Abstract
A laser diode (λ = 780 nm) probe, from which an half-circular beam irradiates in-focus to an objective surface and the diffraction pattern formed on the suface near the focal point is detected by a two-part-divided photo-diode throughout the same optical path, is proposed. The principle of the measurement is discussed by the diffraction pattern change analysis. The response characteristics of the probe prepared are measured; the obtained dynamic ranges are ±1 μm-2 nm for f=3.6 mm, and ±100-0.2 μm forf =23 mm lens. When the output signal, the difference currents of the two parts of the detector, is normarized by the summation of them, it becomes a simple function of displacements inspite of the condition of the material surface; the displacement response curves for a mirror sample, a low reflectivity glass sample and a steel sample having a mean roughness of 1.3 μm, are quite similar.
