Two-Dimensional Simulation of and Experiments on the Forward-Backward Modes Coupled Unstable Resonator

A new type of laser resonator, the forward-mode and backward-mode coupled unstable resonator, was two-dimensionally analyzed using a partially coherent input field. Under the optimum output power condition, the oscillating mode was annular even at the far field. The experiments with transverse electric atmospheric (TEA) CO2 laser qualitatively showed the same results as those calculated.