Nonresonance mechanisms of biological effects of coherent and incoherent light

Two mechanisms of the nonresonance action of light on biological systems are considered. The first of them is caused by gradient effects arising upon interaction of a biological system with spatially inhomogeneous radiation. The second mechanism is determined by light-induced dipole-dipole interactions between biological particles. The first mechanism is characteristic of coherent radiation. A speckle structure arising upon interaction of coherent light with a biological system gives rise to gradient forces, which depend on the intensity of the incident light and the properties of an object. It is shown that the action of the gradient forces on microparticles causes a selective increase in the kinetic energy of the particles. Due to random pulsations of speckles in living tissue, this effect is equivalent to an increase in the “partial” temperature of the particles, which depends on their size and properties. The second mechanism manifests itself both upon coherent and upon incoherent irradiation of a biological object. This mechanism is determined by interactions between oscillating dipole moments of neighboring particles (cells, organelles, biomolecules) induced by incident radiation. The second mechanism is shown to be observed for linearly polarized radiation only. For each mechanism, the forces acting on biological particles are calculated.