Modeling laser beam-rock interaction.

Leong, K. H.

Argonne National Laboratory

关键词: Heat Flux;    Reflection;    Photons;    Heat Transfer;    Absorption;   

DOI  :  10.2172/822584
RP-ID  :  ANL/TD/TM03-03
RP-ID  :  W-31-109-ENG-38
RP-ID  :  822584

美国|英语

来源: UNT Digital Library

【 摘 要 】

The optimal use of lasers requires the understanding of the primary parameters pertinent to laser beam-material interactions. Basically, the laser beam is a heat source that can be controlled to deliver a wide range in intensities and power. When interacting with a material, reflection at the surface, and transmission and absorption through the material occur. The material interaction process is governed by the irradiance (power/unit area) of the incident beam and the interaction time resulting in an amount of heat/energy applied to the material per unit area. The laser beam is a flexible heat source where its intensity and interaction with materials can be controlled by varying the power and size of the beam or the interaction time. For any material, a minimum amount of energy has to be absorbed for the material to be ablated by the laser beam, i.e., a solid has to be heated to liquefy and then vaporize. Under certain conditions, the photon energy may be able to break the molecular bonds of the material directly. In general, the energy absorbed is needed to vaporize the material and account for any heat that may be conducted away. Consequently, the interaction is a heat transfer problem. The relevant parameters are the heat flux and total heat input to the material. The corresponding parameters for the laser beam- material interaction are the irradiance of the beam and the interaction time. The product of these two parameters is the energy applied per unit area. A high irradiance beam may be able to ablate a material rapidly without significant heat transfer to surrounding areas. For drilling or cutting materials, a high intensity beam is required for laser ablation with minimal heat lost to the surrounding areas. However, at high beam irradiance (>1 GW cm{sup -2} for Nd:YAG beams), plasma formed from ionization of gases and vapor will partially absorb or diffract the beam. Reduced penetration of the material results. Similarly, in welding using CO2 lasers where the beam irradiance is {approx}1 MW cm{sup -2}, the plasma plume formed decreases penetration. A high velocity jet of inert gas is usually used to blow away the plasma.