Purchase this article with an account.
Richard Olmstead; Model of Plasma Characteristics across the Anterior Lens and Aqueous Boundary. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1841.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study was to investigate the expected laser plasma characteristics across the anterior lens and aqueous boundaries.
A laser plasma model was developed that describes the evolution of plasma developed from focusing a short pulse laser. This model included plasma shielding characteristics in the description of the plasma evolution. The model characteristics in water where compared the moving breakdown model to validate performance. The model was then applied to the anterior boundary between the lens and the anterior chamber where the characteristics of the boundary was described by using an energy level model to represent the different constituents of the boundary. The aqueous, capsule, and fibrous mass were modeled having a binding energy of 6.5eV, 7.5eV, and 6.8eV respectively. The focal position of the laser pulse in an F/4 system relative to the boundary was then analyzed to determine the characteristics of the laser interaction across the boundary. The threshold for plasma ignition was defined as 10^21 electrons/cm^3.
Laser plasma characteristics vary corresponding to approximate location relative to the anterior lens and aqueous boundary. The ignition points of plasma along the laser pulse vary corresponding to the threshold condition necessary to ignite the various materials that the laser is focused across. Additionally, plasma shielding resultant from plasma ignition further upstream can shield plasma formation in the capsule resulting in the capsule not being completely dissected by the laser plasma. The plasma model predicted this for a laser pulse that was 3 times the plasma threshold focused 100 microns from the capsule in the fibrous mass of the lens.
Our model describes the plasma evolution across the boundaries of three materials where the Rayleigh range of the focused laser pulse overlaps the boundaries of the materials. This results in interesting plasma evolution characteristics that can be described by looking at the boundary as a varied energy level system. Our model is indicative of requirements on axial placement of a laser beam relative to a boundary where the incident pulse interacts with multiple materials in one pulse of a laser. This is of importance if the plasma is intended to be used to dissect tissue.
This PDF is available to Subscribers Only