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The angular spectrum method(ASM)is a popular numerical approach for scalar diffraction calculations.However,traditional ASM has an inherent problem in that nonuniform sampling is precluded.In an attempt to address this limitation,an improved trigonometric interpolation ASM(TIASM)is proposed,in which the fast Fourier transform(FFT)is replaced by a trigonometric interpolation.The results show that TIASM is more suitable to situations in which the source field has a simple and strong frequency contrast,irrespective of whether the original phase distribution is a plane wave or a Fresnel zone plate phase distribution.