Abstract: An apparatus and method for detecting beam misalignment in a thickness measurement system employing two opposed distance measurement sensors. The apparatus includes a first and second distance measurement sensor configured to direct respective light beams toward opposite sides of a measurement space, and a rotatable support member disposed between the sensors for receiving and rotating a sample about a rotation axis. The sample has at least one surface inclined at a tilt angle relative to a propagation direction of a corresponding light beam. A controller obtains thickness measurements from the sensors at a plurality of rotational positions of the rotatable support member and detects a presence of beam misalignment between the first and second light beams based on a variation in the thickness measurements across the plurality of rotational positions.

Abstract: A bench-top device for measuring thickness of a sample includes two distance sensors facing each other across a gap. A sample tray for supporting the sample is positioned in the gap. The distance sensors are attached to arms of a movable frame. An actuator is configured to move the frame in a scan direction orthogonal to the arms.