The construction and operating principles of a two-color pump/probe spectrometer are described. This instrument is capable of obtaining ground-state absorption spectra, both singlet-singlet and triplet-triplet excited-state absorption spectra, photoproduct spectra, and stimulated fluorescence spectra. In addition, time-dependent measurements can be made with an impulse response of 250 ps and a free temporal range of 13 ns.
The advent of the laser has unlocked several new Raman processes which have provided new approaches to many important diagnostic problems. These applications include biochemistry, high resolution spectroscopy, combustion engineering, structural chemical analysis, chemical kinetics, surface chemistry, etc. Included in these techniques are: Coherent Anti-Stokes Raman Spectroscopy (CARS) , Raman Induced Kerr Effect (RIKES), and Stimulated Raman Gain. A brief review of these methods and their utility are described with the main emphasis on CARS. Variations of the techniques, e.g., BOXCARS, are also discussed and their use in making temperature and concentration measurements in hostile environments such as turbulent media are presented.
The design and construction of an extremely simple and inexpensive photodetector are described. Using a commercially available photodiode, the circuit is shown to be useful for observation of subnanosecond sources from the ultraviolet to beyond 1 μm.
The ability to obtain a stable tunable picosecond pulse train from a synchronously pumped dye laser is shown to permit the use of modulated gain spectroscopy to study the lifetime, spectral, and concentration-dependent behavior of fluorescent species. The fluorescence of rhodamine-B in ethylene glycol at concentrations from 3μM to 5mM was observed over the range from 570 to 640 nm; a fluorescence lifetime of 2.2 ns was obtained.
