A New Method for Exposing Mammalian Cells to Intense Laser Radiation Using the Evanescent Fields Created in Optical Waveguides

Abstract

A new technique using optical waveguides has been developed for studying the effects of moderate to high power laser radiation on cells [1]. A monolayer of attached cells covering a wide area on the waveguide surface is exposed to the evanescent tail produced by the propagating waveguide mode. The optical radiation-cell interaction is limited to involve only the high power density and intense electric field strength associated with the evanescent tail. It is well established that extremely high power densities (10⁵ to 10⁸ watts/ cm²)are obtained in the waveguide when a waveguide mode is excited by a moderate power (1–2 watts), continuous wave (CW) laser [2–3]. These optical power densities create intense electric fields at optical frequencies ranging from 10³ to 10⁵ volts/cm within the waveguide. The evanescent tail of such a waveguide mode extends into the medium above the waveguide and creates an intense electric field at the interface between the waveguide and the medium. By adjusting the input laser power and waveguide parameters, the electromagnetic field intensity and distance of penetration into the cell of the evanescent tail can be varied over a wide range. The importance of intense electromagnetic field induced kinetic effects and photochemical reactions in producing lethal effects in cells has been stressed by previous investigators [4–6]. This report describes the reduced survival measured for monolayers of EMT-6 mammary sarcoma cells exposed to the evanescent tail created in a waveguide.