Phase locked backward wave oscillator pulsed beam spectrometer in the submillimeter wave range

We have developed a new submillimeter wave pulsed molecular beam spectrometer with phase stabilized backward wave oscillators (BWOs). In the frequency ranges of 260-380 and 440-630 GHz, the BWOs output power varies between 3 and 60 mW. Part of the radiation was coupled to a novel designed harmonic mixer for submillimeter wavelength operation, which consists of an advanced whiskerless Schottky diode driven by a harmonic of the reference synthesizer and the BWO radiation. The resulting intermediate frequency of 350 MHz passed a low noise high electron mobility transistor amplifier, feeding the phase lock loop (PLL) circuit. The loop parameters of the PLL have been carefully adjusted for low phase noise. The half power bandwidth of the BWO radiation at 330 GHz was determined to be as small as 80 MHz, impressively demonstrating the low phase noise operation of a phase locked BWO. A double modulation technique was employed by combining an 80 Hz pulsed jet modulation and a 10-20 kHz source modulation of the BWO and reaching a minimum detectable fractional absorption of 2 × 10-7. For the first time, a number of pure rotational (Ka=3←2, Ka=4←3) and rovibrational transitions in the van der Waals bending and stretching bands of the Ar-CO complex were recorded. © 1998 American Institute of Physics.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

HIGH-RESOLUTION SPECTROSCOPY ON DOUBLY DEUTERATED AMMONIA UP TO 2.6 THz

Author Institution: I. Physikalisches Institut, Universitat zu Koln, Zulpicher Str.77, 50937 Koln, Germany; Department of Radiophysics, N. Novgorod State University, RussiaHigh accuracy spectra of ND$_2$H up to frequencies of 2.6 THz have been recorded by the use of frequency multiplication techniques in combination with phase locked, high power backward wave oscillators (BWO). For the first time we used novel superlattice (SL) devices as key-element for the generation of higher order harmonics in spectroscopic applications. Odd multiplication factors up to 11 have been achieved and used to measure ground state transitions of the pure rotation and inversion-rotation spectra of ND$_2$H in the frequency range between 0.08 and 2.58 THz with accuracies of several kilohertz. Energy levels up to quantum numbers $J=18$ and $K_a=9$ have been accessed. A greatly extended experimental dataset was obtained with significantly improved accuracies. Besides a technical description of the spectrometer setup, a short presentation and analysis of the spectra will be given in the talk. The improved molecular parameters, derived in the analysis, allowed to generate predictions that can be regarded as a reliable basis for future astronomical high resolution observations throughout the microwave to terahertz regions. These predictions will be available in the Cologne Database for Molecular Spectroscopy (www.cdms.de)