Adrian Hofer

A room temperature 19-channel magnetic field mapping device for cardiac signals

We present a multichannel cardiac magnetic field imaging system built in Fribourg from optical double-resonance Cs vapor magnetometers. It consists of 25 individual sensors designed to record magnetic field maps of the beating human heart by simultaneous measurements on a grid of 19 points over the chest. The system is operated as an array of second order gradiometers using sophisticated digitally controlled feedback loops.

Cs*Hen exciplexes in solid He4

We present a theoretical and experimental study of the laser-induced formation process and of the emission spectra of Cs*He(n) exciplexes in the hcp and bcc phases of solid helium. Two different exciplex molecules are detected: a linear triatomic Cs*He2, which can exist in two electronic states: APi(1/2) and BPi(3/2), and a larger complex, where six or seven He atoms form a ring around a single cesium atom in the 6P(1/2) state. A theoretical model is presented, which allows the interpretation of the experimentally observed spectra.

Mapping the Cardiomagnetic Field with 19 Room Temperature Second-Order Gradiometers

We present a laser pumped 19 channel second-order magnetometer system for measuring magnetic fields produced by the beating human heart. Each field sensor is a room-temperature paraffin-coated cesium vapor cell operated in a standard M x magnetometer configuration based on optically detected magnetic resonance with circularly polarized D1 pumping on the F = 4 →F′ = 3 component of the D1 transition. Dynamic magnetic field maps are derived from the simultaneous recording at 19 grid points. The system has been successfully used for recording (in less than 2 minutes) cardiac field maps of more than 30 healthy subjects. We also report a recording of the MCG of a patient with a nonspecific intraventricular conduction defect, which represents the first detection of a cardiac anomaly by an atomic magnetometer array.