Two-Dimensional simulation of thermal blooming effects in ring pattern laser beam propagating into absorbing CO2 gas

Thermal blooming has been evaluated numerically in two-dimensional for CO2 laser beam transmitting through high pressure CO2 gas. Thermal blooming occurs when a portion of the laser beam is absorbed when transmitted through an absorbing medium such as atmosphere. High pressure gas medium is very useful for experimental simulations. In our calculation the beam was assumed to have an initially ring pattern. The ring pattern beam can be generated by unstable resonators. Using ray optics theory as well as wave optics, the transmission of such beam was assessed through the CO2 gas and the results were compared. Both the blooming effect and the wind effect were considered in the calculations. The results show a major deformation occurs on the beam due to blooming effect. According to these results, unlike the Gaussian beam in which a ring pattern formed through the propagation into an absorbing media, for the ring pattern beam, in the absence of the gas flow, a symmetrical twofold pattern is formed due to blooming effect. The results also show that such symmetry can be deformed in the presence of the gas flow. The calculations also show that the wave optics gives mu ch precise results especially for the small Fresnel numbers ) 1 / ( 2 ≈ = z ka N f , while those of the ray optics theory is valid only for high Fresnel numbers.