Preliminary Study Of Fe³⁺ Masing Effect In Sapphire

The whispering gallery mode maser oscillator is expected to have better frequency stability in the short integration time and ultra-low phase noise than a Cryogenics Sapphire Oscillator（CSO）,making it a great candidate as a secondary microwave frequency standard.For iron ion maser,the iron ion concentration in the sapphire directly determines the success of the maser.Iron ion concentration inside sapphire is related to the contamination of raw materials and the growth process,but the relationship between iron ion concentration and maser cannot be quantitatively controlled at present.Even though this kind of maser has been investigated for about ten years,its physics and engineering have still lots of room for improvement.This thesis mainly relies on whispering gallery mode technology and Zeeman splitting map to characterize iron ions in sapphire,to increase Fe³⁺ions concentration inside sapphire by annealing,and finally to build the first prototype of maser in the laboratory.In order to characterize iron ions in sapphire,a microwave non-invasive material characterization technique based on whispering gallery mode was used.At 4 K temperature,we have improved the resolution from ppb to ppt in the Ka frequency band,making this microwave characterization technology of large materials a unique contactless characterization method.In order to search for iron ions,we characterized iron ions in two sapphire samples（M₁,M₂）by microwave technology.Before characterization,we obtained the Hamiltonian equation,electron spin resonance（ESR）frequency and g-factor of paramagnetic ions in sapphire through extensive investigation and calculations.Based on these information,the theoretical Zeeman splitting diagram is drawn to support the characterization of iron ions.By comparing the experimental results with the theoretical map,we found only partial transition lines of the mixed transition lines of iron ions.In order to obtain more transition lines of iron ions,we use the method of annealing iron ions at high temperature in air to achieve the change of valence states of iron ions in sapphire so that paramagnetic ions are enhanced significantly.After annealing,we have four transition lines of iron ions and two transition lines of unknown ions in each sapphire sample.In M₂,the Q-value of the doublet mode of WGH_17,0,0reaches above 2×10⁹by adjusting microwave coupling.The anomalous bi-stable curves of iron ions were measured in this ultra-high Q mode.The anomalous bi-stable curve shows the saturation absorption of iron ions in M₂,which provides a foundation for the construction of a maser system.The iron ion concentration of both sapphires was calculated and analyzed at low temperature.The concentration of active iron ions in M₂while exciting WGH_17,0,0mode was（6.46±0.01）ppb.Based on the anomalous bi-stable iron ions in M₂and the concentration of iron ions,we built a maser prototype in the laboratory.