Terahertz Impulse Imaging With Sparse Arrays and Adaptive Reconstruction

Terahertz (THz) impulse imaging has many applications in security and nondestructive testing. Sparse THz arrays can dramatically reduce array complexity for imaging applications requiring a large field of view. Sparse arrays employing narrowband waves suffer from grating lobe artifacts that severely degrade image quality. However, the short coherence length of single-cycle THz pulses provides an opportunity to overcome this limitation. Grating lobe artifacts can be suppressed with an adaptive weighting factor based on the temporal coherence of signals from neighboring array elements. The spatial coherence of signals across the entire array can further improve image quality in an adaptive manner. We experimentally demonstrate a 56 × 56 element 2-D sparse THz array that adaptively suppresses grating lobe artifacts by 30 dB. The success of this adaptive processing relies on the single-cycle nature of the pulses employed in THz impulse imaging.