Photoionization Cross Section Measurements Of The Excited States Of Aluminum In The Above-Threshold Region

The photoionization cross section is described as the probability that an electron being emitted from its electronic state while photos and atoms interact with each other.Photoionization cross section measurements of the excited states have important applicationins in numerous fields such as plasmaphysics,upper atmosphericscience and astrophysics,meanwhile it is a charcharacteristic parameter in photodissociation dynamics.However the existing data almost come from the theoretical calculations,which requires accurate experimental data to test and improve the theoretical calculation dateIn this experiment,we obtained free aluminum atoms by using laser vaporization and a supersonic gas jet.We make the photoionization cross sections measurements of the excited states of aluminum by using the technique of the laser pump-probe and resonance ionization in conjunction with a molecular beam and time of flight(TOF)mass spectrometer.The photoionization cross sections were deduced from the dependence of ion yields on the laser intensity of probe laser.Based on relation of ion signal intensity and pump-probe delay,we obtained the lifetimes of the excited states.In this experiment,we got the the(1+1)REMPI spectrum of free AlI atoms in the256nm-258 nm wavelength range.The photoionization cross section of 3s2 nd y(2D 3/2)and 3s2 nd y(2D5/2)at and above the threshold region(0.56eV-2.23eV)obtained in measurements are in the range of 6.6±0.9Mb to 3.3±0.5Mb.The upper limit of the overall root-mean-square error in the absolute photoionization cross-section measurements is 17%.And by recording the relationship between the photionization signal and the delay time between the pumb laser and probe laser,we can obtain excited state lifetimes of 3s2 nd y(2D 3/2)and 3s2 nd y(2D5/2).The lifetimes are30.7±2.3ns and 9.0±2.0ns,respectively,with an uncertainty of 5%.