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It is a homodyne detector with a low pass filter. An external reference signal is required to operate SU-1. All operating parameters (amplification, time constant and phase) are manually adjustable. Also this detector is used to measure phase shift of the signal. Schematic diagram of the detector SU-1 is provided in fig. 1.
Fig. 1. SU-1 schematic diagram.
The principle of operation of SU-1 is based on orthogonality of two sinusoidal functions. When a product of two sinusoidal functions with non-matching frequencies f1 and f2 is integrated over time well above their periods, the result is zero. On the other hand, when f1 = f2, and both functions are in phase, integrated average is equal to half of the product of the functions’ amplitudes.
SU-1 multiplies input signal to reference signal (from built-in generator or external source) and integrates the product over specified time (usually from milliseconds to a few seconds). The result is a DC signal, and the effect of any other signal not matched by frequency to the reference is dampened to almost zero. Same-frequency component that is not in phase with the reference signal is attenuated too (since same-frequency sinusoidal and cosinusoidal waves are orthogonal).
SU-1 is to be used to amplify high-noise signal produced by the following means of detecting of THz radiation: electro-optical detection of pulsed THz radiation and of detection of THz radiation using the following detectors: Golay detectors, cooled bolometers, pyro-electric THz radiation detectors, semiconductor THz radiation detectors, novel THz radiation detectors.
The figures 2 and 3 respectively show the signal dependence on SU-1 gain factor and time constant. This signal is a temporal shape of THz impulse obtained by EOD.
Fig.2. Signal level at various gain factor settings.
Fig. 3. Signal level at various time constant settings
Fig. 4. Sample application of SU-1 within THz radiation detector based on
THz scanning Fabry-Perot interferometer with Golay Detector
SU-1 package includes
Following accessories for SU-1 can be supplied separatly:
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