Modeling of the diffraction gratings produced in As-S thin films
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We have used a coupled wave analysis and solved numerically the coupled wave equations to model the performance of the diffraction gratings produced by the metal photo-dissolution effect in As - S thin films. This analysis is based on the material properties of arsenic sulphide silver doped films. We have analyzed both a sinusoidal and a square wave profile to consider both the holographic gratings and gratings produced by a mask exposure technique. Our model computes the diffraction efficiency versus two parameters (Omega) and (xi) where (Omega) is a thickness parameter and (xi) is a modulation parameter which is related to the change in the refractive index of the films. For the case of the sinusoidal profile the result of our model for very small values of (Omega) fits very well with the Bessel functions of the first kind which is the expected analytic results. As we change (Omega) from a small value of on the order of 0.01 to a value of on the order of 10, fewer diffraction orders become important in the replay of the grating with a red wavelength. For (Omega) on the order of 10 only one significant order is seen in the replay. The same results are generally obtained for the square grating. The angular response of the efficiency for a typical grating shows that the efficiency is a maximum near the Bragg angle. This result is in good agreement with the experimental results of the diffraction efficiency measurements obtained on a grating with the same parameters.
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