Abstract: An apparatus comprising a movable optical element having an optical axis and including one or more focusing elements, an image sensor positioned along the optical axis and substantially normal thereto, and a radiation source attached to the movable optical element, wherein the radiation source directs a beam of radiation onto the sensor at a selected angle relative to the optical axis. A process comprising positioning a sensor along, and normal to, an optical axis of a movable optical element, projecting a radiation beam onto the sensor from a radiation source attached to the movable optical element, wherein the radiation beam is at a selected angle relative to the optical axis, and adjusting the position of the movable optical element until the position where the radiation beam falls on the sensor corresponds to the position where the radiation beam is expected to fall on the sensor when the movable optical element is in focus. Other embodiments are disclosed and claimed.

Abstract: A method of writing data on a disk includes the step of writing a first subset of data on a disk such that an amount of write power to write the first subset of data is adjusted in a closed-loop operation. A write-power signal representing the amount of write power to write the first subset of data is measured. After a write interruption, such as from a buffer under-run, a second subset of the data is written on the disk in an open-loop operation using the measured write power, such that the second subset of data is adjacent to the first subset of data.

Abstract: A compliant wafer chuck for supporting a substrate in which an upper body of the chuck is allowed to tilt relative to the base.