Gradiometer and Method of Changing an Optical Path Length to Directly Obtain a Value of a Gradient of Gravity

摘要

A gradient of gravity is defined by a change in the optical path length required to maintain equality in optical path lengths of two beam arms which direct light beams to impinge upon and reflect from two freefalling test masses.

主权项

1. A gradiometer for measuring a gradient of gravity between two predetermined separated locations using first and second light beams, comprising:
first and second test masses which are released for simultaneous freefall solely under the influence of gravity with each test mass at a different one of the two separated locations; an arrangement of optical elements which directs the first and second light beams to traverse first and second separate and different beam arms respectively, each beam arm having an optical path length along which the light beams traverse, the first beam arm directing the first light beam to impinge upon and reflect from at least the first test mass during the simultaneous freefall of both test masses, the second beam arm directing the second light beam to impinge upon and reflect from at least the second test mass during the simultaneous freefall of both test masses; the arrangement of optical elements interferometrically combining the first and second light beams into an output light beam after the first and second light beams have traversed the first and second beam arms during the simultaneous freefall of test masses; a dynamic optical path length adjusting element located within one of the beam arms and operative in response to an applied control signal to change the optical path length of the one beam arm in a predetermined relation to a magnitude of the applied control signal; and an optical path control system receptive of the output light beam while the test masses freefall simultaneously and operative to supply the control signal at a magnitude which causes the dynamic optical path length adjusting element to maintain the optical path length of the one beam arm equal to the optical path length of the other beam arm during the simultaneous freefall of the test masses; and wherein: the magnitude of the control signal directly defines the gradient of gravity.