Total Internal Reflection TIR

In total internal reflection the transmitted wave amplitude has the form 

Equation (3.37) describes a wave propagating along the boundary in the plane of incidence whose amplitude decreases exponentially with distance from the boundary. The penetration depth 5 of this wave into medium 2 at which its amplitude decreases by a factor of e is given by 

This quantity has the order of magnitude A for incidence angles far from the critical angle, i.e., the wave has only a vanishing (or evanescent) tail penetrating into medium 2. For this reason the wave (3.37) which appears in total internal reflection is called an evanescent wave (EW). 

---

A feature of interest is the possibility of obtaining the condition of total internal reflection (TIR). Under this condition, the fundamental beam impinges on the interface from the liquid with the highest index of refraction yielding a SH intensity enhancement of more than a hundred times. Two TIR angles exist, given by the following relationships ... 

The background problem can be further overcome when using a surface-confined fluorescence excitation and detection scheme at a certain angle of incident light, total internal reflection (TIR) occurs at the interface of a dense (e.g. quartz) and less dense (e.g. water) medium. An evanescent wave is generated which penetrates into the less dense medium and decays exponentially. Optical detection of the binding event is restricted to the penetration depth of the evanescent field and thus to the surface-bound molecules. Fluorescence from unbound molecules in the bulk solution is not detected. In contrast to standard fluorescence scanners, which detect the fluorescence after hybridization, evanescent wave technology allows the measurement of real-time kinetics (www.zeptosens.com, www.affinity-sensors.com). 

The light can propagate along the fibre usually by totally internal reflection (TIR) as indicated in fig. 18. TIR is controlled by the angle of incidence and also by the refractive indices of the media involved in the propagation. 

To learn that the most common errors encountered with in situ UV-visible spectroelectrochemistry are those resulting from total internal reflection (TIR), which causes ringing , and by working at wavelengths beyond the band edge. 

A second problem that occurs with OTEs is the need to avoid total internal reflection (TIR) within the layer of glass substrate. TIR is best avoided by ensuring that the incident light beam of the spectrometer (which is horizontal) strikes the glass at a perpendicular angle, which is achieved by positioning the OTE exactly vertically within the cell housing. 

Total internal reflection (TIR) of light within the thin ITO layer removes light of frequencies corresponding to the thickness of the film so, if light of A. = 500 nm is removed, then only red and blue remain, which therefore gives the purple colour. 

Figure 19. (a) Cross-sectional view of the calculated field distribution in a total internal reflection (TIR) coupler in a 2 pm SOI waveguide, and (b) an etched TIR structure in SOI. 

More recently, cells using total internal reflectance (TIR) probes have become readily available. The spectrum in Figure 5.3 was obtained, again at temperature and pressure, from an Ir catalysed carbonylation of methanol in a Parr autoclave modified to take a Sentinel IR probe. 

Optical waveguides generally confine light by means of the total internal reflection (TIR) effect, which is accomplished at the interfaces of a high refractive index dielectric medium (core) surrounded by a lower refractive index medium (cladding and substrate) (Fig. 5) [48,49]. 

Table 2 Different materials employed in the fabrication of total internal reflection (TIR) and antiresonant reflecting optical waveguide (ARROW) waveguides...

A four-layer microchip has been constructed to generate total internal reflection (TIR) and an evanescent field (see Figure 7.8). Surface-adhered Nile red-labeled fluorescent microspheres (1 pm) are excited by the evanescent field for fluorescent measurement. An essential feature on the chip was the micromirror that was constructed by depositing Au/Cr on the slanted wall (54.7° due to anisotropic etch of Si). Operation near the critical angle 0C assures strong evanescent intensity [695]. 

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. 

Total internal reflection (TIR) at the interface of an optically dense medium to an optically rare one has been of continuous interest over the years. Closely related to this phenomenon is the existence of an evanescent wave in the second (rare) medium, a fact first mentioned and even proved by Newton (3). 

Figure 1. Total internal reflection (TIR). n,y. refractive index Sr critical angle for TIR the angle of incidence must be larger than 6r dp penetration depth o)...

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 sum-frequency response at aqueous interfaces is very weak because of the small number of adsorbed molecules present and the poor polarizability of most liquids. To compensate for the low sum-frequency efficiency, pulsed lasers are used. Since the sum-frequency intensity increases with the peak intensity of the incident beams, picosecond and femtosecond pulses are optimal, although these shorter pulses result in larger IR bandwidths. Nanosecond systems are generally much simpler to operate and have narrower IR bandwidths, but can contribute to significant heating of the interface unless an optical coupling scheme such as total internal reflection (TIR) [6] or other mechanisms such as sample rotation [32] are employed. 

It is well known that both nanometre and nanosecond-picosecond resolutions at an interface can be achieved by total internal reflection (TIR) fluorescence spectroscopy. Unlike steady-state fluorescence spectroscopy, fluorescence dynamics is highly sensitive to microscopic environments, so that time-resolved TIR fluorometry at water/oil interfaces is worth exploring to obtain a clearer picture of the interfacial phenomena [1]. One of the interesting targets to be studied is the characteristics of dynamic motions of a molecule adsorbed on a water/oil interface. Dynamic molecular motions at a liquid/liquid interface are considered to be influenced by subtle changes in the chemical/physical properties of the interface, particularly in a nanosecond-picosecond time regime. Therefore, time-resolved spectroscopy is expected to be useful to study the nature of a water/oil interface. 

For large mode numbers A > 70 a simple plane wave model (PWM) has been deduced. Its main idea is, that the light wave circulates around exploiting the process of multiple total internal reflection (TIR, see Fig. la) and finally interferes with itself when having completed one full circulation within the resonator. To enforce constructive interference the total phase... 

When a light beam has an incident angle exceeding the critical angle, a total internal reflection (TIR) occurs at the interfaces and, as a consequence, the... 

---