Transmission of a Gaussian beam through an array of dielectric wedges.

摘要

The practical application of high-energy laser beams in laboratory, industrial, medical, and military environments has become common. With advances in beam generation and control, some interest is now being directed at methods of devising protective shields against high power laser radiation.; This dissertation examines in array of low absorption, optically transparent dielectric wedges that has potential applications as a shield against high energy CW laser beams. A detailed analysis is presented of the transmission properties of an array of two-dimensional wedges. Assuming wedge dimensions large in terms of wavelength, transmission through the shield is analyzed using techniques of physical optics. The response of a single wedge to plane wave excitation is evaluated. The plane wave response of the wedge array is then derived using Floquet's theorem. Using superposition of plane waves, the response to a gaussian beam is determined from the plane wave response.; Numerical results show attenuations of 30dB and 45dB at a distance equal to one incident beam radius behind the shield, for material refractive indices of 1.5 and 2.5, respectively.; To assess the range of validity of the physical optics approximation, a separate analysis of an infinitely extended wedge is carried out taking account of edge diffraction effects. The results show that the physical optics approximation is adequate on the wedge surfaces at distances on the order of several tens of wavelengths from the wedge corners. At optical wavelengths it is more realistic to assume the wedge corners rounded. One then finds that corner leakage dominates. It is shown that corner leakage can be mitigated by using several identical wedge arrays displaced relative to each other. By proper alignment, the attenuation performance of a pair of wedge arrays will be at least as good as that of the single array neglecting corner leakage.