Attenuated total-reflection waveguide

Figure 20-21 Attenuated total reflectance sensor for Cu2+. Light traveling through the waveguide is attenuated (decreased) in the cation-exchange film in the presence of Cu2. [Data from T. Shtoyko, I. Zudans. C. J. Sellskar,...

Fig. 3 Schemes of fundamental hollow waveguide (HWG) structures. ATR attenuated total reflection...

Mendes SB, Li LF et al (1996) Broad-band attenuated total reflection spectroscopy of a hydrated protein film on a single mode planar waveguide. Langmuir 12(14) 3374—3376... 

An antibody is immobilized on the surface of a waveguide (a quartz, glass, or plastic slide, or a gold- or silver-coated prism), and binding of an antigen is measured directly by total internal reflection fluorescence, surface plasmon resonance, or attenuated total reflection. 

To accomplish this goal, high surface area silica films were fabricated and applied to the surfaces of iirfrared transparent transmission substrates (silicon) and Attenuated Total Reflection (ATR) waveguides. Data will be presented that illustrates the capability of this approach in reproducibly detecting the pesticide phosmet at detection limits of 200 ppb, while also discussing the advances needed to lower this detection limit to the single ppb range. 

Another technique that is important for optical immunosensor development is internal or attenuated total reflection spectroscopy (Fig. 126). A waveguide (slide or fiber) having a high refractive index is coated with a layer of immobilized antibody. The incident light... 

In internal reflection, at angles of incidence larger than the critical angle, electromagnetic radiation is totally reflected (attenuated total reflectance, ATR. see Section 16.2.2.4 and Fig. 5). This special ca.se is very important in analysis for two approaches. First, simple transportation of radiation within the fiber (or a waveguide). Second, in total reflection, an evane.scent field appears in which the electrical field vector decays exponentially in the optically less dense medium. Every change within the medium with lower refractive index influences the field vector coupled to the field in the optically denser medium. Therefore, the totally reflected radiation contains information about effects on the other side of the phase boundary (the medium with lower refractive index) [20], [144]. Various principles to interogate this effect are known and used in evanescent field sensors. 

The most studied NLO devices are the light intensity or phase modulators. Basic modulators are the reflective-type ones such as the attenuated-total-reflection (ATR) and resonant grating waveguide modulators. 

For solid samples with a low surface area, such as thin films or single crystals, attenuated total reflection (ATR) method is often used. In this technique, a plate of a single crystal waveguide such as Ge is place in contact with the sample and the IR beam is passed through the IR-transmitting crystal in a manner such that it alternately undergoes total internal reflection from its front and rear faces. At each reflection, some of the IRradiation may be absorbed by species adsorbed on the solid sample surface. 

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