Study On Ionization Diagnosis In Hydrocarbon-Free Diode Pumped Rubidium Vapor Laser

The diode pumped alkali vapor lasers(DPALs)combine the advantage of electrically driven and compact configuration of solid-state lasers and the advantage of high efficient convective thermal management of gas lasers,which has the most potential as the candidate for the megawatt laser system.Although DPAL works among the typical three-level scheme,it has multiple high levels with low ionization energy which contributes to the effects of high-level transition and ionization during the operation of the laser system.Those effects have several negative effects on the performance of DPALs and may become more obvious in high power scaling.To deal with this problem,we carry out the research of experiment and theory.1.A multi-level flowing gas model for DPALs is established and the performance of laser is simulated.Consider the relaxation channels involved high-level atoms including the process of radiation and collision based on the three-level model.Establish the multi-level flow model of DPAL coupled with the temperature and flow field;stimulate the quality of hydrocarbon-free Rb DPAL and analyses the impact on the laser of different high-level process.The result indicates that the process of photoionization and energy pooling contribute the most part to the degree of ionization of the system while the high-level processes have limited influence on the laser efficiency(<2%).The quenching effect shows the greatest influence on the laser efficiency and leads to its decrease(~8%).2.The impact of plasma on the pump process and the laser power transmittance are analyzed.By comparing the resonate plasma frequency and the frequency of laser light field,the simulation result shows that the plasma in DPAL leads no absorption of pump and laser light.3.The experiment of hydrocarbon-free Rb DPAL is carried out under the following condition:pump power density:2.6kW/cm~2,pump length 2cm,the pressure of buff gas,6atm He.Study waveform of pump light and laser,the impact of pump intensity and temperature of gain medium and the factors which influences the efficiency of laser.4.The experiment of ionization degree diagnosis under the operation of DPAL is carried out and achieved the maximum ionization degree 0.0089%with pump power density 2.6kW/cm~2 and the temperature of gain cell of 165?under the condition of quasi-CW pump.Conduct the experiment of CW pump and the result shows that the lasers power decreased with time and suspended after 50s which is the consequence of heat accumulation without active thermal management.The maximum degree of ionization is 0.57%under CW pump condition.The increase of ionization degree relates with the process of high-level stimulation and ionization which have been enforced by the temperature raise.5.The main reason for the low efficiency of DPAL in the experiment is the lager energy loss of the window of gain cell whose single-pass transmittance is only 70%.Conduct the design of the nanostructure of window applied in DPAL with the consider of the characteristic of corrosivity and adsorbability of alkali atom and the existing anti-reflection and anti-adsorbability structure and calculate the impact of this nanostructure as the window on the resonant mode.