Performance of a radio-frequency two-photon atomic magnetometer in different magnetic induction measurement geometries

TL;DR

This paper explores the use of a two-photon atomic magnetometer for radio-frequency magnetic induction measurements, demonstrating improved sensitivity, phase retrieval, and a self-compensation setup for defect detection across different geometries.

Contribution

It introduces a novel two-photon process analysis, a phase retrieval method, and a self-compensation configuration for enhanced magnetic induction measurements.

Findings

Spectral components of the two-photon process are identified.

A phase retrieval method for two-photon interactions is demonstrated.

A self-compensation setup enables high-contrast defect detection.

Abstract

Measurements monitoring the inductive coupling between oscillating radio-frequency magnetic fields and objects of interest create versatile platforms for non-destructive testing. The benefits of ultra low frequency measurements, i.e., below 3 kHz, are sometimes outweighed by the fundamental and technical difficulties related to operating pick-up coils or other field sensors in this frequency range. Inductive measurements with the detection based on a two-photon interaction in rf atomic magnetometers address some of these issues, as the sensor gains an uplift in its operational frequency. The developments reported here integrate the fundamental and applied aspects of the two-photon process in magnetic induction measurements. In this paper, all spectral components of the two-photon process are identified, which result from the non-linear interactions between the rf fields and atoms. A method for the retrieval of the two-photon phase information, which is critical for inductive measurements, is also demonstrated. Furthermore, a self-compensation configuration is introduced, whereby high contrast measurements of defects can be obtained due to the sensor's insensitivity to the primary field, including using simplified instrumentation for this configuration by producing two rf fields with a single rf coil.