Abstract
Light shifts are an important source of noise and systematics in optically pumped magnetometers. We demonstrate that the long spin-coherence time in paraffin-coated cells leads to spatial averaging of the vector light shift over the entire cell volume. This renders the averaged vector light shift independent, under certain approximations, of the light-intensity distribution within the sensor cell. Importantly, the demonstrated averaging mechanism can be extended to other spatially varying phenomena in anti-relaxation-coated cells with long coherence times.
Highlights
Light shifts in alkali atoms have been researched since 1960s [1, 2], the effect of laser-induced vector light shifts (VLS) in coated cells has been little explored in the literature
In this work we demonstrate that the same reasoning can be applied to the VLS in paraffin-coated cells, making it, under realistic assumptions, a function of the total light power averaged over the cell volume, rather than the local intensity
To see whether the VLS is averaged by the atoms in a paraffin-coated cell, we measure the dependence of the magnetic resonance (MR) center shift as a function of the laser beam (LS beam) area for a given total power (5.5 μW)
Summary
Light shifts in alkali atoms have been researched since 1960s [1, 2], the effect of laser-induced vector light shifts (VLS) in coated cells has been little explored in the literature. Paraffin-coated cells enable the atoms to undergo a number of wall collisions (up to 106 [23]) without depolarization In this way, thermal atoms sample the entire cell volume during their spin relaxation time and become sensitive to average, rather than local magnetic field [24]. The optical frequency of the light-shift laser is fardetuned from the relevant atomic transitions compared to the Doppler width, and the beam-intensity profile is assumed flat (top hat). Each individual atom interacting with the light-shift beam acquires a phase advance or retardation φ in its Larmor precession proportional to the change in the Larmor frequency due to the vector light shift in the beam δν and the time t spent in it during the spin coherence time T2. If the width of the MR stems from a combination of different phase-diffusion processes the contributions add in quadrature
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