Transmission oblique angle

Transmission spectra for the sample 1 in parallel and perpendicular polarizers were measured for different angles of incidence in visible and nesu infrared ranges. The obtained results indicate an optical axis lying along the pores. At oblique angles the anisotropy increases with increasing angle of incidence (Fig. 1). 

Fig. 2 presents transmission spectra for the light polarized perpendicular to the pores for the sample 2. The transmittance rises with increasing of the angle of incidence, whereas the transmission minimum has a red shift. At normal incidence PBG disappeared. The presence of PBG in the sample 2 at oblique angles indicates to its satisfactory optical quality and highly ordered pore structure. 

The formulae (22.5), (22.6), and (22.7) are given for perpendicular waves only. Based on a limited set of data, van der Meer et and Wang et al. analyzed the effects of oblique wave attack on wave transmission. With increasing incident wave angle / , Kt tends to decrease and the obliquity of the transmitted wave / t is a little smaller than the incident / . The influence of wave obliquity on transmission is more evident for smooth structures, where it results proportional to cos / / , and hardly observable for rubble LCBs. The deviation of transmitted waves (obliquity reduced to about 80%) can be interpreted as refraction of the average wave due to spectral change and reduced nonlinearity of transmitted waves. Explanation of effects is provided in Wang et al. ... 

Table VIII shows partial results obtained from a group of calculations involving thinner slabs and other than normal incident angles. To facilitate comparison with the work of Kirn et al, on gamma-ray penetration, the slab thicknesses were varied so as to keep the optical path lengths constant for different angles of incidence. The results are generally similar, in that obliquity decreases transmission for thin slabs and increases it in thicker slabs.

The FTIR spectrum of the PTFE film deposited by laser ablation was identical to that of the target [54], but that of the film produced by SR etching showed some visible differences (see Fig. 29). Obviously, the C-F2 deformation bands at 640 and 513 cm-1 appear much smaller in the bottom trace. To understand why these 640 and 513 cm-1 bands were so small in the SR case, we measured both normal and oblique transmission of FTIR with an incident angle of 0 and 80° [58]. Two FTIR spectrometers (PERKIN-ELMER and JASCO) were used to measure spectra in the range 400-3000 cm-1. For a cross-check, the film was also deposited on a metallic surface and infrared reflection absorption spectroscopy [62] was carried out to confirm our oblique transmission measurements. Typical changes in the FTIR transmission... 

Fig. 30 Typical changes in FTIR transmission spectra of the PTFE films deposited on Si(100) substrates at Ts=RT by SR etching (a) and laser ablation (b). The bottom trace is a spectrum for the normal incidence (incident angle=0°) and the top trace is for the oblique incidence (incident angle=80°). Reproduced with permission from J Phys Chem 2000, B26, 6212-6217. Copyright 1998 Am Chem Soc...

The reflection and transmission (refraction) of light obliquely incident on the interface between two isotropic media is entirely controlled by the angle of incidence and the complex refractive indices of the media, being described by the Fresnel reflection and refraction equations (see Appendix). Originally worked out for transparent materials, these equations apply with complete generality when the refractive indices are complex rather than simple numbers. If the refractive indices are complex numbers, the angles of refraction must also be complex. For a description of the meaning of such quantities, see ref. 3. 

Under oblique incidence ( j=incidence angle, 2=refraction angle, with nisin i = n2 sin 2), the reflection and transmission coefficients depend on the polarization of the incident wave with respect to the incidence plane (see Fig. 6.1). If the polarization (direction of the electric field Eq) is perpendicular to the incidence plane (so-caUed s-polarization), the electric field is everywhere parallel to the interface, and using the same rules as above for the boundary conditions, its amplitude at the interface is now E()X2niCosi+n2Cosg>2), stiU much smaller than Eg [15]. However, if the polarization lies in the incidence plane (so-caUed p-polarization), the electric field has a component parallel to the interface and a component perpendicular to the interface. The parallel... 

High contrast and uniformity of transmission characteristics at oblique incidence are also beneficial features of the SBE mode which considerable improve the legibility of supertwist displays. Better viewing angles than that for the 90° twist structure seem to be a peculiar feature of highly twisted chiral nematics. Figure 4.23 demonstrates this for a 200° supertwist cell in comparison with the usual 90° twist cell [127]. 

Transmission characteristics at oblique incidence wideness of viewing angles (an example is shown in Fig. 4.27 for a twist cell). 

A generalization of this approach is to deposit a quarterwave dielectric mirror onto a metal reflector. In this way, very high reflectance is obtained for near-normal incidence. For more oblique incident angles the aU-dielectric part will be transmissive, but in that case the metal part will reflect these beams, albeit with a lower reflectance. In this way the benefits of both types of the used structures are simultaneously employed. In [251] the authors mention the use of hybrid reflectors consisting of a Bragg-type dielectric mirror with an additional thin metal reflector deposited on its backside. 

The 2D x-ray systems are very effective in testing single-sided assemblies. With the use of a sample manipulator, an oblique view angle enhances inspection of both single- and doublesided assemblies with some loss of magnification due to increase in distance between source and detector. Experience is needed in discerning between bottom-side board elements and actual solder and component defects. This can be very difficult or impossible on extremely dense assemblies. As discussed previously, certain solder-related defects such as voids, misalignments, solder shorts, etc. are easily identified by transmission systems. However, even an experienced operator can miss other anomalies such as insufficient solder, apparent open connections, and cold solder joints. 

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