Optical Shop Testing

Chapter 15 - Surface Profilers, Multiple Wavelength, and White Light Intereferometry

15.1.   INTRODUCTION TO SURFACE PROFILERS

Over the last 25 years, driven by both the development of new technologies such as
fast computers and solid state devices and the necessity to precisely inspect these
increasingly tiny engineering surfaces, the field of surface metrology has exploded in
both its technological sophistication and its range of application. Advances in
illumination sources, such as lasers, and in solid state detectors and optoelectronic
devices in general have fueled the development of a wide range of instruments that
can not only map surface topography but also determine other features such as
displacement or dispersion. Innovative techniques and technologies have greatly
increased the range of measurable objects, so now even difficult surfaces with high
slopes or steps and narrow, deep trenches can be measured. Many of these surface
profiling techniques were developed from distance measuring or focus detection
techniques, and they often require scanning to obtain the surface profile. This chapter
describes instruments such as the stylus profiler, scanning probe microscope, confocal
microscope and the interferometric optical profiler that are most often used to
determine surface topographies of not only very small, typically engineering
surfaces, but also smooth and large surfaces such as aspheres and glass plates.

The first part of this chapter describes scanning probe microscopes and stylus
profilers. Then optical methods are detailed with a specific focus on techniques
developed over the last 15 years that have found commercial and industrial application.
This section describes both interference microscopes that employ both monochromatic
and white light illumination and also confocal microscopes that have
recently been fairly used to measure engineering surfaces. The next part of this
chapter reviews work done in multiple wavelength interferometry, namely two and
multiple wavelength, wavelength scanning, and spectrally resolved white light
interferometry. White light and multiple wavelength techniques are often applied to
other methods, such as speckles and holography as well as fringe and structured light
projection procedures. Finally, we provide a short overview of optical ranging
techniques and polarization interferometers.

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