# Optical Effects Induced by Bloch Surface Waves in One-Dimensional Photonic Crystals
## 3 Vizualization and Scattering  
Since the BSWs are surface waves, the surface roughness has a significant effect on their propagation. This effect is well known for the SPPs [27]. Depending on the degree of roughness, its presence leads to an increase in the angular width and a decrease in depth of the surface wave resonance, as well as to rescattering the wave both in the propagation plane and out of it. In the case of the BSW, this can also be observed [28]. Scattering of the BSW in the propagation plane leads to a deflection of the BSW from the original propagation direction and to the appearance of a set of wave vectors of scattered waves fanning away from the original direction (Figure 4a). Since the length of the wave vectors of the scattered BSWs remains unchanged, they are coupled back to the prism at the same angle as the unscattered BSW. As a result, if the screen is placed into a beam reflected from a photonic crystal, the arc, caused by the BSW scattering in the propagation plane, will be clearly visible in addition to the central spot corresponding to the unscattered BSW, as shown in the Figure 4b. Scattering of the BSW on the surface roughness out of the plane of the BSW propagation to the free space makes it possible to microscopically visualize the BSW in the far field. This fact can be very convenient in experimental work. In this case, the part of the incident light is rescattered out-of-plane and detected by the microscope objective lens. In microscope images shown in Figure 5a the BSW is spatially distributed in a pattern stretched in the propagation direction. By the intensity profile of  
Figure 3: **(a)** The model angular reflectance spectrum of the one-dimensional photonic crystal below the light line; **(b–e)** Experimental angular reflectance spectra (circles) of samples with 9, 11, 13 or 15 bilayers, and their fits according to numerical models (curves). Incident light is \(s\)-polarized. Dips in the spectra correspond to BSW excitation; **(f)** The model angular spectrum of the phase of the complex reflection coefficient. Reprinted with permission from [PERSON]. [PERSON], [PERSON], [PERSON], Phys. Rev. Lett. 108, 123901 (2012). Copyright (2012) by the American Physical Society [26]. the obtained images, it is possible to determine the mean free path of the BSW. In Figure 5a, the BSW propagation length is approximately 200 \(\upmu\)m, that is, at least four times larger than the length of surface plasmon propagating along the gold films in the visible spectral range. The BSW propagation length can significantly increase depending on the coupling conditions. Figure 4: **(a)** Schematic describing the scattering of the BSWs in the plane of the propagation on the surface of the photonic crystal in the Kretschmann configuration; k\({}_{SEW}\) is the wave vector of the BSW, and k\({}_{SEW}^{scatt}\) is the wave vector of the scattered component of the BSW. **(b)** Scattering pattern of surface electromagnetic waves in the total reflection direction. Reprinted from [PERSON], [PERSON], [PERSON], JETP Lett. 91, 382 (2010) with permission of Springer [28]. Figure 5: BSW spatial distribution imaged by collecting **(a)** the light scattered by microdefects on the 1D photonic crystal surface, and **(b)** the fluorescence emitted by organic dyes on the 1D photonic crystal surface; **(c)** Fluorescence intensity profile along the BSW propagation direction. Reprinted from [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], Appl. Phys. Lett. 94, 231122 (2009) with the permission of AIP Publishing [29]. The excitation of the BSW substantially changes the distribution of the electromagnetic field in a photonic crystal. The field is localized near the surface. This leads to an increase in the optical effects in the near-surface layer of the photonic crystal, which depend on the intensity of the incident field. As an example, the fluorescence enhancement of the Rhodamine 6G dye applied in a thin layer on the surface of a photonic crystal [29] can be considered.