I. Minin, O. Minin, J. Salvador-Sánchez, J. Delgado-Notario, J. Calvo-Gallego, P. F. Baranov, M. Ferrando-Bataller, K. Fobelets, J. Velázquez-Perez, Y. Meziani
In the present work, we report on resolution enhancement of a terahertz imaging system using the terajet effect. A wavelength-scaled particle (a Te on cube for simplicity) was used to localize incident radiation to a subwavelength volume and focus it directly onto the objects under imaging. A strained-silicon modulation field effect transistor was used as a direct detector of an incident terahertz beam at 0.3 THz. At first, the terahertz imaging of the objects was performed without the cube. A clear enhancement of the resolution of the terahertz image was obtained when the cube was placed in the focal point of the terahertz beam in front of the object of interest.
A simple millimeter wave and terahertz (THz) receiver scheme that uses subwavelength focusing of electromagnetic beam on the point-contact detector area with waveguide dimensions is studied. A detection system with such an optical coupling scheme is implemented, where the signal to be detected is coupled to a detector through a mesoscale dielectric particle lens based on terajet effect. We have experimentally demonstrated an enhancement of the point-contact detector sensitivity higher than 6 dB and with 1.5 times decreasing of the noise equivalent power value. The results show that the proposed method could be applied to reduce the size and increase the sensitivity of various THz systems, including imaging, which would enable significant progress in different fields such as physics, medicine, biology, astronomy, etc.
We investigated room temperature detection of terahertz radiation by using two different types of transistors (Strained Silicon Modulation field effect transistor, GaAs PHEMT). Experimental results show a good level of response under excitation at 0.3 THz. Competitive performance parameters were obtained (NEP and responsivity) in comparison with other detectors. Enhancement of the photoresponse signal by imposing a dc drain-to-source current (Ids) was observed experimentally. Inspection of hidden objects by using those devices within a terahertz imaging setup was demonstrated at 300 GHz and a better image was obtained under Ids.
We study theoretically and experimentally the plasmonic THz detection by the asymmetric dual-grating-gate HEMT at room temperature without source-to-drain bias. We derive the analytical expressions of photocurrents due to the plasmonic drag and ratchet effects, and we discuss about their frequency dependences. We also compare the theory to the experimentally obtained frequency dependence. It is demonstrated that they agree qualitatively well.
We report on ultrahigh sensitive, broadband terahertz (THz) detectors based on asymmetric double-grating-gate (A-DGG)
high electron mobility transistors, demonstrating a record responsivity of 2.2 kV/W at 1 THz with a superior low
noise equivalent power of 15 pW/√Hz using InGaAs/InAlAs/InP material systems. When THz radiation is absorbed
strong THz photocurrent is first generated by the nonlinearity of the plasmon modes resonantly excited in undepleted
portions of the 2D electron channel under the high-biased sub-grating of the A-DGG, then the THz photovoltaic response
is read out at high-impedance parts of 2D channel under the other sub-grating biased at the level close to the threshold.
Extraordinary enhancement by more than two orders of magnitude of the responsivity is verified with respect to that for
a symmetric DGG structure.
We investigated the emission of terahertz radiation from a doubly interdigitated grating gates high electron mobility transistor. The experiment was performed using Fourier spectrometer system coupled with high sensitive 4 K Silicon bolometer under the vacuum. The observed emission was explained as due to the excitation of the plasma waves by means of hot 2D plasmons. We also investigated the optical stimulation of the plasma waves by subjecting the device to a CW 1.5 µm laser beam. Dependence of the emission on the gate bias (i.e. on electron density) was observed and interpreted as due to the self oscillation of the plasma waves.
We have designed and fabricated our original terahertz plasmon-resonant emitter incorporating doubly interdigitated grating gates and
a vertical cavity into an InGaP/InGaAs/GaAs high-electron mobility transistor (HEMT) structure. The fabricated device is subjected to
1550-nm, 1-mW (a) a single CW-laser, (b) 4-THz photomixed dual CW-laser, and (c) a 70-fs pulsed-laser illumination at room
temperature. In case of (a), terahertz emission due to the plasmon modes of self oscillation is detected by a Si bolometer under certain
bias conditions. In case of (b), a resonant peak of injection-locked 4-THz oscillation is clearly observed on the device photoresponse.
In case of (c), an impulsive radiation followed by relaxation oscillation is observed by electrooptic sampling, whose Fourier spectrum
exhibited resonant peaks of plasmons' harmonic modes up to 4 THz. Estimated radiation power exceeds 0.1 μW, resulting in excellent
conversion efficiency of the order of 10-4.
In this work, we present new results of numerical analyses for the radiation properties of our plasmon-resonant
photomixer. The photoresponse of plasmon excitation is first calculated from the Dyakonov-Shur theory, which
is input to the electromagnetic simulator based on a frequency-dependent finite differential time-domain method.
This procedure allows us to distinguish the structure-dependent transmittance property from the responsivity
of plasmon excitation.
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