We investigated the operation of an all-optical rubidium-87 atomic magnetometer with amplitude-modulated light. To study the suppression of spin-exchange relaxation, three schemes of pumping were implemented with room-temperature and heated paraffin coated vacuum cells. Efficient pumping and accumulation of atoms in the F=2 ground state were obtained. However, the sought-for narrowing of the resonance lines has not been achieved. A theoretical analysis of the polarization degree is presented to illustrate the absence of light narrowing due to radiation trapping at high temperature.
A self-oscillating magnetometer based on nonlinear magneto-optical rotation using amplitude-modulated pump light and unmodulated probe light (AM-NMOR) in Rb has been constructed and tested towards a goal of airborne detection of 87 magnetic anomalies. In AM-NMOR, stroboscopic optical pumping via amplitude modulation of the pump beam creates alignment of the ground electronic state of the rubidium atoms. The Larmor precession causes an ac rotation of the polarization of a separate probe beam; the polarization rotation frequency provides a measure of the magnetic field. An anti-relaxation coating on the walls of the atomic vapor cell results in a long lifetime of 56 ms for the alignment, which enables precise measurement of the precession frequency. Light is delivered to the magnetometer by polarization-maintaining optical fibers. Tests of the sensitivity include directly measuring the beat frequency between the magnetometer and a commercial instrument and measurements of Earth's field under magnetically quiet conditions, indicating a sensitivity of at least 5 pT/%Hz. Rotating the sensor indicates a heading error of less than 1 nT, limited in part by residual magnetism of the sensor.
Phase-shift cavity-enhanced techniques have been used to measure optical losses with relatively simple electronics. Instead of measuring the phase shift, in this work the intensity modulation frequency is varied using feedback to keep the phase shift locked to a target value. The modulation frequency then becomes a signal from which cavity losses can be estimated. The technique is applied with a super luminescent diode to measure losses resulting from the addition of acetylene to a cavity containing nitrogen at ambient temperature and pressure. The technique, phase-shift feedback cavity ring down, is compared to phase-shift cavity ring-down spectroscopy.
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