Recently, our group produced spin-polarized hydrogen (SPH) atoms at densities of at least 1019 cm−3 from the photodissociation of hydrogen halide molecules with circularly polarized UV light and measured them via magnetization-quantum beats with a pickup coil. These densities are approximately 7 orders of magnitude higher than those produced using conventional methods, opening up new fields of application, such as ultrafast magnetometry, the production of polarized MeV and GeV particle beams, such as electron beams with intensities approximately 104 higher than current sources, and the study of polarized nuclear fusion, for which the reaction cross sections of D–T and D–3He reactions are expected to increase by 50% for fully polarized nuclear spins. We review the production, detection, depolarization mechanisms, and potential applications of high-density SPH.

We introduce a novel and sensitive ns-resolved atomic magnetometer, which is at least three orders of magnitude faster than conventional magnetometers. We use the magnetic field dependence of the hyperfine...

In a recent publication [arXiv:2010.14579], we introduced a new type of atomic magnetometer, which relies on hydrohalide photo-dissociation to create high-density spin-polarized hydrogen. Here, we extend our previous work and present a detailed theoretical analysis of the magnetometer signal and its dependence on time. We also derive the sensitivity for a spin-projection noise limited magnetometer, which can be applied to an arbitrary magnetic field waveform.A broad range of physical objects and processes generate magnetic fields which upon detection can convey important information about the nature and structure of their origin. As a result, magnetic field detection lies at the heart of many scientific and technological applications, which can benefit significantly from advances in magnetometry [1].Different magnetic field sensors have been developed which offer distinct advantages and are attractive for particular applications. In general terms, an ideal magnetometer should present high-sensitivity, wide bandwidth detection, highperformance over a large dynamic range and operating conditions, as well as capability for miniaturization when used for magnetic field imaging.Recently, a new type of atomic magnetometer was demonstrated based on high-density spin-polarized atomic H (SPH) [2], which has the potential to address satisfactorily the above requirements for magnetometry. The spinpolarized ensemble is produced by photo-dissociating hydrohalide gas with a circularly-polarized laser pulse [3][4][5]. Magnetic field detection is achieved by monitoring the dynamics of the H hyperfine coherences, which are created in the optical pumping process without the need for external magnetic fields.This paper is an extension of the work presented in [2], analytically deriving equations for the spin-dynamics, the magnetometer signal and the quantum spin-projection noise.We will consider the magnetometer scheme with mutually orthogonal directions for optical pumping, magnetic field direction and spin-probing, as shown in Fig. 1. Without loss of generality we take the magnetic field to be in the z direction, the optical pumping along the y axis and the probe axis in the x direction. Monitoring of spins is realized with an inductive pick-up coil, which detects the magnetic flux generated by the H spins. Since the electron magnetic moment is more than three orders of magnitude larger than the proton magnetic moment, the coil is to a very good approximation only sensitive to the H electron spins. In the following, we will assume a pickup coil with a response time much shorter than the hyperfine interaction period and neglect complications arising from a non-spherical polarized region or from geometrical factors in the coupling of the magnetic field from spins to the coil. For simplicity, we will assume that the observable is d Ŝx dt , where Ŝi expresses the dimensionless electron spin operator in the i direction.

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We introduce a novel and sensitive ns-resolved atomic magnetometer, which is at least three orders of magnitude faster than conventional magnetometers. The magnetic field dependence of hyperfine beating of high-density spin-polarized H atoms, produced from the rapid photodissociation of HCl gas with sub-ns laser pulses, results in a few nT sensitivity for a spin-projection limited sensor with 10 nl measurement volume after 1 ns measurement time. The magnetometer will allow ultrafast continuous B-field measurements in many fields, including spin chemistry, spin physics, and plasma physics.