Optical tunneling

However, photons are not actually reflected at the interface, but rather tunnel into the low-index material by optical tunneling. As a result, the reflected beam of fight is shifted along the interface by a small amount (Ax = 2Goos-Haenchen shift. This shift is ty pically small for fluid diagnostic applications (Ax < 1 pm) as compared to the field of view. A typical field of view for the magnification of microscope objectives is on the order of several hundred micrometers. 

Observation of Nonsequential Double Ionization of Helium with Optical Tunnelling. 

Figure 22.2 (a) Waveguide prism coupling setup, where the electromagnetic radiation is coupled, by means of "optical tunneling" across an air gap, to the film to be analyzed... 

In this chapter we study the phenomenon of optical cross-talk between pairs and between arrays of cylindrically symmetric or slowly varying fibers. Crosstalk arises because the fields of a fiber extend indefinitely into the cladding and interact with any other fiber which may be present. This interaction excites the fields of the second fiber, which in turn interact with the fields of the first fiber. Consequently there will be an exchange of power between the two fibers as the fields propagate. The amount of cross-talk, or power exchange, depends on the overlap of the fields of the two fibers. In ray language, cross-talk is associated with frustrated internal reflection or, equivalently, optical tunneling. 

Consider a medium whose continuous refractive-index profile n(x) varies slowly over a distance equal to a wavelength. A ray path in the region x < 0 of Fig. 35-4(a) touches the turning-point caustic at x = x,p. When there is no path in the region beyond the caustic, the ray is totally reflected from the caustic and no power is lost, i.e. T=0. However, if a transmitted ray originates at the radiation caustic x = x j, then optical tunneling occurs, as described in Chapter 7, and power is lost from the path at x,p to the path at x. If the local plane-wave fields have propagation constant P, then the values of x,p and x are determined by Eq. (35-31). 

Ren B, Li W H, Mao B W, Gao J S and Tian Z Q 1996 Optical fiber Raman spectroscopy combined with scattering tunneling microscopy for simultaneous measurements ICORS 96 XVth Int. Conf on Raman Spectroscopy ed S A Asher and P B Stein (New York Wley) pp 1220-1... 

Takahashi S, Futamata M and Ko]ima I 1999 Spectroscopy with scanning near-field optical microscopy using photon tunnelling mode J. Microscopy 194 519... 

A wide variety of measurements can now be made on single molecules, including electrical (e.g. scanning tunnelling microscopy), magnetic (e.g. spin resonance), force (e.g. atomic force microscopy), optical (e.g. near-field and far-field fluorescence microscopies) and hybrid teclmiques. This contribution addresses only Arose teclmiques tliat are at least partially optical. Single-particle electrical and force measurements are discussed in tire sections on scanning probe microscopies (B1.19) and surface forces apparatus (B1.20). 

At T < tunneling occurs not only in irreversible chemical reactions, but also in spectroscopic splittings. Tunneling eliminates degeneracy and gives rise to tunneling multiplets, which can be detected with various spectroscopic techniques, from inelastic neutron scattering to optical and microwave spectroscopy. The most illustrative examples of this sort are the inversion of the... 

Since the susceptibilities can be extracted from the optical spectra of these active modes, a quantitative description based on dissipative tunneling techniques can be developed. Such a program should include the analysis of the motion of the reaction complex PES, with the dissipation of active modes taken into account. The advantage of this procedure is that it would allow one to confine the number of PES degrees of freedom to the relevant modes, and incorporate the environment phenomenologically. 

For SFM, maintaining a constant separation between the tip and the sample means that the deflection of the cantilever must be measured accurately. The first SFM used an STM tip to tunnel to the back of the cantilever to measure its vertical deflection. However, this technique was sensitive to contaminants on the cantilever." Optical methods proved more reliable. The most common method for monitoring the defection is with an optical-lever or beam-bounce detection system. In this scheme, light from a laser diode is reflected from the back of the cantilever into a position-sensitive photodiode. A given cantilever deflection will then correspond to a specific position of the laser beam on the position-sensitive photodiode. Because the position-sensitive photodiode is very sensitive (about 0.1 A), the vertical resolution of SFM is sub-A. 

A new chapter in the uses of semiconductors arrived with a theoretical paper by two physicists working at IBM s research laboratory in New York State, L. Esaki (a Japanese immigrant who has since returned to Japan) and R. Tsu (Esaki and Tsu 1970). They predicted that in a fine multilayer structure of two distinct semiconductors (or of a semiconductor and an insulator) tunnelling between quantum wells becomes important and a superlattice with minibands and mini (energy) gaps is formed. Three years later, Esaki and Tsu proved their concept experimentally. Another name used for such a superlattice is confined heterostructure . This concept was to prove so fruitful in the emerging field of optoelectronics (the merging of optics with electronics) that a Nobel Prize followed in due course. The central application of these superlattices eventually turned out to be a tunable laser. 

Valette-Hamelin approach,67 and other similar methods 24,63,74,218,225 (2) mass transfer under diffusion control with an assumption of homogeneous current distribution73 226 (3) adsorption of radioactive organic compounds or of H, O, or metal monolayers73,142,227 231 (4) voltammetry232,233 and (5) microscopy [optical, electron, scanning tunneling microscopy (STM), and atomic force microscopy (AFM)]234"236 as well as a number of ex situ methods.237 246... 

As stressed in the introduction, the main difficulty ofthe voltaic cell method of investigating systems is its lack of molecular specificity. Therefore, complementary information should be obtained by using techniques sensitive to the polar ordering and arrangement of molecules in a surface or interfacial layer, such as optical, spectroscopic, and scanning tunneling microscope methods. " ... 

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