It is well known in spectroscopy of complex organic molecules that the large width of their absorption and emission bands is largely due to the existence of a continuous set of vibrational sublevels in each electronic state. The spectroscopic properties of dye molecules in solution are in addition influenced by the surrounding medium.(1-3) For several decades it had been believed that because of the fast energy exchange between the vibrational sublevels the fluorescence spectrum of organic dye in solution was independent of the frequency of the exciting light. In 1970 it was shown (4) for the first time that apart from molecular vibrations there is another cause of the substantial broadening of electronic spectra of organic molecules in solution, namely, the fluctuations of the structure of the solvation shell surrounding the molecule. The variation of the local electric field caused by the fluctuation of the shell structure leads to a statistical distribution of the frequencies of the electronic transitions of the molecules and, therefore, to inhomogeneous broadening of the dye spectrum.This broadening was experimentally demonstrated (4)(5)(6) from the dependence of the fluorescence spectrum of a dye solution on the exciting radiation frequency at 77°K. Later, Personov et al.(7) observed inhomogeneous broadening of electronic spectra from frozen solutions of complex molecules at lower (liquid helium) temperatures. It was shown that at liquid helium temperatures discrete fluorescence spectra of complex molecules with

A new approach to the understanding of biological activity caused by low-intensity laser radiation, in which coherence is a factor of paramount importance, has been developed. It is based on the dipole interaction of gradient laser fields with cells, organelles and membranes. The laser intensity gradients in an object arise due to the interference of the light scattered by the tissue with the incident light beam (speckle formation). Apart from speckles, different types of light spatial modulation can be created deliberately using different schemes for beam interference.It is shown that gradient laser fields may cause spatial modulation of the concentration of particles and increase their ‘partial temperature’. This paper presents the results of experimental observation of trapping of different types of particles, including human lymphocytes, in the interference fields of the He–Ne laser. The sweep-net effect on particles of different sizes on moving the laser field is demonstrated and crystal-like self-organization of particles in the laser gradient field is observed.The influence of gradient laser fields on erythrocyte rouleaus, on the apoptosis of human lymphocytes as well as on their chromosome aberrations is demonstrated. It may be concluded from the experimental studies that the influence of an interference laser field with a rightly chosen period can stimulate the repair system of a cell, increasing its viability.

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