NUCLEATION OF NANOPORES IN GLASS OPTICAL FIBERS UNDER INFLUENCE OF TENSILE STRESS: EXPERIMENT I. Santiago Nuñez 1 , M.G. Shlyagin 1,2* , S.A. Kukushkin 3,4,5 1 CICESE, Centro de Investigación Científica y de Educación Superior de Ensenada, Ensenada, C.P. 22860 Mexico 2 Ioffe Physical-Technical Institute, St. Petersburg 194021, Russia 3 Institute of Problems of Mechanical Engineering, Bolshoi 61, V.O., St. Petersburg, 199178, Russia 4 Peter the Great St. Petersburg Polytechnic University, Polytechnicheskaya 29, Saint Petersburg, 195251, Russia 5 ITMO University, Kronverkskiy 49, Saint Petersburg, 197101, Russia *e-mail: mish@cicese.mx Abstract. The article reports on observation of nanopores nucleated under a tensile stress in the core of the germanosilicate optical fibers doped with boron. Pores were observed with an atomic-force microscope on the faces of cleaved fiber tips. Under certain experimental conditions, pores form a quasi-periodic structure and their sizes are in a good agreement with predictions of the earlier proposed model based on the theory of phase transitions. The theoretically estimated threshold stress level for effective nucleation of pores corresponds well to the results of experimental observations. 1. Introduction Optical glass attracts considerable research interest as promising structural material for traditional applications as well as for high-tech applications in optoelectronics, lasers and optical communications. Despite the large amount of research activities performed in glasses and other brittle materials, some aspects of glass fracture and its strength still are not clear in details. The difficulty is in the complicated structure of amorphous materials and very strong influence of technological process parameters on the final properties of glass, even for glass samples with the same chemical composition. In this context, research on mechanical strength, radiation induced damage, and laser processing of glass are actual fields of scientific research in technology and physics. Oxide-based glass materials, such as fused quartz or silicate glass, are considered as typical brittle materials. Usually, glass fracture occurs without detectable deformation by a rapid crack propagation. When a critical external tensile load is applied to a uniform glass sample, the direction of crack propagation coincides well with the direction perpendicular to the tensile force vector. A commonly accepted mechanism is based on the break of interatomic bonds in the glass structure leading to a very smooth mirror-like rupture surface. However, the real technical strength of the glass is much below than the one estimated using an inter-atom bond strength. The empirical model of crack propagation in brittle solids, developed almost 100 years ago [1], is based on existence of defects (micro-cracks) operating as stress concentrators in a volume of the brittle material or on surface of the material sample. In recent years, there exists significant and increasing interest to interaction of intense laser radiation with solids. Laser processing of materials is now a rapidly progressing field of technology. In optics, a micron-size local permanent modification of the glass properties is very Materials Physics and Mechanics 29 (2016) 125-132 Received: October 17, 2016 © 2016, Institute of Problems of Mechanical Engineering © 2016, Peter the Great St. Petersburg Polytechnic University