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Water-guided laser processing have been widely used because of low heat affected zone and high aspect ratio processing. However, its processing point is not determined and must be measured with several μm accuracy. For this purpose, in-process measurement method was proposed. Measurement beam of optical comb is coaxially introduced to processing beam so that absolute distance of optical path in water-guide is measured with using optical comb tandem pulsed interferometer in water. To verify the principle of proposed method, in-water absolute distance measurement was evaluated. Repeatability of in-water measurement was under 100 nm and 1.0 mm displacement of target mirror in water was properly measured with under 1 μm error from reference displacement sensor. From these results, it is confirmed that proposed method properly works in-water environment.

A new laser tracker using an optical frequency comb with ball lenses as a reference and targets is proposed. In this system, high-accuracy absolute length measurement based on pulsed interferometry of an optical comb is utilized. By using a ball lens with a refractive index of 2.0 as a reference, it can avoid the error caused by reference point displacement. As targets, ball lenses have a wider acceptance angle than a conventional retroreflector. In this work, two new designs of the laser tracker are proposed. The simulation and experimental investigation of the refractive index characteristics of a ball lens were examined to obtain the optimal parameters for each design. Using these designs, the one-axis absolute length measurement of as much as 10 m was performed, and its combined uncertainty was evaluated to be [(0.145 µm)2  +  (3.05  ×  10−7l)2]1/2, where l is measured length. [ABSTRACT FROM AUTHOR]

We propose a novel absolute measurement method for precisely measuring the internal distance between two points, using a tandem low-coherence interferometer. In this method, a beam splitter is positioned between two plane mirrors, the locations of which are accurately determined at the nanometre level using tandem low-coherence interferometry. Using a He–Ne laser interferometer as a reference length standard, an internal distance of up to 100 mm was measured remotely, with a measurement uncertainty of 178 nm (k  =  2). [ABSTRACT FROM AUTHOR]