Spectral Continuum

In some cases the interference caused by a background spectrum line which directly coincides with the desired analyte can be avoided by background correction. For example, the OH molecular line overlaps the A11 line at 308.2 nm. Because the OH signal is relatively constant, it can be subtracted out with the blank signal. However, this will add background noise that can interfere with the determination at low analyte concentrations. This type of problem is much greater when the spectral line originates from a concomitant line which directly overlaps the analyte line, like the coincidence of the Cu I line at 213.859 nm with the Zn I line at 213.856 nm, or that of the 

As I line at 228.812 nm with the Gd I line at 228.802 nm. In such a case, an alternative line should be used. However, this may also be problematic if the analyte has few sensitive lines, as in the case of cadmium. When a higher resolution spectrometer, such as an echelle spectrometer, is used the lines are farther apart than their physical widths. However, interference is still possible through broadened line wing overlap or stray light. 

---

A continuum source provides a broad distribution of wavelengths within a particular spectral range. This distribution is known as a spectral continuum. 

Plasma Appearance and Spectra The typical plasma has a very intense, brilliant white opaque core topped by a flame-like tail. The core, which extends a few millimeters above the tube, produces a spectral continuum with the atomic spectrum of argon superimposed. The continuum is typical of ion-electron recombination reactions and bremsstrahlung, which is continuum radiation produced when charged particles are slowed or stopped. 

Continuum source A source that emits a spectral continuum of wavelengths examples include tungsten filament lamps and deuterium lamps used in absorption spectroscopy. 

Deuterium lamp A source that provides a spectral continuum in the ultraviolet region of the spectrum radiation results from application of about 40 V to a pair of electrodes housed in a deuterium atmosphere. 

X-ray sources, like ultraviolet and visible emitters, often produce both continuum and fine spectra both types are of importance in analysis. Continuum radiation is also called whhe radiation or hremsstrahfung. Brenisstrahlung means radiation fhat arises from retardation of particles such radiation is generally a spectral continuum. 

Figure 10.6. Atomic absorption with A) a sharp-line source and (B) a spectral-continuum source. AA = absorption line half-width AA, = source line half-width S = spectral bandwidth of monochromator. Adapted from G. D. Christian and F. J. Feldman, Atomic Absorption Spectroscopy Applications in Agriculture, Biology, and Medicine, New York Wiley-Interscience, 1970, p 58, by permission of John Wiley and Sons.

Spectral continuum. Spectral interference caused by one of the matrix components emitting a continuum spectrum at the analyte line wavelength, may be overcome by changing the analyte line or by using chemical separation. For example, in the emission spectrum of aluminium an unstructured continuum begins at 212 nm and continues down below 190 nm (Figure 133). This causes a problem with the emission lines of cadmium (at... 

A typical experimental arrangement used in our lab for studying molecular Rydberg states is exhibited in Fig. 5.38. The pump laser is a single-mode cw dye laser, which is amplified in two pulsed amplifier cells pumped by a nitrogen or excimer laser. The spectral continuum is provided by the broad fluorescence excited in a dye cell by part of the excimer laser beam. Since this spectral continuum is only formed within the small pump region in the dye cell, it can be transformed... 

A small fraction of the pump beam generates a broad spectral continuum in a sapphire plate. The larger fraction is frequency doubled and sent by beam splitters into three BBO crystals for parametric amplification. The seed beam collimated from the focal spot in the sapphire plate is also imaged into the three BBO crystals, where they are superimposed on the frequency-doubled pump beams. The three parametric amplifiers can be independently tuned by changing the orientations of the crystals. The total tuning range is only limited by the spectral bandwidth of the seed beam continuum. 

Fig. 10.23 Spectral continuum emitted by the plasma spots along the propagation path of terawatt laser pulses in the atmosphere [1472]...

Fig. 4.12. (a) Diffraction limited intensity distribution I x2) in the plane B for different widths b of the entrance slit, (b) The width hx2 h) of the entrance slit image S2 x2) with and without diffraction by the aperture a. (c) Intensity I x2) in the observation plane as a function of entrance slit width b for a spectral continuum c and for a monochromatic spectral line (m) with diffraction solid curves) and without diffraction dashed curves)... 

Figure 2.16 a Absorption of a parallel light wave with cross section A travelling into the z-direction. b Exponential decrease of the transmitted intensity I(z). c Absorption profile of in incident spectral continuum with an intensity hole around the centrefrequency a>o... 

White LEDs are also available in which the light from a blue LED (luGaN) strikes a phosphor, which emits a spectral continuum typically in the range of 400 -800 nm. Such LEDs are being used to make lighting products such as flashlights. They have the advan-... 

Each physiological effect can be evaluated and categorized on a broad spectral continuum from mild to... 

---