Monochromator, control

The use of high-resolution grating monochromators for the Isolation of the selected wavelengths Is of crucial relevance to spectrochemical measurements. The remarkable advances In the functioning of monochromator control systems have considerably improved the precision with which these units can select a given wavelength. 

Fluorometry and Phosphorimetry. Modem spectrofluorometers can record both fluorescence and excitation spectra. Excitation is furnished by a broad-band xenon arc lamp foUowed by a grating monochromator. The selected excitation frequency, is focused on the sample the emission is coUected at usuaUy 90° from the probe beam and passed through a second monochromator to a photomultiplier detector. Scan control of both monochromators yields either the fluorescence spectmm, ie, emission intensity as a function of wavelength X for a fixed X, or the excitation spectmm, ie, emission intensity at a fixed X as a function of X. Fluorescence and phosphorescence can be distinguished from the temporal decay of the emission. 

The original motivation for the preparation of regular metallic multilayers of carefully controlled periodicity was the need for X-ray reflectors, both to calibrate unknown X-ray wavelengths and to function as large and efficient monochromators, especially for soft X-rays of wavelengths of several A. This was first done by... 

Monochromators. Replica gratings and narrow band-pass filters are used commonly, more so than quartz prisms. Computer control of the monochromator is available in some instruments, so that optimum intensity at the desired wavelength or maximum absorption by the examined substance can be obtained. 

Scattering on the Triple-Axis-Diffractometer [1,2] at the HASYLAB high-energy beamline BW5 is performed in the horizontal plane using an Eulerian cradle as sample stage and a germanium solid-state detector. The beam is monochromatized by a singlecrystal monochromator (e.g. Si 111, FWHM 5.8 ), focused by various slit systems (Huber, Riso) and iron collimators and monitorized by a scintillation counter. The instrument is controlled by a p-VAX computer via CAMAC. 

Emission spectrometer incorporating a sample nebulizer, grating monochromator, photomultiplier detection system and microprocessor controller. Excitation by dc-arc plasma jet, or inductively coupled plasma. Laser excitation sometimes used. 

The fluorescence spectra of dilute solutions (A < 0.05) of the compound and the standard must be recorded under exactly the same experimental conditions (slits of the monochromators, high voltage of the photomultipliers, gain of the electronic devices). The temperature of the sample holder must be controlled because the... 

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