Optical transmission ranges

Vitreous siUca has a wide range of commercial and scientific appHcations. Its unique combination of physical properties iacludes good chemical resistance, minimal thermal expansion, high refractotiness, and excellent optical transmission from the ultraviolet to the near-iafrared. 

Optical Properties. The optical transmission of vitreous siUca is influenced by impurities and the forming process. Ultrapure vitreous siUca has the abihty to transmit from the deep ultraviolet, through the visible, and into the near-infrared spectral range. 

The term solid-state laser refers to lasers that use solids as their active medium. However, two kinds of materials are required a host crystal and an impurity dopant. The dopant is selected for its ability to form a population inversion. The Nd YAG laser, for example, uses a small number of neodymium ions as a dopant in the solid YAG (yttrium-aluminum-gar-net) crystal. Solid-state lasers are pumped with an outside source such as a flash lamp, arc lamp, or another laser. This energy is then absorbed by the dopant, raising the atoms to an excited state. Solid-state lasers are sought after because the active medium is relatively easy to handle and store. Also, because the wavelength they produce is within the transmission range of glass, they can be used with fiber optics. 

Optics Issues relative to hygroscopic optics and the need to pay attention to mirror mounts relative to vibration and/or thermal effects have already been addressed. Zinc selenide is an important alternative material, especially when antireflection (AR) coated. If potassium bromide absolutely has to be used for its lower transmission range (down to 400 cm ) then a protective coating such as Parylene must be used. Most process analyzers use protective windows between the spectrometer and the sample interface. If used, back reflections from the window surfaces into the interferometer must be avoided because these will cause photometric errors. Such reflection can be eliminated by wedging or tilting the optical windows, relative to the beam path. 

Mhe usable range is normally less than the transmission range because of the higher optical attenuation that results from the extended optical... 

An important application for garnets is for isolators in optical communications systems. Reflections from end-faces of components and interconnections in an optical transmission line have a destabilizing effect on the operation of the laser sources and have to be eliminated. This is achieved using an optical isolator , the optical analogue (2 typically in the range 1.30—1.55 /mi) of the microwave isolator described in Section 9.5.5. 

Bruker has introduced an FT-Raman microscope which is an accessory to an FT-IR spectrometer (42). The coupling between the microscope and the Raman module is made by NIR-fiber optics. In the wavelength range of the Raman experiment excited by a Nd YAG laser, the fiber optics transmission is at a maximum, thus allowing the experiment to be successful (43). Spatial resolution down to 5//m can be achieved. The technique appears to be a capable adjunct to FT-IR microscopy. 

Janai and Moser (1982) have used chemical-vapor-deposited amorphous silicon films that were deposited at 600°C on silica (fused quartz) substrates. Information was recorded in films with thickness d between 2500 and 5000 A by irradiation with a ruby laser pulse of 50 nsec duration and an energy density ranging from 0.4 to 1.5 J cm-2. The upper energy limit is known to be above the threshold for laser melting in a-Si (Baeri et al., 1980). To determine the optical transmission density difference... 

Because of the wide transmission range and low phonon energies of fluoride glasses, the observation of numerous rare-earth laser lines is possible at wavelengths beyond 2 fim, where the transmission of silica fibers is extremely poor. Laser sources around 2 /jm are of special interest because they belong, not only to the eye-safe spectral domain, but also to an optical transparency window of the atmosphere. Two fluoride glass fiber lasers have been demonstrated in that region. First, a Ho3+ laser with the 5I7 -> 5I8 transition at 2.024 /on which delivers 250 mW with 60%... 

Due to the high optical quality of crystals and their wide transmission range, fluorides are well suited for the study of spectroscopic properties. They have brought a major contribution to the knowledge of luminescence processes. 

Because of the optical quality and chemical stability of crystals, the low probability of non radiative processes and the wide transmission range, fluorides are the most appropriate materials for solid state lasers with specific wavelengths. Thus the 4f - 4f line emissions of lanthanide ions have been used in order to obtain infrared laser radiation up to 4.34 fxm and blue or green radiation by up-conversion pumping. Tunable laser operation in the ultraviolet has been demonstrated using the broad 5d 4f emission of Ce3+. Tunable lasers in the UV or IR ranges have also been experimented using Ag+, Pb+, 3d ions. 

Fig. 7 shows the optical transmittance spectrum of the entire ZnO-TFT in the wavelength range between 200 nm and 2500 nm (including the glass substrate with 1.1 mm thickness). The average optical transmission in the visible part of the spectrum is 80% while at 550 nm (maximum sensitivity for the human eye) it is 85%, which indicates that transmission losses due to the ZnO-TFTs in comparison with the uncoated glass substrate are negligible... 

Optical material Chemical composition Transmission range (in 1Q4 cm ) " Refractive index Range of refr. index measurement.s Remarks -a n 0 3 c... 

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