Bi-directional short pulse ring laser

A method of detecting magnetic susceptibility, the method comprising:

• a) providing a bi-directional pulsed ring laser, a modulator, an oscillator, and a coil;
• b) providing an electrical signal to control the frequency of the light pulses within the ring laser with the modulator;
• c) inserting the coil within the oscillator for determining the frequency of oscillation of the oscillator when the inductance of the coil is modified by changes in magnetic susceptibility of the environment around the coil;
• and
• d) detecting the change in phase between the arrival times of the bi-directional pulses at the modulator and the electrical signal of the modulator to determine the change in frequency of the oscillator.

A bi-directional pulsed ring laser, said laser comprising:

• a laser having a cavity and light pulses propagating bi-directionally within said cavity;
• a pump;
• and
• a substance having a light-intensity dependent index of refraction greater than that of other components in the laser, said substance located in proximity to a beam waist of the laser cavity, said substance altering the laser beam diameter within the laser cavity as a function of light intensity.

A magnetic susceptibility detector comprising:

• a bi-directional pulsed ring laser;
• a modulator providing an electrical signal to control the frequency of the light pulses within the ring laser;
• an oscillator;
• a coil for determining the frequency of oscillation of said oscillator;
• and
• a detector for detecting the change in phase between the arrival times of the bi-directional pulses at the modulator and the electrical signal of the modulator to determine the change in frequency of the oscillator.