Dichroic reflective polarizer

In layer i, the electric field of the down-going light is contributed by the transmission of the down-going light in layer (i + 1) and the reflection of the up-going light in later i. 

In the same way we can get the relation between the electric fields of the up-going and downgoing light in layer i and the electric fields of the up-going and down-going hght in layer (/ - 1), 

Below the stack, there is incident light and reflected light q =  

From the above equation, we can calculate , and Er as functions of Using Cayley-Hanulton 

The reflectance is maximized when phase retardation angle = 2m+1)ti. The 

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Figure 11.5 Schematics of common types of polarizer. Top low-power dichroic sheet polarizer (for linear TT-polarization). Bottom high-power caldte Gian polarizer, splitting unpolarized light into orthogonally linear-polarized components for the extraordinary through and the ordinary reflected beams...

The external reflection of infrared radiation can be used to characterize the thickness and orientation of adsorbates on metal surfaces. Buontempo and Rice [153-155] have recently extended this technique to molecules at dielectric surfaces, including Langmuir monolayers at the air-water interface. Analysis of the dichroic ratio, the ratio of reflectivity parallel to the plane of incidence (p-polarization) to that perpendicular to it (.r-polarization) allows evaluation of the molecular orientation in terms of a tilt angle and rotation around the backbone [153]. An example of the p-polarized reflection spectrum for stearyl alcohol is shown in Fig. IV-13. Unfortunately, quantitative analysis of the experimental measurements of the antisymmetric CH2 stretch for heneicosanol [153,155] stearly alcohol [154] and tetracosanoic [156] monolayers is made difflcult by the scatter in the IR peak heights. 

The optical setup for time-resolved micro-luminescence measurements is based around an Axiotech 100 HD Zeiss microscope, modified to allow laser injection and fluorescence collection. The sample is observed either under transmission or reflection of polarized white light, or under UV illumination (HBO lamp). A set-up consisting of a dichroic mirror, for the selection of the excitation wavelength, and an objective (Epiplan Neofiuar obj. > 350 nm Ealing/Coherent reflection obj. < 350 nm) is used to focus the laser beam on the sample (spatial resolution over 5 pm with a x50 objective). The lim-... 

Mechanical deformation induces orientation into the polymer samples and polarized infrared can be used to characterize this orientation either by direct measurement of the dichroic ratio 287,289) or by spectral subtraction 286), three dimensional sample tilting 68,286), or internal reflection spectroscopy 130). 

Dichroic behaviour of the polymer crystals with intense absorption and reflection spectra peaking at ca. 2 eV for light polarized parallel to the polymer chain. 

Fig. 3.3 Infrared spectra with attenuated total reflectance using polarized light for lipid A from E.coli and from Rhodobacter capsulatus. The two lipid A have identical backbone structures, but differences in the acylation pattern. As can be seen, the vibrational bands corresponding to diglucosamine ring vibrations have different dichroic ratios, which is indicative for a different inclination of the backbones with respect to the membrane normal...

Next, we consider the absorbance due to a dichroic adlayer adsorbed onto the waveguide surface with the optical constants as indicated in Fig. 4. The optical properties of the dichroic layer are described by the different extinction coefficients k, ky, and k in each Cartesian direction. The reflectance of the waveguide-adlayer-cover system follows the analysis found in Macleod [9] with the anisotropic coefficients taken from Horowitz and Mendes [10]. By assuming a thin and weakly absorbing adlayer, the following expressions are obtained for the absorbance as measured through a guided mode at each polarization [8] ... 

This technique was employed to monitor the B —> A transition of DNA as a function of the relative humidity (Pilet and Brahms, 1973 Pohle et al., 1984). The investigated bands are those which reflect the vibrations of the phosphate groups. As shown by Fig. 4.7-3, which presents the polarized infrared spectra of a salmon sperm DNA hydrated film with 93% RH (top, B form) and 58% RH (bottom, A form), the dichroism of the two phosphate bands changes. The B form of the antisymmetric PO2 stretching vibration around 1230 cm is non-dichroic, while that of the A form is perpendicular. The B form of the symmetric PO2 stretching vibration around 1090 cm is perpendicular, while that of the A form is parallel. A simple computation, for instance for the latter band, shows that the value of the angle between the transition dipole moment of this vibration and the double helical axis varies between 68 ° (B form) and 49 ° (A form). This parameter is an extremely sensitive indicator of a B A transition and may also be employed to show the inhibition of a B —> A transition by various classes of molecules, such as proteins (Liquier et al., 1977 Taillandier et al., 1979) or drugs (Fritzsche and Rupprecht, 1990). 

In ATR-FTIR excitation occurs only in the immediate vicinity of the surface ol the reflection element, in an evanescent wave resulting from total internal reflection. The intensity of the evanescent field decays exponentially in the direction normal to the interface with a penetration depth given by (1.7.10.121, which for IR radiation is of the order of a few hundreds of nm. Absorption leads to an attenuation of the totally reflected beam. The ATR spectrum is similar to the IR transmission spectrum. Only for films with a thickness comparable to, or larger than, the penetration depth of the evanescent field, do the band intensities depend on the film thickness. Information on the orientation of defined structural units can be obtained by measuring the dichroic ratio defined as R = A IA, where A and A are the band absorbances for radiation polarized parallel and perpendicular with respect to the plane of incidence, respectively. From this ratio the second-order parameter of the orientation distribution (eq. [3.7.13]) can be derived ). ATR-FTIR has been extensively used to study the conformation and ordering in LB monolayers, bilayers and multilayers of fatty acids and lipids. Examples of various studies can be found... 

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