Polychromatic interferometry

Claim 1

IN A SYSTEM FOR THE INSPECTION OF A FLAT SURFACE BY THE METHOD OF INTERFERENCE FRINGES, THE COMBINATION WHICH COMPRISES A LAMP CONSTRUCTED TO RADIATE WHITE LIGHT, AN OPAQUE SHIELD DISPOSED IN A PLANE NORMAL TO THE PATH OF THE LIGHT OF SAID LAMP, SAID SHIELD BEING PIERCED BY N ELONGATED SLITS, ILLUMINATED BY SAID LIGHT, AND THUS CONSTITUTING INDIVIDUAL WHITE LIGHT SOURCES, SAID SLITS BEING DISPOSED PARALLEL WITH EACH OTHER AND SPACED APART IN A DIRECTION NORMAL TO THEIR LONG DIMENSIONS, A COMMON ELEMENT FOR DISPERSING, IN A DIRECTION NORMAL TO THE LONG DIMENSIONS OF THE SLITS, LIGHT RAYS THAT EMERGE FROM ALL OF THE SLITS, MEANS FOR FOCUSING THE DISPERSED RAYS IN A SECOND PLANE, THUS TO FORM A MULTIPLE RAINBOW IMAGE CONSTITUTED OF N LIKE, CONTINUOUS, PARTIALLY SUPERPOSED, SIMILARLY ORIENTED RAINBOWS, EACH OF LENGTH L IN THE DIMENSION NORMAL TO THE LONG DIMENSIONS OF THE SLITS, THE SPACINGS AMONG THE SEVERAL SLITS BEING SO COORDINATED WITH THE DISPERSIVE POWER OF THE DISPERSING ELEMENT THAT SAID RAINBOWS ARE MUTUALLY STAGGERED IN THE DIRECTION OF THEIR LENGTHS BY DISTANCES NO GREATER THAN L/N, WHEREBY AT EACH POINT OF SAID MULTIPLE RAINBOW IMAGE, ONLY N DISCRETELY DIFFERENT LIGHT WAVELENGTHS APPEAR, ONE FROM EACH OF THE SEVERAL CONSTITUENT RAINBOWS, MEANS FOR SELECTING FOR PROJECTION TOWARD EACH SINGLE ELEMENT OF THE SURFACE UNDER TEST, LIGHT RAYS FROM ESSENTIALLY A SINGLE POINT OF SAID MULTIPLE RAINBOW IMAGE, INCLUDING AN ESSENTIALLY MONOCHROMATIC SEGMENT OF EACH OF SAID RAINBOWS, A REFERENCE SURFACE DISPOSED IN OPTICAL RELATION TO SAID FLAT SURFACE, AND MEANS FOR DIRECTING SAID SELECTED LIGHT RAYS ONTO BOTH OF SAID SURFACES, THEREBY TO DEVELOP A SET OF INTERFERENCE FRINGES THAT ARE REPRESENTATIVE OF THE GEOMETRICAL CONTOURS OF SAID FLAT SURFACE.