Evaluation of Measurement Properties Depending on Optical Coupling of Whispering Gallery Mode (WGM) Resonance -- Based Diameter Measurement

For the insurance of the measurement accuracy of micro-Coordinate Measurement Machine (CMM), it's necessary to know the micro-CMM's probe diameter accurately. For the measurement of microsphere diameter, we proposed a method using Whispering Gallery Mode (WGM) resonance. By measuring the WGM resonant wavelength and estimating the mode number, we can derive the microsphere diameter accurately through WGM dispersion equation. Up to now we can measure the WGM resonant wavelength accurately and have proposed an estimation method for WGM mode number, but we haven't verified the estimation accuracy of WGM mode number. Therefore, we are attempting to measure WGM mode number directly by using a Scanning Near-field Optical Microscopy (SNOM) probe to measure the spatial period of the WGM electric field on microsphere surface. Through this study, we can verify the correctness of the proposed WGM mode number estimation method by identifying the mode generated within the microsphere, thereby providing experimental evidence for its general applicability. The purpose of this study is to experimentally determine the mode number of WGM resonance, and thus we conducted the two-dimensional scan on microsphere surface with a SNOM probe and analyzed whether the WGM electric field distribution was appropriately measured to ensure the accuracy of the mode number determination.

Keywords: Micro-CMM, Microsphere, WGM resonance, Mode number, Near-field light, SNOM probe.

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