Nonlinear Optics and Solid-State Spectroscopy

The laser microprobe employs a pulsed laser to vaporize minute amounts of the sample. The vapor temperature, however, in the case of low-power lasers is not sufficient to provide adequate excitation for spectrochemical analysis. The sample vapor is therefore further excited as it passes between two auxiliary electrodes above the sample. The optimum excitation conditions have been examined by Quillfeldt using the commercial laser-microspectral analyzer LMA 1 (Carl Zeiss, Jena). Spectrochemical determinations of Fe, 

Mn and Ca in garnets with a Jarrell-Ash laser microprobe, using ruby and neodymium lasers have shown that reliable data on the abundance of the different elements can be obtained in a very short time. 

The laser microprobe is especially useful for handling toxic or radioactive materials since analysis can be performed with very small samples. 

The advantages of this technique are that they are applicable to probes in ultra high vacuum, where any impurities are excluded, and also to samples at atmospheric pressure. The diameter of the evaporated cavity can be varied between 10 jam and 1 mm, and the quantity of the evaporated material may be less than 10 g. Solids in any desired form, crystalline or powered, are accessible to analysis. 

Besides the spectroscopic investigations of solids by laser-excited spontaneous Raman or Brillouin scattering already discussed in Sections III.6 and 7, much new insight into the optical properties and the structure of solids has been gained by studying nonlinear optical effects. (Surveys and more detailed information about nonlinear optics can be found in refs. 306-308)) 

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