Instrumental noise effect in an optical heterodyne profiler

An optical heterodyne profiler has been developed for measuring surface roughness at Brookhaven National Laboratory. The height measurement sensitivity and lateral resolution are 1.1 Å and 4 µm, respectively, when a 40× objective is used. A Zeeman-split He-Ne laser is the light source. A noncontact measurement system is designed as an optical common-path interferometer. Optical and electronic common-mode rejection techniques are employed to minimize the effects of environmental conditions. The effect of the system noise is analyzed in detail. The effect of varying the number of samples at each sampling point is shown. The comparisons of the system noises with different objectives, 5×, 10×, 20×, and 40×, are presented.