We demonstrate bio-medical imaging using a Terahertz quantum cascade laser. This new optoelectronic source of coherent Terahertz radiation allows building a compact imaging system with a large dynamic range and high spatial resolution. We obtain images of a rat brain section at 3.4 THz. Distinct regions of brain tissue rich in fat, proteins, and fluid-filled cavities are resolved showing the high contrast of Terahertz radiation for biological tissue. These results suggest that continuous-wave Terahertz imaging with a carefully chosen wavelength can provide valuable data on samples of biological origin; these data appear complementary to those obtained from white-light images.
A terahertz (THz) imaging system based on narrow band microbolometer sensors (NBMS) and a novel diffractive lens was developed for spectroscopic microscopy applications. The frequency response characteristics of the THz antenna-coupled NBMS were determined employing Fourier transform spectroscopy. The NBMS was found to be a very sensitive frequency selective sensor which was used to develop a compact all-electronic system for multispectral THz measurements. This system was successfully applied for principal components analysis of optically opaque packed samples. A thin diffractive lens with a numerical aperture of 0.62 was proposed for the reduction of system dimensions. The THz imaging system enhanced with novel optics was used to image for the first time non-neoplastic and neoplastic human colon tissues with close to wavelength-limited spatial resolution at 584 GHz frequency. The results demonstrated the new potential of compact RT THz imaging systems in the fields of spectroscopic analysis of materials and medical diagnostics.
Room-temperature detection and imaging in transmission and reflection geometries at 0.591 THz with planar asymmetrically shaped InGaAs diodes (also called bow-tie diodes) are demonstrated in direct and heterodyne mode. The sensitivity of the diodes is found to be 6 V/W in direct mode, and the noise-equivalent power (NEP) in direct and heterodyne mode is estimated to be about 4nW / (Wurzel aus Hz) and 230 fW/Hz for a local-oscillator power of 11 µW, respectively. The improvement of the dynamic range by heterodyning over direct power detection amounts to about 20 dB using pixel read-out times relevant to real-time imaging conditions
Multilevel phase Fresnel lenses (MPFLs) with a high numerical aperture for 0.58 THz frequencies were developed. The components based on a monocrystalline silicon wafer are prepared by patterning by a high-speed industrial-scale laser direct writing (LDW) system. Two consistent series of the terahertz-MPFLs with phase quantization levels varying between 2 and the continuous kinoform shape for the focal lengths of 5 and 10 mm were produced employing inherent flexibility of the LDW fabrication process. The focusing performance was studied at the optimal 0.58 THz frequency using a Gaussian beam profile and scanning 2D intensity distribution with a terahertz detector along the optical axis. The efficiency of the terahertz-MPFL was found to be dependent of the number of subzones. The position and orientation angles of the patterned plane of the silicon wafer were considered to reduce the effect of standing waves formation in the experiment.
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