Zero-order gratings are grating structures with a period that is small compared with the wavelength of light. Only the directly transmitted or reflected light, the zero diffraction order, is nonevanescent and propagates in a distance from the grating. Thus the grating behaves like a slab of ordinary homogeneous material with an effective refractive index. By varying the material composition, i.e., by variation of the duty cycle of the grating, the effective refractive index can be changed. A grating with variable duty cycle therefore behaves like a material with distributed index. Based on such artificial materials, distributed-index elements are proposed. The physical principle is demonstrated with water waves.
The accuracy of phase shifting interferometers is impaired by mechanical drifts and vibrations, intensity variations, nonlinearities of the photoelectric detection device, and, most seriously, by inaccuracies of the reference phase shifter. The phase shifting procedure enables the detection of most of the errors listed above by a special Lissajous display technique described here. Furthermore, it is possible to correct phase shifter inaccuracies by using an iterative process relying solely on the interference pattern itself and the Fourier sums used in phase shifting interferometry.
Quarterwave plates can be made as holographic gratings in positive photoresist. We studied the effect of the grating period and relief depth on the phase retardation and on the rotation of the polarization of the transmitted light. Experiments were performed with gratings of different periods, which also exhibit an antireflection property.
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