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Chapter 1:
Known Methods: An Assessment of the State of the Art—Newton and Fizeau
The subject of this assessment is surfaces whose final production processes include lapping, polishing, or micromachining. The majority of these processes relate to optical components, and many of them carry optical specifications for mechanical applications such as air-bearing techniques. Measuring departures from flatness is a common denominator. A useful compendium of interferometric techniques and applications was assembled by D. Malacara, A. Cornejo, and A. V. R. K. Murty.1 One of the procedures involved in the practice of an optician is illustrated in Fig. 1.1: an optical glass, the reference, is placed onto the semifinished work. The reference is illuminated by a spectral lamp l behind an extended diffusing screen and is observed. The observer sees a fringe pattern, the interpretation of which is explained in Fig. 1.2. Actual fringe patterns are shown in Figs. 1.5(a) and (b), and Fig. 2.1(b). Such patterns appear to be similar to cartographic contour lines. This assessment procedure, which creates what is known as Newton’s rings, is as simple to handle as it is to comprehend; it is the last option using low-cost instrumentation for mechanical/optical metrology with submicrometric resolution before expensive hardware and software need to be introduced. In that sense, the importance of interferometry to the precision engineer can be compared to that of a stethoscope to the general medical practitioner. This is our starting point for the assessment of the fascinating methods and instruments of interferometry.
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