Schematic diagram of the measurement setup.
(a) -plane and -plane power patterns measured for a full-wave dipole in resonance at . The high-resistivity Si substrate has a hyperhemispherical form to reduce the divergence of the beam. (b) Microphotograph of the dipole antenna and finger structure of the photoactive area.
(a) The curve of the SIS mixer in the absence of LO signal and pumped by a photonic LO signal at for two different LO power levels. (b) Corresponding IF power performance for hot and cold blackbodies.
[(a) and (b)] Beam characterization at 50 and from the lens aperture plane. (c) The waist size of the propagating LO beam was measured at different distances from the photomixer lens aperture plane. The data points were fitted to a Gaussian-beam propagation curve. From the fit, the minimum waist (beam waist) was extracted. The dimensions of the photomixer substrate lens were calculated to synthesize an ellipse. The position of the beam waist coincides with the lens-to-air interface.
Schematic of the quasioptical setup. A first MP diplexer transforms the circular polarization from the log-spiral antenna photomixer to vertical. The paraboloidal mirror makes the diverging LO beam convergent. The second MP diplexer injects the hot and cold load signals.
The curve of the HEB without LO power and pumped by the photomixer at . The pumped curve has been averaged to eliminate the scatter which resulted from standing waves and microphony. Due to the hysteretic HEB characteristic in the unpumped case, the superconducting branch and the normal conducting branch of the curve are separated. The resistance in the superconducting branch (straight line at left) comes from a series resistance in the bias circuit. When irradiated by the local oscillator power, the HEB becomes nonhysteretic as shown in the lower curve. The difference in current at a given bias voltage between the two curves is proportional to the absorbed local oscillator power.
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