Masaki Michihata

Scanning dimensional measurement using laser-trapped microsphere with optical standing-wave scale

Abstract. We propose a laser trapping-based scanning dimensional measurement method for free-form surfaces. We previously developed a laser trapping-based microprobe for three-dimensional coordinate metrology. This probe performs two types of measurements: a tactile coordinate and a scanning measurement in the same coordinate system. The proposed scanning measurement exploits optical interference. A standing-wave field is generated between the laser-trapped microsphere and the measured surface because of the interference from the retroreflected light. The standing-wave field produces an effective length scale, and the trapped microsphere acts as a sensor to read this scale. A horizontal scan of the trapped microsphere produces a phase shift of the standing wave according to the surface topography. This shift can be measured from the change in the microsphere position. The dynamics of the trapped microsphere within the standing-wave field was estimated using a harmonic model, from which the measured surface can be reconstructed. A spherical lens was measured experimentally, yielding a radius of curvature of 2.59 mm, in agreement with the nominal specification (2.60 mm). The difference between the measured points and a spherical fitted curve was 96 nm, which demonstrates the scanning function of the laser trapping-based microprobe for free-form surfaces.

Precise Diameter Measurement of a Microsphere Based on Polarization Analysis of Whispering Gallery Mode Resonance

Whispering gallery mode (WGM) resonance is used for the diameter measuring method of a microsphere smaller than φ 1 mm. It is aimed to achieve measurement accuracy better than 10 nm. There are two electromagnetic modes for WGMs, and then mis-detection of the electromagnetic mode expands measurement errors more than 100 nm, so it is indispensably to distinguish the electromagnetic mode. As theoretical simulation implies, polarization mode of WGMs can be selectively excited by controlling polarization of the incident light in optical coupling. Based on the analysis, it was proofed experimentally that the polarization of WGMs could be classified. As a result, the diameter measurement for a microsphere was performed with measurement error of ± 1 nm.

Hybrid probing technique for coordinate measurement with optically trapped micro sphere

Engineered surfaces have been fabricated to provide enhanced properties such as low friction, anti-adhesive behavior, or low reflection of light. At micro-scales, surface force highly affects the functionality of mechanical parts. In order to reduce surface force such as friction, micro mechanical parts that have engineered surfaces are demanded. In order to investigate the functionality of the textured micro parts, it is necessary to evaluate both the three-dimensional shape and the surface topography along with its geometry. Then we propose novel hybrid probing technique using an optically trapped micro sphere. Tightly focused laser beam makes it possible for a dielectric micro sphere to sustain near the focal point in the air. The dynamic behavior of the micro sphere changes as the result of the interaction of the surface. Therefore, the surface is detected by monitoring the micro sphere. This enables the three-dimensional shape measurement of the substrate. On the other hand, Surface topography is imaged with the lensing effect of the trapped micro sphere. Therefore, this trapped sphere is used as both a probe for coordinate metrology and a micro-lens in optical microscopy in this study. This present investigation deals with the development and fundamental validation of the hybrid probing system with the optically trapped micro sphere. The measurement result with high performance was demonstrated using the tilted diffraction grating.