Microsoft Word - ASPE_ExAbstract_Absolute_Gap_v8.docx

INTRODUCTION The absolute distance between two surfaces is a parameter of interest in many applications. Examples include wavelength standards, etalons, gage block calibrations, the measurement of sphere diameters, etc. Many interferometric techniques exist for making such a measurement. Of these, the highest precision methods that do not involve modifications to the surfaces are based on the method of exact fractions [1] and wavelength tuning [2]. The former method is limited due to the phase resolution attainable from analysis of a static fringe pattern, while the latter technique requires a wide tuning range to measure relatively small separations (of the order of a few mm).