Diffraction total internal reflection

There are various thin-film optical switch principles based on interference, diffraction or total internal reflection (TIR). The TIR switch, the essentials of which are shown in Fig. 8.18, depends on TIR of light passing from one medium to another of lower refractive index. TIR occurs for small differences in refractive indices when the angle of incidence approaches 90°, i.e. for light almost parallel to the surface of the material with the lower refractive index. 

Fig. 4. Schematic representation of surface diffraction from dielectric pattern, based on total internal reflection (TIR) and attenuated total reflection (ATR) coupling geometries, respectively.

The local field generated by total internal reflection [23] or by the SPR [14-18] can be diffracted by gaining (or losing) discrete momenta Ak = mg, generated by the periodic surface structure of periodicity A (Fig. 4). The diffraction angle deviates in discrete increments from the specular-reflection angle (i.e., zeroth-order diffraction) in fulfillment of the corresponding momentum match condition ... 

Crystals may not be too perfect The condition for Bragg139 reflection, Eq. (8.3.2), is also the condition for total internal reflection. Thus, an absolutely perfect millimeter-sized crystal will reflect internally almost all of the X-ray beam, even at the Bragg angles. However, each crystal contains crystalline domains, 1-10 pm in size, which are slightly misaligned with each other (by seconds or a few minutes of a degree) this is what permits the observation of X-ray diffraction peaks. If the diffracted intensity is unacceptably low, a quick thermal shock to the crystal may help micro-shatter the crystal and form those domains. 

Unique information about the unit cell in quasi-crystaUine monolayers can be obtained from X-ray °, neutron , heUum or low energy electron diffraction (LEED) data. In the grazing incidence X-ray diffraction (GIXD) experiment the beam is directed at the coated surface at a low angle and experiences total internal reflection from the metal support underneath the monolayer. The analysis of reflectivity and diffraction pattern of this reflected beam provides information about the molecular structure of the crystalline films, the thickness and refractive index of the layers and the roughness of the surface s . These experiments, however, require sophisticated and expensive equipment and are not therefore used routinely for monolayer characterization. 

Total internal reflection fluorescence (TIRF) microscopy is one of the more complicated techniques for more advanced users of fluorescence microscopy techniques. In order to obtain fluorescent information about small features less than 0.5 pm, this technique uses decaying evanescent waves to probe a focal volume below the diffraction limit of light. 

Epithermal and fast neutrons can be eliminated entirely by using diffraction to extract a narrow range of wavelengths from the beam (Byun et al. 2002). Several orders of diffraction can be summed to increase the flux. The best beams are those from neutron guides, which operate by total internal reflection in a narrow channel. Neutrons incident on a surface at... 

In total internal reflection microscopy, the light is confined only to the z-direction, resulting in the diffraction-limited resolution in the xy-plane. In the last two decades a novel optical microscopy has been developed aiming at high spatial resolution by the three-dimensionally localized optical field, optical near-field . Details on the structural analysis using the near-field microscopy is described in the next section. 

It is possible to combine the reflection and diffraction of atoms by using a standing evanescent wave (Hajnal and Opat 1989). The required optical wave field can be produced by total internal reflection of a laser beam at the surface of a refractive medium and retroreflecting of the light back along its original path. The evanescent field decreases exponentially in the direction perpendicular to the surface and is... 

The numerical aperture (more exactly the square of the numerical aperture) describes the light collection efficiency of an objective and thus determines resolution and sensitivity. The values of numerical apertures above unity can be reached only if one takes advantage of total internal reflection. For that purpose, the objective and object holder are connected by a medium with high index of refraction (e.g., an immersion oil or water). In this way light is refracted via the immersion medium towards the normal of the objective (Fig. 8.4). Hence a larger number of Airy diffraction orders reach the imaging system and thus the contrast increases. 

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