On the nonlinearity of the process of generating nonequilibrium hot electrons in the biological tissues of the eye in optical Femto Lasik technologies during laser vision correction
Garif G. Akchurin1,2, George G. Akchurin1,3, Yuri A. Avetisyan1, Sergey V. Zarkov1, Alexander N. Yakunin1, Vladimir Yu. Maksimov3, Valery V. Tuchin1,2,4; 1Institute of Precision Mechanics and Control, Federal Research Centre “Saratov Scientific Centre of the Russian Academy of Sciences”, Saratov, Russia; 2Department of Optics and Biophotonics and Science Medical Center, Saratov State University, Saratov, Russia; 3Laser Vision Correction and Microsurgery Center, Saratov, Russia; 4Laboratory of Laser Molecular Imaging and Machine Learning, Tomsk State University, Tomsk, Russia
Abstract
Laser vision correction technologies emerged over 30 years ago with the development of mode-locked solid-state lasers capable of generating pulses with nano-, pico-, and femtosecond durations. Unlike earlier keratoplasty techniques, modern femtosecond technologies enable the separation of transparent corneal cells without physical contact, utilizing a controlled sequence of cavitational nanobubbles. A focused laser beam with a characteristic diameter of 5–7 microns creates a controllable two-dimensional surface of nanobubbles within the cornea through spatial scanning; these nanobubbles have a lifetime on the order of a nanosecond and do not heat the corneal cells. Femtosecond lasers with a wavelength of 800 nm—and a corresponding photon energy of 1.58 eV—have traditionally been used for such optical technologies. In the adopted model, the cornea is represented as a dielectric with a bandgap of 6.3 eV (water). The solution to the quantum electrodynamics problem implies that the absorption probability equals the five-photon absorption cross-section multiplied by the incident intensity raised to the fifth power. As a result, the number of hot electrons generated—which are responsible for the formation and temperature dynamics of the nanobubble that separates corneal cells—becomes proportional to the fifth power of the laser beam intensity. This relationship is of significant importance to ophthalmic surgeons and optical engineers for the precise control of the surgical corneal cell separation process.
Speaker
Akchurin Garif G.
Institute of Precision Mechanics and Control, Federal Research Centre “Saratov Scientific Centre of the Russian Academy of Sciences”, Saratov, Russia
Russia
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