Light beam, Cary

Fig. 24. The laser beam expander in the Cary 81 spectrometer (exaggerated). Only that part of the expanded plasma light transmitted through the expander is shown.

Measured extinction spectra for aqueous suspensions of polystyrene spheres—the light scatterer s old friend—are shown in Fig. 11.19. Water is transparent only between about 0.2 and 1.3 jam, which limits measurements to this interval. These curves were obtained with a Cary 14R spectrophotometer, a commonly available double-beam instrument which automatically adjusts for changing light intensity during a wavelength scan and plots a continuous, high-resolution curve of optical density. To reproduce the fine structure faithfully, the curves were traced exactly as they were plotted by the instru-... 

Absorption spectra of 2-nitroanisole in supercritical C02, N20, Freon-13, ammonia and C02-methanol mixtures were obtained on a Cary model 1605 spectrophotometer operated in the dual beam mode. The gases used as supercritical solvents were of the highest purity available from the supplier (Matheson) and were further filtered prior to use. The mixed solvent system of C02-methanol was obtained from Scott Speciality Gases (15.4 wt% methanol), and other mixtures were made in the laboratory. Spectra of 2-nitroanisole in n-pentane, methanol, tetrahydrofuran and acetonitrile (Burdick A Jackson) were obtained using quartz cells with a 1-cm light path and with a pure solvent blank in the reference beam. Vapor phase and supercritical fluid spectra were obtained using an air reference. 

Cary 14 diagram (ca. 1953) The arrows on the optical diagram trace the path of the UV and vis radiation through the instrument. Radiation from the D2 or W lamp is directed to the monochromator entrance slit D by appropriate lenses and mirrors. From mirror E it travels to prism F where it is refracted, then to mirror G which reflects it to variable-width intermediate slit H. Mirror I reflects the radiation to grating J and from there the monochromatic beam is directed to mirror K and exits the monochromator through slit L. Semicircular mirror O, driven by motor Q, chops the beam at 30 Hz and alternately sends half the beam to the reference and half to the sample. Elements V, V1, W, and W1 pass the separated beams to the phototube. The light pulses of the two beams are out of phase with each other so that the phototube receives light from only one beam at a time. The photomultiplier for UV-vis work is shown at X and the NIR detector for 700-2600 nm is shown at Y. 

The 488.0 nm Coherent Radiation Model 520-B argon-ion laser of 300 mW power was focused on the center of the drop and the Raman light is detected perpendicular to both the laser beam and the sample tube. Qualitative polarization measurements were made by rotating the plane of polarization of the laser beam with a half-wave plate. In most of the spectra, it was not necessary to use a spike filter to attenuate the plasma lines. The spectra were recorded using a modified Cary 81 spectrophotometer employing a 9558A EMI photo-multiplier counting detection system. 

Another kind of instability was observed in the work with the Cary spectrophotometer at Natick. The O.D. readings decreased as if a decomposition of the complex was taking place. This phenomenon was not observed with the single-beam spectrophotometer at Riso. A simple test in which a complex solution was exposed to intense ultraviolet light showed that a few minutes exposure decreased the optical density some 50%. A procedure, which takes care of this problem is described in Ref. 15. 

The fluorescence lifetime measurements were performed with a streak camera (Agat SF 3M, VNIIOFI, Russia). A Nd YAG laser with excitation wavelengths of 532 and 266 nm (the second and fourth harmonic of fundamental radiation) was used as a light source. The laser radiation parameters of the fluorimeter were as follows (for 532 nm) pulse energy 160 (ij, duration 20 ps (fwhm), beam diameter 5 mm. The error in determining the fluorescence lifetimes in time intervals of several nanoseconds did not exceed 5 %. In addition to the laser equipment, the Cary 100 spectrophotometer (Varian, Inc., USA) and the Cary Eclipse spectrofluorimeter (Varian, Inc., USA slits width was 5 nm) were used for optical density measurements and fluorescence registration, respectively. 

The Varian Cary. 300 shown in Figure 13-23 use.s a premonochromator in front of the same double-bcam-in-lime instrument shown in Figure 13-22. The second monochromator reduces the stray-light levels to 0.000041% at 370 nm and 0.00008% at 220 nm. This extends the absorbance range to 5.0 absorbance units. Most of the other characteristics are identical to that of the Varian Cary 100. Both units have a double-chopper arrangement that ensures nearly identical light paths for both beams. The two beams strike the photomultiplier tube at es.sentially the same point, which minimizes errors due to photocathode nonuniformity. 

UV-visible spectra were determined using a Varian Cary 100 Bio-UV-Visible split-beam spectrophotometer running with Cary WinUV scan application with a capacity of measuring six samples at a time. Samples were scanned at 500 nm. A high-intensity Xe flash lamp was used as the source for UV light, which permits taking 80 data per second. 

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