Losses in media have become fresh elements in the designing of asymmetric acoustic transmission and reflection without the nonlinear effect. In this paper, we demonstrate the diffraction control by equipping fine-tuned losses in a non-Hermitian acoustic grating. Compared to the Hermitian grating without losses, the positive first order diffracted wave with negative incidence will be suppressed perfectly, but the negative first order diffracted wave with positive incidence will be enhanced counterintuitively in the lossy diffraction grating. The physical mechanism is that losses can modulate the magnitudes of Bloch wave vectors through the interplay with the real modulation of the refractive index. Absorption is demonstrated as a powerful way to control the acoustic diffraction.

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