Research On Microwave Source Technology For Portable Cold Atom Gravimeter

Atomic interferometers have shown their unique advantages in the field of precision measurement.The gravimeter based on cold atom interferometer technology has broad application scenarios in the fields of geophysical research,national defense and military.Based on the portable cold atom interference absolute gravimeter,we designed and implemented an integrated,low-noise microwave source,which is used to drive electro-optic modulator to generate high-performance Raman lasers.Besides,we proposed a scheme to generate arbitrary shapes of Raman lasers by controlling the power of microwave source and conducts related experimental tests.The main work of the paper is as follows:1.The author studied the basic principle of the Mach–Zehnder type cold atom interferometer,and analyzed the influence of phase noise between two Raman lasers on sensitivity of gravity acceleration measurement.We also analyzed the principle of stimulated Raman adiabatic passage（STIRAP）to achieve quantum state transfer.2.The author proposed a low-noise integrated microwave source scheme based on direct digital synthesizer,direct frequency multiplication and frequency mixing,and developed a microwave source system including a power stabilization module and a phase-locked loop module with a volume of 465mm×450mm×35mm.The experimental results show that the relative standard deviation of the 6.834GHz signal power is 8.5×10^-4@8h,the long-term stability of frequency is 1×10^-13@1000s,the absolute phase noise is-34.5d Bc/Hz@1Hz,-79.4d Bc/Hz@10Hz,-99.3d Bc/Hz@100Hz,-108.8d Bc/Hz@1k Hz,-113.7d Bc/Hz@10k Hz,-115.7d Bc/Hz@100k Hz,-116.8d Bc/Hz@1MHz.3.A method to generate arbitrary shapes of Raman lasers applied to STIRAP is proposed.We realized two arbitrary shapes of Raman lasers separated in time by controlling the power of the microwave source.And we realized the real-time detection of arbitrary shapes of Raman lasers by beating Raman lasers with a reference laser.The experimental results show that the actual waveform is consistent with the designed waveform.Compared with methods such as optical phase-locked loops,this method will not deteriorate the relative phase noise of Raman lasers,which is only determined by the phase noise of the microwave source.Finally,the atomic state transfer transition experiment verifies that STIRAP improves the robustness to the experimental parameters.