Iterative denoising phase retrieval method for twin-image elimination in continuous-wave terahertz in-line digital holography

•An iterative denoising phase retrieval method is proposed to solve the twin-image problem in continuous-wave terahertz in-line digital holography.•The positive absorption constraint and the denoising processing are combined to be applied simultaneously at the object field to further enhance the object constraint.•The complex object field is decomposed into real and imaginary parts for denoising respectively.•The iterative denoising phase retrieval method exhibits good robustness to noises existing in the hologram. In this paper, an iterative denoising phase retrieval method is proposed to solve the twin-image problem in continuous-wave terahertz in-line digital holography. The iterative algorithm is based on the classical error reduction algorithm by adding the positive absorption constraint and a new image denoising for the object field to improve the quality of the reconstructed images. At certain geometrical parameter, the twin-image can be treated as noise superimposed in the object plane. The object field is considered as a complex function affected by the twin-image, and then the denoising process embedded in each iteration is applied to the real and imaginary parts of the object field, respectively. The validity of this approach is demonstrated by the high-quality imaging of samples like the Siemens star and the cicada's wing, which are almost free from the twin-image. Also, the proposed method exhibits good robustness to noises existing in the hologram, and the reconstructed images show better quality compared with other popular phase retrieval methods and denoising algorithm. This work would be helpful to expand the application of continuous-wave terahertz in-line digital holography in biomedical imaging and nondestructive testing.