T. Scholtes

Characteristics and performance of an intensity-modulated optically pumped magnetometer in comparison to the classical M x magnetometer

We compare the performance of two methods for the synchronization of the atomic spins in optically pumped magnetometers: intensity modulation of the pump light and the classical M(x) method using B(1) field modulation. Both techniques use the same set-up and measure the resulting features of the light after passing a micro-fabricated Cs cell. The intensity-modulated pumping shows several advantages: better noise-limited magnetic field sensitivity, misalignment between pumping and spin synchronization is excluded, and magnetometer arrays without any cross-talk can be easily set up.

Light-shift suppression in a miniaturized Mx optically pumped Cs magnetometer array with enhanced resonance signal using off-resonant laser pumping.

The performance of an optically pumped Mx magnetometer with miniaturized Cs cell at earths magnetic field strength (50 μT) is investigated. Operation using detuned high intensity laser light is shown to be superior to the conventional resonant operation in terms of the projected shot-noise-limited ( 50 fT/√Hz) and the actual noise-limited sensitivity using a noise compensation method. The Zeeman light shift effect, emerging due to the off-resonant circularly polarized laser radiation and leading to a strong orientational dependence of the measurement, is suppressed by averaging two identical magnetometer configurations pumped with oppositely circularly polarized light. A residual heading error within the range of 14 nT, limited by the present experimental characterization setup, was achieved.

Light-narrowed optically pumped M{sub x} magnetometer with a miniaturized Cs cell

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 (42 fT/{radical}(Hz) in a cell of only 9.3 mm{sup 3} 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 {mu}T magnetic fields, by using only a single high-intensity laser beam both for pumping and probing of atomic spins.

A full optically operated magnetometer array: An experimental study

We show the operation of an optically pumped magnetometer array in a 50 μT magnetic field. The various components for a fully optical and non-magnetic detector unit were constructed and evaluated, from which a prototype unit was assembled with fiber coupled electronics. In this unit the magnetometers were operated using the intensity modulated method and heated with an off-resonant laser. Calculations on the temperature distribution were used to design the magnetometer array. Different magnetometers in such a detector unit were characterized and showed identical performance. Without applying noise reduction schemes, the obtained magnetic field resolution is a factor 2.5 above the shot noise level down to frequencies of about 7 Hz.

An optically pumped magnetometer working in the light-shift dispersed Mz mode

We present an optically pumped magnetometer working in a new operational mode—the light-shift dispersed Mz (LSD-Mz) mode. It is realized combining various features; (1) high power off-resonant optical pumping; (2) Mz configuration, where pumping light and magnetic field of interest are oriented parallel to each other; (3) use of small alkali metal vapor cells of identical properties in integrated array structures, where two such cells are pumped by circularly polarized light of opposite helicity; and (4) subtraction of the Mz signals of these two cells. The LSD-Mz magnetometer’s performance depends on the inherent and very complex interplay of input parameters. In order to find the configuration of optimal magnetometer resolution, a sensitivity analysis of the input parameters by means of Latin Hypercube Sampling was carried out. The resulting datasets of the multi-dimensional parameter space exploration were assessed by a subsequent physically reasonable interpretation. Finally, the best shot-noise limited magnetic field resolution was determined within that parameter space. As the result, using two 50 mm3 integrated vapor cells a magnetic field resolution below 10 fT/√Hz at Earth’s magnetic field strength is possible.

Dichroic atomic vapor laser lock with multi-gigahertz stabilization range

A dichroic atomic vapor laser lock (DAVLL) system exploiting buffer-gas-filled millimeter-scale vapor cells is presented. This system offers similar stability as achievable with conventional DAVLL system using bulk vapor cells, but has several important advantages. In addition to its compactness, it may provide continuous stabilization in a multi-gigahertz range around the optical transition. This range may be controlled either by changing the temperature of the vapor or by application of a buffer gas under an appropriate pressure. In particular, we experimentally demonstrate the ability of the system to lock the laser frequency between two hyperfine components of the (85)Rb ground state or as far as 16 GHz away from the closest optical transition.

Improving the sensitivity of optically pumped magnetometers by hyperfine repumping

Most optically pumped magnetometers based on alkali atom vapor cells and pumped by a single narrow-band laser suffer from a loss of signal since atoms become trapped in the ground hyperfine states that are not coupled to the laser beam. This can be counteracted by additional optical repumping of these ground-state levels. We study hyperfine repumping using cesium vapor cells with partly overlapped ground-state splitting due to their nitrogen buffer-gas filling. We implement two methods of repumping and compare them to the conventional case of F=4 pumping: F=3 repumping with an additional repumper laser and combined pumping/repumping in the light-narrowing mode, where a single high-power laser is tuned near the F=3 transitions. All these modes are investigated for two different methods of spin-phase synchronization: the Mx and intensity modulation methods. For both methods, any kind of repumping results in a clear improvement of the magnetometer sensitivity compared to no repumping, but in the Mx mode it is more pronounced (about 50 versus 200  fT/√Hz for a 50  mm3 Cs vapor cell). The mechanisms responsible for the distinct results in the different working modes are discussed.

Characterization of the global network of optical magnetometers to search for exotic physics (GNOME)

The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) is a network of geographically separated, time-synchronized, optically pumped atomic magnetometers that is being used to search for correlated transient signals heralding exotic physics. The GNOME is sensitive to nuclear- and electron-spin couplings to exotic fields from astrophysical sources such as compact dark-matter objects (for example, axion stars and domain walls). Properties of the GNOME sensors such as sensitivity, bandwidth, and noise characteristics are studied in the present work, and features of the networks operation (e.g., data acquisition, format, storage, and diagnostics) are described. Characterization of the GNOME is a key prerequisite to searches for and identification of exotic physics signatures.