Abstract: Nondestructive characterization of each of the layers (d.sub.n) of a multilayer thin film structure (25) is obtained by directing a first beam of radiation (40) into an optical coupler (37) having a base (38) in contact with the surface of the structure (25). The angle of the beam entering the coupler is such that the beam is reflected from the base with an evanescent wave component passing from the coupler and coupling into the multilayer thin film structure as a real beam. The real beam is reflected from the layers of the thin film structure (25) back in the coupler (37) where it combines with the beam (51) reflected from the base and exits the coupler with an intensity related to the characteristics of the structure layers. A servo motor (46) rotates the coupler to scan the first beam therein and a detector (50) detects the intensity of the combined beams exiting the coupler during the scanning thereof by the first beam.

Abstract: A laser beam (FIG. 1; 28) is reflected from a first oscillating galvanometer controlled mirror (14) onto a second oscillating galvanometer controlled mirror (15). The laser beam is reflected from the second mirror as a pattern (29) having an annular cross section by individually controlling the amplitude and phase relationships of the oscillations of the mirrors. The annular beam is directed at a frustoconical reflector (21) which reflects the annular beam radially inward to heat a portion of a glass preform (25) positioned along the axis of the reflector to form a melt zone therein from which an optical fiber (36) is drawn.Additionally, the amplitude of the mirror oscillations are modulated to vary the diameter of the annular beam to cause the beam to reciprocate along a portion of the length of the preform to expand the size of the melt zone.