Spectrometer Using superconductor MIxer Receiver (SUMIRE) for laboratory submillimeter spectroscopy

Recent spectroscopic observations by sensitive radio telescopes require accurate molecular spectral line frequencies to identify molecular species in a forest of lines detected. To measure rest frequencies of molecular spectral lines in the laboratory, an emission-type millimeter and submillimeter-wave spectrometer utilizing state-of-the-art radio-astronomical technologies is developed. The spectrometer is equipped with a 200 cm glass cylinder cell, a two-sideband (2SB) superconductor-insulator-superconductor (SIS) receiver in the 230 GHz band, and wide-band auto-correlation digital spectrometers. By using the four 2.5 GHz digital spectrometers, a total instantaneous bandwidth of the 2SB SIS receiver of 8 GHz can be covered with a frequency resolution of 88.5 kHz. Spectroscopic measurements of CH3CN and HDO are carried out in the 230 GHz band so as to examine the frequency accuracy, stability, sensitivity, as well as the intensity calibration accuracy of our system. As for the result of CH3CN, we confirm that the frequency accuracy for lines detected with sufficient signal-to-noise ratio is better than 1 kHz, when the high-resolution spectrometer having a channel resolution of 17.7 kHz is used. In addition, we demonstrate the capability of this system by spectral scan measurement of CH3OH from 216 GHz to 264 GHz. We assign 242 transitions of CH3OH, 51 transitions of 13CH3OH, and 21 unidentified emission lines for 295 detected lines. Consequently, our spectrometer demonstrates sufficient sensitivity, spectral resolution, and frequency accuracy for in-situ experimental-based rest frequency measurements of spectral lines for various molecular species.

A new off-point-less observing method for millimeter and submillimeter spectroscopy with a frequency-modulating local oscillator

We propose a new observing method for single-dish millimeter and submillimeter spectroscopy using a heterodyne receiver equipped with a frequency-modulating local oscillator (FMLO). Unlike conventional switching methods, which extract astronomical signals by subtracting the reference spectra of off-sources from those of on-sources, the FMLO method does not need to obtain any off-source spectra; rather, it estimates them from the on-source spectra themselves. The principle uses high-dump-rate (10 Hz) spectroscopy with radio frequency modulation achieved by fast sweeping of a local oscillator of a heterodyne receiver. Because sky emission (i.e., off-source) fluctuates as $1/f$ and is spectrally correlated, it can be estimated and subtracted from time series spectra (a timestream) by principal component analysis. Meanwhile, astronomical signals remain in the timestream since they are modulated to a higher time-frequency domain. The FMLO method therefore achieves (1) a remarkably high observation efficiency, (2) reduced spectral baseline wiggles, and (3) software-based sideband separation. We developed an FMLO system for the Nobeyama $45\:$m telescope and a data reduction procedure for it. Frequency modulation was realized by a tunable and programmable first local oscillator. With observations of Galactic sources, we demonstrate that the observation efficiency of the FMLO method is dramatically improved compared to conventional switching methods. Specifically, we find that the time to achieve the same noise level is reduced by a factor of 3.0 in single-pointed observations and by a factor of 1.2 in mapping observations. The FMLO method can be applied to observations of fainter ($\sim$mK) spectral lines and larger ($\sim$deg$^{2}$) mapping. It offers much more efficient and baseline-stable observations compared to conventional switching methods.

Электродинамические характеристики alpha-лактозы моногидрата в терагерцовом диапазоне-=SUP=-*-=/SUP=-

Using methods of infrared, terahertz, and submillimeter spectroscopy, experimental transmission and reflection spectra of α-lactose monohydrate have been obtained at room temperature in the frequency range from 5 to 5000 cm^–1. The experimental spectra of dense pressed tablets and powdered samples have been analyzed in terms of the model of a classical oscillator. Certain parameters of absorption bands of the resonant and quasi-relaxation types are markers by which components can be selected in heterogeneous pharmacological and organic preparations using the methods of coherent submillimeter and pulsed terahertz spectroscopy.