We investigate the ground-state Hanle effect in alkali-metal vapor irradiating by a resonant elliptically polarized light wave. The magneto-optical resonances are observed as a change in the ellipticity parameter of the light wave polarization when scanning the transverse magnetic field near zero. We use a miniature ( ≈ 0.125 cm^3 ) glass caesium vapor cell heated to a relatively low temperature of ≈ 85^∘ C. Under the current experimental conditions, the sensitivity of magnetic-field measurements is limited by a technical noise, reaching 180 fT/ √(Hz) in a 200 Hz bandwidth. Our estimates show that, after eliminating technical noise, the sensitivity could be on the order of 10 fT/ √(Hz) . The proposed scheme is promising for the development of a vector zero-field atomic magnetometer with reduced heat dissipation of the sensor head and relaxed requirements for magnetic shielding compared to counterparts operating in the spin-exchange relaxation-free regime. These features are of particular value for medical applications. Schematic representation of the magnetometer sensor head with a cesium cubic vapor cell containing buffer gas

We study the magnetic-field-induced frequency shift (MFS) of the reference resonance in a coherent population trapping (CPT) microwave atomic clock. It is shown that the use of the Pound-Drever-Hall-like technique for frequency locking provides brilliant opportunities for mitigating the MFS. Using a 0.125 cm(3) rubidium vapor cell with a buffer gas, we have measured a residual sensitivity of the reference CPT resonance frequency to be approximate to 70 mu Hz/mG over approximate to 6 mG interval. It means that a fractional frequency shift is extremely small ( approximate to 1x10(-14 )mG(-1)). The results contribute to the development of a new-generation CPT-based miniature atomic clock with improved long-term frequency stability. The proposed method is sufficiently versatile and can be adapted for other excitation schemes in atomic clocks, including those based on Ramsey-like or double-resonance techniques.

We investigate the magnetic-field-induced frequency shift (MFS) of the clock “0–0” transition in the microwave quantum frequency standard (atomic clock) based on coherent population trapping (CPT) in 87Rb vapor. To scan the CPT resonance and to form the error signal, a method analogous to the Pound–Drever–Hall (PDH) technique in the optical frequency range is employed, where the modulating frequency (fm) significantly exceeds the resonance linewidth (FWHM). The experiments demonstrate that this technique offers brilliant capabilities for controlling the sensitivity of the clock transition frequency to magnetic field variations in the vapor cell compared to the conventional method with low-frequency modulation (fm≪FWHM). Specifically, the PDH technique provides several optimal values of the bias magnetic field generated by the solenoid, at which the “0–0” transition frequency exhibits extremely low sensitivity to small variations in the external magnetic field. Furthermore, these magnetic field values can be easily adjusted by changing fm, which is relevant for the optimization of the atomic clock’s operating regime. The experimental results show that by using the PDH technique, the influence of MFS on the clock transition can be suppressed down to ≈3.2×10−13δB2mG−2. These findings can be leveraged both to relax stringent requirements for magnetic field shielding in state-of-the-art CPT-based miniature atomic clocks and to build a new generation of such clocks with long-term frequency stability better than 10−12.

We study a resonant interaction of an elliptically polarized light wave with Rb-87 vapor (D-1 line) exposed to a transverse magnetic field. A 5x5x5 mm(3) glass vapor cell is used for the experiments. The wave intensity is modulated at the frequency Omega(m). By scanning Omega(m) near the Larmor frequency Omega(L), a magnetic resonance (MR) can be observed as a change in the ellipticity parameter of the wave polarization caused by the circular dichroism of the medium. This method for observing MR allows to significantly improve the signal-to-noise ratio compared to a classical Bell-Bloom scheme using a circularly polarized wave. Under current experimental conditions, the sensitivity of the magnetic field sensor is estimated to be approximate to 130 fT/root Hz in a approximate to 2.1 kHz bandwidth. The proposed technique confidently competes with other widely used Bell-Bloom-like schemes based on the Faraday rotation of the light wave polarization, while being more simple and robust. The results can be used to develop a miniature all-optical magnetic field sensor for medicine and geophysics.

A new method of atomic sub-Doppler spectroscopy was developed. The key feature is that the new method uses dual-frequency laser beams in two different optical scheme: with linearly polarized counterpropagating beams with a mutual angle between the polarizations equal to 90 and 45 degrees,, respectively. Due to the CPT effect, a resonance of the opposite sign relative to the saturated absorption resonances was observed.

The state-of-the-art miniature atomic clocks (MACs) are based on the phenomenon of coherent population trapping (CPT) in alkali-metal atomic vapors (Rb or Cs). Increasing frequency stability of the clocks is an urgent issue that will lead to significant progress in many fields of application. Here, we examine a light field configuration composed of two bichromatic light beams with opposite handedness of their circular polarization. The beams are in resonance with optical transitions in the Cs D$_1$ line ($\lambda$$\approx$$895$ nm). This configuration has already been known for observing CPT resonances of an increased contrast compared to a standard single-beam scheme. However, in contrast to previous studies, we use a scheme with two independent pump and probe beams, where the probe beam transmission is separately monitored. The experiments are carried out with a buffer-gas-filled $5$$\times$$5$$\times$$5$ mm$^3$ vapor cell. It is shown that the resonance's line shape acquires asymmetry which can be efficiently controlled by a microwave (Raman) phase between the beams. As a proof of concept, we study the way how this asymmetry can help to significantly mitigate the influence of ac Stark (light) shift on a long-term frequency stability of CPT clocks. The experimental verification is performed both with a distributed-Bragg-reflector (DBR) laser and a vertical-cavity surface-emitting laser (VCSEL). The latter has a particular importance for developing MACs. The results of experiments are in qualitative agreement with analytical theory based on a double $\Lambda$ scheme of atomic energy levels.

The combination of atomic spectroscopy, integrated photonics, and microelectromechanical systems leads the way to the demonstration of microcell-based optical atomic clocks. Here, we report the short-term stability budget of table-top Cs microcell-stabilized lasers based on dual-frequency sub-Doppler spectroscopy (DFSDS). The dependence of the sub-Doppler resonance properties on key experimental parameters is studied. The detection noise budget and absolute phase noise measurements are in good agreement with the measured short-term frequency stability of the laser beatnote, at the level of 1.1 × 10 − 12 τ − 1 / 2 until 100 s, currently limited by the intermodulation effect from a distributed-feedback laser setup. The fractional frequency stability of the laser beatnote at 1 s is about 100 times greater than that of commercial microwave chip-scale atomic clocks and validates interest in the DFSDS approach for the development of high-performance microcell-based optical standards.

The results of an experimental comparison of the parameters of the coherent population trapping (CPT) resonance for the 87 Rb D 1 line and the light shifts during the detection of signals from different cross-sectional areas of the interaction of laser radiation with atoms are presented. A method is proposed to search for zero-light-shift operating conditions and their automatic stabilization, which would improve the long-term stability of CPT-resonance-based microwave frequency standards.

Nonlinear resonances in alkali metal vapor, which are detected by the magneto-optical rotation of the linear polarization of light, are actively used in quantum magnetometry to fabricate atomic magnetometers. The magneto-optical rotation in most such sensors is due to magnetic birefringence, and rotation angles usually do not exceed tens of milliradians. In this work, an experiment where magneto-optical resonances of linear polarization rotation of a probe wave are due to strong dichroism induced in a medium by a counterpropagating pump wave has been proposed. Both waves are in resonance with the F g = 2 → F e = 1 optical transition in the 87 Rb D 1 line (λ ≈ 795 nm). Experiments have been carried out with a 2-cm-long cylindrical cell filled with a buffer gas, and the maximum rotation angle is ≈390 mrad (22°) at a width of resonance of about 300 nT. The results show that the configuration proposed for the observation of magneto-optical rotation is promising for the fabrication of compact high-sensitivity atomic magnetometers.

The absorption of a light wave interacting with optical transitions in the D 1 line of an alkali metal atom subjected to microwave radiation that is in resonance with magnetic dipole transitions between hyperfine ground-state components, has been investigated. It is known that when scanning a longitudinal magnetic field ( B || k , where k is the wavevector), one may observe a magneto-optical resonance due to the ground-state Hanle effect. In addition, the effect of double radio-optical resonance takes place because of the presence of the resonance microwave field. The joint influence of these effects on the formation of a narrow magneto-optical resonance in light wave absorption has been studied theoretically and experimentally. It has been shown analytically that the effects compete with each other and destructively act on the resonance formation. As a result, the amplitude of the resonance is small and its shape is complicated. However, in the presence of a buffer gas the pressure of which is such that the hyperfine splitting of the ground state remains spectrally unresolved, it becomes possible to observe a magneto-optical resonance with a relatively large amplitude. Experiments have been carried out with the use of a miniature glass cell ( V ~ 0.1 cm 3 ) filled with 87 Rb vapor and a buffer gas argon (a pressure of about 95 Torr). In particular, the theoretically predicted resonance narrowing with increasing light field intensity has been experimentally observed. A configuration for magneto-optical resonance excitation suggested here may be applied in quantum magnetometry to measure weak permanent magnetic fields and resonance microwave fields using cells filled with alkali metal vapor.

Zero-field level-crossing resonances (LCRs) underlay one of the most robust and simplest techniques in atomic magnetometry. LCR-based miniaturized magnetic field sensors have already found relevant applications in biology and medicine. Such sensors utilize a single circularly polarized light wave to interact with alkali-metal atoms (usually Rb or Cs) and to observe the LCR in a vapor-cell transmission when a transverse magnetic field is scanned around zero value. A high-temperature regime ( T ≈ 120 − 160°C) is required to achieve a desirable sensitivity of measurements. It can be a problem for some applications, especially in a multi-channel mode of operation. Here, we consider two spectroscopy techniques that can provide high-contrast and narrow LCRs under a relatively low temperature of the cell (≤60°C). These techniques imply using two light waves: the pump wave to polarize the atoms and the probe one to register the resonance. A cubic glass cell of 5×5×5 mm 3 size is used in the experiments. It is filled with cesium vapors and neon as a buffer gas. The results can be used for developing a miniaturized low-power high-sensitivity magnetic field sensor for biomedical applications.

Magnetite (Fe 3 O 4 ) 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 Fe 3 O 4 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.

Experimental parameters of the resonance of coherent population trapping (CTP) on D1 line in Rb-87 and light shifts are compared under modulation of the laser pump current at frequencies of 3.4 and 6.8 GHz. Reproducibility of the parameters of a laser with a vertical cavity needed for long-term stability of an atomic clock is considered. The instabilities of atomic CPT-clock obtained for 1 s are 1.2 x 10(-11) and 3 x 10(-12) for frequencies of 3.4 GHz and 6.8 GHz, respectively.

The ground-state Hanle effect (GSHE) in alkali-metal atomic vapors using a single circularly polarized wave underlies one of the most robust and simplest techniques in atomic magnetometry. This effect causes a narrow (subnatural-width) resonance in the light wave intensity transmitted through a vapor cell. Usually, GSHE-based sensors operate in the spin-exchange-relaxation-free (SERF) regime. However, this regime requires a relatively high temperature of vapors (150 C or higher), leading to a relatively large heat release and power consumption of the sensor head. Besides, without applying special measures, SERF regime significantly limits a dynamic range of measurements. Here, we study a pump-probe scheme involving a single elliptically polarized wave and a polarimetric detection technique. The wave is in resonance with two adjacent optical transitions in the cesium D1 line (894.6 nm) owing to their overlapping in presence of a buffer gas (Ne, 130 Torr). Using a small (0.1 cm$^3$) glass vapor cell, we demonstrate a possibility of observing subnatural-width resonances with a high contrast-to-width ratio (up to 45 %/mG) under a low-temperature (60 C) regime of operation thanks to a strong light-induced circular dichroism. Basing on a $\Lambda$ scheme of atomic energy levels, we obtain explicit analytical expressions for the line shape. The model reveals a linewidth narrowing effect due to openness of the scheme. This result is unusual for magneto-optical atomic spectroscopy because the openness is commonly considered as a undesirable effect, degrading the resonance characteristics. We estimate a sensitivity of 1.8 pT/$\surd$Hz with a 60 fT/$\surd$Hz sensitivity in the photon-shot-noise limit. The results contribute to the theory of GSHE resonances and can be applied to development of a low-temperature high-sensitivity miniaturized magnetic field sensor with an extended dynamic range.

A pump – probe configuration is used to register zero-field level-crossing resonances in Rb vapour contained in a cell with antirelaxation coated walls. The scheme is applied to detect the weak magnetic field generated by a current-carrying micro-wire (metallised track). Such micro-wires can be employed in neural prostheses and hybrid bionic systems as micro-electrode arrays. More specifically, the operation of such live micro-wire belonging to a neuronal – electrode interface is demonstrated, which indicates the possibility of remote testing of the operation (conducting/nonconducting) of micro-wires for in neural implants.