Experimental And Theoretical Study Of Pulsed Optically Pumped Rubidium Frequency Standard

Atomic clocks have been recognized as critical equipment for the global navigationsatellite systems, and their performances determine the positioning accuracy and lifetime ofthe satellite navigation systems. China’s Beidou （Compass） satellite positioning system willuse homemade Rb AFS. In order to ensure reliability, for technology diversity, it is of greatimportance to study new type atomic clocks with high precision.The advantages such as simple physical operation, compactness and small size, make Rbvapor cell atomic clocks preferred for satellite navigation systems. In order to reduce the lightshift and cavity pulling shift, Pulsed Optically Pumped Rb atomic clock has been theoreticallyand experimentally studied in this thesis, in which the pumping, interrogation, and detectionphases are separated in time and during clock interrogation the atomic sample behaves as apure two-level system avoiding the coupling between microwave and optical coherences. Alaboratory POP87Rb atomic clock prototype has been realized based on the detection of selffree-induction microwave signal. Meanwhile microwave induced Autler-Townes splitting inelectromagnetic induced transparency has been studied theoretically and experimentally. Themain works and results we have accomplished are shown as followings:1．In the formalism of the ensemble-averaged density matrix and in the rotating-waveapproximation, a set of equations describing the POP clock dynamics with a three-level modelhas been obtained, the optimum physical parameters are derived, and theoretical expressionsdescribing the Ramsey pattern with microwave detection or optical detection are given. Whenatoms are submitted to π/2Ramsey pulses, theoretical study indicates that:1) with microwavedetection, the full width at half maximum （FWHM） is1/4T, and the atomic line quality factoris increased by a factor of2with respect to the traditional approaches.2) the light-shift effectmay be canceled and the cavity-pulling effect may be strongly reduced. A better medium-termfrequency stability is expected.2. The required performances and characteristics of optics and physics package havebeen analyzed, laser system, microwave cavity, Rb vapor cell, quantization field and time sequence have been developed. Theoretically studied the influence of buffer gases ratiobetween Ar to N2on temperature coefficient, and signal to noise ratio, and an optimum valuehas been found. The parameters of microwave cavity have been theoretical and experimentalstudied, such as mode, quality factor, filling facor, coupling factor etc.3. Based on the theoretical and experimental work carried out, a prototype87Rb atomicclock has been designed and realized. To reduce the light shift and cavity pulling shift, anoptimum microwave pulse area bigger than π/2has been found experimentally, by measuringthe center frequency of Ramsey fringes and the output power at end of first Ramsey pulse andsecond Ramsey pulse versus the microwave area. The Ramsey fringes in microwave andoptical domain have been measured with FWHM of65Hz and150Hz respectively. Thefrequency stability achieved is4.5×10^-13τ^-1/2（=1¹00s）, which is among the best stabilityachived by vapor cell standard in the world.4. Autler-Townes doublet splitting in electromagnetically induced transparency （EIT）induced by an additional microwave field has been studied theoretically and experimentally,in which a fourth level has been coupled to the coupeling or probe transition level of Λ-typeEIT system. The frequency difference of Autler-Townes doublets depends on microwave fieldintensity and detuning, providing a way to measure the adjacent transition frequency and theeffective microwave Rabi frequency putted on the Rb atoms in POP atomic clock. Bycontrolling the microwave field, the frequency, shape and depth of the two Autler-Townesdoublets can be manipulated, which maybe used to light storage and has potential applicationsin quantum computation.