Document Type : Research Paper

Authors

• S. Beheshtipour
• J. Karimisabet ¹
• R. Neshati ²
• D. Ahadpour ²

¹ Nuclear Fuel Cycle Research School, Nuclear Science and Technology Research Institute, AEOI, P.O.Box: 11365-3486, Tehran - Iran

² Photonic and Quantum Technologies Research School, Nuclear Science and Technology Research Institute, AEOI, P.O.Box: 14395-836, Tehran – Iran

Abstract

In this research, temporal variations in intense TEA CO2 laser pulses passing through SF6 gas-filled cells with a pressure of 10- 150 mbar have been characterized at different energy fluences and gas pressures. It has been shown that for every fluence there is a certain cut-off pressure at which the pulse spike is completely quenched. While the pulse tail escapes, saving appreciable fractions of its initial energy. Experimental evidence along with FTIR spectrometry data have clearly revealed incisive laser-induced multi-photon dissociation of SF6 molecules in these conditions, pronounced as the main responsible for these behaviors.

Highlights

1. O. Wood, P. Gordon, S. Schwarz, Saturation of infrared absorption in gaseous molecular systems, IEEE J. Quantum Electron, 5(10), 502-513 (1969).

 

2. C.K. Rhodes, A. Szöke, Transmission of Coherent Optical Pulses in Gaseous SF6, Phys. Rev. Lett., 184(1), 25 (1969).

 

3. J. Armstrong, O. Gaddy, Saturation behavior of SF6 at high pressure and laser intensity, IEEE J. Quantum Electron., 8(10), 797-802 (1972).

 

4. H. Stafast, W.E. Schmid, K.L. Kompa, Absorption of CO2 laser pulses at different wavelengths by ground-state and vibrationally heated SF6, Opt. Commun., 21(1), 121-126 (1977).

 

5. E.A. Ballik, et al., High pressure SF6 pulse transmission near 10.4 μm, Can. J. Phys., 55(22), 1956-1961 (1977).

 

6. B.K. Garside, R.S. Taylor, E.A. Ballik, Saturation characteristics of SF6 absorption at the 10.4 μm band of CO2, Can. J. Phys., 55(10), 849-854 (1977).

 

7. I. Kitazama, Nonlinear absorption of SF6 with He and H2 additives for a TEA CO2 laser, Opt. Commun., 53(1), 27-32 (1985).

 

8. T.F. Deutsch, S.R.J. Brueck, ν3 mode absorption behavior of CO2 laser excited SF6, J. Chem. Phys., 70(5), 2063-2073 (1979).

 

9. I. Kitazima, H. Iwasawa, Slow Relaxation Processes in SF6 Gas After Pumping by a CO2 Laser Pulse, Laser Chemistry, 11(1), 39-48 (1991).

 

10. H. Kleiman, S. Marcus, CO2 laser pulse shaping with saturable absorbers, J. Appl. Phys., 44(4), 1646-1648 (1973).

 

11. V.N. Bagratashvili, V.N. Burimov, A.P. Sviridov, Change in the profile of a high-power infrared laser pulse during its passage through an absorbing molecular gas, Sov. J. Quantum Electron., 15(2), 283 (1985).

 

12. I. Burak, J.I. Steinfeld, D.G. Sutton, Infrared saturation in sulfur hexafluoride, J. Quant Spectrosc Radiat Transf, 9(7), 959-980 (1969).

 

13. R.S. Taylor, et al., A vibrational‐bath model for the dynamics of SF6 absorption near 10.4 μm as a function of wavelength and absorbed energy, J. Appl. Phys., 48(11), 4435-4443 (1977).

 

14. K. Silakhori, et.al., Utilizing NH3 laser pulses in multiphoton dissociation process of CCl4 molecules with 13C isotope selectivity, JonSat, 30, 38-45 (2009), (In Persian).

 

15. E.P. Velikhov, et al., Isotope separation by multiphoton dissociation of molecules with high-power CO2 laser radiation, I. Practical Methods, Quantum Electron, 9(2), 179 (1979).

 

16. K.J. Olszyna, et al., Megawatt infrared laser chemistry. II. Use of SiF4 as an inert sensitizer, Tetrahedron Lett., 18(19), 1609-1612 (1977).

 

17. A.T. Znotins, Absorption Properties of SF₆ near 10.6 µm, M.S.C thesis., McMaster University, (1978).

 

18.P. Mathieu, G. Otis, High Efficiency, Tail-Free Pulses From TEA-CO2 Lasers, In Laser Radar Technology and Applications I, 663, 74-78, SPIE. (1986).

 

19. P. Deb, U.K. Chatterjee, A model for short pulse absorption in a real SF6 saturable absorber, Opt. Quantum Electron, 25, 113-122 (1993).

 

20. J.L. Lyman, S.D. Rockwood, S.M. Freund, Multiple‐photon isotope separation in SF6: Effect of laser pulse shape and energy, pressure, and irradiation geometry, J. Chem. Phys., 67(10), 4545-4556 (1977).

 

21. J.G. Black, et al., Collisionless Multiphoton Dissociation of SF6: A Statistical Thermodynamic Process, Phys. Rev. Lett., 38(20), 1131 (1977).

Keywords

• CO2 laser pulse shaping
• Multiphoton dissociation
• SF6