BWO-Characterization of Materials and Devices at Frequencies 100-1000 GHz
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BWO-Characterization of Materials and Devices at Frequencies 100-1000 GHz. Volkov A.A., Anzin V.B., Goncharov Yu.G., Gorshunov B.P., Komandin G.A., Spector I.E. Institute of General Physics, Russian Academy of Sciences, Vavilov st. 38, 117942, Moscow, Russia. ABSTRACT We have developed multipurpose spectral technique for amplitude and phase measurements at frequencies 100-1000 GHz based on the use of backward wave oscillators (BWOs) as sources of probing radiation. It utilizes to the utmost all the remarkable advantages of BWOs such as high radiation intensity, monochromaticity, polarization, as well as high speed and wide range of frequency tuning. Extremely simple and flexible open-space measurement geometries are used. The developed technique seems to be the most appropriate and promising for the reliable, precise and mass characterization of materials and devices at millimeter-submillimeter waves. INTRODUCTION Backward Wave Oscillators (BWOs) are classical electrovacuum microwave generators along with the klystrons, magnetrons and travelling wave oscillators, possessing two important distinguished abilities: to generate extremely short wavelength – down to λ≈0.2mm, and electronically tune the working frequency in a broad range – up to ±30% from central value. On the basis of BWOs we have developed an efficient measurement technology for characterization of materials and devices in the millimeter-submillimeter (MM-SBMM) wavelength spectral domain (λ ~ 3-0.3 mm, ν ~ 100-1000 GHz) [1,2]. The methods developed are of a hybrid type, combining features of both microwave technology and infrared spectroscopy: "high quality" monochromatic MM-SBMM radiation is treated by optical means in an open space. As a result, the information of the highest quality is obtainable rapidly in a real time scale, yielding spectra of both parts (real and imaginary) of the complex either transmissivity/reflectivity of devices or dielectric function (permittivity, absorptivity, conductivity, etc.) of materials under study. Using the BWO-based method we have performed a great body of investigations on a) electrodynamic properties of various quasioptical MM-SBMM devices and b) dielectric properties of wide range of substances. Polarizers, attenuators, cut-off and band pass filters, phase shifters, etc., have been investigated in the a) case. In the b) case we have studied single crystals and ceramics, glasses and polymers, powders, composites, liquids, films, fibers, etc. EXPERIMENTAL DETAILS Figures 1 and 2 present typical emission potentialities of BWOs and BWO-based measurement geometries. The later are principally of optical type and hence highly flexible: they are easily modified and fitted to the specific challenge by simple rearrangement of components – generator (BWO), detector (Golay Cell) as well as lenses, splitters, diaphragms, polarizers, phase-shifter, attenuator and modulator (not shown). The object under study (sample) is placed into the radiation beam and its transmission/reflection coefficients or/and correspondent phase
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