An active stabilization system for a holographic setup based on detection of phase shift between the interference pattern and a reference hologram is described. Its basic feature is the possibility of operating for 0, pi or +/-pi/2 at will, always in a null-detection mode. The reference hologram may be a previously recorded permanent hologram or a real-time (even reversible) one. The use of the open loop response of the stabilization system is developed for analyzing its performance, which allows closer insight into parameters limiting Its behavior. The effects of different noise sources are analyzed in detail. The real-time effect in a positive resist is successfully employed for operating the stabilization setup for recording an improved grating in this material.

A simple graphical method is developed for calculating modulation and groove-to-period ratio of a shallow lamellar grating from its diffraction spectra and for simultaneously checking its assumed shape. It applies to both reflection nd transmission and to the conducting or dielectric nature of both the grating and its substrate. The effect of noise and distortion is briefly discussed. The method is illustrated for the limiting case of a reflecting metallic grating. Uses will be presented in subsequent papers. This paper describes a graphical method for carrying out such calculations and for rapidly assessing its worth. This method is applied to a lamellar metallic grating for illustrative purposes. A subsequent paper (part 2) will be concerned with systematic experimental results and applications to thin film measurements. The determination of a grating profile having a given diffraction efficiency curve

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A method of measuring thin film thickness is described, based on a previous paper where the authors analyzed a graphical means for grating modulation calculation. Metallic or dielectric films on any substrate may be measured, and precision was shown to be comparable with that achieved ellipsometrically at least in the 300-1500-A thickness range. The method is non-contact and destructive: the grating is recorded on the film. Measurements are simple, requiring a low-power He-Ne laser and a photodetector, and may be carried out at a distance from the sample. Experimental results are presented for three types of sample, including measurements by reflection and transmission. II. Theory The thickness of a thin film is measured by recording a lamellar grating in its full depth. The problem of film thickness measurement is then converted into one of grating modulation. In Part 1 we showed that the latter may be easily done with a nomogram. 1 The latter provides the grating modulation h (which actually represents the film thickness), its bar-to-period width ratio aid (not relevant for our present purpose), and a criterion for checking whether the grating on the sample fulfils the required theoretical conditions. 1 Figure 1 is a schematic description of a rectangular grating re-The authors are with