Representation of FET and circuitry. (a) FET with the dominant parasitic elements highlighted (gate resistance , gate-source and gate-drain capacitances and ). (b) Classical resistive mixing with a FET. The radiation field is coupled to both the gate and—through the shunt capacitance —the drain making the transistor a power detector. (c) waveguide representation of the pair of differential equations describing nonresonant self-mixing. The gray area of the waveguide indicates the transistor. Dark-gray inset: Specifications of quantities used in the methods section.
Spatio-temporal carrier dynamics and induced dc voltage along the channel for 6 GHz radiation. All simulations performed with reduced set of equations (i.e., nonresonant model). (a) Sheet density (in terms of the relative carrier sheet density ) along the channel as a function of time. , voltage dependence of sheet density according to Eq. (6), amplitude of applied ac voltage: 1 mV, channel length: 250 nm, gate voltage: 0.1 V above threshold, zero source-drain bias voltage. Capacitor is simulated by setting an ac short between gate and drain. Open-drain boundary condition for voltage detection is realized by setting the dc component for current at the drain to zero. (b) Left axis: Spatial evolution of the amplitude of the density oscillations (black full line). Right axis: Spatial development of rectified dc potential (blue full line). The dashed lines in (b) depict the same quantities as the full lines but without capacitive shunting of drain and gate.
Spatio-temporal carrier dynamics and induced dc voltage along the channel for 600 GHz radiation. All simulations for ac-shunted gate and drain. (a) Distribution of relative sheet density along the channel as a function of time. Transistor parameters as in previous figure. (b) Full lines: Simulations performed with the reduced set of equations describing nonresonant mixing. Dashed lines: Simulations with full set of equations.
Simulated voltage responsivity vs dc gate bias voltage for different external load resistances . Threshold voltage: 0.6 V. The inset shows the model circuit providing the basis of the simulations (ideal voltage source in series with internal resistance , and external load).
Upper panel: micrograph of the FPA; pixel size: . Lower panel: Measured beam intensity profile using a central pixel of the FPA.
Measured responsivity of a representative device of the FPA. Inset: Noise-equivalent power of five different devices of the FPA. All measurements performed at room temperature.
0.65 THz image taken of a postal envelope in transmission mode. Its hidden content is revealed: a ring, a hair clip, a paper clip, adhesive tape, and a dextrose tablet. Note also the interference pattern by the paper. The image was obtained by raster scanning with a central four-pixel linear segment of the FPA, each detector reads out by its own external lock-in amplifier. The image, shown with a linear intensity scale in Refs. 31 and 33, is displayed here with the intensity given on a logarithmic scale in order to illustrate the substantial dynamic range.
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