Study On Fast Measurement Of Atomic Concentration In Rubidium DPAL

Diode Pumped Alkali vapor Lasers（DPALs）are a promising candidate for a new generation of all-electric,lightweight compact strategic high energy laser source.It is vital for the gain characteristics and the laser output level,so establishing the method and device for the real-time and on-line measurement of the alkali metal atomic concentration.The main conventional measurement method of alkali metal atom concentration is obtained by scanning and fitting the absorption spectrum of D line（5S→5P,rubidium atom D₁line 795 nm,D₂line 780 nm）at present.However,under the operation condition of DPALs,the atomic concentration is as high as 10¹³-10¹⁴cm^-3,and the strong absorption coefficient of D-line leads to the complete absorption of the probe laser in the central region of the spectrum.It is called“optically thick”.The serious loss of absorption spectrum information makes it difficult to obtain high confidence data,and the scanning method cannot realize real-time measurement.Based on the above problems,this paper proposes a measurement of rubidium atom concentration which using 420 nm（5S→6P）with a small absorption cross-section.It is able to achieve accurate and real-time measurement under the high atoms concentration.The details are as follows:1、The method of alkali metal atom concentration measurement was sorted out,combined with the actual demand of DPALs high concentration and real-time measurement.The limitations of the current D-line absorption spectrum measurement method were pointed out,The method of rubidium DPALs atom concentration measurement using 5S→6P transition was proposed for the first time in the world.2、Theoretical modeling and simulation research.The theoretical model of atomic absorption was established,and the feasibility of 420 nm measurement method was verified theoretically.The influences of gain length,medium temperature and buffer gas pressure on atomic concentration measurement were analyzed,and the applicable parameters were defined.3、The experimental research based on 420 nm atomic concentration measurement is carried out.Firstly,the measurement results of 795 nm were compared with 420 nm.The consistent test results were obtained within the common applicable concentration range(10¹¹-10¹²cm^-3),and the error is less than 7%.It verified the feasibility of the method.The applicability of the method was further verified under the higher concentration.The concentration level can be effectively extended to 10¹⁴cm^-3,which satisfied the actual operation concentration conditions of DPALs.The atomic concentrations of low and high buffer pressure rubidium gas vapor cell were measured and analyzed in real time using this method respectively.4、Extended application of the 420 nm method and carried out the real-time measurement of DPALs population distribution under pumping.The longitudinal pumping rubidium DPAL laser output is realized in QCW mode,and the efficiency is evaluated and analyzed.The time variation law of the population at 5²S_1/2level was obtained using 420 nm probe laser measurement.Combined with the analysis of quasi-two-level model,the energy level distribution states of 5²P_1/2and 5²P_3/2were calculated and made the error analysis.It also carried out to deepen the understanding of the dynamic mechanism of the laser.