A fast scan submillimeter spectroscopic technique (original) (raw)

Fast Scan Submillimeter Spectroscopy Technique (FASSST): A New Analytical Tool for the Gas Phase

CHIMIA

A new FAst Scan Submillimeter Spectroscopic Technique (FASSST) for analytical applications is described. It is based on voltage tunable Backward Wave Oscillators (BWOs), afast scan to 'freeze' frequency instability, and optical calibration methods. FASSST, due to its high resolution, is used to record the gas phase rotational spectra of mixtures of molecules (e.g. aromatic or heterocyclic compounds). This technique provides an unambiguous identification of the individual component compounds. The combination of FASSST with gas chromatography is expected to be an excellent method for qualitative and quantitative analysis.

High Resolution Spectroscopy with Submillimeter-Wave

2003

Abstract. In order to explain the characteristic features of planetary atmosphere, detection and precise measurements of environmentally important gases such as CO, C10, NO becomes necessary. Since most of the polyatomic molecules have (ro-vibrational) transitions in ...

Submillimeter-Wave Atmospheric and Astrophysical Spectroscopy

Applied Optics, 1975

The paper describes the results and methods of work which has been in progress during the past five years at the U.K. National Physical Laboratory and Queen Mary College, London on the submillimeter spectrum and its application to atmospheric and astrophysical problems. The paper begins with descriptions of the spectroscopic techniques evolved and used, which provide spectral resolution more than half an order of magnitude finer than previously available, particularly at the lower frequency end of the range, from 15 cm-' to 25 cm-1. Excellent signal-to-noise ratios and reproducibility have been obtained and applied as shown in the second part of the paper to both atmospheric studies (chiefly at NPL) and astrophysical problems (chiefly at QMC). The former are illustrated with aircraft-borne measurements of minor species, such as H 2 0, 03, HNO 3 , and other gases, the latter with a consideration of the cosmic background at submillimeter wavelengths. A common thread is provided by developments in observational and interpretational spectroscopic techniques needed to overcome problems peculiar to this region of the spectrum. Our current progress in understanding the region and also prospects for future submillimeter spectroscopy are each brought into review in this work.

A millimeter/submillimeter spectrometer for high resolution studies of transient molecules

Review of Scientific Instruments, 1994

A design is presented for a mlllimeter/submillimeter direct absorption spectrometer for studies of the pure rotational spectra of metal-bearing free radicals. The spectrometer operates in the frequency range of 65-550 GHz with an instrumental resolution of 200-1000 kHz and an absorption sensitivity of a few ppm. The instrument utilizes phase-locked Gunn oscillators as the tunable, coherent source of radiation from 65-140 GHz. Higher source frequencies are obtained with Schottky diode multipliers. The gas cell and optics path are designed utilizing Gaussian beam optics to achieve maximum interaction between molecules and the mm-wave radiation in the reaction region. Scalar feedhorns and a series of PTFE lenses are used to propagate the source signal. The gas cell is a cylindrical tube 0.5 m in length with a detachable Broida-type oven. The detector for the spectrometer is a helium-cooled InSb hot electron bolometer. Phase-sensitive detection is achieved by FM modulation of the Gunn oscillators and use of a lock-in amplifier. Spectra are recorded by electrical tuning of the Gum-r oscillator, which is done under computer control. The millimeter and sub-mm rotational spectra of several free radicals have been observed for the first time using this instrument, including CaOH, MgOH, CaH, MgF, and BaOH. ')NSF Presidential Faculty Fellow. b)NASA Space Grant Fellow. ')NRAO is operated under cooperative agreement with the NSF.

A computer-controlled submillimeter Fourier spectrometer

IEEE Transactions on Instrumentation and Measurement, 1989

A system for a submillimeter wave Fourier transform spectroscopy (FTS) has been automated for the measurement of the power absorption coefficient of liquids in the wavenumber range 10-400 cm-'. The interferometer is interfaced with a RM380Z Research Machines microcomputer. Software and hardware have been developed to automate the process of collecting and storing the data. Some points of relevance to the analysis of interferometric data are reviewed including the use of phase modulation, the resolution of spectra computed using the discrete Fourier transform, and the necessity of proper optical filtering in spectrometers which use Fourier transform techniques. Spectra measured using the FTS system described here have been compared with results obtained recently using a tunable submillimeter laser and a good agreement is found between the two sets of data.

Spectrometers for (sub) mm radiometer applications

The autocorrelation spectrometer is one of 5 types of spectrometers being considered for space based (sub)millimetre heterodyne systems. The advantages of the digital autocorrelation spectrometer compared to Chirp Transform, Acousto Optical and Filterbank spectrometers are; stability, compactness, high reliability and variability in bandwidth and resolution. FFT spectrometers based on the latest generation of FPGA devices now promise a cost effective alternative for low to medium bandwidth applications with high resolution requirements. Omnisys has designed and implemented several generations of autocorrelation chip sets and spectrometers. This range from the ODIN satellite spectrometers now in LEO to our current 8 GHz single chip spectrometer under development. The ODIN chip set was a breakthrough at the time (1998). The power consumption was lowered by a factor of 50 compared to state of the art. Since then we have further improved the power consumption with a factor of 40, and we are now reaching 8 GHz of bandwidth for a single spectrometer chip.

A medium resolution ground based submillimeter spectrometer

Infrared Physics & Technology, 1994

We present a submillimeter spectrometer based on a cooled scanning FabryyPCrot working at 1.4 K temperature and using gold inductive grids deposited on quartz substrates as reflective faces. The detection is achieved by an array of 24 silicon bolometers cooled at 0.1 K by an adiabatic demagnetization refrigerator. This spectrometer will be operated at the focus of the 10m ground based antenna of the Caltech Submillimeter Observatory and is the precursor of balloon borne or space instruments. It is mainly dedicated to high redshift galaxy observations, and especially to the CII line (158 pm) studies in these objects. The observations will be carried out in two atmospheric windows centered on 350 and 450 pm, and the spectrometer will be able to detect galaxies at a redshift of about I-2 with a FIR luminosity of a few lOi2 L 0