Gauge block interferometer using three frequency-stabilized lasers

We have developed a gauge block measurement system that uses three frequency-stabilized lasers. The stabilized lasers are as follows: an I-2-stabilized offset locked He-Ne laser (633 nm), an I-2-stabilized Nd:YAG laser (532 nm), and a Rb-stabilized diode laser (780 nm). The I2-stabilized offset locked He-Ne laser is commercially available (Nihonkagaku Engineering Co., Ltd.) and its relative wavelength uncertainty is 2.5 x 10(-11). An I-2-stabilized Nd:YAG laser and a Rb-stabilized diode laser was developed in our institute and their relative wavelength uncertainties are 5 x 10(-12) and 1 x 10(-9), respectively. In the measurement system, laser beams were introduced to the interferometer using an optical multimode fiber. An interferometric fringe pattern was taken using a CCD camera and the excess fraction parts were calculated from the fringe pattern using the Fourier transform method. The excess fraction part obtained from the Rb-stabilized semiconductor laser was used only to determine the integer part of the fringe order, because the accuracy and stability of the wavelength were not sufficient for the long gauge block measurements. This interferometer can measure gauge blocks of up to 1000 mm long and the standard uncertainty of the interferometer is about 75 nm for a 1000 mm long gauge block.