Optical Waveguide Lightmode Spectroscopy

In the latter half of the 17th century Newton (1730) demonstrated the existence of an evanescent field when light falls on the interface between dense and rare optical media and is totally reflected back into the dense medium. During the intervening years the phenomenon has been extensively studied, and has given rise to important measurement techniques for investigating interfacial phenomena (cf. Table 1). The overall approach is for the optically dense medium (typically a transparent dielectric) to form the substrate in contact with the optically rare medium (typically an aqueous solution) from which particles accumulate at the interface between the two media. Any change of electronic polarizability within the evanescent field, which decays exponentially into the rare medium, gives rise to a change of phase of the totally internally reflected light, which is essentially

Table 1. Theoretical foundations of different optical techniques for investigating interfacial phenomena and their experimental development, with the names of the pioneering contributors and of the instrument makers. Acronyms: SAR, Scanning Angle Reflectometry; SPR, Surface Plasmon Resonance. SAR does not make use of the evanescent field as such. In SPR, the field is generated by the collective vibrations of electrons in a thin metal film deposited at the interface

Table 1. Theoretical foundations of different optical techniques for investigating interfacial phenomena and their experimental development, with the names of the pioneering contributors and of the instrument makers. Acronyms: SAR, Scanning Angle Reflectometry; SPR, Surface Plasmon Resonance. SAR does not make use of the evanescent field as such. In SPR, the field is generated by the collective vibrations of electrons in a thin metal film deposited at the interface

Technique

Theoretical basis

Experimental

Laboratory

Large-scale

demonstration

instruments

commercialization

SAR

Fresnel (1818) Bousquet (1957)

Schaaf et al. (1985)

-

Not anticipated

Ellipsometry

Fresnel (1818) van Ryn van Alkemade (1883)

Jamin (1850)

Rudolf (1976)

Not anticipated

SPR

Maxwell-Garnett (1906)

Turbadar (1959)

Biacore (1990)

Anticipated?

OWLS

Tien (1977)

Ramsden (1993a)

MicroVacuum (2001)

Corning (2006)

the parameter measured. Table 1 provides a brief historical survey of the relevant developments up to the present.

Ample comparison of these different techniques has been made elsewhere (e.g. Ramsden 1994, 1997); the next table summarizes some advantages and disadvantages. We shall take a further comparative look in Sect. 2.4.

Table 2. Brief summary of some of the pertinent advantages and disadvantages of different optical techniques. Regarding the sensitivity, OWLS is intrinsically about 10 times more sensitive than SPR (for the determination of a single parameter) (Lukosz 1991). SPR only occurs with the p polarization; practically, SAR also has that restriction. See the chapter in this volume by Poksinski and Arwin concerning ellipsometry

Technique Advantages Disadvantages

SAR Comprehensive theoretical Slow analysis Not very sensitive

Ellipsometry Very versatile No closed form solutions of equations

Extensive literature Not very sensitive

SPR Strong commercial development No closed form solutions of equations

Not very sensitive Requires a metal substrate

OWLS Highly informative closed Cannot be used with opaque substrates form solutions of equations Compatible with other photonics

Very sensitive; versatile devices

Was this article helpful?

0 0

Post a comment