Evaluation strategy of spheroidal distortion for micro-sphere based on Whispering Gallery Mode resonance
The demand for measuring the diameter of the spherical object, which is used for the CMM stylus, for example, is now rising and its measurement error is desired to be less than several 10 nm for the spherical object whose size is around 100 μm. To achieve this, the measurement method based on WGM resonance is remarkable. But as long as we rely on this method, the model of the object must be a perfect sphere, and this assumption should not always be valid. Practically, a measured sphere has the rotational symmetry so that it suffices to evaluate the spheroidal distortion to know the macro-distortion. According to this motivation, we proposed the new measurement method to appreciate the degree of distortion for the object based on WGM resonance. Degeneracy for azimuthal direction disappears if the object distorted spheroidal-like. Hence, we can measure the interval between the resonant wavelengths for different azimuthal mode number and evaluate the degree of spheroidal distortion.