth. Developed intracavity contacted VCSELs suitable for use in compact atomic magnetometers for magnetoencephalographic systems.
Abstract We demonstrate the possibility of using vertical-cavity surface emitting lasers with intracavity contacts and a rhomboidal oxide current aperture for creating compact optically pumped 133Cs atomic magnetometer operating in non-zero magnetic fields, which is promising to use in magnetoencephalographic systems. The magnetic resonance parameters were studied in a two-beam MX optically pumped magnetic field sensor scheme based on the effect of the magnetic resonance line narrowing at high laser pumping and high concentrations of alkali-metal atoms. The ultimate sensitivity of OPM was estimated by the ratio of the magnetic resonance steepness to the probe light shot noise level. It is shown that a magnetic sensor based on the vertical-cavity surface emitting lasers and a compact (0.125 cm3 volume) Cs vapor cell can achieve a shot noise-limited sensitivity better than 15 fT in 1 Hz bandwidth. Developed intracavity contacted VCSELs suitable for use in compact atomic magnetometers for magnetoencephalographic systems.
Abstract A variant of the scheme of a magnetometric sensor based on cesium atomic vapor is proposed and experimentally investigated. The sensor uses magnetic resonance excitation by modulated light of an hyperfine optical pumping that is transverse to the magnetic field. It is shown that, for a cell with a volume of 0.125 cm3, the variational sensitivity of such a scheme, estimated from the ratio of the steepness of the signal in the center of the magnetic resonance to the shot noise of the detecting radiation, reaches a level of <10 fT/Hz1/2 in the frequency band width of the order of 850 Hz. The sensor, which does not emit radio frequency fields, is designed for use in magnetoencephalographic complexes. Possible ways to improve the performance of the scheme for detecting relatively fast (~4.2 kHz in a field of 0.1 mT) signals of the precession of proton magnetic moments in promising ultra-weak field tomography schemes are considered.
Magnetic sensors developed for application in magnetoencephalography must meet a number of requirements; the main ones are compactness, sensitivity and response speed. We present a quantum optically pumped atomic sensor with cell volume of 0.5cm3 that meets these requirements and is operable in nonzero magnetic fields. The ultimate sensitivity of the sensor was estimated as (using the criteria of the ratio of the slope of the magnetic resonance signal to the shot noise spectral density) to be better than 5 fT/Hz1/2. The actual sensitivity, measured in a gradiometric scheme, reaches 13 fT/Hz1/2 per sensor. We also present a novel and fast algorithm for optimization of the geometric properties of non-zero field sensor array with respect to maximization of the information transfer rate for cortical sources.
A new generation of small low-power atomic sensors, including clocks, magnetometers, and gyroscopes, is being developed based on recently available MEMS and VCSEL technologies.These sensors rely on spectroscopic interrogation of alkali atoms, typically rubidium or cesium, contained in small vapor cells.The relevant spectroscopic wavelengths (in vacuum) are 894.6 nm (D1) and 852.3 nm (D2) for cesium, and 795.0 nm (D1) and 780.2 nm (D2) for rubidium.The D1 wavelengths are either preferred or required, depending on the application, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources because of their low power consumption and circular output beam.This paper describes the required VCSEL characteristics for atomic clocks and magnetometers.The fundamental VCSEL requirement is single-frequency output with tunability to the particular spectroscopic line of interest.Singlepolarization and single-transverse-mode operation are implicit requirements.VCSEL amplitude noise and frequency noise are also important because they contribute significantly to the sensor signal-to-noise ratio.Additional desired VCSEL attributes are low cost, low power consumption, and several years of continuous operating lifetime.This paper also describes the 894-nm VCSELs that we have developed for cesium-based atomic sensors.In particular, we discuss VCSEL noise measurements and accelerated lifetime testing.Finally, we report the performance of prototype atomic clocks employing VCSELs.
We demonstrate a way of operating an optically pumped magnetometer with miniaturized cesium cell using the light-narrowing effect. The magnetometer setup shows improvement of shot-noise-limited sensitivity (42fT/Hz in a cell of only 9.3mm3 volume) due to the suppression of spin-exchange relaxation to a large extent and the use of a strikingly increased fraction of alkali-metal atoms for signal generation, working even in $\ensuremath{\mu}\mathrm{T}$ magnetic fields, by using only a single high-intensity laser beam both for pumping and probing of atomic spins.
This paper presents a novel scheme on the integration of chip-scale SERF magnetometer using a vertical-cavity surface-emitting laser(VCSEL) as pumping and detecting laser. The fabrication and integration process of the whole system based on stacking PCB boards consist of VCSEL, optical components, rubidium vapor cell, photo-detector, three axis Helmholtz coils. By calculation and measurement, it was found that the module is designed with a minimum output power of 0.15mW and a competitive volume of 1.4×1.4×2.5cm3. Experiments show that the sensitivity of chip-scale SERF magnetometer based on VCSEL is around 1.87pT/Hz1/2in magnetic shield environment, the integration and miniaturization design process of the magnetometer can be empolyed for magnetoencephalography(MEG) measurement.
Spin-exchange relaxation-free (SERF) atomic magnetometers have emerged as highly promising candidates for ultra-weak magnetic field detection, particularly in biomagnetic imaging, owing to their exceptional sensitivity, amenability to miniaturization, and near-room-temperature operation. While current miniaturized magnetometers typically employ laser chips with fixed optical power, the quantitative impact of laser power on critical performance metrics remains to be fully elucidated. This study systematically investigates the influence of laser power on sensitivity, bandwidth, and dynamic range by incorporating considerations of power broadening, saturation absorption, and noise constraints. A miniaturized probe, integrated with an actively controlled vertical-cavity surface-emitting laser (VCSEL), was developed for experimental validation. Theoretical and experimental results consistently demonstrate that as optical power increases, sensitivity exhibits a non-monotonic dependence, whereas both bandwidth and dynamic range manifest a monotonic upward trend, aligning well with theoretical simulations. The optimized sensor achieved a peak sensitivity of 16 fT/√Hz at 300 μW, while the bandwidth and dynamic range reached 230 Hz and ±5.4 nT at 500 μW, respectively. This work establishes a robust theoretical and experimental framework for the comprehensive performance optimization of laser-integrated miniaturized atomic magnetometers.