Research On Signal Sampling Technology Of Narrowband Microwave Spectrometer

Fourier Transform Microwave Spectrometers are the main tools for measuring molecular rotational transitions and the key apparatuses for studying molecular rotational spectroscopy.Based on quantum mechanics,rotational spectroscopy is critical to analyzing molecular structures of materials and deciphering molecular signals from the deep space captured by radio telescopes.In such fields,microwave spectrometers have been playing their indispensable roles.At present,many nations in the world are focusing on developing and optimizing microwave spectrometers by improving the resolution,sensitivity and the range of applications as well.NASA has also set up funds for studying the rotational spectra of potential interstellar molecules in laboratories.Research in rotational spectroscopy just gets started in China.Currently,we are actively exploring the instrumentation on the microwave spectrometers,expecting to make a significant contribution to the related scientific fields.In this paper,we used the narrowband Fourier Transform Microwave Spectrometer newly developed in our laboratory to study the signal sampling technique and proposed several methods to solve the sensitivity problem of microwave spectrometers.Firstly,both the homodyne and heterodyne detection modes were implemented during the construction of our microwave spectrometer,with the resulting effects of the two modes on the rotational spectroscopic signals discussed by the contrast experiments.Later,the multiple-pulse free induction decay technology was proposed and proved that it could improve the noise-signal ratio of the data acquired by the narrowband Fourier Transform Microwave Spectrometer.Finally,by taking 2-fluorobenzonitrile as the sample,we used the narrowband microwave spectrometer in the homodyne detection mode to collect the rotational spectroscopic data by multiple-pulse free induction decay technology.We also used the SPFIT/SPCAT program to assign and fit the spectroscopic data.By doing so,we further proved that multiple-pulse free induction decay technology can indeed enhance the sensitivity by our microwave spectrometer.