Laser-induced profile modification: Effect of electron response

Abstract

Physical processes which occur at the critical surface such as resonance absorption and scattering of the incident laser light are very sensitive to the exact form of the laser induced density profile. The presence of ‘‘overdense bumps’’ in density profiles has been seen experimentally and calculated theoretically using a simple isothermal model. These structures are important, in that they could, in an experimental situation, reflect a significant amount of light before it reaches the critical surface and considerably affect the physics occuring within a laser pellet target. A generalization of a previous calculation by using an arbitrary equation of state (density response of the electrons to the electrostatic potential φ) of the form ρ=ρ(φ) is obtained. In particular, two models for the electronic response (one including the effects of the presence of trapped electrons within the overdense shock structures) calculating the resulting effect on the produced density profiles are investigated. Qualitatively, it is found that the presence of overdense structures and their one-dimensional stability within an underdense plasma is unaffected by the more general electronic response. Conditions for the existence of these structures are discussed and a detailed comparison with full particle in cell (PIC) code simulations is made, emphasizing the trapped electron model where excellent agreement is obtained.