| The development of a nanoscale absolute interferometric dilatometer, which is used for measurements of coefficients of thermal expansion of low expansion materials and other types of dimensional instabilities, requires an interferometer that is highly sensitive and highly stable. Two original interferometer configurations, a single-pass balanced heterodyne interferometer and a double-pass balanced heterodyne interferometer, are presented. Based on a series of theoretical and experimental analyses, the double-pass balanced heterodyne interferometer is selected for use in the dilatometer. Compared to the prior work in this field, a new approach with this interferometer is to determine the dimensional change of a sample by double-ended measurements using a single doublepass balanced interference system, which provides for nanometer levels of uncertainty. Experimental measurements of an aluminum sample in a laboratory environment have shown that the interferometer is capable of fulfilling the designed functions. Analysis of uncertainty suggests that an interferometer with such design, which is situated in a vacuum chamber with precision temperature control, should be able to measure dimensional changes with an uncertainty of nanometer level. The measurement error associated with a cat's-eye retroreflector for use in interferometric measurements of micro-displacement is also analyzed, and a compensation method is suggested.; The method for measurements of dimensional instability using an optical coordinate measuring machine is also presented by measuring the dimensional instabilities of springs using the View Voyager 12x12. |
