| Electron paramagnetic resonance(EPR)is a nondestructive technique for the investigation of paramagnetic species with unpaired electrons.EPR spectroscopy provides valuable information on the structure and dynamics about the sample.So it is widely issued and developed rapidly.Up to now,it is widely used in chemistry,physics,biology and some other various branches of science.EPR spectrometer is used for perfoming EPR measurements.It consists of magnet,microwave bridge,sample probe,control and readout unit and etc.With the improvement of microwave devices and noise reduction schemes,a variety of EPR spectrometers with outstanding performance have been built in different frequency bands.Such spectrometers often employ resonant cavities to get high signal to noise ratio,causing the setups to operate over a narrow frequency range.The narrow band performance leads to limitations in the study of the applications of EPR spectrometers.Facing the narrowband EPR spectrometers,this thesis analyzes the limitations of the applications of resonant cavity and the advantages of broadband EPR techniques.A broadband EPR spectrometer operating continuously from L band to Ku band is built with a metallic coplanar waveguide utilized as the probe.The spectrometer is capable of performing EPR measurements in both continuous wave and pulsed modes.The performance of the spectrometer is tested with a sample,named 2,2diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl(DPPH),at room temperature.In the continuous wave mode,the sensitivity of the spectrometer is estimated to be 3.32×1012 spins/Gauss(?)at 13 GHz,by the phase-sensitive amplitude detection technique.It is an obvious improvement of the sensitivity compared to previous works by professor Martin Dressel,whose detectable minimum number of spins is 1016@0.5 GHz/1014@30 GHz.EPR measurements with the spectrometer allow operation with four different modulation-sweeping combinations including frequency-sweep,field-sweep and frequency-modulation,field modulation.In the pulsed mode,inversion recovery experiments are carried out to obtain the spin-lattice relaxation time(T1)of DPPH.The values of T1 are close to 80 ns from 2-15 GHz at room temperature.A control and readout system(CRS)based on field programmable gate arrays(FPGA)is used in the spectrometer.It includes a square wave pulse generator,an arbitrary wave generator,a data acquisition module and data processing module.In addition,combining broadband EPR techniques with radiofrequency techniques and laser techniques,we realize broadband optical detected magnetic resonance(ODMR)based on Nitrogen-vacancy(NV)centers in diamond.Using a Ω-type antenna as microwave antenna and a home-built Halbach Array to apply static magnetic field,we polarize more than 90%of the 14N nuclear spins within the NV centers.Basic ODMR pulsed measurements are also performed here.Meanwhile,based on the hybrid method,including frequency-locking and flux concentration,we realized a high-dynamic-range vector magnetometry with NV centers in diamond.A sinusoidal magnetic field with peak-to-peak value 95.72 Gauss and frequency 0.10 Hz is measured by the system.This technique offers orders-of-magnitude increase in dynamic range compared to open-loop methodologies. |
