Imaging at terahertz frequencies (0.1-10 THz, wavelengths 3 mm-30 µm) has proven to be useful in the biomedical field. Still, the acquisition time is an important hurdle. Here, we discuss recent developments toward achieving real-time THz imaging. First, we demonstrate a spectral encoding algorithm to reconstruct a 4500-pixels image with 45 measurements. Second, we improve the image resolution using a super-resolution algorithm specifically developed for the THz. Third, we discuss our most recent work on the fabrication of an THz photoconductive antenna array for imaging. These works pave the way for future applications of THz imaging in biomedical science.
This review highlights recent and novel trends focused on metallic (plasmonic) and dielectric metasurfaces in photoconductive terahertz (THz) devices. We demonstrate the great potential of its applications in the field of THz science and technology, nevertheless indicating some limitations and technological issues. From the state-of-the-art, the metasurfaces are, by far, able to force out previous approaches like photonic crystals and are capable of significantly increasing the performance of contemporary photoconductive devices operating at THz frequencies.
We propose a novel technology for fabricating plasmonic photoconductive antennas (PCAs) based on superlattice (SL) with increased height of the plasmonic gratings up to 100 nm. We passivate the surface of the SL by Si3N4, etch there windows and deposit Ti/Au antenna metallization. The plasmonic gratings are formed by electron-beam lithography with Ti/Au metallization followed by lift-off. Then an Al2O3 anti-reflection coating layer for reduction of the Fresnel reflection losses is used on the top of the plasmonic gratings, which also serves for maintaining its mechanical stability and providing the excitation of guided modes at the resonant wavelengths of the subwavelength slab waveguide formed by the metal gratings. Current-voltage measurements under femtosecond laser illumination reveal strong increase of the transient photocurrent generated by the fabricated plasmonic PCA which is 15 times higher than for conventional one (i.e. without the plasmonic gratings). The obtained terahertz (THz) power spectra demonstrate 100-times increase of the THz power in the plasmonic PCA. The results might be of interest to the needs of THz spectroscopy and imaging systems, in particular, operating with low-power lasers.
We present the results of numerical and experimental study of the photoconductive antennas (PCAs) based on GaAs and its ternary compounds. We produced three photoconductive materials with different indium content, which then were applied for fabrication of the THz PCAs. These PCAs were used as emitters of the THz pulsed spectrometer. We evaluated the stationary transient current generated by the PCAs, simulated their I-V characteristics, and compared them with the experimental ones. Using the finite integration method, we studied the thermal properties of the PCAs and demonstrated significant influence of the heat-sink on the leakage currents of the InGaAs-based PCA. We showed that the heat-sink reduces the operation temperature of the InGaAs-based PCAs by 40-64 % depending on the indium content. The observed results might be interesting for applications of the PCAs in THz pulsed spectroscopy and imaging.
We have developed a method of terahertz (THz) solid immersion microscopy for imaging of biological objects and tissues. It relies on the solid immersion lens (SIL) employing the THz beam focusing into the evanescent-field volume and allowing strong reduction in the dimensions of the THz beam caustic. By solving the problems of the sample handling at the focal plane and raster scanning of its surface with the focused THz beam, the THz SIL microscopy has been adapted for imaging of soft tissues. We have assembled an experimental setup based on a backward-wave oscillator, as a continuous-wave source operating at the wavelength of λ = 500 μm, and a Golay cell, as a detector of the THz wave intensity. By imaging of the razor blade, we have demonstrated advanced 0.2λ-resolution of the proposed THz SIL configuration. Using the experimental setup, we have performed THz imaging of a mint leaf revealing its sub-wavelength features. The observed results highlight a potential of the THz SIL microscopy in biomedical applications of THz science and technology.
Metamorphic InхAl1–хAs buffer design influence on electrophysical and structural properties of the MHEMT nanoheterostructures was investigated. Electrophysical properties of the nanoheterostructures were characterized by Hall measurements, while the structural features were described with the help of transmission electron microscopy. The strained superlattices inserted in the metamorphic buffer are shown to filter threading dislocations preventing their penetration in active region. Moreover, the increase of period number in superlattices enhances such effect. Step-graded metamorphic buffer permitted to reach the minimal surface roughness with rather high electron mobility.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.