Study on Laser Trapping Probe for Measuring Fine Machined 3-D Form with High Aspect Ratio

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We propose a new probing technique for the nano-CMM (Coordinate Measuring Machine) which makes it possible to measure a fine machined 3D form with high aspect ratio. The micro-particle optically trapped at the tip of sharpened optical fiber with the diameter of micrometer order and the length of millimeter order is used as the laser trapping probe.Fundamental studies to establish such a micro-probe technique are carried out based on Finite Difference Time Domain (FDTD) simulations of radiation field at the tip of sharpened optical fiber. Moreover, in order to check basic properties for the micro-probe, the forced vibration technique of a micro-particle is developed.Main results of this study are summarized as follows ;(1) The simulation system based on FDTD method is developed. This system makes it possible to analyse radiation pressure for a small dielectric particle illuminated by the infrared laser light traveling in the optical fiber of which tip is sharpened in the cone shape with … More the tip radius of less than 1 μm.(2) The simulation results make it clear that the force of 0.52 pN/mW is exerted on a silica particle of 5 μm in diameter illuminated by the infrared laser light coming out from the sharpened optical fiber with cone angle of 36 degree. It is possible to sustain a small dielectric particle at the tip of the optical fiber by radiation pressure in air.(3) We propose the new forced vibration technique to investigate fundamental properties as a positional detection probe. The optical system with the modulated Laser Diode (LD) and the Acousto-Optic Deflector (AOD) device is developed. Using the modulated LD laser light, vibration is given to a particle by radiation pressure exerted on it. The AOD device is used for wiggling a particle in lateral direction.(4) We measured a spring constant of the laser trapping probe, which is an important dynamical parameter as a probe for the nano-CMM, using the new forced vibration technique. Resonant frequency of 823 Hz to 870 Hz are obtained from fitting curves for amplitude and phase response with taking account of a spring-damper model. Then the spring constant of 1.4x10^<-5> N/m to 1.6x10^<-5> N/m is determined from the resonant frequency. Less