Subject optical glasses

The telecommunication industry requires optical glass fibers with very high strength (>1 GPa) over very long lengths (>1 km). For example, the True Wave single mode fiber of Lucent Technologies is routinely subjected to a proof stress of 0.7 GPa (see below) while the Weibull modulus is claimed to be 147 (Kummer,... 

Special durability tests have been made on optical glass. Qualitative gradings of durability were developed and listed in the glass catalogues. Quantifying such chemical attack is extremely difficult and has been the subject of international research. 

Fij . 17. Weibull plots of optical glass fibers subjected to pulse-irradiation and continuous wave treatments. The use ol pulsed exeitner radiation lowered the liber t racture strength by as rniich as a factor of 4 compared to the liber that was subjected to a CW argon-ion laser. The lower fracture strength ol pulse-irradiated liber is a result of the formation of microcracks in the material (after Varelas el al.. 1997). 

Dimming Test. To determine the durability of optical glass the surface is subjected to the action of air saturated with water vapour at a definite temperature (usually 80°C) for a specified period. Any dimming of the surface is then observed. 

Thermodyne Test. A test to determine the durability of optical glass in contact with moist air. Freshly broken or optically polished surfaces, sealed off in a flask together with a quantity of water, are subjected to a series of temperature cycles, each of 2 h duration, from 15 to 60°C in air saturated with water vapour... 

The design and manufacture of optical glass and the techniques for generating and polishing precision lens and mirror surfaces comprise some of the more technically sophisticated areas of glass science and technology. Many treatises and books have been written on those subjects, so the coverage in this chapter can be only superficial. 

Although there seems an optical trickery at work in his newly discovered visual Jewishness— He took the glasses off and slowly put them on again to observe the distortion —Newman s torrent of associations confounds the notions of objectivity and subjectivity, revealing his presumptive Jewishness as a complicated interplay of physicality and character ... 

However, due to other favorable properties, such as optical transparency and ease of formability, glasses find wide industrial use and, as a result, have been the subject of much investigation. 

One of the properties of a class of materials known as chalcogenide glasses is that they exhibit a wide spectrum of photoinduced effects. Photoinduced phenomena have recently been extensively studied (see corresponding references in previous sections), partly as an interesting subject for fundamental research in the field of disordered sohds and partly due to the potential apphcation of these phenomena in opto(photo)electronics (xerography and xeroradiography, optical memories, optical circuits, photoresists, etc.). 

This review will be concerned with fluorescent-lifetime studies upon condensed systems (that is, glasses, liquids, or crystals) containing rare-earth ions, and will to a large extent deal only with trivalent ions pumped by optical means. Laser phenomena themselves will not be considered, because a number of very excellent review articles (5-7) and books (8, 9) already exist on this subject. 

The reflecting stereoscope is not open to any single practical or theoretical objection. As an optical instrument it is absolutely perfect, being subject to no defects of distortion or aberration. For any scientific purpose, therefore, the reflecting stereoscope should always he preferred to the Other. The reflectors may be made of polished speculum metal if objection be raised to glass mirrors, and the pictures may he taken simultaneously in a camera with double lenses two and a half inches from centre to centre. 

To pursue the subject of the stereoscope through all its details, as exhibited in the tubular reflecting, the single and double reflecting stereoscopes, the opera-glass, reading stereoscopes, el cetera, is incompatible with tho limits of this work the student who may desire further acquaintance with the subject is referred to Brewster- on the Stereoscope, or any of tlie works on optical science which are to bo found in libraries, The following remarks will not be out of place — ... 

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