We present the characterization of a Zero-bias Schottky diode-based Terahertz (THz) detector up to 5.56 THz. The detector was operated with both a table-top system until 1.2 THz and at a Free-Electron Laser (FEL) facility at singular frequencies from 1.9 to 5.56 THz. We used two measurement techniques in order to discriminate the sub-ns-scale (via a 20 GHz oscilloscope) and the ms-scale (using the lock-in technique) responsivity. While the lock-in measurements basically contain all rectification effects, the sub-ns-scale detection with the oscilloscope is not sensitive to slow bolometric effects caused by changes of the IV characteristic due to temperature. The noise equivalent power (NEP) is 10 pW/$\sqrt{\mathrm{Hz}}$ in the frequency range from 0.2 to 0.6 THz and 17 pW/$\sqrt{\mathrm{Hz}}$ at 1.2 THz and increases to 0.9 $\mathsf{\mu }$W/$\sqrt{\mathrm{Hz}}$ at 5.56 THz, which is at the state of the art for room temperature zero-bias Schottky diode-based THz detectors with non-resonant antennas. The voltage and current responsivity of ∼500 kV/W and ∼100 mA/W, respectively, is demonstrated over a frequency range of 0.2 to 1.2 THz with the table-top system.

High-power coherent terahertz (THz) radiation from accelerator facilities such as free-electron lasers (FELs) is frequently used in pump-probe experiments where the pump or probe (or both) signals are intense THz pulses. Detectors for these applications have unique requirements that differ from those of low-power table-top systems. In this study, we demonstrate GaAs antenna-coupled field effect transistors (FETs) as a direct THz detector operating across a broad frequency spectrum ranging from 0.2 THz to 29.8 THz. At approximately 0.5 THz, the maximum current responsivity (ℜ _I ) of 0.59 mA/W is observed, signifying a noise equivalent power (NEP) of 2.27 nW/√Hz. We report an empirical roll-off of f⁻³ for an antenna-coupled GaAs TeraFET detector. Still, NEP of 0.94 μW/√Hz and a current responsivity ℜ _I = 1.7μA/W is observed at 29.8 THz, indicating that with sufficient power the FET can be used from sub-mm wave to beyond far-infrared frequency range. Current and voltage noise floor of the characterized TeraFET is 2.09 pA and 6.84 μV, respectively. This characteristic makes GaAs FETs more suitable for applications requiring higher frequencies, ultra-broadband capabilities and robustness in the THz domain, such as beam diagnostics and alignment at particle accelerators.

We demonstrate a versatile and compact approach to generate and control terahertz frequency combs by applying radio frequency modulation to a ring-shaped quantum cascade laser. By harmonically driving the device well above threshold, we induce the formation of phase-coherent sidebands with tunable spacing across a broad radio frequency range (1.5–14.5 GHz), independent of the laser’s cavity modes. The RF generated comb exhibits narrow beat notes with linewidths down to 3.5 Hz and a linear phase profile, as verified by optical beat note analysis, indicating the important role of the phase modulation. Unlike classical phase modulation, we observe a simultaneous increase in total terahertz output power and driving current, reflecting an enhanced laser efficiency and photon-assisted transport. The presented approach enables flexible manipulation of frequency grids and spectral power distribution in both single-mode and multimode regimes, including subharmonic injection locking for spectral broadening. Our results highlight the potential of radio frequency-modulated quantum cascade lasers as customizable, high-efficiency terahertz comb sources for spectroscopy, sensing, and communication applications.

Terahertz (THz) domain is quickly developing with various applications such as beam diagnostics at particle accelerators, spectroscopy, communications, space science, etc. However, often requiring fast intermediate frequency (IF) electronics. We present the design of a double mirror stub (DMS) based a planar broadband bias tee having an isolation port S 31 with 14.45 GHz bandwidth below −10 dB and S 33 with 13.1 GHz bandwidth above −2 dB. CST simulation and measured results are in very good agreement. The bias tee will be a part of a new generation of on-chip THz detectors based on zero-bias Schottky diode and high electron mobility field effect transistor (HEMT).

Field effect transistor (FET) based terahertz rectifiers are promising candidates for sensitive, room-temperature operated high speed (THz) detectors, e.g. in communication, medical, biochemical, security, quality control applications, or beam diagnostic applications at particle accelerators. This paper investigates the equivalent circuit in the intermediate frequency band from 0.1 to 65 GHz with S-parameter measurements in order to enable implementation with high speed post detection electronics. Preliminary results are obtained by de-embedding On-Wafer measurements and compared with theoretical expectations from hall measurements and a simplified equivalent circuit. The knowledge of the channel behavior and impedance is mandatory for impedance matching to IF circuitry in advanced detector designs.

Modern wireless communication systems imperatively demand the integration of filter to signal combiner circuits owing to a significant rise in enthusiasm for the integration of frequency-dependent circuits in a single network. The pivotal nature of the proposed circuit to assimilate signal frequency filtering of thirty-five harmonics boasting superior high-end suppression and power combining capabilities below 2 GHz threshold. The radial microstrip transmission line has been designed to ensure not only efficiency but also the compactness particularly when the filter resonator units are integrated into the circuit. The design, analysis and practical verification of the circuit has also been meticulously presented along with robust functionality. The scaled version of the proposed circuit would be the preeminent solution for the high frequency noise rejection specifically to the beam diagnostics applications at accelerator facilities.