ISSN 0030-400X, Optics and Spectroscopy, 2013, Vol. 115, No. 2, pp. 264–273. © Pleiades Publishing, Ltd., 2013. Original Russian Text © V.A. Sterligov, Ya.A. Gritsaienko, Ya. Men, A. Savchenko, 2013, published in Optika i Spektroskopiya, 2013, Vol. 115, No. 2, pp. 305–315. 264 1. INTRODUCTION Interaction of plasmon polaritons with different micro- and nanoobjects is a rich source of information about these objects. A number of high-sensitivity bio- logical and chemical sensors have been designed based on this process. Angular dependences of specular reflection coefficient are generally analyzed with this goal in mind. However, it was shown in [1, 2] that the use of elastic scattering of surface plasmon polaritons (SPPs) for these purposes has a number of advantages. Processing SPP scattering data yields new and valu- able information on the optical properties of surface and the objects located on it. In this study processes of SPP scattering by a dif- fraction grating (DG) were analyzed. DG was etched in a thin transparent dielectric layer, deposited on a metal film surface, along which SPPs propagate. We chose this object because it exhibited significant (by more than four orders of magnitude) enhancement of SPP scattering in comparison with scattering of S- polarized excitation light [3]. Studying the spatial distribution of the intensity of light scattered by SPPs has a number of specific fea- tures; in particular, the range of variation in this inten- sity may be as high as several orders of magnitude, and, hence, special procedures should be implemented to record intensity in these limits. Under these condi- tions, one has to measure weak signals comparable with the intrinsic photodetector noise and the level of spurious signals. Thus, lock-in detection must be used to measure correctly working signals with necessary sensitivity. In addition, normalization of measured values also calls for measuring the probe laser beam intensity, which may significantly exceed the levels of scattered light intensity. To perform these optical experiments, one should provide spatial displacement of the photodetector, a change in the angle of incidence of laser beam, etc. In principle, these experiments can be implemented on commercial equipment; however, their cost may be sev- eral hundreds of thousands of dollars in this case. Here, these problems are solved using simple and inexpensive solutions, which, however, provide fairly high characteristics of the measuring system. Using the solutions developed, we analyzed the scattering of SPPs and evanescent waves from a thin DG deposited on the metal film surface along which SPPs propagate. 2. REFRACTION OF A LIGHT BEAM BY A PRISM The Kretschmann scheme, in which a metal film is deposited on a face of a transparent prism, is often used to generate SPPs. The latter are excited by illumi- nating this film with a light beam passing through the prism. The Kretschmann scheme is shown in Fig. 1a. A laser beam is incident on the side face of the prism at a point М, is refracted on this face, and arrives at a point N on the hypotenuse face. Having denoted the angle of incidence of the refracted beam on the hypot- enuse face as Γ and the angle of incidence of the pri- mary beam with respect to the hypotenuse face plane as γ, one can show that there is a kind of analog of Snell’s law (which will be referred to as Snell’s law for a prism with an angle ψ): . ( ) ( ) sin sin n γ-ψ = Γ-ψ PHYSICAL OPTICS Enhancement of Scattering of Surface Plasmon Polaritons by Surface Defects: Technique and Results V. A. Sterligov a , Ya. A. Gritsaienko a , Ya. Men b , and A. Savchenko c a Institute of Physics, National Academy of Sciences of Ukraine, 03028 Kyiv, Ukraine b Institut für EBS, Universität Ulm, 89081 Ulm, Germany c Microbiology and Tumorbiology Centrum, Karolinska Institutet, 17177 Stockholm, Sweden e-mail: vaster04@yahoo.com Received November 19, 2012 Abstract—The intensities of scattering of surface plasmon polaritons by regular surface structures signifi- cantly exceed (by several orders of magnitude) the intensities of scattering of evanescent surface waves from these structures. When plasmon polaritons are scattered by diffraction grating grooves a few micrometers wide, the scattering from the trailing edge of a grating groove greatly exceeds the scattering level from the groove leading edge. Some of our original developments are presented that make it possible to put into effect an inexpensive software–hardware optical complex with a wide dynamic range, high sensitivity, and digital lock-in detection based on the use of a computer sound card. DOI: 10.1134/S0030400X13070199