ABSTRACT
In this chapter, we discuss the case where the wavelength of the electromagnetic radiation is much smaller than the size of typical objects. Since details smaller than about 0.3 mm are difficult to resolve with the naked eye, this chapter is concerned with waves whose frequencies are high enough that their wavelengths are smaller than 0.3 mm. Since f = c/λ (Equation 1.15), this means that the frequency will be in the range of 3 × 108 (m/s)/0.3 × 10-3 (m) = 1 × 1012 (Hz)= 1 THz and higher. The lowest end of this frequency range intersects with the millimeter-wave band, so named because its wavelengths are fractions of a millimeter up to a few millimeters (see Figure 1.31 for a graph of the various electromagnetic regions). At somewhat higher frequencies are the far-infrared waves, then the near-infrared waves whose wavelengths are on the order of micrometers, named far and near according to their relative closeness to visible light wavelengths. Higher in frequency (shorter in wavelength) is the very important visible wavelength range (between 400 and 700 nm), where many significant discoveries and devices such as lasers have been made, undoubtedly due to the significance of light in human vision. At slightly higher frequencies are the ultraviolet (UV) waves. At much higher frequencies are the soft, then hard, x-rays.
