Detection of Groundwater Through Ultra-Sensitive Magnetic Measurements with Ultra-Short Pulse Lasers

The goal of this project is to develop instrumentation to detect sources of groundwater or monitor the growth/decay of large aquifer layers through changes in magnetic susceptibility.

Two approaches are being pursued: either by developing instrumentation capable of detecting minute changes of the vertical component of the earth magnetic field, averaged over large distances, or instrumentation capable of directly measuring changes in magnetic susceptibility. The common thread in these instrumentations is the use of ultra-short pulse ring lasers as differential phase spectrometers.

The basic principle is to translate a differential phase shift into a frequency difference between the two output beams of a ring laser. Magnetic field changes are translated into phase shifts when the intracavity beams traverse a resonant atomic vapor inside the cavity. New stabilization techniques had to be developed to stabilize the pulsed laser to a narrow atomic transition. Basic stabilization research was performed with a Ti:sapphire laser. Optical parametric oscillators and solid state diode pumped lasers were developed in order to lead to a practical instrument that could be used in the field. Progress on fiber laser research leading to the development of magnetic susceptibility detector is also reported.