Optical components

7 Glass Ceramiis for Fiber Bragg Grating Athermalization 

The understanding of the position of the lithium ions in P-eucryptite has evolved over the years. Pillars and Peacor determined that there are four sixfold channels in the unit cell, each containing Li ions. In only one channel do the Li atoms reside within the layers of Al atoms, the so-called Li(l) site. The remaining three channels, which are symmetrically equivalent, contain Li(2) and Li(3) sites, which reside within layers of SiO tetrahedra (see Section 1.3.1). While at low temperatures the Li ions are observed to reside in these three distinct sites, at temperatures above 482 C, the lithium ions become disordered over the two sites Li(l) and Li(2). This order-disorder transformation has not been observed to have any effect on the thermal expansion behavior. 

Xu et al. (1999) also discovered that the thermal contraction of the c-axis of p-eucryptite is inhibited as the crystal is cooled below room temperature. By contrast, c continues to increase until it is saturated near 20°C. This yields average CTE values, from 20 to 298 K for ordered crystals, of+ 18.1 X 10 K along the a-sxes and +109.5 X 10 K along the c-axis. Curiously, in the disordered crystals over the same temperature range, both axes are negative, —10.4 X 10 for a and —85.3 X 10 K for c. Xu et al. (1999) attribute the inhibition of -axes contraction with cooling below room temperature to strengthening localization of Li ions. 

Rgure 4-20 Thermal expansion/contraction behavior of a 8-eucryptite solid solution glass-ceramic heated at 1300°C for different lengths of time and differing resulting grain size (4 h in a microcrack on cooling). 

CTE hysteresis is usually observed in such microcracked materials when subjected to thermal cycles (Cillery and Bush, 1959), and this is also with P-eucryptite glass-ceramics. On initial cooling, the random network of microcracks develop, and those nearly perpendicular to the -axes of adjacent grains of similar orientation open significantly, accommodating contraction, while those perpendicular to the c-axes of adjacent grains with similar orientations remain closed and bulk expansion results. A variety of random microcracks, some open to various degrees and some closed can be seen in Fig. 4-22, 

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Such requirements are meant to change the usual configurations and technologies usually associated with photothermal set-up. These changes mainly affect the IR detection devices, the optical components associated with the excitation and detection flux and the signal acquisition hardware and software. Figure 9 presents a sketch of the so-called pre-industrial demonstrator built from those different improvements. 

The principle of optical triangulation has been known since the time of the early Greeks, and indeed optical triangulation has been used for hundreds of years in applications such as surveying, camera auto-focus and even smart-bombs. With the advent of low-cost, compact electro-optic components such as lateral-effect photodetectors, diode lasers and micro-optics, laser-based triangulation sensors can now be employed for applications that were, heretofore, considered uninspectable. 

Ippen E 1997 Characterizing optical components for ultrafast laser applications Optics 1997/98 Catalog (Irvine, CA Newport Corp.) pp 8-2-8-3... 

The market for optical fiber worldwide in 1992 was 2.8 billion corresponding to 10 million fiber kilometers (Mfk) (38). This can be broken down into the U.S. market (3.7 Mfk), the rest of North America (0.4 Mfk), northern Europe (4.1 Mfk), eastern Europe (2.6 Mfk), the Pacific Rim (2.8 Mfk), and elsewhere (0.3 Mfk). Most of the optical fiber is manufactured by only a few companies, the largest of which are AT T and Coming. Other producers include Alcatel, Eujikura, Eurakawa, Northern Telecom, Pirelli, and Sumitomo. The market for optical fibers is projected to reach 3.5 biUion by 1998. In addition, according to ElectroniCast (San Mateo, Ca.), the total market for passive optical components, optical electronics, connectors, and fiber-optic cable is predicted to increase from 1.76 billion (U.S.) in 1992 to over 4 billion in 1997, and 10 billion by 2002. 

A small but artistically interesting use of fluorspar is ia the productioa of vases, cups, and other ornamental objects popularly known as Blue John, after the Blue John Mine, Derbyshire, U.K. Optical quaUty fluorite, sometimes from natural crystals, but more often artificially grown, is important ia use as iafrared transmission wiadows and leases (70) and optical components of high energy laser systems (see Infrared and RAMAN spectroscopy Lasers) (71). 

Optical windows of highly purified magnesium fluoride which transmit light from the vacuum ultraviolet (140 nm) into the infrared (7) are recommended for use as ultraviolet optical components for use in space exploration. 

W. D. Rogatto, "Electro-Optics Components," inj. S. Accetta andD. L. Shumaker, eds.. The Infrared Electro-Optical Systems Handbook, Vol. 3, SPIE Optical Engineering Press, Bellingham, Wash., 1993. 

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). 

Dehydration or Chemical Stabilization. The removal of surface silanol (Si—OH) bonds from the pore network results in a chemically stable ultraporous soHd (step F, Fig. 1). Porous gel—siHca made in this manner by method 3 is optically transparent, having both interconnected porosity and sufficient strength to be used as unique optical components when impregnated with optically active polymers, such as fiuors, wavelength shifters, dyes, or nonlinear polymers (3,23). 

Stabilization. A critical step in preparing sol—gel products and especially Type VI siHca optical components is stabilization of the porous stmcture as indicated in Figure 1. Both thermal and chemical stabilization is required in order for the material to be used in an ambient environment. The reason for the stabilization treatment is the large concentration of hydroxyls on the surface of the pores of these high (>400 /g) surface area materials. 

Many chlorine compounds, including methyl chlorosilanes, such as ClSi(CH2)3, Cl2Si(CH3)2, Cl3Si(CH3) tetrachlorosilane [10026-04-7] SiCl chlorine, CI2 and carbon tetrachloride, CCl, can completely react with molecular surface hydroxyl groups to form hydrochloric acid (40), which then desorbs from the gel body in a temperature range of 400—800°C, where the pores are still interconnected. Carbon tetrachloride can yield complete dehydration of ultrapure gel—siUca optical components (3,23). 

Mumber Density and Volume Flux. The deterrnination of number density and volume dux requires accurate information on the sample volume cross-sectional area, droplet size and velocity, as well as the number of droplets passing through the sample volume at any given instant of time. Depending on the instmmentation, the sample volume may vary with the optical components and droplet sizes. The number density represents the number of droplets contained in a specified volume of space at a given instant. It can be expressed as follows, where u is the mean droplet velocity, t the sample time, andM the representative cross-sectional area at the sampling location. 

Optical Coatings. Thin surface coatings are appHed to optical components to improve performance. Wideband antireflection coatings for the visible and ir regions need materials with a refractive iadex of for the best efficieacy. Cerium fluoride, a stable material resistant to humidity damage, has a suitable iadex, 1.63 ia the visible, 1.59 ia the iafrared, and is transparent over the range 0.5 p.m to 5 p.m. It is one of the compounds used to build up the multilayers deposited on lenses, sensors, and the like. 

A variety of commercial instruments are available for PL measurements. These include spectrofluorometers intended primarily for use with liquids in a standard configuration, and simple filter-based systems for monitoring PL at a single wavelength. For use with opaque samples and surfaces, a few complete commercial systems are available or may be appropriately modified with special attachments, but due to the wide range of possible configuration requirements it is common to assemble a custom system from commercial optical components. 

A Q-switched, frequency-quadrupled Nd—YAG laser (X, = 266 nm) and its accompanying optical components produce and focus the laser pulse onto the sample surface. The typical laser spot size in this instrument is approximately 2 pm. A He-Ne pilot laser, coaxial with the UV laser, enables the desired area to be located. A calibrated photodiode for the measurement of laser energy levels is also present... 

From a practical sense, MOKE is a versatile technique it is an optical method the polarization measurement is fairly easy to do the necessary optical components are common and relatively inexpensive and it has no intrinsic vacuum requirements. 

Polymers have come a long way from parkesine, celluloid and bakelite they have become functional as well as structural materials. Indeed, they have become both at the same time one novel use for polymers depends upon precision micro-embossing of polymers, with precise pressure and temperature control, for replicating electronic chips containing microchannels for capillary electrophoresis and for microfluidics devices or micro-optical components. 

The Laboratoire d Astrophysique de Marseille is developing since several years an expertise in the design and characterization of micro-optical components, as well as in their integration in astronomical instruments. 

In fact we could find many other requirements, but those three are directly related to the optical properties of the detector. At this point we could simply describe the various optical components of the detector, but it is more interesting to understand what led to the choice of some particular properties of those... 

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