Brewster angle measurement

The TIR and ATR effects are not the only possible phenomena which are useful in studying the surface properties such as the director orientation at the boundaries, the surface order parameter, the anchoring energy, etc. Such useful techniques as Brewster angle measurements [215] and ellipso-metric studies [216] should also be mentioned. But the discussion of these methods is beyond the firamework of this book. 

Stine KJ et al (2006) Interaction of the glycoalkaloid tomatine with DMPC and sterol mono-layers studied by surface pressure measurements and brewster angle microscopy. J Physical Chem B 110 22220... 

Deb and Yoffe [134] examined the decomposition of thallous azide under the action of ultra-violet light in the wavelength region 3200-3800 A. Two exciton bands 3415 and 3348 A have been observed in thallous azide by low-temperature spectroscopy (Nikitine and Gross s method). The refractive index has been measured by the Brewster angle method, the electron energy levels have been estimated and the results of the photochemical decomposition have been related to the electron energy level and to measurement of photoconductivity [33],... 

Methodologies to assess interface properties of amphiphiles are surface tension measurements (Phan et al. 2006 Golding and Sein 2004 Miller et al. 2004), ellip-sometry (Dickinson 2003a Murray 2002) and Brewster angle microscopy (Grigoriev et al. 2006 Rodrguez Patino et al. 2001). Both and P NMR have been applied in order to study the conformation and dynamics of P-casein at the oil-water interface of emulsions (ter Beek et al. 1996). Their NMR results showed that the protein at the interface has mobile regions with httle secondary structure in which the motions are rather slow. 

Figure 6.4-12 Measured reflectance of p-polarized radiation close to the Brewster angle of polyfmethyl methacrylate).

If the incidence angle of / -polarised radiation is equal to the Brewster angle aB, the reflectivity from the pure (i.e., slick-free) water surface is close to zero. As a consequence, the water surface appears to be dark. In the presence of a film-forming substance, however, the slick patches represent a different optical medium that gives rise to a measurable reflectivity, which in turn makes the slick domains visible by their lighter appearance. This effect can be recorded by a Charge-Coupled-Device [CCD]-camera. 

BAS measures the optical response of a sample using % and Rp( >B). The optical response is obtained as the wavelength (or frequency)-dependent complex dielectric function e = e-i+ (where i and 2 are the real and imaginary parts of the dielectric function, respectively), and analytical expressions have been derived to determine e(co) from rp and Rp(%). For a sample with purely dielectric properties, for example, = 1, the Brewster angle is given by... 

Reflection. A more accurate method for determining the n of a gemstone is to measure the critical angle (the Brewster angle, 6b) for reflection using a reflectometer. The principle is that the refractive index of a material is given by... 

If the interface is not sharp, but is characterized by a certain spatial profile of the dielectric constant of a given medium, e z), the ellipticity coefficient p is finite at the Brewster angle. In this case, the Brewster angle is defined as the angle, where the phase shift of the p-polarized wave is n/2. The value of the ellipticity coefficient at the Brewster angle therefore carries information about the sharpness of the interface. As we can measure this value very precisely, we can determine the parameters of the spatial profile of the dielectric constant with great precision. 

The state of polarization of light, reflected from an interface, depends strongly on the profile of the dielectric constant across that interface. This simple principle is used in the Brewster angle reflection ellipsometry (BAE), where one measures the ellipticity coefficient of light, reflected from an interface. The method is sensitive enough to detect extremely small changes in the structure of liquid crystalline-solid interfaces. Subnanometer resolution of the adsorption parameter is routinely achieved. The method is therefore very useful for the study of liquid crystal interfaces, where the surface-induced variation of the order can be observed [5,25,33-41]. 

FIGURE 9.6 Overview of the experimental apparatus for measuring laser-induced fluorescence and photodissociation action spectra of gas phase ions stored in a 3-D quadrupole ion trap. Optical component abbreviations Lenses (L1-L4) P-BaBj04 crystal (BBO) Mirrors (M1-M8) Shutter (Sh) Irises (Irl-lr2) Pinholes (PH1-PH2) Brewster-angle windows (BWl-BW2) Neutral density filter (ND) Long-pass filter (LP). L3 is inside the ring electrode (see Figure 9.7). 

At the Brewster angle, for a truly sharp interface, ip is zero and <5 changes discontinuously from Ji to zero. In the presence either of roughness at the interface or of a thin layer of some third medium, ip does not go all the way to zero and the change in (3 as a function of angle of incidence becomes less abmpt. Under these conditions ellipsometry is very sensitive to the presence of thin adsorbed layers, and provides an accurate measure of the amount adsorbed. 

Figure 2.12 refers to a substrate with the optical constants = 3.4 and 3 = 1, which was chosen as a model substrate because its characteristics are close to those of doped silicon and one form of carbon [75]. Analysis of the cnrves in Fig. 2.12a (see also 1.4.15°) shows that the reflectance of p-polarized radiation from the clean substrate Ro,p ((pi) is close but not eqnal to 0 at angles of incidence (pi close to the pseudo-Brewster angle of the substrate, The value Ro,p cps it changes sign, while its maximum is observed, as for transparent Si, in the spectra measured at angles of incidence larger than (ps.

---