Abstract: A servotrack writing apparatus (10) for use on computer disk drive workpieces (12). A writer controller (58) puts the writing apparatus (10) in the role of master to direct the workpiece (12) as a slave to position its read-write head (36) and to write the servotracks. A tracking section (54) provides a modulated light beam (72) from which a reflected portion is detected by a bi-cell photo sensor (70) and processed in the writer controller (58) to determine the position of a thru-hole (40) or a detection region (42) in the actuator arm (24) of the workpiece (12). The writer controller (58) may use a lock-in amplifier (102, 104) for the processing the reflected portion of the light beam (72). A reference arm (44) is locked and moved in a synchronous relationship with the actuator arm (24).

Abstract: What is disclosed is an improved high resolution laser interferometer (10) which gains an increase accuracy through elimination of a source of temperature change error by causing a reference laser beam (16) to traverse the same distance within glass as does a measurement laser beam (18). The inventive arrangement of optics combines a polarizing cube (24), a cube corner retroreflector (28), a right angle reflector (30), and two or more quarter wave plates (32), (34) and (36)to produce the desired result. An equally preferred alternate embodiment (210) of the invention combines the first preferred embodiment (10) with an etalon (240) to directly measure the refractive index of air. This measurement is then used to adjust readings obtained using the first preferred embodiment (10) to further improve accuracy.

Abstract: What is disclosed is an improved high resolution laser interferometer (10) which gains an increase in available resolution by means of increasing the number of reflections of a measurement laser beam (16) from a plane mirror (20) and thus by increasing the number of Doppler shifts undergone by the measurement laser beam (16). The inventive arrangement of optics combines a polarizing cube (24), a cube corner retroreflector (28), a right angle reflector (30), and one or more quarter wave plates (32) and (34) to produce the desired result. In the practice of the present invention, the measurement laser beam (16) is directed from a laser head (12) such that it is affected four times by any movement of the objective plane mirror (20) in a measurement plane (22) before being compared to a reference laser beam (16) in a signal analysis unit (14). The reference laser beam (16) is routed in a conventional manner to the signal analysis unit (14).