Page 18 - Modern Optical Engineering The Design of Optical Systems

Chapter
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Optics Overview

1.1 The Electromagnetic Spectrum
This book deals with certain phenomena associated with a relatively
narrow slice of the electromagnetic spectrum. Optics is often defined
as being concerned with radiation visible to the human eye; however,
in view of the expansion of optical applications in the regions of the
spectrum on either side of the visible region, it seems not only prudent,
but necessary, to include certain aspects of the infrared and ultraviolet
regions in our discussions.
The known electromagnetic spectrum is diagramed in Fig. 1.1 and
ranges from cosmic rays to radio waves. All the electromagnetic
radiations transport energy and all have a common velocity in vacuum
10
of c 2.998 10 cm/s. In other respects, however, the nature of the
radiation varies widely, as might be expected from the tremendous
range of wavelengths represented. At the short end of the spectrum,
we find gamma radiation with wavelengths extending below a billionth
of a micron (one micron or micrometer 1 m 10 6 m) and at the long
end, radio waves with wavelengths measurable in miles. At the short
end of the spectrum, electromagnetic radiation tends to be quite particle-
like in its behavior, whereas toward the long wavelength end the
behavior is mostly wavelike. Since the optical portion of the spectrum
occupies an intermediate position, it is not surprising that optical
radiation exhibits both wave and particle behavior.
The visible portion of this spectrum (Fig. 1.2) takes up less than one
octave, ranging from violet light with a wavelength of 0.4 m to red
light with a wavelength of 0.76 m. Beyond the red end of the spectrum
lies the infrared region, which blends into the microwave region at a

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