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THz Beam Modulation By Optical Illumination of a Semiconductor Substrate

Ketelaar, Tim (2018) THz Beam Modulation By Optical Illumination of a Semiconductor Substrate. Master's Thesis / Essay, Astronomy.

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For the instrumentation development of the Atacama Large Millimeter Array (ALMA) located in Chili, we consider the modulation of submm/THz radiation by utilising properties of semiconductor materials. In essence, a semiconductor substrate is illuminated with different light sources, modifying the semiconductor properties. Exactly these properties are of interest which alter the propagation of THz radiation. In particular, a high-resistivity slab of silicon (Si) has been used. The first experiment involves a calibration which relates the intensity of THz radiation to the intensity of optical illumination. The dependence turned out to be a modified inverse power law. In the second experiment we go into detail on the spectral properties of absorption in the Si substrate using the Fourier Transform Spectrometer (FTS) setup. A frequency dependence of the THz transmission was found, which is in favour of the local oscillators used in ALMA. Subsequently, measurements were performed with a heterodyne receiver system. In this experiment, investigations have been made regarding the noise temperature contributions of THz modulation due to the Si substrate. As was consistent for all light sources, the additional noise temperature is within the noise of the measurement. In addition, measurements have been carried out to study the phase noise contributions at different frequency offsets from the central carrier wave. Up to the spectral resolution of ALMA (100 KHz) there is no significant contribution in terms of phase noise power. Consequently, the method of optical illumination of a semiconductor substrate to modulate THz radiation as presented in this thesis is deemed suitable for use in a low noise heterodyne system.

Item Type: Thesis (Master's Thesis / Essay)
Supervisor name: Barychev, A.M.
Degree programme: Astronomy
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 05 Oct 2018
Last Modified: 10 Oct 2018 10:17

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