Numerical Investigation of the Tri-Atomic Ions Formation during Laser Ionization Based on Resonance Saturation

M. A. Abdelati^1*, M. A. Mahmoud², Y. E. E. Gamal¹

¹National Institute of Laser Enhanced Sciences, Cairo University, El Giza, Egypt.
²Physics Department, Faculty of Science, Sohag University, Sohag, Egypt.

DOI: 10.4236/jamp.2014.212131                

Abstract

We present a theoretical investigation of plasma generation in sodium vapor induced by laser radiation tuned to the first resonance line (3S-3P) at λ = 589 ns. A set of rate equations that describe the rate of change of the ground and excited states population as well as the temporal variation of the electron energy distribution function (EEDF), beside the formed atomic ion Na+, molecular ion  and tri-atomic ions are solved numerically. The calculations are carried out at different laser energy and different sodium atomic vapor densities under the experimental conditions of Tapalian and Smith (1993) to test the existence of the formed tri-atomic ions. The numerical calculations of the electron energy distribution function (EEDF) show that a deviation from the Maxwellian distribution due to the super elastic collisions effect. In addition to the competition between associative ionization (3P-3P), associative ionization (3P-3D) and Molnar-Horn- beck ionization processes for producing , the calculations have also shown that the atomic ions Na+ are formed through the Penning ionization and photoionization processes. These results are found to be consistent with the experimental observations.

Keywords

Plasma, Laser, Collisional Ionization, Association Ionization, Tri-Atomic Ions, Photoionization, Electron Energy Distribution Function

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Lucatorto, T.B. and McIlrath, T.B. (1976) Efficient Laser Production of a Na+ Ground-State Plasma Column: Absorption Spectroscopy and Photoionization Measurement of Na+. Physical Review Letters, 37, 428. http://dx.doi.org/10.1103/PhysRevLett.37.428
[2]	Carre, B., Roussel, F., Spiess, G., Bizau, J.M., Gerard, P. and Wuilleumier, F. (1986) Zeitschrift für Physik D Atoms, Molecules and Clusters, 1, 79.
[3]	Stacewicz, T., Gorbunov, N.A. and Kozlowski, P. (1998) Excitation of Sodium Atoms by 330-nm Laser Pulses. Applied Physics B, 66, 461-465. http://dx.doi.org/10.1007/s003400050419
[4]	Leonov, A.G., Chekhov, D.I. and Starostin, A.N. (1997) Mechanisms of Resonant Laser Ionization. JETP, 84, 703-715. http://dx.doi.org/10.1134/1.558204
[5]	Gorbunov, N.A., Grochola, A., Kruk, P., Pietruczuk, A. and Stacewicz, T. (2002) Studies of Electron Energy Distribution in Plasma Produced by a Resonant Laser Pulse. Plasma Sources Science and Technology, 11, 492. http://dx.doi.org/10.1088/0963-0252/11/4/316
[6]	Kosarev, N.I. and Shaparev, N.Ya. (2006) Resonance Laser-Induced Ionisation of Sodium Vapour Taking Radiative Transfer into Account. Quantum Electronics, 36, 369. http://dx.doi.org/10.1070/QE2006v036n04ABEH013153
[7]	Tapalian, C. and Smith, W.W. (1993) Chemical Physics Letters, 211, 425.
[8]	Mahmoud, M.A. (2005) Electron Energy Distribution Function in Laser-Excited Rubidium Atoms. Journal of Physics B: Atomic, Molecular and Optical, 38, 1545. http://dx.doi.org/10.1088/0953-4075/38/10/012
[9]	Mahmoud, M.A. and Gamal, Y.E.E. (2012) Kinetics of Plasma Formation in Sodium Vapor Excited by Nanosecond Resonant Laser Pulses. Indian Journal of Physics, 86, 659-666. http://dx.doi.org/10.1007/s12648-012-0093-3
[10]	Measures, R.M. (1977) Efficient Laser Ionization of Sodium Vapor—A Possible Explanation Based on Superelastic Collisions and Reduced Ionization Potential. Journal of Applied Physics, 48, 2673. http://dx.doi.org/10.1063/1.324135
[11]	Vriens and Smeets, A.H. (1980) Physical Review A, 22, 940.
[12]	Drawin, H.N. and Felenbok, P. (1965) Data for Plasma in Local Thermodynamic Equilibrium. Gauthier-Villarrs, Paris.
[13]	Kushawaha, S.V. and Leventhal, J.J. (1982) Associative Ionization in Laser-Excited Sodium Vapor. Physical Review A, 25, 346. http://dx.doi.org/10.1103/PhysRevA.25.346
[14]	Babenko, E., Tapalian, C. and Smith, W.W. (1995) Associative Ionization in Laser-Excited Sodium 3p+3d Collisions. Chemical Physics Letters, 244, 121-126. http://dx.doi.org/10.1016/0009-2614(95)00878-8
[15]	Allegrini, M., Alzetta, G., Kopystynska, A., Moi, L. and Orriols, G. (1976) Electronic Energy Transfer Induced by Collision between Two Excited Sodium Atoms. Optics Communications, 19, 96-99. http://dx.doi.org/10.1016/0030-4018(76)90394-1
[16]	Huennekens, J. and Gallagher, A. (1983) Cross Sections for Energy Transfer in Collisions between Two Excited Sodium Atoms. Physical Review A, 27, 771. http://dx.doi.org/10.1103/PhysRevA.27.771
[17]	Aymar, M., Luc-Koenig, E. and Combert-Farnoux, F. (1976) Theoretical Investigation on Photoionization from Rydberg States of Lithium, Sodium and Potassium. Journal of Physics B: Atomic and Molecular Physics, 9, 1279. http://dx.doi.org/10.1088/0022-3700/9/8/013
[18]	Laughlin, C. (1978) One- and Two-Photon Ionisation of the 3s and 3p States of Na I. Journal of Physics B: Atomic and Molecular Physics, 11, 1399. http://dx.doi.org/10.1088/0022-3700/11/8/011
[19]	Geltman, S. (1977) Journal of Physics B: Atomic and Molecular Physics, 10, 3507.
[20]	Bezuglov, N.N., Klyucharev, A.N. and Sheverev, V.A. (1987) Associative Ionisation Rate Constants Measured in Cell and Beam Experiments. Journal of Physics B: Atomic and Molecular Physics, 20, 2497. http://dx.doi.org/10.1088/0022-3700/20/11/018