Laser‐induced thermoelastic deformation: A three‐dimensional solution and its application to the ablation of biological tissue

Abstract

Under certain conditions, laser light incident on a target material can induce an explosive removal of some material, a process called laser ablation. The photomechanical model of laser ablation asserts that this process is initiated when the laser-induced stresses exceed the strength of the material in question. Although one-dimensional calculations have shown that short pulsed lasers can create significant transient tensile stresses in target materials, the stresses last for only a few nanoseconds and the spatial location of the peak stresses is not consistent with experimental observations of material failure in biological tissues. Using the theory of elasticity, analytical expressions have been derived for the thermoelastic stresses and deformations in an axially symmetric three-dimensional solid body caused by the absorption of laser light. The full three-dimensional solution includes three stresses, radial, circumferential and shear, which are necessarily absent in the simple one-dimensional solution. These stresses have long-lived components that exist for eight orders of magnitude longer in time than the acoustic transients, an important point when the details of dynamic fracture are considered. Many important qualitative features are revealed including the spatial location of the peak stresses, which is more consistent with experimental observations of failure.

The thermoelastic basis of short pulsed laser ablation of biological tissue.

“…In this regime we have been able to obtain an analytical solution by setting &2u/dt2 = 0 in Eq. 1 (10). We use this result to check that the numerical solution in regime 2 approaches the analytical solution in regime 3 as time approaches infinity.…”

Dynamics of laser induced thermoelastic expansion of native and coagulated ex-vivo soft tissue samples and their optical and thermo-mechanical properties

“…Since the numerical solutions of the wave equation require excessive computation time and resources, they are not used to describe all of dynamics for the thermoelastic expansion. However a solution to the thermoelastic wave equation when a range of properties for biological tissues are applied leads to three distinguishable time regimes [5]; the first regime is shortly after the pulse when the internal stresses resulting from the nonuniform temperature distribution cause thermoelastic deformation of the absorbing area. The time scale of this regime is determined by the optical attenuation depth and speed of sound in the sample (for soft tissues like liver around few hundred nanoseconds).…”

Laser ablation of human tooth

“…1-7 Laser-teeth interaction has gained lot of importance in the past few years. 9 Interaction of ultraviolet ͑UV͒ lasers with teeth has recently gained importance. It can be used to provide temporary laser-induced analgesia of teeth during dental procedures.…”