Dynamic scan detection of focal spot on nonplanar surfaces: Theoretical analysis and realization

A new approach called dynamic-scan-detection is presented to detect the focal spot on nonplanar surfaces, which is a key technique for laser direct writing on nonplanar surfaces. From the depth response properties of a confocal system on a nonplanar surface, the approach scans the axial shift of intensity response peak by oscillating the modified pinhole in the axial direction, and demodulates the defocus by measuring the length of time between two peaks of measured intensity waveform in one period. Compared with conventional methods, this approach features easy implementation, wide depth measurement range without deterioration of the depth discrimination property, dynamically adjustable scan amplitude, and more importantly, suppression of common-mode noise or variable system factors. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3597327]