Evanescent light wave reflection

The idea of reflecting an electron beam by an evanescent light wave is illustrated in Fig. 13.8. The internal reflection of a laser beam at a dielectric-vacuum interface produces an evanescent light wave with an intensity distribution given by... 

Incorrect conclusion 1 above is sometimes said to derive from the reciprocity principle, which states that light waves in any optical system all could be reversed in direction without altering any paths or intensities and remain consistent with physical reality (because Maxwell s equations are invariant under time reversal). Applying this principle here, one notes that an evanescent wave set up by a supercritical ray undergoing total internal reflection can excite a dipole with a power that decays exponentially with z. Then (by the reciprocity principle) an excited dipole should lead to a supercritical emitted beam intensity that also decays exponentially with z. Although this prediction would be true if the fluorophore were a fixed-amplitude dipole in both cases, it cannot be modeled as such in the latter case. 

Let us consider the possibility of reflection of electrons by an evanescent laser wave formed due to total internal reflection of femtosecond laser pulses from a dielectric-vacuum interface [4] (Fig. lb). Such a laser field was considered elsewhere [7, 8] to effect the mirror reflection of atoms (references to the latest works on the mirror reflection of atoms can be found in Refs. 9 and 10). The light intensity distribution in the evanescent wave in the vacuum may be represented in the form [11]... 

One can distinguish between methods in which absorption of the evanescent surface wave in different wavelength regions is measured (these are often called attenuated total reflection methods), and methods which use the evanescent wave to excite other, spectroscopic phenomena, like fluorescence and Raman scattering or light scattering. As the methods of conventional fluorescence spectroscopy have been shown to be exceptionally successful in studies of proteins and other biopolymers, their evanescent surface-sensitive counterparts will be reviewed first. 

Sensing of evanescent waves with an optical tip has been proposed for use as an optical device to sense AFM forces by means of an optical microlever which is illuminated by a laser under conditions of total internal reflection and which is connected to an atomic force tip [77], Thus tunneling photons from the microlever to the optical tip at the evanescent light coupling may be used for the feedback loop. This instrument combines noncontact AFM and PSTM techniques. 

The analyte directly affects the optical properties of a waveguide, such as evanescent waves (electromagnetic waves generated in the medium outside the optical waveguide when light is reflected from within) or surface plasmons (resonances induced by an evanescent wave in a thin film deposited on a waveguide surface). 

Simultaneous with the light s reflection off the internal surface of the fiber is the creation of an electromagnetic field at the external surface of the fiber core. This field extends into the surrounding media and is called the evanescent wave. The intensity of the field decays exponentially as the distance from the surface of the probe increases. The effective distance this field penetrates the external media is less than one wavelength of light and is very sensitive to the incident angle the refractive indexes of the internal media (n ), and external media (n2). For the typical optical fiber used in an immunoassay with a fused silica core surrounded by an aqueous media, the penetration depth of the evanescent wave is on the order of 100 nm. 

Let us first consider the scheme suggested by Cook and Hill (1982). When a plane traveling light wave is totally reflected internally at the surface of a dielectric in a vacuum, a evanescent wave is generated on the surface (Fig. 7.1). By application of Fresnel s reflection formulas (Born and Wolf 1984), the intensity of evanescent wave is given by... 

By using a curved evanescent wave, one can, in principle, obtain focusing of an electron beam simultaneously with reflection. Of course, all these potentialities of laser-induced reflective electron optics should be the subject matter of future studies, specifically into the damage threshold of the materials used for the formation of the high-intensity femtosecond evanescent laser light waves. 

Figure 3(a) shows a schematic of a TIRF setup. The incident laser light is reflected at the glass-water interface of the miao-fluidic chamber, which results in an evanescent electromagnetic wave. The exponential decay over about 100 nm enables selective illumination of molecules immediately at the glass-water interface (Figure 3(a), inset), which makes selective visualization of cellular stmctures as well as single-molecule studies possible. " ... 

PTM Photon tunneling microscopy [12] An interface is probed with an evanescent wave produced by internal reflection of the illuminating light Surface structure... 

---