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Figure I.1 Microreliefs of (a) a reflecting and (b) a transmitting DOE

techniques (cutting, milling, engraving, grinding, etc.). However, DOE technology similar to microlithographic technologies in terms of both concept and the equipment used is a matter of concern throughout this book. One of the main steps in this technology involves taking account of the periodicity of the phase φ(u, v) and subsequently reducing its values to the interval [0, 2π]. In that case, the diffractive optical element only several wavelengths in microrelief height takes the place of the conventional optical elements of up to several thousand wavelengths in width. Figure I.2 shows the correspondence between the conventional optical element and the DOE.

It is seen that the relief on the DOE surface can have a regular zone structure. By way of illustration, the microrelief of a Rayleigh zone plate has a circular structure (see Fig. I.2b), whereas the microrelief of diffractive gratings is built of periodically located grooves. In the general case, the surface microrelief is irregular, as is the case for kinoforms and digital holograms [1,2], with zones to be described by curves (or fringes) which are more complicated than straight lines and circumferences. A distinction

Figure I.2 An example of realization of the same phase function by means of (a) conventional and (b) diffractive optical elements