ISSN 1060-992X, Optical Memory and Neural Networks (Information Optics), 2010, Vol. 19, No. 4, pp. 330–337. © Allerton Press, Inc., 2010. 330 1. INTRODUCTION Laser tweezers, also known as (single beam gradient force) optical traps, are based on pN force gener- ation during the interaction of highly focused laser beams with dielectric particles, including cells and organelles. Light, as a carrier of momentum, exerts pressure which can be used to accelerate particles. If a light beam of sufficient radiation pressure is directed against gravity, particles can be transduced into “gravity- free” conditions. As a spin-off of Ashkin’s initial studies on optical particle trapping, optical cell micro- manipulation by laser light became possible [1]. By focusing a single laser beam with a high numerical aperture (NA) objective, a gradient field of light intensity is created with the highest intensity values in the focal volume and the lowest in the periphery. Inter- action with objects of a higher refractive index than the surrounding medium results in the formation of gra- dient forces. If the interaction is primarily determined by beam refraction and when the absorption is negli- gible, the net force acts toward the focal volume. The net force (trapping force) of the order of pN can be used to “pull” and to confine micrometer- and nanometer-sized objects in the focal volume (Fig. 1). When using highly focused near infrared (NIR) laser beams (micro-beams), pigment-free cells can be optically trapped and manipulated in three dimensions without physically touching them. In particular, contact-free cell movement can be performed by changing the foci of the laser beam in the desired direc- tion. Alternatively, the stage with the sample can be moved without displacement of the trapped cell. Typical laser sources for optical trapping are the Nd:YAG laser at 1064 nm and laser diodes. Often, the laser beam is coupled by light fibres or directly to a microscope with CCD camera and focused to a dif- fraction-limited spot by objectives with NA > 1. Motor-driven mirrors in combination with joy-sticks allow manoeuvring the position of the tweezers [2]. Simulation of Lazer Light Propagation and Thermal Processes in Red Blood Cells Exposed to Infrared Laser Tweezers (λ = 1064 nm) I. Krasnikov a , A. Seteikin a , and I. Bernhardt b a Amur State University, 21, Ignat’evskoe shosse, Blagoveshensk, 675021 Russia b Universitat des Saarlandes, P.O. Box 151150, Saarbrucken, Germany, D-66041 e-mail: drpooh@mail.ru, seteikin@mail.ru, i.bernhardt@mx.uni-saarland.de Received October 22, 2009; in final form, September 20, 2010 Abstract—Continuous-wave laser micro-beams are generally used as diagnostic tools in laser scan- ning microscopes or, in the case of near-infrared micro-beams, as optical traps for cell manipulation and force characterization. Because single beam traps are created with objectives of high numerical aperture, typical trapping intensities and photon flux densities are in the order of 10 6 W/cm 2 and 10 3 cm –2 s –1 , respectively. These extremely high fields may induce two-photon absorption processes and anomalous biological effects. We studied effects occurring in red blood cells (RBCs) radiated by near-infrared laser tweezers λ = 1064 nm). The main idea of our study was to investigate the thermal reaction of RBCs irradiated by laser micro-beam. It is supported by the fact that many experiments have been carried out on RBCs using laser near infrared tweezers. Usually they are relatively long last- ing and the thermal aspects of such experiments are not examined. In the present work it has been identified that the laser affects a RBC with a density of absorbed energy at approximately 10 7 J/cm 3 , which causes a temperature rise in the cell of about 10–15°C. Keywords: laser tweezers, red blood cell, Monte-Carlo method, heat-conduction. DOI: 10.3103/S1060992X10040119