Exploring dynamics, disorder, and anharmonicity in THz spectra of crystalline materialsBurnett, Andrew D.; Kendrick, John; Knox, Craig S.; Vaughan, Matthew T.; Towler, Calum N.; Ali, Mannan; Sasaki, Satoshi; Linfield, Edmund H.; Davies, A. Giles; Freeman, Joshua R.
doi: 10.1117/12.2681358pmid: N/A
Terahertz spectral measurements of crystalline materials are known to be particularly sensitive to both the material’s long-range order and lattice dynamics. Here we explore a range of materials including common crystalline organic materials such as α-lactose monohydrate and l-cysteine through to engineered materials including topological insulators (Bi2(Te(1−x)Sex)3) where structure and disorder can be more finely controlled. By comparing variable temperature THz spectral measurements to ab-initio simulations using a range of methods and structures we can begin to unpick the origins of these spectra, and how they are influenced by dynamics and disorder across the lattice.
High-energy multicycle THz pulse generation in artificial PPLN crystalAvetisyan, Y. H.; Makaryan, A. H.; Bakunov, M. I.
doi: 10.1117/12.2673386pmid: N/A
In this report, we theoretically show that intense multicycle terahertz (THz) pulses can be generated by optical rectification in an artificial periodically poled lithium niobate (PPLN) structure formed by placing a phase-shift mask in front of a large aperture stoichiometric lithium niobate (SLN) crystal. In contrast to the common scheme with a triangular prism-shaped congruent LN crystal, THz generation is studied for a rectangular trapezoid SLN sample having a small angle ( 26) of the inclined surface. A matching Si-prism is attached to the trapezoid base to guide the generated THz wave into free space. It is shown that the number of field oscillations (from nearly single-cycle to many cycles) can be varied by the changing of the pump beam linear size in the crystal. Also, there is a possibility of tuning the generation frequency (in the range of 0.4 - 0.8 THz) by building a mask image in the SLN with various demagnification. According to estimates, the energy of narrowband THz pulses at a frequency of 0.5 THz in SLN crystal at temperature 100 K is 265 J at a pump pulse energy of 220 mJ. This corresponds to a pump-to-THz conversion efficiency of 0.12 %.
Analysis of terahertz spectra of water and NaCl solutions obtained in attenuated total reflectance configurationMendoz-Galván, Arturo; Justo Guerrero, Manuel Alejandro; Strupiechonski, Elodie
doi: 10.1117/12.2681947pmid: N/A
This research addresses the complex issues encountered when studying biological and chemical samples in the terahertz (THz) range, mainly due to water's high absorption properties. Using THz-Attenuated Total Reflectance (ATR) spectroscopy, we investigate water and NaCl solutions and provide both experimental data and a comprehensive interpretation of the optical phenomena observed. . Our focus lies in understanding the changes in ATR responses in the THz range for solutions in both bulk and thin film forms, using a non-linear regression analysis of effective optical functions. Moving beyond the traditional low-absorption limit, our study highlights the need for precise equations. We further reveal the significant impact on the optical constants n and k of solutions when NaCl is introduced, offering valuable insights for interpreting spectral data for lossy samples using ATR. Our work seeks to deepen understanding and encourage further research of biological and chemical solutions at THz frequencies.
Fast and sensitive THz detection by an asymmetric-dual-grating-gate epitaxial-graphene-channel FET based on plasmonic and photothermoelectric rectification effectsTamura, Koichi; Tang, Chao; Ogiura, Daichi; Suwa, Kento; Fukidome, Hirokazu; Takida, Yuma; Minamide, Hiroaki; Suemitsu, Tetsuya; Otsuji, Taiichi; Satou, Akira
doi: 10.1117/12.2676102pmid: N/A
This paper reviews recent advancements in the research of THz detection by an asymmetric dual-grating gate structure epitaxial-graphene-channel field effect transistor (ADGG-EG-FETs). We designed and fabricated ADGG-EGFET for plasmonic (PL) detection, and it performed a high sensitivity and fast response to irradiated THz with 0.95 THz. The behavior of measured dependence on gate bias voltage cannot be explained only by the PL effect. We found such a phenomenon as a new current-driven phototermoelectric (PTE) detection assisted by electrostatic carrier drift/diffusion under the application of DC drain biases. Furthermore, we analyze the response speed of our fabricated detector to reveal the transition point between PL and PTE detection mechanisms. The minimum output pulse width was ~190 ps when one ADGG bias was at the Dirac voltage (i.e., charge neutrality point) to promote the PL detection, whereas the pulse width was ~200 ps when both ADGG biases were at well-doped levels to promote the PTE detection. Compared with the input pulse width of 155 ps, the intrinsic response time of the detector was estimated to be 10 ps for the PL and 20 ps for the PTE detection. This can be quantitatively explained by the characteristic relaxation times of the momentum relaxation for the PL, and the energy relaxation of the hot electrons by optical-phonon emission for the PTE detection. These results indicate that the ADGG-EG-FETs THz detectors are promising for applications in 6G to 7G-class THz wireless communication systems.
Terahertz detectors based on vacuum electronicsBuchmann, Tobias Olaf; Sebek, Matej; Kawai, Naoya; Katsuyama, Kota; Lange, Simon J.; Jepsen, Peter Uhd
doi: 10.1117/12.2681570pmid: N/A
We report on various metasurfaces for the purpose of THz driven electron field emission and subsequent detection using vacuum electronics. The underlying principle is based on strong localised field enhancement at metal and semimetal emission points, which bends the vacuum potential temporarily to allow for field emission of electrons from the parent material. The structures are investigated for varying electric field strength using electron time-of-flight measurements as well as electron multiplication and visualisation on a phosphor screen. Measured properties include the emitted electron energy, their count, and the emission threshold. From the recorded data, the local field enhancement for each structure is extracted and compared to simulated values. Subsequently, optimised metasurfaces are implemented into handheld devices that serve as easy-to-use THz detectors. These devices include photomultiplier tubes which operate at frequencies from THz to infrared, as well as live imaging devices with kilohertz framerates. The investigated metallic structures include standard dipole antennas, double split-ring resonators, bow-tie designs, hybrid split-ring and dipole designs, and logarithmic spirals. Semimetallic structures are based on structured and unstructured graphene, which show different emission characteristics. All samples are investigated using strong-field THz radiation generated using lithiumniobate tilted pulse front setup, as well as commercial THz-TDS instruments. In conclusion, we present a holistic overview of the current state-of-the-art THz-PMTs and image intensifiers.
Group IV terahertz photoconductive emitterLee, Pin-Han; Chen, Wang-Chien; Yang, Shang-Hua
doi: 10.1117/12.2680712pmid: N/A
THz photoconductive antennas (PCAs) have found widespread use in THz generation, detection, and various applications such as sensing, imaging, and communication. For achieving ultrafast operation, most commercially available THz PCAs rely on III-V epitaxial materials due to their high mobility and ultrafast response. However, launching the entire device fabrication process through IC foundries presents significant challenges, thereby limiting the capability of device mass production. In this study, we propose the use of GeSn alloys as the photoconductive material for THz generation. Furthermore, the use of GeSn alloys can potentially offer additional advantages such as cost-effectiveness, scalability, and improved performance.
THz dual-pulse generation and manipulation with high degrees of freedomLuo, Chih-Wei; Wei, Hao-Keng
doi: 10.1117/12.2680835pmid: N/A
The carrier frequency of the modern telecommunication system had been raised to hundreds of GHz and aimed at the THz regime. Besides, THz waves have been intensively applied in many fields, e.g., spectroscopy, imaging, and communications. However, there is a rarity of available techniques for modulating few-cycle THz waves on picoseconds timescale. Here we report a simple/reliable system without spatial light modulators (SLMs) for generating circularly polarized THz dual pulses with variable helicity, frequency, and interval. These degrees of freedom allow us to arbitrarily control the THz double pulses of interests, which have potential applications in imaging, spectroscopy, and next-generation communications.