Optical applications

Crosslinked products exhibit superior optical transparency, heat resistance, and adhesion, as well as improved dimensional stability, solvent resistance, and chemical resistance. In addition, crosslinking prevents the occurrence of cracks in films. 

Crosslinkable COCs are obtained by the modification with an alkoxysilyl group (2,47). A series of more or less complicated silyl modified norbomene derivates have been described (48). As a side effect, the silyl group improves the adhesion properties of the materials. 

The crosslinkable COCs have been suggested for the use as alternatives for a glass substrate of a liquid crystal display devices and an electroluminescence (EL) display devices. Moreover, a crosslinkable COC can be used as a polarizing film, surface protective film, retardation film, transparent conductive film, light diffusion film, film for EL display devices, transparent conductive composite material, anti-reflection film, etc. Methods how to prepare these types of films have been described in detail (47). 

Disposable cuvette cartridges for optical measurements have been developed (49). The cartridge is formed from three flexible thin layers. The middle layer is an adhesive sheet with cut out regions, typically between 30 and 50, serving as optical chambers bounded 

Toners find use in electrophotography (50). The basic invention of electrophotography originates from Carlson and was filed in 1938 (51). The first commercial black and white copier, the Xerox A was released in 1949 and the first color copier was introduced in 1973. 

A CVD diamond coating is yet to be produced with the optical clarity of single-crystal diamond and, for that reason, CVD diamond has found little application so far in optics. Typically CVD diamond coatings are translucent. Some are nearly white, some have a black tinge.  

The rough surface of CVD diamond is also a drawback since an optically smooth coating is an essential requirement for most optical applications. The surface can be smoothed to some degree by increasing the nucleation density and by deposition strongly 100 textured coatings where the surface consists of flat 100 faces more or less parallel to the substrate.I  

Advances in deposition techniques have now made possible the fabrication of free-standing shapes such as the 7.6 cm (3 ) diameter hemispherical dome for IR-window applications shown in Fig. 13.10 which may eventually replace the present IR materials. 

Silicon etched to expose diamond layer bonded to infrared window 

Diamond for X-ray Windows. CVD diamond is an excellent material for windows of x-ray spectrometers. In thin cross section, it is transparent to the x-rays generated by low-energy elements such as boron, carbon, and oxygen (see Ch. 11, Sec. 7.0, and Fig. 11.14) and is superior to beryllium which is the present standard material. Such a window is now commercially available and is shown schematically in Fig. 13.11 It is leak-tight to helium and capable of withstanding at least one atmosphere differential pressure. 

Ceria also exhibits optical properties suitable for potential applications. Ceria has characteristics ideal for use as a broad-spectrum inorganic sunscreen in personal care products it is quite transparent to visible light, but has excellent ultraviolet absorption ability. Thin ftims of ceria have a high refractive index n = 2.05), and dc 

Because of the high refractive index of ceria in the visible range (2.05 eV), ceria appears natural on the skin without imparting an excessively pale white look. Therefore, ceria is used as a UV-shielding material for cosmetics. However, the photocatalytic activity of ceria, which facilitates the generation of reactive oxygen species and has raised safety concerns, must be suppressed for such applications.  

The activity can be reduced in various ways, such as doping ceria with 

Babu et al synthesized Eu -doped ceria nanoparticles of 10 nm by room temperature chemical precipitation and annealed at different temperatures to study the effects on luminescence.The number of Ge ions in the ceria nanoparticles decreased after annealing. The emission intensity varied with the wavelength of excitation and observed transitions indicated the presence of Eu in different symmetry environments. 

There are several opportunities in specific chapters for the reader to glean information related to optical applications of materials. As such, no particular chapter has been devoted to this topic. Particular care has been placed toward construction of the index in this regard. 

The growing use of fibre optic cables has stimulated the demand for ancillary components to facilitate connections and other requirements. One interesting development at Toronto University in Canada has been the production of a new hybrid plastic which can produce light at the wavelengths used in fibre optic communications thus paving the way for an optical computer chip. 

previously three times the price of such competing optical resins as acrylic and PC, were pioneered in Japan for such optical applications as film and sheet for LCD. They have also made inroads into the market as light-guide panels for laptop compnters where resulting weight savings have justified the price premium. 

PAI with a higher refractive index than conventional fluorinated PI consist of chlorinated monomers. When using such a PAI type as a material for the core of an optical fiber, the selection range on the material for cladding becomes more wide. In addition, the coating performance and the adhesiveness to a substrate are improved compared to a conventional PI. Imide containing monomers based on 3,5,6-trichloro-4-chloroformyl phthalic acid anhydride have been proposed for optical applications, since the refractive index is sufficiently high.  

After formation of the intide monomer by reaction of the phthalic end groups, the PAI is formed by the reaction of the chloroformyl groups with an additional diamine. Essentially, the same diamines are utilized for the imidization reaction. 

4- Diamino-4 -(4-nitrophenyl-diazenyl)azobenzene 4-(4 -Nitrophenyl-diazenyl)phenyl-l,3-diamine 

The infrared band of the N=N linkage overlaps with that of the C=C vibration of the benzene ring at around 1600 cm. The PAls exhibit high glass transition temperatures and high thermal stability. Lateral alkyl substituents increase the light-induced orientation effect.  

Electrochromism is the reversible change in optical properties of a material caused by redox reactions. The redox reactions can be initiated when the material is placed on the surface of an electrode. When the electro-chromic material is capable of showing several colors, it is addressed as polyelectrochromic. 

At microwave frequencies in the range 72-145 GHz, the critical parameters for high-power transmission are the dielectric characteristics of the window material the dielectric loss factor tan 5 and the permittivity e[. (or the refractive index n = because they affect power absorption and reflection [42]. The dielectric loss factor tan 8 in low loss samples is usually measured as the decrease in the Q factor of a resonant cavity [43]. Low dielectric loss materials find application as the output windows of high-power microwave tubes. A specific case is that of windows for Gyrotron tubes operating in the 70-170 GHz frequency region with output powers in excess of 1 MW, as will be discussed later. 

Values of the dielectric loss of CVD diamond have been measured over the past 3 years as a suitable material grade for dielectric window applications was being developed [5]. For open resonant cavity measurements, samples are usually required to be of at least 30 mm in diameter and of thickness in excess of 0.87 mm depending on the measurement frequency and the accuracy required. For recent CVD diamond, values of tan 5 below 10 have been achieved. A specific example is a window 100 mm in diameter and 1.6 mm thick which exhibited a tan 8 value of 0.6 ( 0.2) 10 . This is the lowest value so far reported for CVD diamond and would enable the material to be used as output windows in Gyrotron tubes of powers in excess of 2 MW as discussed in 2.4. 

In this section, applications will be discussed which illustrate the versatility and advantages of CVD diamond as an infrared and multi-spectral window material. We describe the use of CVD diamond optical elements including CVD diamond domes and flat plates as windows for IR seekers or imaging systems in high-speed flight or other mechanically aggressive environments. Then we describe the use of CVD diamond windows for the transmission of high-power IR laser beams. 

2 Applications of Diamond Synthesized hy Chemical Vapor Deposition 

This glass-ceramic is characterized by high thermal shock resistance. It is pre-dominandy used to produce oven doors, through which burners can be monitored and problems detected visually. In addition, the glass-ceramic can be used as an alternative in every application using borosUicate or silicate glass. 

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Optical Applications. Vitreous siUca is ideal for many optical appHcations because of its excellent ultraviolet transmission, resistance to radiation darkening, optical polishing properties, and physical and chemical stabiUty. It is used for prisms, lenses, cells, wiadows, and other optical components where ultraviolet transmission is critical. Cuvettes used ia scatter and spectrophotometer cells are manufactured from fused siUca and fused quart2 because of the transmissive properties and high purity (222). 

M. Okawata, T. Kitao, T. Hirashima, and M. Matsuoka, Organic Colorants A Handbook of Selected Dyesfor Electro-Optical Applications, Elsevier, Amsterdam and New York, 1988. 

A second set of examples deals with the analysis of near-surface regions of glasses which normally have so-called altered or leached layers. The altered layer is found for soda-lime glasses and for many glasses used for optical applications. The chan-... 

The film that is selected for the application mainly controls the properties these products deliver to the customer. However, in the case of optical applications where transmission of the light is needed, the choice of pressure sensitive adhesive and the quality of the application to the substrate become very critical. Even for the non-optical uses, the PSAs have to perform reliably under sometimes very demanding circumstances. 

Since niobates and tantalates belong to the octahedral ferroelectric family, fluorine-oxygen substitution has a particular importance in managing ferroelectric properties. Thus, the variation in the Curie temperature of such compounds with the fluorine-oxygen substitution rate depends strongly on the crystalline network, the ferroelectric type and the mutual orientation of the spontaneous polarization vector, metal displacement direction and covalent bond orientation [47]. Hence, complex tantalum and niobium fluoride compounds seem to have potential also as new materials for modem electronic and optical applications. 

There are plastics that are transparent and translucent in the unpiginented state. They have a range of optical properties that make them interesting for a wide spectrum of optical applications that extends from windows to lens systems to sophisticated applications involving action via polarized light. Used for over a half century are aircraft canopies (thermoformed) and windows in many different structures. 

In using fiber optics the designer is mainly concerned with a standardized material which has specific characteristics in terms of optical performance. Fiber optics made of plastics can be affected by exposure to the environment with deterioration of performance. Heat is an important environmental factor and the most likely cause of damage in optical applications. The heat can be generated by the light sources used. Some of the infrared generated by light sources can be removed with the use of appropriate filters. 

Plastics are suitable for most optical applications that utilize transparent materials, including color carriers. Color filters have all types of standard transmission characteristics that can be made and, because of the uniqueness of the plastic structure, a large number of dichroic and trichroic materials are possible that have different colors when viewed from different angles. One application for this is in polarizing filters. 

Since the end of the 1970s, the polyimides have been introduced for the production of electronic components mainly for the passivation. But more and more they are interesting for the integrated circuits and multichip modulus fabrications. Processability and dielectric and thermomechanical properties are the most attractive features of these materials for the electronic31 and electro-optical applications.32... 

Electron microscopy, 163-164 Electro-optic applications, polyimide, 269 Electrophilic aromatic substitution, 329-334, 398... 

Inevitably, there is a certain degree of overlapping between these two general classifications. For instance, CVD optical applications are found as both coatings and fibers while fibers are used in optics as well as in structural and mechanical applications. These relationships will be reviewed in the several chapters on applications. 

The present chapter deals with the CVD of metals and some metal alloys and intermetallics. The metals are listed alphabetically. The range of applications is extensive as many of these materials play an important part in the fabrication of integrated circuits and other semiconductor devices in optoelectronic and optical applications, in corrosion protection, and in the design of structural parts. These applications are reviewed in greater depth in Chs. 13 to 19. 

The number of oxides is large since most metallic elements form stable compounds with oxygen, either as single or mixed oxides. However, the CVD of many of these materials has yet to be investigated and generally this area of CVD has lagged behind the CVD of other ceramic materials, such as metals, carbides, or nitrides. The CVD of oxides has been slower to develop than other thin-film processes, particularly in optical applications where evaporation. 

Tin oxide, Sn02, has unusual physical properties. It is a good electrical conductor. It is highly transparent to the visible and highly reflective to the infrared spectrum. It is deposited extensively by CVD mostly for optical applications. Its characteristics and properties are summarized in Table 11.6. 

The infrared (IR) of wavelength immediately above the visible ranging from 0.7 to 3 im (for present optical applications). IR radiation is a major source of heat. 

The ultraviolet (UV) with a range of wavelength immediately below the visible (from 0.19 to 0.4 im for optical applications). 

The following is a listing of recent optical applications, either present or potential, where CVD may play a maj or role. 

Abstract Optical Parametric Oscillators provide a very efficient source of tunable coherent radiation. The principle of different kinds of OPOs are described. OPOs are used in astronomy for Laser Guide Star systems, and they may be used for other nonlinear optics applications in astrophysics, such as frequency conversion or parametric amplification. 

Cone-Shaped Dipolar Dendrimers for Nonlinear Optical Application 216... 

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