A Quasi-Optical Multiplier for Terahertz Spectroscopy

Abstract

The rotational ÄT-structure (K = 0, ... 6) of the a-type transition (J = 65 -64) of the symmetric top molecule methylcyanide, CH3CN, has been recorded at 1.2 THz employing a newly designed quasi-optical frequency multiplier. A planar Schottky diode is used as non-linear element for producing the harmonic power and is mounted in the focus of an off-axis antenna across a short single ridged waveguide. The 2nd harmonic of the fundamental frequency is filtered with adichroic plate and is focused onto the InSb bolometer after passing an absorption cell. The multiplier is driven by a high power backward wave oscillator with a fundamental frequency near 600 GHz.

Ground state spectrum of methylcyanide

“…The 107 and 29 ground state rotational transitions were newly measured or remeasured using the Cologne and Tsukuba spectrometers, respectively, with accuracies from 10 to 60 kHz. The nitrogen hyperfine structures were resolved only partly for 19 low-J transitions (see Table 1) and therefore all the high-quality hyperfine data available from literature (see [3,[16][17][18][19][20][21][26][27][28][29][30]) have been incorporated into our least square analysis to perform the detailed nitrogen quadrupole coupling analysis. All the partly or completely overlapped transitions were used to simulate the envelope maxima that were fitted to the experimental frequencies in the least square procedure.…”

“…Besides the transitions measured in this study, we have completed our data set with measurements from the maser beam spectrometer [2], from the classical acetonitrile studies [12][13][14][15]18,26,27] for the low-J transitions, and by high frequency studies from the last decade [28][29][30]. The total number of the ground state rotational transitions in the extended data set was 286.…”

Pure Rotational Spectrum of HCN in the Terahertz Region: Use of a New Planar Schottky Diode Multiplier

“…In this study we report Doppler-limited, highly accurate measurements of the rotational spectrum up to 2 THz. By employing different frequency-generating techniques such as BWOs as fundamental frequency sources (5), frequency multipliers pumped by BWOs (6), and a frequency-stabilized laser sideband system with the use of BWOs for generating the sidebands (7,8), we have essentially opened the terahertz region for broadband scanning spectroscopy with an achievable absolute accuracy of about Ϯ1 kHz in the best of cases.…”

Transmission features of frequency-selective components in the far infrared determined by terahertz time-domain spectroscopy

“…The transmission characteristic of a FSC is determined by the shape and the arrangement of the apertures that perforate the component with a given thickness. FSC's have a broad range of applications, owing to their different transmission functions, and are used as filters 2,3 in frequency multipliers, 4 as laser-cavity output couplers, 5 or as Fabry-Perot interferometers. 6 By exploitation of the transmission and reflection behavior of FSC's, broadband signals can be divided into two frequency ranges.…”