Development of a Non-Contact Focusing Probe for the Measurement of Micro Cavities
Kuang-Chao Fan*,**, Ke Zhang*, You-Liang Zhang*,
and Qing Zhang*
*School of Instrument Science and Opto-Electronic Engineering, Hefei University of Technology, 193 Tunxi Rd, Hefei, 230009, China
**Department of Mechanical Engineering, National Taiwan University, 1, Sec. 4, Roosevelt Rd., Taipei, 10617, Taiwan
The measurement of microcavities is a challenging task if the cavity is smaller than the diameter of the micro touch-trigger probe. This paper presents a noncontact method using a blue-ray DVD pickup head as the sensor. It is based on a focusing principle holding that reflected light intensity is maximal when the tested surface is at the focus point of the probe. When a focused beam scans the edge of the cavity, reflected light intensity is gradually reduced. Theoretical analysis is used to derive the light intensity equation for when the focused beam is passing along the edge. Experimental tests of the developed probe were carried out in association with a nanopositioning stage. The edge position is obtained up to a resolution of 1 nm and a standard deviation of about 30 nm. This performance is beyond the diffraction limit of optical microscopes.
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