Laser induced fluorescence diagnostic for measuring small magnetic fields

Abstract

A novel, spatially and temporally resolved diagnostic is being developed to measure small B fields by detecting Zeeman shifts much smaller than the transition linewidth. This diagnostic technique will be used to measure magnetic fields associated with intense ion beam propagation through a low-pressure gas, as envisioned for particle beam fusion. High sensitivity is achieved by a variation on the Babcock technique using laser-induced fluorescence (LIF) spectroscopy. The LIF from a J=1→0 transition in a probe species is viewed parallel to B. In this direction, ΔM=0 fluorescence is not observed, while ΔM=±1 fluorescence is right- and left-circularly polarized and can be measured separately using polarization filters. If a narrow-band pump laser is tuned to a half-maximum point of the unsplit transition line, the presence of the magnetic field shifts one of the ΔM=±1 absorption transitions into resonance with the laser and shifts the other transition further out of resonance. For small field strengths, the difference in the fluorescence signals is proportional to the Zeeman split.