Properties of Diffraction Grating Anomalies

Values provided by three different theories of the diffraction by gratings are compared with measurements made at millimetre wavelengths. The results based on the integral equation method of Pavageau and Bousquet give the best agreement with the experimentally-determined shapes of Wood anomalies. The wavelength dependence of P polarization anomalies is considered. Some properties of first-order P polarization resonance anomalies are demonstrated. The existence of second-order P resonances is shown. Second, third and fourth-order S polarization resonance anomalies have been found to occur for sinusoidal profile gratings at groove depths given by a simple formula. These anomalies cause large changes in grating efficiency to occur in very short wavelength intervals, and so might prove useful in spectroscopy.