Enabling Technology for 3D Mueller Polarimetric Imaging at Terahertz Frequencies

Project: Research

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Mueller polarimetric imaging (MPI), as one of polarimetric imaging modalities, is an effective tool for enhancing the imaging contrast. It can also decipher additional information on the material and structural properties of the imaged object due to their different responses to various polarization states of the probing waves. MPI is a proven imaging approach in microwave and optical domains. However, little work has been done at THz regime on its distinctive advantages in areas where the subjects under study are characterized by non-ionizing, high sensitivity to water molecules and lowenergy vibrations of macromolecules. The lack of commercially available THz linear and circular polarizers discourages the popular use of MPI.We have successfully demonstrated MPI at 0.3 THz both in reflection and transmission modes. MPI results in 4-by-4 Mueller matrix images that can further be decomposed to reveal the degree of depolarization of the polarized incident wave upon interaction with the imaged object; the transmittance or reflectance of the object depending on incident polarization; and the phase difference between the orthogonally polarized components of the incident wave reflecting from or propagating through the object. The linear and circular components of these decomposed images are sensitive to oriented and chiral structures, respectively. Nevertheless, these THz wave interactions with the materials, in particular biomaterials, are frequency dependent. Furthermore, Mueller matrix images are 2D projection of a 3D object.With a raster scanning mechanism in the transverse plane using translational stages, THz time-domain spectroscopy (TDS) can provide axial resolution and form 3D image of an object. This is achieved by using deconvolution signal processing of the measured reflected or transmitted signal against a reference signal. Taking advantages of the distinctive properties of THz waves, we propose to combine the high polarization sensitivity of MPI and the axial resolution of the TDS imaging to advance THz 3D imaging.In this project, we propose to design, fabricate and test THz wideband polarizers and reflectors using metasurface technologies. Wideband linear and circular polarizers make it possible for MPI to have a wide range of frequencies using TDS. Reflectors with focal planes vary with frequencies and this allows us to revolve the axial resolution with higher accuracy. To address the time-consuming raster scanning, we propose to adopt a two-rotating-mirror approach for the 2D scanning with emphasis on uniform spot shape across the scanning region. Successful designs will be incorporated into our timedomain and frequency-domain THz spectrometers for 3D imaging. 


Project number9043002
Grant typeGRF
Effective start/end date1/10/20 → …