Pieter J. M. Kerstens

Photothermal displacement measurement of transient melting and surface deformation during pulsed laser heating

A photothermal displacement method has been developed to probe the pulsed laser-induced transient melting and surface deformation of Ni–P hard disk substrates. A probing He–Ne laser beam is aligned collinearly with the near-infrared nanosecond pulsed heating beam. The He–Ne beam spot is scanned on the microfeatures formed on the sample surface by the pulsed laser heating. The deflection signals show the variation of the feature shape resulting from different pulse energies of the heating laser beam. The transient deflection signal also reveals that the time scale of the surface motion is in the range of several hundred nanoseconds.

Photothermal displacement detection and transient imaging of bump growth dynamics in laser zone texturing of Ni–P disk substrates

A novel photothermal displacement method has been applied to probe the pulsed laser-induced feature formation of Ni–P hard disk substrates in the laser zone texturing process. The deflection signals of the reflected probing beam show the variation of the feature shape resulting from different pulse energies of the heating laser beam. A laser flash photography system is also developed to visualize the feature growth dynamics. This system has nanosecond time resolution and about one micron spatial resolution. Both techniques show clearly the transient melting and deformation process and the time scale of such deformation.

Fast confocal image processing for inspection

The measurement of surface topography is an important inspection task as it provides useful information for process and quality control. A candidate technique for such an application is confocal imaging. The advantages of confocal imaging are that it is a noncontact measurement, can be operated at high speed (greater than 10 megapixels/sec) and submicron resolution, and provides height information in multilayered semitransparent materials. In this paper, we present a scheme for the fast processing of confocal images. The scheme consists of measuring the response function of the confocal system and deriving a deconvolution filter based on this response. The input signal is deconvolved in order to improve the depth resolution and then processed to identify significant peaks. These peaks represent the position of different surfaces in the object being inspected. For semitransparent materials, our scheme is capable of detecting up to two surfaces at a given location.