Modeling of rough-surface effects in an optical turning mirror using the finite-difference time-domain method

A finite-difference time-domain (FDTD) method is applied to calculate the forward-reflected and back-reflected powers of a guided mode from a rough turning mirror in a bent waveguide of a high-power laser array. By segmenting this large problem into a number of smaller problems, the simulation region can be shrunk to a small area containing only the details of the rough-surface mirror. By launching the incident wave judiciously, the computation time grows linearly with the length of the mirror. A farfield transformation of the calculated time-domain scattered field yields forward-reflected and back-reflected powers. The computer time needed to analyze this large turning-mirror system is reduced to about 3 min of CRAY time, compared to several hours for a brute-force approach using a full mesh.<
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