Spectroscopic techniques excitation sources

Besides flame AA and graphite furnace AA, there is a third atomic spectroscopic technique that enjoys widespread use. It is called inductively coupled plasma spectroscopy. Unlike flame AA and graphite furnace AA, the ICP technique measures the emissions from an atomization/ionization/excitation source rather than the absorption of a light beam passing through an atomizer. 

The response function and the associated analytical merits for absorption spectroscopic techniques (e.g., NIR, UV-vis and infrared) are determined by the optical path length, detector gain, signal averaging and spectral resolution. The LIF detection performance is also governed by these parameters but is also influenced by critical parameters associated with the excitation source (e.g., optical power, pulse rate, etc.) as previously discussed. ... 

Table I. Better-Known Spectroscopic Techniques According to the Excitation Source and Measured Emission0...

Atomic Fluorescence Spectrometry. A spectroscopic technique related to some of the types mentioned above is atomic fluorescence spectrometry (AFS). Like atomic absorption spectrometry (AAS), AFS requires a light source separate from that of the heated flame cell. This can be provided, as in AAS, by individual (or multielement lamps), or by a continuum source such as xenon arc or by suitable lasers or combination of lasers and dyes. The laser is still pretty much in its infancy but it is likely that future development will cause the laser, and consequently the many spectroscopic instruments to which it can be adapted to, to become increasingly popular. Complete freedom of wavelength selection still remains a problem. Unlike AAS the light source in AFS is not in direct line with the optical path, and therefore, the radiation emitted is a result of excitation by the lamp or laser source. 

However, in an attempt to integrate the SFA and spectroscopic techniques, the use of silver for optical interferometry has been seen as a drawback due to the fact that it precluded sufficient excitation source intensity to illuminate the buried interface. In order to circumvent this problem Mukhopadhyay and co-workers in an experimental set-up where the SFA was combined with fluorescence correlation spectroscopy (FCS) used, instead of silver, multilayer dielectric coatings that allowed simultaneous interferometry and fluorescence measurements in different regions of the optical spectrum [75]. Using this set-up they succeeded in measuring diffusion in molecularly thin films with singlemolecule sensitivity. 

Photothermal deflection spectroscopy — Photothermal deflection is a photothermal spectroscopic technique used to detect the changes in the refractive index of the fluid above an illuminated sample by the deflection of a laser beam. There are two sources from which the thermal deflection effect might appear. One of them is produced by a gradient in the refractive index after a thermal excitation where the density also varies with temperature, in the so-called mirage effect. And the other one is produced by the topographical deformation of the surface over which the laser beam is reflected. This effect is known as photothermo-elastic effect or surface photothermal deflection [i]. 

Until quite recently, direct measurements of o(>d2)(X) were limited by the very real experimental difficulties associated with the highly efficient deactivation of O ( D2) by O3, as well as the need to provide a sensitive probe for atomic oxygen atoms in the ground Pj state as well as in the electronically excited D2 state. The development of resonance spectroscopic techniques for time-resolved detection of O ( Pi) has permitted monitoring of this state at densities of ca. 10 cm with an instrumental bandwidth in excess of 10 MHz. When combined with the use of high intensity photolysis sources such as the excimer lasers and frequency quadrupled Nd/YAG, it has proved possible to measure directly the yield of 0( D2) and O( Pj) at several discrete wavelengths in the middle ultraviolet. 

As this discussion suggests, LEI spectrometry shares many of the properties of other atomic spectroscopic techniques while possessing unique features which complement or supersede other methods. Since a laser is the excitation source, no spectral... 

Photoemission spectroscopy (PES) is by far the most widely used and powerful spectroscopic technique for interface research. XPS and UPS are complementary techniques that utilize different light sources, e.g., x-ray and ultraviolet, to excite electrons in solids via photoelectric effect and then collect the escaped photoelectrons with an energy analyzer. In general, photoemission experiments for interface formation studies are performed in the following way. The study begins with the photoemission analysis of a clean surface of the material that will eventually form one side of the... 

Semiconductor lasers are ideal excitation sources, and they have already been demonstrated to be remarkably versatile and useful in a number of spectroscopic applications, as indicated by Ishibashi and cowotkers (22,23). These solid-state devices are inexpensive, small, easy to use, long-lived, and require little maintenance. The problem with semiconductor lasers is that powerful singlemode lasers are only available at NIR wavelengths, although this is likely to change in the near future. Until this work, however, no report had been made of the use of diode lasers for SERS. Recently, we demonstrated NIR SERS with a diode-laser excitation source and investigated the characteristics of the technique (Angel, S.M. Myrick, M.L. unpublished data). 

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