We measured the rate of velocity-changing collisions (VCCs) between alkali atoms and background gas in buffer-gas-free anti-relaxation-coated cells. The average VCC rate in paraffin-coated rubidium vapor cells prepared in this work was 1 × 10 6 s −1 , which corresponds to ∼ 1 mm in the mean free path of rubidium atoms. This short mean free path indicates that the background gas is not negligible in the sense that alkali atoms do not travel freely between the cell walls. In addition, we found that a heating process known as "ripening" increases the VCC rate, and also confirmed that ripening improves the anti-relaxation performance of the coatings.

We performed scattering experiments using a rubidium (Rb) atomic beam on paraffin films and measured the angular and velocity distributions of scattered atoms. The paraffin films were prepared in various ways and characterized by atomic force microscopy and X-ray diffraction. The films exhibited various roughnesses and crystal structures. The paraffin films preserved the spin polarization of the scattered atoms. The measured angular distributions of all prepared films were consistent with Knudsen's cosine law. The velocity distributions were well fitted by Maxwell's distribution, characterized by a temperature much closer to the film temperature than to the atomic-beam temperature. We therefore concluded that the Rb atoms were well thermalized with the paraffin films via single scattering events. * hatakeya@cc.tuat.ac.jp 1 arXiv:1807.02329v1 [physics.atom-ph]

We describe a magnetic source imaging camera (MSIC) allowing a direct dynamic visualization of the two-dimensional spatial distribution of the individual components B x ðx; yÞ; B y ðx; yÞ and B z ðx; yÞ of a magnetic field. The field patterns allow-in principle-a reconstruction of the distribution of sources that produce the field B by inverse problem analysis. We compare experimentally recorded point-spread functions, i.e., field patterns produced by point-like magnetic dipoles of different orientations with anticipated field patterns. Currently, the MSIC can resolve fields of %10 pT (1 s measurement time) range in a field of view up to $20 Â 20 mm 2 . The device has a large range of possible applications. As an example, we demonstrate the MSIC's use for recording the spatially resolved N eel magnetorelaxation of blocked magnetic nanoparticles.In recent years, optically pumped atomic magnetometers (AMs), also known as optical magnetometers, operated by laser light have achieved intrinsic magnetometric sensitivities in the fT= ffiffiffiffiffiffi For mapping magnetic field distributions over extended regions of space, one may scan a single (scalar or vector component) magnetometer through the volume of interest, a very time-consuming method. Taue et al. 4 have demonstrated 10 pT magnetometric and mm spatial resolutions by scanning a single high-sensitivity AM through the field produced by an object. AMs have recently been deployed for eddy current imaging of electrically conductive materials yielding a sub-mm resolution. 5,6 Very recently, a flux-guide based AM microscope has demonstrated a resolution of 250 lm and a sensitivity of 23 pT= ffiffiffiffiffiffi Hz p . 7 However, such sequential measurements are speed-limited by the involved mechanical motion and can hence not be used for time-and space-resolved recordings or direct field visualization. A more efficient approach involves arrays of individual magnetometers, [8][9][10][11] each containing an individual vapour cell and a photodetector. The spatial resolution in that case is determined by the number of sensors, the achieved signal/noise ratio, and source reconstruction algorithms.In most AM-based field-mapping devices, the magnetometric information of interest is encoded into the intensity (or polarization) of atomic resonance radiation. Nonlinear magneto-optical effects (reviewed, e.g., in Ref. 12) form the basis for such an optical encoding. In this letter, we describe a magnetic source imaging camera (MSIC) that builds on this principle. We detect fluorescence from a single atomic vapour cell by a CCD camera, the camera pixels playing the role of individual photodetectors. The parallel recording and processing of all camera pixels can be interpreted in terms of an identical number of magnetometer signals, which make the MSIC a magnetometer with a high spatial resolution. Such a device has the potential for a wealth of practical applications, ranging from screening for magnetic material contaminations to biomedical imaging.In the past, several experimen...

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