Current generation by running holographic gratings and photo-induced self-organization in the suspension of microorganisms

Summary form only given.We have observed nonlinear optical and photoelectric responses in suspensions of microorganisms (different species of algae). Also we have seen a self-organization of the laser scattering in the circular rings for different tested wavelengths (633, 474, and 515 nm with power /spl sim/0.05-0.1 mW). A light beam from a He-Ne laser at 633 nm was used to look at special structures generated by a suspension of Chlamydomonas renhardtii. The incident power, 6 mW of unexpanded beam with a diameter of 2 mm, resulted in algae moving along helical trajectories away from the light spot. First, the algae began to move clockwise and then, after 1-2 min they moved counterclockwise. If a small spot was brought on the cuvette, the algae manifested negative phototaxis such that all the algae concentrated in the upper and bottom parts of the cuvette after moving away from the illuminated area. The transmission increased to about 1.3 times for the beam at wavelength 633 nm. No positive phototaxis was detected at any laser wavelength. A current of about 100-120 nA was detected under light illumination of 10 mW/cm/sup 2/ and without running fringes. After the grating began to move, there was a distinct change of electric current up to 900-1000 nA. The change of direction of running fringes resulted in the current changing its sign. The value of the current does not depend on the speed on the running fringes, which was varied from 0 to 10/sup 3/ /spl mu/m/sec. Further, there was a drop of of current with time. After 2-3 h of illumination of the cuvette with running fringes, there was a degradation of the current down to 100 nA corresponding to illumination without running fringes.