Development Of Vacuum Microwave Method For Microwave Spectrometer

Fourier Transform Microwave(FTMW)spectrometer is one of the most important instruments used to precisely measure the rotational spectra of molecules,free radicals,and ions.The molecular geometry and electronic structure based on microwave spectroscopy can provide not only the standards for computational chemistry,but also new challenges and opportunities.The rotational spectroscopic data in the microwave region have always been of great importance for the long-range remote sensing measurements.Because the signal decoding of molecular spectra from the deep space captured by radio telescopes,mostly depends on the laboratory spectral analysis provided by microwave spectrometers.Therefore,it is of great significance to use microwave spectrometers to obtain the characteristic rotational spectra of molecules,free radicals and ions existing in interstellar medium,which can provide key spectral data and search guidance for the radio survey in deep space and the exploration of the origin of life.The Vacuum Microwave Fabry-Perot Cavity is one of the core components to design and construct the Narrowband FTMW spectrometer.In this paper,we designed the Vacuum Microwave Fabry-Perot Cavity with auxiliary devices,the vacuum chamber and the linear actuator.The microwave Fabry-Perot cavity consists of two inner-reflecting aluminum mirrors with small spherical radius,in a near-confocal arragement so that the molecular beam can be maximally covered by the exciting microwave,thereby greatly improving the sensitivity.Because the operating frequency of Fabry-Perot cavity is determined by the distance of the two mirrors,precisely controlling the position of the linear actuator connected to the moving mirror by using the automatic software can form a resonant standing wave with a bandwidth less than 1MHz inside the cavity.In this way,microwave energy will be stored to effectively stimulate the sample molecules transiting from low rotational energy level to the higher level.The Fourier Transform Microwave Spectrometer were constructed by assembling the Fabry-Perot Cavity along with other modules,and were well tested for specific applications.Based on the fitting and analysis results of spectroscopic data collected by FTMW spectrometer,the high working performance of the Fabry-Perot cavity was verified with high resolution and sensitivity.