Renewal of the gage-block interferometer at INRIM

The Hilger and Watts interferometer in use at INRIM for the calibration of gage blocks up to 100 mm has been recently upgraded with stabilized He-Ne laser sources providing traceable wavelengths at 633 nm, 543 nm and 594 nm. The new set-up has been validated by an internal comparison with reference gage blocks in use for the periodical verification of the overall measuring system. The fringe order ambiguity determined with the exact fractions method by using the two wavelengths at 633 nm and 543 nm has been tested and compared with that obtained by using all the three wavelengths