Higher-Order Lloyd Interferometer

The Lloyd moiré interferometer was introduced in Appl. Opt. 6, 1707 (1967), as a means of testing interferometrically a path across very large surfaces in oblique to grazing incidence. The width of the path is determined by the optics in use. For any sensible angle of incidence, the Lloyd interference fringes will be very narrowly spaced, but they are transformed into conveniently visible fringes by a moiré grating. The precision of the Lloyd moiré interferometer is limited by the very large angle of incidence and by the relatively poor definition of the moiré fringes. The objective of the present paper is to show an improved Lloyd interferometer technique, which with equally simple instrumentation permits one to vary and increase the sensitivity in testing large surfaces in oblique incidence by decreasing the angle of incidence.