Gauging interferometer systems

Claim 1

IN AN INTERFEROMETER OF THE TYPE THAT INCLUDES A SOURCE FOR PRODUCING A BEAM OF A MONOCHROMATIC LIGHT, A RETROREFLECTOR, MEANS FOR DIVIDING SAID BEAM INTO FIRST AND SECOND PARTS THAT ARE DIRECTED ALONG RESPECTIVE PATHS, ONE OF SAID PATHS INTERSECTING SAID RETROREFLECTOR, SAID RETROREFLECTOR BEING TRANSLATABLE WITH RESPECT TO SAID DIVIDING MEANS ALONG THE LIGHT PATH THEREBETWEEN AND BEING ORIENTED WITH RESPECT TO SAID DIVIDING MEANS FOR RECOMBINATION OF SAID PARTS FROM THE DIVIDING MEANS FOR RECOMBINATION WITH THE OTHER PART IN AN INTERFERENCE FIELD, MEANS FOR DIRECTING SAID OTHER PART TO SAID INTERFERENCE FIELD, WHEREBY THE TRANSLATION OF THE RETROREFLECTOR PRODUCES CYCLIC VARIATIONS IN THE NET INTENSITY OF LIGHT AT A POINT IN SAID INTERFERENCE FIELD, PHOTOELECTRIC MEANS FOR PRODUCING AN ELECTRICAL SIGNAL OF A MAGNITUDE THAT CORRESPONDS TO THE LIGHT INTENSITY AT SAID POINT, MEANS RESPONSIVE TO SAID ELECTRICAL SIGNAL FOR PROVIDING A FIRST INTERFERENCE SIGNAL HAVING A CYCLIC VARIATION CORRESPONDING TO THE CYCLIC VARIATION IN INTENSITY OF LIGHT AT THE POINT IN THE INTERFERENCE FIELD THAT RESULTS SOLELY FROM THE TRANSLATION OF THE RETROFLECTOR, THE IMPROVEMENT THAT COMPRISES, MEANS FOR CYCLICALLY VARYING THE OPTICAL LENGTH OF THE PATH OF ONE OF SAID FIRST AND SECOND BEAM PARTS TO PRODUCE A FURTHER CYCLICAL VARIATION IN SAID ELECTRICAL SIGNAL IN ADDITION TO ANY VARIATION THEREIN RESULTING FROM THE TRANSLATION OF SAID RETROFLECTOR, THE OPTICAL LENGTH OF THE PATH OF SAID ONE BEAM PART BEING CHANGED BY A DISTANCE LESS THAN THAT REQUIRED TO PRODUCE ONE INTERFERENCE FRINGE IN THE INTERFERENCE FIELD, AND THE FREQUENCY OF THE CYCLICAL VARIATION IN THE OPTICAL LENGTH OF THE PATH OF SAID ONE BEAM PART BEING SUCH THAT THE FREQUENCY OF THE FURTHER CYCLICAL VARIATION IN THE ELECTRICAL SIGNAL IS HIGHER THAN THE MAXIMUM ANTICIPATED FREQUENCY OF THE ELECTRICAL SIGNAL THAT RESULTS SOLELY FROM SAID TRANSLATION OF THE RETROREFLECTOR, MEANS PROVIDING A SECOND INTERFERENCE SIGNAL HAVING A CYCLIC VARIATION CORRESPONDING SOLELY TO THE CHANGE IN PHASE OF SAID FURTHER CYCLICAL VARIATION IN SAID ELECTRICAL SIGNAL RELATIVE TO THE PHASE OF THE CYCLICAL VARIATION IN THE OPTICAL LENGTH OF SAID ONE OF THE PATHS, AND REVERSIBLE COUNTING MEANS RESPONSIVE TO SAID FIRST AND SECOND INTERFERENCE SIGNALS TO PRODUCE A COUNT CORRESPONDING TO THE CYCLIC VARIATIONS IN SAID FIRST INTERFERENCE SIGNAL, THE SECOND INTERFERENCE SIGNAL CONTROLLING THE DIRECTION OF COUNTING OF THE COUNTING MEANS.