Transient Evolution Of Laser Pumped Magnetic Resonance In Rubidium Vapor

Spectroscopy research based on spin transient coherent effect can provide a lot of information about the microscopic dynamics of matter.It is an important branch of spectroscopy.It has been more than 50 years since the discovery of photon transient coherent effect in 1964.As for the transient evolution of atomic optical magnetic resonance,researches are gradually paying attention to it.With the rapid development of atomic magnetic measurement based on optical magnetic resonance,the study of transient coherent effect in optical magnetic resonance is becoming more and more important.In this paper,firstly,we built a research platform of rubidium atom optical magnetic resonance.In the experiment,one laser beam acts as the pump light and the probe light at the same time.After passing through a paraffin-coated rubidium atom cell,the laser is detected by a photodiode.By scanning the frequency of the RF field,we can get the transmitted light intensity curve as a function of RF frequency,as known as the optical magnetic resonance signal.Atomic magnetometer based on optical magnetic resonance can measure the external magnetic field by the RF frequency value corresponding to the resonance peak.We analyzed the variation of peak line width with various laser power,RF power and other parameters at the laboratory temperature of 20?,to optimize the optical magnetic resonance signal with better signal noise ratio.Secondly,by increasing the frequency scanning rate of RF field,we observed the transient evolution of optical pump magnetic resonance in rubidium atoms.In the case of high frequency scanning rate of RF field,the traditional Lorentz line shape of optical magnetic resonance signal will become asymmetric,and a small oscillation will gradually appear on the right side,then we study the influence of different laser power and RF power.Thirdly,in order to study the characteristics of the oscillation,we suddenly turn on the RF field to the resonance Lamor frequency,and find the transmitted signal is in the form of sinusoidal damping decay.Furthermore,we analyze the evolution of the oscillation frequency and decay rate with the intensity of RF field and laser power,and find that the oscillation frequency is almost proportional to the amplitude of RF field.Moreover,when the laser power is small,the RF field plays a major role in decay rate,while when the laser power is large,the RF field basically has no effect on decay rate.Furthermore,when the RF amplitude is larger,the transient evolution is insensitive to the laser power.Finally,we numerically calculate the transient coherent effect in various cases of optical magnetic resonance by using the four-level density matrix equation.The theoretical calculation is very consistent with the experimental results,and further explain the dynamic evolution of this transient phenomenon.We hope that our experimental and theoretical explanation will be helpful to people's understanding of transient coherent effects and to atomic magnetic measurement based on optical magnetic resonance.