Scientific basis for traceable dimensional measurements in a nanometer range: methods and concepts

Abstract

New parallax-free methods of interferometric length measurements, developed recently at INMETRO (Brazil), give the possibility to exclude, practically completely, the uncertainties related to the wringing procedure of a gauge block to a reference plate. It is shown experimentally that the uncertainty of the length measurement by optical interferometry can be reduced to the value of about 1 A. The temperature measurements of a material artefact are demonstrated with the uncertainty of less than 0. 1 milli-Kelvin. There are no basic restrictions for the improvement of the practical realization of the SI length unit, based on the measurements of material length standards by optical interferometry to the level of -o.oo1 ppm. Two new, independent length specifying parameter for a gauge block are introduced, i.e. the mechanical and optical lengths of a block, which correspond to the length measurements with the uncertainty level indicated above. Parallax-free measurements of the optical length of the block has been performed for a 'free" block in unperturbed state. Basically new concept for length metrology, i.e. the concept of a free, unperturbed artefact, has been introduced into the length measurements.

Principal length specifying parameters of material artifacts, their physical meaning, methods for their measurements, and typical uncertainties

“…The coefficients A, B and C in(18) are related to the Fresnel amplitude reflection coefficients r1 and r2, corresponding to the oil/quartz and oil/steel interfaces, observed at normal incidence: (( 1 -n2 )2 + k22) I (( 1 + 2 )2 + k22)}"2 ; r1 =( nq*_1) I ( nq*+1); 2 = I no and nq* = nq I n0 (21).We can introduce a new variable R* by equation: R = -;ko / (4 ,r no) arctan {(A Sin A) /( B Cos zl -C)} (21), that measures the fraction of the interference order directly from the position of the it-shifted fringe corresponding to the light reflection from the border quartz /air, and the measurements are performed in the opposite direction relative to the experiment 1 inFig.2. Resolving (21) and fmding the dependence of d on the variable R ,we present the final result as:…”