Optical gauge block metrology in KRISS

Gauge block measurement by using optical interferometry in Korea Research Institute of Standards and Science (KRISS) is described. A partially modified commercial Twyman-Green type gauge block interferometer equipped with three frequency stabilized lasers which are coupled into one single mode optical fiber, is used for the measurement of gauge blocks of nominal length up to 250 mm. Fringe scanning Fourier transform method is used to obtain the excess fraction value from the interference fringes