الفهرس | Only 14 pages are availabe for public view |
Abstract CO2 molecule is one of the most thoroughly investigated molecules because it is common in our planetary atmosphere and it is also the principal constitute gas of CO2 laser. In this work, numerical simulations have been used to study laser induced break-down in CO2 gas and the interaction of a laser induced plasma. The formulations are based on an electron cascade model previously developed by Evans and Gamal. This model solves numerically the time-dependent Boltzmann equation simultaneously with a set of rate equations describing the population density of the formed excited states. It includes the possible kinds of interactions between electrons, molecules and photons. Calculations are carried out under the experimental conditions of Simeonsson and Miziolek where molecular CO2 at the atmospheric pressure is irradiated with the first four harmonics of a Nd: YAG laser that cover a wavelength range from the near infrared to the UV (1064, 532, 355 and 266 nm) with pulse duration varies as 8 ns for the wavelength 1064 nm and 7 ns for the shorter three wavelengths. The experimentally determined threshold irradiance in this measurements is found to be 2.2 1010, 1.81010, 3.01010 and 1.01010 W/cm2 in a descending manner with the laser wavelengths respectively. Taking all these considerations into account, calculations are carried out using a computer program written in Fortran 77 to investigate the phenomenon of laser induced breakdown in CO2 gas. |