
268 OPTICS FOR ENGINEERS
• The amount of light in each order can be controlled through proper choice of the blaze
angle.
• The dispersion angles are determined by the grating pitch or period.
• The resolution is determined by the apodization function.
• Littrow gratings are used to select the wavelength in lasers with multiple gain lines.
8.8 FRESNEL DIFFRACTION
In the early sections of this chapter, we have considered diffraction in the Fraunhofer zone. We
noted that far beyond this zone, the integrand in Equation 8.32 varies rapidly, and numerical
integration is difcult. Fortunately, geometric optics works well here, so we can obtain some
very good ...