Spectral apparatus

The cardinal element of a spectrometer, the spectral apparatus which is necessary for the selection or discrimination of radiation of different wavelengths, has been discussed above. It is used in connection with elements which generate, transport, and detect radiation. These components of an optical system are ... 

Radiation sources 136 Spectral apparatus 136 Sample techniques 138 Theory 138... 

With quartz fibers it is easier to lead the optical emission into the spectral apparatus, however, it should be mentioned that the transmittance decreases seriously below 220 nm. This may give rise to detector noise limitations for analytical lines at lower wavelengths. 

Spectral apparatus are used to produce the spectrum or to isolate narrow spectral ranges, without further spectrum deconvolution. In dispersive spectral apparatus, the spectrum is produced with a prism or a diffraction grating. In non-dispersive spectral apparatus, spectral areas are isolated from a radiation beam, without any further spatial deconvolution, by reflection, interference or absorption in an interferometer or a filter monochromator, respectively. The filter is now only of use in flame emission spectrometry. 

A dispersive spectral apparatus contains an entrance collimator, a dispersive element and an exit collimator (for an example discussion, see Refs. [48, 49]). 

The entrance aperture dimensions should not be made smaller than so and ho, as then diffraction will limit the resolution that can be obtained. The value of // W is a measure of the amount of radiation energy entering the spectral apparatus. 

The ratio (Ix/Iu) and the calibration constants cu for a given element and line depend on the radiation source and the working conditions selected but also on the spectral apparatus [338, 339] ... 

Cu, oo describes the influence of the radiation source, (dfJy/dl) is the spectral radiation density for the background intensity, B0 is the radiant density for an analytical line at the concentration c = 1 and A7L is the physical width of the analysis line. The second term (Ai) describes the influence of the spectral apparatus. 

Direct coincidence of lines when the wavelength difference is less than the spectral bandwidth of the spectral apparatus. 

Fig. 98. ICP-optical emission spectrometer, (a) gas supply, (b) sampler, (c) peristallic pump, (d) nebulizer, (e) nebulization chamber, (f) hf generator, (g) ICP torch, (h) spectral apparatus, data acquisition, data processing.

The detection of the fluorescence radiation differs in resonant and in non-resonant AFS. In the first case, the radiation is measured in a direction perpendicular to that of the incident exciting radiation. However the system will suffer from stray radiation and emission of the flame. The latter can be eliminated by using pulsed primary sources and phase-sensitive detection. In the case of non-resonant fluorescence, stray radiation problems are not encountered, although the fluorescence intensities are lower, which necessitates the use of lasers as primary sources and spectral apparatus that will isolate the fluorescence radiation. A set-up for laser excited AFS (Fig. 126) may make use of a pulsed dye laser pumped by an excimer laser. The selection of the excitation line is then done by the choice of the dye and... 

FIGURE 9. Block diagram of time-resolved spectral apparatus, [after Fig. 1, J. Polym. Sci., Polym. Phys. Ed. 1, 1499 (1978).]... 

A non-element-specific signal component may be produced by reflections in the spectral apparatus (stray radiation) or by radiation from other orders. 

The product of the minimum resolvable frequency interval Av and the maximum difference in transit times through the spectral apparatus is equal to 1. 

Sf is the spectral slit width corresponding to the physical width of the spectral line (AAf) and Rf = A/AAf, the resolution required to resolve the line width, s is the slit width corresponding to the optical aberrations in the spectral apparatus and is... 

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