Valerio Biancalana

Cesium coherent population trapping magnetometer for cardiosignal detection in an unshielded environment

We present encouraging results obtained with an experimental apparatus based on coherent population trapping and aimed at detecting a biological (cardiac) magnetic field in a magnetically compensated but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection to cancel common mode magnetic noise. Synchronous data acquisition with a reference (electrocardiographic or pulse-oximetric) signal makes possible improvement of the signal-to-noise ratio in off-line averaging. The setup has the significant advantages of working at room temperature with a small-size head, and the possibility of fast adjustments of the dc bias magnetic field, which makes the sensor suitable for detecting a biomagnetic signal at any orientation with respect to the axis of the head and in any position on the patients chest, which is not the case with other kinds of magnetometers.

Long-term drift laser frequency stabilization using purely optical reference.

We describe an apparatus for the stabilization of laser frequencies that prevents long-term frequency drifts. A Fabry–Perot interferometer is thermostated by referencing it to a stabilized He–Ne laser (master), and its length is scanned over more than one free spectral range allowing the analysis of one or more lines generated by other (slave) lasers. A digital acquisition system makes the detection of the position of all the laser peaks possible, thus producing both feedback for the thermostat and the error signal used for stabilizing the slave lasers. This technique also allows for easy, referenced scanning of the slave laser frequencies over range of several hundred MHz, with a precision of the order of a few MHz. This kind of stabilization system is particularly useful when no atomic or molecular reference lines are available, as in the case of rare or short lived radioactive species.

All optical sensor for automated magnetometry based on coherent population trapping

An automated magnetometer suitable for long lasting measurement under stable and controllable experimental conditions has been implemented. The device is based on Coherent Population Trapping (CPT) produced by a multi-frequency excitation. CPT resonance is observed when a frequency comb, generated by diode laser current modulation, excites Cs atoms confined in a π/4× (2.5) × 1 cm, 2 Torr N2 buffered cell. A fully optical sensor is connected through an optical fiber to the laser head allowing for truly remote sensing and minimization of the field perturbation. A detailed analysis of the CPT resonance parameters as a function of the optical detuning has been made in order to get high sensitivity measurements. The magnetic field monitoring performances and the best sensitivity obtained in a balanced differential configuration of the sensor are presented. OCIS 120.4640, 020.1670, 300.6380. This work has been submitted to JOSA B for publication [Josa B (7) 2007]An automated magnetometer suitable for long lasting measurement under stable and controllable experimental conditions has been implemented. The device is based on coherent population trapping (CPT) produced by a multifrequency excitation. CPT resonance is observed when a frequency comb, generated by diode laser current modulation, excites Cs atoms confined in a π/4×(2.5)2×1 cm3, 2 TorrN2 buffered cell. A fully optical sensor is connected through an optical fiber to the laser head allowing for truly remote sensing and minimization of the field perturbation. A detailed analysis of the CPT resonance parameters as a function of the optical detuning has been made in order to get high sensitivity measurements. The magnetic field monitoring performances and the best sensitivity obtained in a balanced differential configuration of the sensor are presented.

Dual channel self-oscillating optical magnetometer

We report on a two-channel magnetometer based on nonlinear magneto-optical rotation in a Cs glass cell with buffer gas. The Cs atoms are optically pumped and probed by free running diode lasers tuned to the D2 line. A wide frequency modulation of the pump laser is used to produce both synchronous Zeeman optical pumping and hyperfine repumping. The magnetometer works in an unshielded environment, and a spurious signal from distant magnetic sources is rejected by means of differential measurement. In this regime the magnetometer simultaneously gives the magnetic field modulus and the field difference. Rejection of the common-mode noise allows for high-resolution magnetometry with a sensitivity of 2 pT/sqrt Hz. This sensitivity, in conjunction with long-term stability and a large bandwidth, makes it possible to detect water proton magnetization and its free induction decay in a measurement volume of 5 cm3.

All-optical magnetometry for NMR detection in a micro-Tesla field and unshielded environment.

An all-optical atomic magnetometer is used to detect a proton free-precession signal from a water sample polarized in a 0.7 T field and remotely analyzed in a 4 microT field. Nuclear spins are manipulated either by pi/2 pulses or by non-adiabatic rotation. The magnetometer operates at room temperature, in an unshielded environment and has a dual-channel sensor for differential measurements.

Multichannel optical atomic magnetometer operating in unshielded environment

A multichannel atomic magnetometer operating in an unshielded environment is described and characterised. The magnetometer is based on

Three-half harmonic generation in laser-plasma interaction: Evidence for plasmon propagation

D_1

Microtesla NMR J-coupling spectroscopy with an unshielded atomic magnetometer.

D1 optical pumping and