Continuous-wave circular polarization terahertz imaging

Abstract

Biomedical applications of terahertz (THz) radiation are appealing because THz radiation is nonionizing and has the demonstrated ability to detect intrinsic contrasts between cancerous and normal tissue. A linear polarization-sensitive detection technique for tumor margin delineation has already been demonstrated; however, utilization of a circular polarization-sensitive detection technique has yet to be explored at THz frequencies. A reflective, continuous-wave THz imaging system capable of illuminating a target sample at 584 GHz with either linearly or circularly polarized radiation, and capable of collecting both cross- and copolarized signals remitted from the target, is implemented. To demonstrate the system’s utility, a fresh ex vivo human skin tissue specimen containing nonmelanoma skin cancer was imaged. Both polarization-sensitive detection techniques showed contrast between tumor and normal skin tissue, although some differences in images were observed between the two techniques. Our results indicate that further investigation is required to explain the contrast mechanism, as well as to quantify the specificity and sensitivity of the circular polarization-sensitive detection technique.

Continuous-Wave THz Imaging for Biomedical Samples

“…The high sensitivity of THz waves to water content in fresh tissues often makes reflection mode imaging more suitable. The CW THz reflection single-point scanning imaging optical geometries are generally set into two types [36][37][38][39][40][41][42]. The incident beam and the reflected beam are set with a certain angle of the first type as shown in Figure 2a.…”

“…They further modified a CW THz circular polarisation-sensitive detection technique for the edge of a tumour in 2016, adding a quarter-wave plate (QWP) to the original linear polarisation-sensitive detection system before the sample at 584 GHz [42]. Fresh ex vivo human non-melanoma skin cancer sections with 5 µm thickness were imaged to demon- They further modified a CW THz circular polarisation-sensitive detection technique for the edge of a tumour in 2016, adding a quarter-wave plate (QWP) to the original linear polarisation-sensitive detection system before the sample at 584 GHz [42]. Fresh ex vivo human non-melanoma skin cancer sections with 5 µm thickness were imaged to demonstrate the ability of the system.…”

“…The intensity of the CRP LP images was higher than in the COP CP images for the reason that the CRP CP THz radiation penetrated the tissue more deeply than the CRP LP THz radiation, and the attenuation of the reflected signal obtained after CRP CP THz radiation illuminated the sample was greater than that used by CRP LP THz radiation. They further modified a CW THz circular polarisation-sensitive detection technique for the edge of a tumour in 2016, adding a quarter-wave plate (QWP) to the original linear polarisation-sensitive detection system before the sample at 584 GHz [42]. Fresh ex vivo human non-melanoma skin cancer sections with 5 µm thickness were imaged to demonstrate the ability of the system.…”

“…Further, they found that the THz images had a higher contrast between the tumour and normal tissues. In 2016, the same research group added a circular polariser to the THz imaging system that is shown in Figure 4 to image fresh human ex vivo NMSC by reflective single-point scanning method [42]. The refractive index changed little due to the structural damage of the tumour tissues.…”

Narrowband terahertz metasurface circular polarization beam splitter with large spectral tunability based on lattice-induced chirality

“…Terahertz polarization manipulation, including generation, detection, conversion and splitting, is essential in a diverse range of terahertz polarization-sensitive applications, such as time-domain spectroscopy and sensing [1], imaging [2] and optical coherence tomography [3], ellipsometry [4] and communications [5]. One important functionality is to split two orthogonally polarized waves, especially left-and rightcircularly polarized waves.…”