_____________ Received July 2005; in final form December 2005. ROMANIAN J. BIOPHYS., Vol. 16, No. 1, P. 63–67, BUCHAREST, 2006 POLARIZATION CHANGES ON TRANSMITTED LASER LIGHT BY A POLYETHYLENE FILM SIMONA DONłU*, TEODORA BREZEANU*, ESOFINA RISTICI*, C. COTÎRLAN*, D. SAVASTRU * , M. RISTICI** , ELEONORA NEME***, ELENA GROSU***, C. OPRAN**** *National Institute of C&D for Optoelectronics INOE-2000, Bucharest **Faculty of Physics, University of Bucharest ***National Institute of C&D for Plastics – INCERPLAST, Bucharest ****“Politehnica” University, Bucharest Abstract. Advances at the plastics manufacturing level in such areas as co-extrusion and the production of specialty polymers and additives, result in the availability of plastics with improved characteristics. We have produced an agricultural photo-selective three layer co-extrusion film, manufactured at a thickness of about 200 μm. The film was made from different types of LDPE and LLDPE for each layer, and special chemical additives were incorporated into the polymers matrixes. Key words: photo selective polyethylene film, PAR (Photosynthetic Active Radiation), He-Ne monochromatic laser, light polarization. INTRODUCTION Light is the main factor responsible for plant growth, as it drives photosynthesis [1]. Plants absorb radiation of 400–700 nm, called PAR (Photosynthetic Active Radiation) in their chlorophyll cells and use it as energy for photosynthesis [2]. To understand the impact of greenhouse glazing on crop production, we have to investigate how light interacts with cladding materials. Based on physical properties, surface orientation, and the number of layers of the glazing material, portions of the incoming light are either transmitted, scattered and/or absorbed. Polymers and particularly polyethylene film were not sufficiently studied for different applications and therefore did not meet all the requirements for agriculture. For this reason, a large number of additives were rapidly developed to improve the performances of these polymers in this original application [3, 4]. In this paper, using red and yellow laser monochromatic radiations, radiation from the middle of PAR range, the influence of the polyethylene film on the polarization properties of the light is studied. The results obtained lead to the