Parylene anti-reflection coating of a quasi-optical hot-electron-bolometric mixer at terahertz frequencies

Parylene C was investigated as anti-reflection coating for silicon at terah ertz frequencies. Measurements with a Fourier-transform spectrometer show t hat the transmittance of pure silicon can be improved by about 30% when app lying a layer of Parylene C with a quarter wavelength optical thickness. Th e 10% bandwidth of this coating extends from 1.5 to 3 THz for a center freq uency of 2.3-2.5 THz, where the transmittance is constant. Heterodyne measu rements demonstrate that the noise temperature of a hot-electron-bolometric mixer can be reduced significantly by coating the silicon lens of the hybr id antenna with a quarter wavelength Parylene C layer. Compared to the same mixer with an uncoated lens the improvement is about 30% at a frequency of 2.5 THz. (C) 2001 Elsevier Science B.V. All rights reserved.