Wavelength continued

FIGURE 5.7 The dependence of the intensity of blackbody radiation on wavelength at two different temperatures. Intensity increases from right to left on the curve as wavelength decreases. As the wavelength continues to decrease, intensity reaches a maximum and then drops off to zero. 

Two UV detectors are also available from Laboratory Data Control, the UV Monitor and the Duo Monitor. The UV Monitor (Fig.3.45) consists of an optical unit anda control unit. The optical unit contains the UV source (low-pressure mercury lamp), sample, reference cells and photodetector. The control unit is connected by cable to the optical unit and may be located at a distance of up to 25 ft. The dual quartz flow cells (path-length, 10 mm diameter, 1 mm) each have a capacity of 8 (i 1. Double-beam linear-absorbance measurements may be made at either 254 nm or 280 nm. The absorbance ranges vary from 0.01 to 0.64 optical density units full scale (ODFS). The minimum detectable absorbance (equivalent to the noise) is 0.001 optical density units (OD). The drift of the photometer is usually less than 0.002 OD/h. With this system, it is possible to monitor continuously and quantitatively the absorbance at 254 or 280 nm of one liquid stream or the differential absorbance between two streams. The absorbance readout is linear and is directly related to the concentration in accordance with Beer s law. In the 280 nm mode, the 254-nm light is converted by a phosphor into a band with a maximum at 280 nm. This light is then passed to a photodetector which is sensitized for a response at 280 nm. The Duo Monitor (Fig.3.46) is a dual-wavelength continuous-flow detector with which effluents can be monitored simultaneously at 254 nm and 280 nm. The system consists of two modules, and the principle of operation is based on a modification of the 280-nm conversion kit for the UV Monitor. Light of 254-nm wavelength from a low-pressure mercury lamp is partially converted by the phosphor into a band at 280 nm. 

The photolytic pathway for A -l,3,4-oxadiazolines (22) (Scheme 8) begins with C-N cleavage to form diradicals (23), followed by ester elimination and generation of diazoalkanes (24). Further photolysis gives the corresponding carbenes. In a study of (22b) and (22c), flash-photolysis and two-wavelength continuous... 

Verdet Constants of Rare-Earth Aluminum Garnets at Various Wavelengths (continued) ... 

Using well-known rhodamines and newer coumarin dyes, one may tune wavelength continuously from 650 nm down to below 400 nm with good power and bandwidth and by frequency doubling, using various crystals, wavelengths down to 260 nm are available with reduced output power. 

The differential reflection spectrometer (also called the differential reflectometer) measures the normalized difference between the reflectivities of two specimens (or two slightly different parts of a specimen) as a function of photon energy. Unpolarized, monochromatic light (having the possibility to vary the wavelength continuously) is alternately deflected to one or the other sample by means of a vibrating... 

Variable wavelength continued) 190-900 nm 190-900 nm Varian Pharmacia LC Star Systems System for biomolecules Star 9060... 

Andrews [9] and others [10] have listed the emission lines of the most commonly available discrete-wavelength lasers (such as ruby, Nd YAG, Er YAG, excimer lasers) over the range 100 nm-10 /u.m. Molecular lasers (HF, CO, CO2, NO) can be tuned to a large number of closely spaced but discrete wavelengths. Continuously tuneable lasers comprise some metal ion vibronic lasers (e.g. alexandrite and Ti sapphire [11]), some diode and excimer lasers, dye and free-electron lasers. Tuneable sources of coherent radiation span the electromagnetic spectrum from 300 nm to 1 mm, with limited tune-ability down to about 200 nm. Wavelength coverages of tuneable lasers have been reported [8]. In operation lasers can be either pulsed (e.g. various metal ion tuneable vibronic lasers, excimer and dye lasers, metal vapour) or continuous wave (major types atomic and ionic gas lasers, dye and solid-state lasers). Most lasers with spectral output in the UV are bulky and expensive devices (especially sub 200 nm) and operate in the pulsed mode. On the contrary, many visible lasers are available which are compact, require low maintenance expenses and operate in continuous-wave (CW) mode. 

TABLE 7.1 Wavelengths of X-Ray Emission Spectra in Angstroms Continued)... 

TABLE 7.2 Wavelengths of Absorption Edges in Angstroms (Continued)... 

In 1817, Josef Fraunhofer (1787-1826) studied the spectrum of solar radiation, observing a continuous spectrum with numerous dark lines. Fraunhofer labeled the most prominent of the dark lines with letters. In 1859, Gustav Kirchhoff (1824-1887) showed that the D line in the solar spectrum was due to the absorption of solar radiation by sodium atoms. The wavelength of the sodium D line is 589 nm. What are the frequency and the wavenumber for this line ... 

A wavelength selector that uses a diffraction grating or prism, and that allows for a continuous variation of the nominal wavelength. 

Lasing substances Physical state Laser wavelength (nm) Pulse length or continuous wave Typical maximum power output (watts)... 

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