The Development And Application Of FPGA Based Digital X-band Electron Paramagnetic Resonance Spectrometer

Electron paramagnetic resonance(EPR)spectroscopy is a method for studying ma-terials with unpaired electrons.A large number of materials have unpaired electrons,such as free radicals,transition metal ions,and defects in materials.EPR spectroscopy provide valuable structural and dynamic information about the sample.So,it has been applied in various branches of science,such as chemistry,biology,medicine,and so on.EPR spectrometers are mainly classified into cw(continuous wave)EPR and pulsed EPR.At present,most of the Chinese researchers in EPR field rely on imported commer-cial spectrometers.These spectrometers are often expensive and difficult to upgrade.More importantly,some key parameters of the commercial spectrometers are limited and cannot satisfy the requirements of new scientific researches.In industry,EPR has been applied in food analysis,radiation dosimetry,etc.These industry applications put higher requirements on the stability,integration and portability of related instruments.To promote the research work in our laboratory,we have performed a series of research about the key technologies of X-band EPR spectrometer.An EPR spectrometer consists of electromagnet,microwave bridge,sample probe,control and readout unit,etc.During the operation of an EPR spectrometer,it is neces-sary to perform multiple process including generation of excitation signals,data collec-tion and synchronous control of each unit.The development of latest digital integrated circuit and software operating system laid a profound basis on the research of digital EPR spectrometer.This thesis is focused on the development of an FPGA(Field Pro-grammable Gate Arrays)based digital X-band EPR spectrometer.The main contents include:1.A control and readout system(CRS)based on FPGA for X-band EPR spectrom-eter was realized.The CRS system includes a square wave pulse generator,an arbitrary wave generator,a data acquisition module with 1 GSPS sampling rate.Compared to commercial spectrometers,the CRS in this work is more flexible and integrated.2.The time resolution of microwave pulse was improved to 50 ps.The delay unit in FPGA chip was utilized to achieve this goal.It was experimentally demonstrated that the frequency resolution of spin noise spectra is improved due to the high time resolution.3.The dual channel arbitrary-waveform-generator is utilized to modulate the mi-crowave pulse.This AWG-based EPR spectrometer have several advantages,such as the possibility of pulse shaping,frequency sweeping,and higher precision of pulse phase.4.The signal acquisition module has two channels with 1 GSPS sampling rate.Data processing module is integrated in the acquisition module.Experiment efficiency was increased due to the high integration design.5.Based on the home-built X-band EPR spectrometer,dynamical decoupling se-quence with multi pulses is utilized to protect the coherence of a molecular qubit ex-ceeding a millisecond.