A fast scan submillimeter spectroscopic technique

Abstract

A new fast scan submillimeter spectroscopic technique ͑FASSST͒ has been developed which uses a voltage tunable backward wave oscillator ͑BWO͒ as a primary source of radiation, but which uses fast scan (ϳ10 5 Doppler limited resolution elements/s͒ and optical calibration methods rather than the more traditional phase or frequency lock techniques. Among its attributes are ͑1͒ absolute frequency calibration to ϳ1/10 of a Doppler limited gaseous absorption linewidth (Ͻ0.1 MHz, 0.000 003 cm Ϫ1 ), ͑2͒ high sensitivity, and ͑3͒ the ability to measure many thousands of lines/s. Key elements which make this system possible include the excellent short term spectral purity of the broadly (ϳ100 GHz) tunable BWO; a very low noise, rapidly scannable high voltage power supply; fast data acquisition; and software capable of automated calibration and spectral line measurement. In addition to the unique spectroscopic power of the FASSST system, its implementation is simple enough that it has the prospect of impacting a wide range of scientific problems.

A NEW APPROACH TO ASTROPHYSICAL SPECTRA: THE COMPLETE EXPERIMENTAL SPECTRUM OF ETHYL CYANIDE (CH3CH2CN) BETWEEN 570 AND 645 GHZ

“…The spectra were recorded using the Fast Scan Submillimeter Spectroscopic Technique (FASSST; Medvedev et al 2004;Petkie et al 1997). In the implementation used here a times 48 solid state multiplier chain (Virginia Diodes) was driven by a rapidly sweeping (Agilent E8256D) synthesizer.…”

The Millimeter‐ and Submillimeter‐Wave Spectrum of13C1‐Methyl Formate (H13COOCH3) in the Ground State

“…The millimeter-and submillimeter-wave spectrum of 13 C 1 -methyl formate in the 110Y377 GHz region was measured with the FASSST system ( Petkie et al 1997;Albert et al 1998;Medvedev et al 2004) using three different backward-wave oscillators as sources of radiation. The spectrum of sulfur dioxide was used as reference to calibrate the frequencies.…”

Generation of widely tunable Fourier-transform-limited terahertz pulses using narrowband near-infrared laser radiation

“…Particularly desired would be narrowband tunable sources to study low-frequency vibrations of polyatomic molecules and molecular clusters, and the rotational motion of small molecules (see, for instance, Refs. [6][7][8][9][10][11] and references therein), and in the identification of possible molecular carriers of astrophysical spectra, for which there is considerable current interest in the context of the new observational facilities ALMA [12] and Herschel [13].…”