On the Power Radiated by Photo Conductive Sources
A. Fiorellini Bernardis (TU Delft - Tera-Hertz Sensing)
Huasheng Zhang (TU Delft - Tera-Hertz Sensing)
Paolo Sberna (TU Delft - EKL Processing)
Juan Bueno Lopez (TU Delft - Electronics)
Andrea Neto (TU Delft - Tera-Hertz Sensing)
Nuria Llombart Llombart (TU Delft - Tera-Hertz Sensing)
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Abstract
The time evolution of voltages and currents in a pulsed photo conductive antenna (PCA) source is evaluated resorting to a rigorous procedure that stems from semiconductor physics first, to define the phenomena involved in the generation of the photocurrent, and then relies on an equivalent circuit in time domain, providing a direct estimation of the power generated by the PCA as well as its spectral distribution. The circuit model is validated via a campaign of measurements of standard PC antenna sources. The saturation phenomena in the THz radiated power occurring at large optical excitation levels, previously observed by the scientific community and associated to different phenomena, are accurately predicted by the present method, which ascribe their main cause to the feedback from the antenna: indeed, the electromagnetic field generated by the device tend to reduce the strength of the forcing field used to accelerate the photo-carriers.