Continuum Light Sources

The stimulated Raman emission exhibits a threshold and only a few vibrational lines are observed, corresponding to the lines of highest intensity in the normal Raman spectrum. For observation of the inverse Raman spectrum, both the continuum and the monochromatic stimulating radiation are supplied. There is no threshold and therefore the complete Raman active spectrum can be obtained if the continuum light source has a sufficient spectral bandwidth. 

Bradshaw, et al. (28). in their experiments, a continuum light source was used although they have since used pulsed laser sources. We have also performed some preliminary experiments (29). The result of these experiments show the necessity of using laser excitation sources if there is to be adequate signal noise to perform measurements in turbulent flows. We are currently assembling a CW laser system for two-line fluorescence in our laboratory. 

With the majority of food products, copper can usually be determined by FAAS. In the few instances of low copper levels, resort has commonly been made to chelation—solvent extraction prior to FAAS measurement [8d, 34, 37m, 217] recent reports on the application of EAAS to analysis of foodstuffs and biological materials have appeared [193, 201, 204, 205, 223, 224], The importance of non-atomic absorption in the determination of copper in plant digests by FAAS has been studied by Simmons [225]. Correction was necessary to arrive at good results, with a continuum light source providing more accurate data than use of a nearby non-absorbing line. 

The unusually large cross section measured at 55.5 nm may result from the absorption by one of the higher members of the autoionizing lines. The line shapes and cross sections of these autoionizing lines are difficult to determine using the line source such as the one used in the present experiment. A sjmchro-tron radiation source may provide an ideal continuum light source for such detailed studies. 

Figure 25F-9 (a) Spectrum of a continuum light source, (b) Interfero-gram of the light source in (a) produced at the output of the Michelson interferometer. 

Figure 13.6 Comparison of transmitted intensities in AAS with a continuum light source (1 and 2), and with a lamp that emits spectral lines (3 and 4). The square region describes the wavelength interval seen by the PMT. The PMT signal is proportional to the white parts in the squares. In this way the resolution is in the source, as expressed by Walsh, who is considered to be one of the pioneers of atomic absorption.

Why will a nonlinear calibration curve and a loss in sensitivity generally occur in atomic-absorption spectroscopy when using a continuum light-source as compared to a sharp-line source ... 

Molecular absorption methods described in the literature are based on the use of continuum light sources (deuterium lamp with a thermal cathode or hollow cathode) or line-like radiation sources (hollow cathode lamps). Measurements using a continuum light source are carried out with a dual-channel instrument. The other channel is needed for the background correction. With a line-like radiation source, a conventional AA spectrometer can be used. In this technique the non-specific absorption is measured with a continuum radiation source. 

Since mercury is present already in the atomic state in the cold vapor technique, there is no need for an atomiser as such. The sample vapor is swept directly from the reduction cell or the amalgamation trap in the carrier gas stream to a 10 cm length T-shaped quartz tube that is moderately heated (to ca. 200 °C to prevent condensation of mercury). This quartz cell is located in the light path of a conventional AA spectrometer where the attenuation of a characteristic Hg line source is measured. Dedicated AA spectrometers (which, in this case, often have a continuum light source) may also be used with longer absorption cells (300 mm pathlength) to increase the sensitivity. 

A system of concave mirrors first described by White was used to obtain 4, 8, 12 or 16 traversals across a rectangular flow tube, and hence path lengths of up to 70 cm. A stabilized deuterium arc was used as continuum light source. A system of this type (Fig. 3.4) was used for kinetic studies of CIO radicals produced by the rapid reaction... 

More recently, electron-ion recombination has been used to produce continuum light sources which promise to have much use. With helium gas, such a source produces useful continuum radiation down to wavelengths of about 300 A. 

R. E. Huffman, J. C. Larrabee, and Y. Tanaka, Rare gas continuum light sources for photoelectric scanning in the vacuum ultraviolet Appl. Opt. 4(12), 1581-1588 (1965). R. L. F. Boyd and N. D. Twiddy, Electron energy distribution in plasmas II. Hydrogen, Proc. Royal Soc. (London) A259, 145-158 (1960). 

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