In order to obtain an accurate Avogadro constant with a relative uncertainty of 1×10-8 to redefine the kilogram, the diameter of a perfect single crystal silicon sphere is required with the measurement uncertainty of 0.3 nm using the X-ray
crystal density method. To achieve this, phase-shifting interferometers have been developed. A laser frequency tuning system calibrated by a Fabry-Perot cavity is proposed to improve the laser wavelength and the phase-shift accuracy. The laser frequency standard deviation of the beat frequency is 85 kHz with a gate time of 0.1 s. The gap distances in the diameter determination interferometer are measured based on the laser tuning system, which are 275.3 nm and 110.5 nm, respectively.
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Xuejian Wu ; Jitao Zhang ; Haoyun Wei and Yan Li
Interferometric determination of the silicon sphere diameter using a laser frequency tuning system calibrated by a Fabry-Perot cavity
", Proc. SPIE 8563, Optical Metrology and Inspection for Industrial Applications II, 85631G (November 20, 2012); doi:10.1117/12.982012; http://dx.doi.org/10.1117/12.982012