MODULATED GAIN SPECTROSCOPY
Abstract
A synchronously pumped dye laser has been used as the basis for construction of a cw pump/probe spectrometer. In addition to the source limited time resolution offered by pump/probe methods in general, this instrument is shown to be capable of spectral measurements by virtue of its tunability. The previously neglected application of this technique to quantitative analysis is considered. Finally, proposal for a radically new design in these experiments is presented. Following a discussion of the theory behind the experiment, particularly regarding transform methods and stimulated processes, the instrument design considerations are outlined. The operating principles are discussed, as well as the difficulties encountered. Chief among these are reflective feedback, noise, and the thermal lens effect. The instrument is demonstrated to be useful for a variety of measurements. Examples of spectral, lifetime, and quantitative applications are given. The spectral profiles reveal a high degree of sensitivity to secondary processes such as excited singlet absorption and triplet triplet absorption. Lifetimes are determined with source limited time resolution of 250 ps. Quantitative analysis has been achieved at levels below 10('-6)M. Future developments are discussed which should yield picosecond time resolution and quantitation at the nonomolar level. In addition, means of separating absorption signals from emission signals, as well as separating singlet and triplet effects, have been outlined. Finally, a radical design change is suggested as a means of overcoming a number of practical difficulties. The proposed scheme would be undisturbed by the thermal lens effect, and would not require many of the troublesome components employed by the current state of the art. A thorough discussion of the principles and operational considerations is included.
Degree
Ph.D.
Subject Area
Analytical chemistry
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