Sapphire construction

These limitations have recently been eliminated using solid-state sources of femtosecond pulses. Most of the femtosecond dye laser teclmology that was in wide use in the late 1980s [11] has been rendered obsolete by tliree teclmical developments the self-mode-locked Ti-sapphire oscillator [23, 24, 25, 26 and 27], the chirped-pulse, solid-state amplifier (CPA) [28, 29, 30 and 31], and the non-collinearly pumped optical parametric amplifier (OPA) [32, 33 and 34]- Moreover, although a number of investigators still construct home-built systems with narrowly chosen capabilities, it is now possible to obtain versatile, nearly state-of-the-art apparatus of the type described below Ifom commercial sources. Just as home-built NMR spectrometers capable of multidimensional or solid-state spectroscopies were still being home built in the late 1970s and now are almost exclusively based on commercially prepared apparatus, it is reasonable to expect that ultrafast spectroscopy in the next decade will be conducted almost exclusively with apparatus ifom conmiercial sources based around entirely solid-state systems. 

Because Raman spectroscopy requires one only to guide a laser beam to the sample and extract a scattered beam, the technique is easily adaptable to measurements as a function of temperature and pressure. High temperatures can be achieved by using a small furnace built into the sample compartment. Low temperatures, easily to 78 K (liquid nitrogen) and with some diflSculty to 4.2 K (liquid helium), can be achieved with various commercially available cryostats. Chambers suitable for Raman spectroscopy to pressures of a few hundred MPa can be constructed using sapphire windows for the laser and scattered beams. However, Raman spectroscopy is the characterizadon tool of choice in diamond-anvil high-pressure cells, which produce pressures well in excess of 100 GPa. ... 

The actual cylinders and pistons of a two-headed pump are constructed in a very similar manner to the single piston pump with a sapphire piston and a stainless steel cylinder. Each cylinder is fitted with nonreturn valves both at the inlet and outlet. The cams that drive the two pistons are carefully cut to provide an increase in flow from one pump while the other pump is being filled to compensate for the loss of delivery during the refill process and thus, a fall in pressure. A diagram of a twin-headed pump is shown in figure 10. 

Figure 6.2 A fourth-order coherent Raman spectrometer constructed with a Ti sapphire regenerative amplifier (Ti sapphire) and noncollinear optical parametric amplifier (NOPA).

The reactor assembly was heated by electric heaters. The maximum operating temperature Is determined by the window construction. Sapphire windows (from EIMAC), brazed into Kovar sleeves, were used the sleeves were then welded directly into the stainless steel reactor housing. We found that the cell so constructed was capable of trouble-free, continuous operation at 450°C operations at somewhat higher temperatures are probably still possible but were not explored. Sapphire was chosen as a window material because it is insensitive to water vapor and is transparent in tljie wave number range of our interest (about 2400 cm to 2000 cm in these experiments). Moreover, the thermal expansion characteristics of the reactor were found to match well with those of the window fixture. 

Figure 7.2 Fast spinning, high pressure NMR sapphire tube with safety and charging device (constructed at ICCOM-CNR, 2003).

A different approach from using a pill-box cuvette is one in which a metal block contains a machined-out cuvette that is placed in the cell compartment of a spectrophotometer, and the pressure is applied directly to the reacting solution.82 The metal block contains two sapphire windows for observation purposes. Reactions that are sensitive to the metal of the constructed cuvette could not be used with this arrangement. 

Ceramic materials, including sapphire, have been used extensively in HPLC pumps for more than 20 years as pistons and check valve components. These materials have also been used to construct heads because of their good chemical stability. The use of ceramics is limited, however, because of high cost and brittleness. Although many systems have one material as the primary construction material, the wetted surfaces of a pumping system can contain several other materials. Therefore, for material-sensitive applications, all the materials in the HPLC eluent flow path should be considered. Materials that may be encountered are polymeric materials for pump seals such as fluoropolymers, polypropylene, and Teflon sapphire pump pistons and check valve seats ruby check valve balls Kalrez, KelF, or ceramic washers and spacers polymer-based transducer components and in older systems connections and joints made with silver solder. 

Radiation at 734 nm from a continuous-wave, single-frequency Ti sapphire laser, will be coupled into a high finesse cavity constructed around the Oxford... 

Two major improvements in the fabrication of an ion-sensitive FET that avoid most of the tedious polymer encapsulauon process have been reported. Matsuo and his coworkers (4, 37) fabricated a probe-type FET with a three-dimensional silicon nitride passivation layer around most of its surface, as shown in Fig. 2. The probe-type FET has one disadvantage Its fabrication requires a three-dimensional process that is uncommon for semiconductor construction facilities. An alternative approach utilizes a silicon-on-sapphire (SOS) wafer for FET fabrication (38, 39). The structure of a SOS-FET is depicted in Fig. 3. It has an island-like silicon layer on a sapphire substrate, in which an ion-sensitive FET is fabricated. The bare lateral sides do not need encapsulation because of the high insulation property of sapphire. 

Lecotrac LTU-25I Coupled to an external probe, this analyzer allows fast in-line measurement. The external probe is constructed of rugged, flexible steel and can be attached to a process line via a 3/8-inch NPT pipe-thread mounting hardware. The probe tip consists of a sapphire window embedded in a stainless steel sleeve using Teflon seals. 

Emission decays were obtained from a fs Tl sapphire laser uorescence upconversion spectrometer whose construction is reported elsewhere [8]. Here we only note that the overall temporal response used in these studies was between 112-125 fs as measured by the FWHM of the cross correlation between the pump and gate pulses. Decays (0-200 ps with a variable step size) were collected at a series of ten emission wavelengths (8 nm bandpass) which were then used to reconstruct time-evolving emission spectra in the manner described in Refs. 8 and 9. From these spectra the solvation dynamics was extracted in the form of the spectral response function,... 

The reaction vessel and other experimental equipment are shown in Fig. 11. The cell is constructed of nickel and Monel in a closed-loop design.. 4 is a cylindrical reaction chamber about 100 ml. in volume and 9 cm. long. Vacuum-tight sapphire windows 3 mm. thick, allow the light to... 

Construction and Operation of the Sapphire NMR Tube. Sapphire was chosen as the material for tube construction because its excellent tensile strength characteristics can be uniformly retained in a tube grown intact as a single crystal. Tubes 5 mm in o.d., with 0.8 mm wall and sealed at one end, were chosen for our prototype and were purchased from Saphikon, Inc. (51 Powers Street, Milford, NH 03055) at the time of our original purchase, the cost of the tubes was approximately 300 each. 

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