Knowledge Bank

Currently under investigation is a thermo-optical $technique1$ utilizing two coincident laser beams incident upon a fluid medium. The frequency of one of the beams corresponds to a region of electronic absorption by the sample. A portion of the absorbed energy of this beam dissipates as heat and a slight temperature gradient appears in the fluid. This gradient produces a divergent lens due to the negative temperature coefficient of the index of refraction. This lens is proved by observing the thermal blooming of the second beam which is absorbed insignificantly by the sample. This method, once refined, not only should detect extremely weak optical transitions and allow a determination of their extinction coefficients, but should also provide information on photophysical parameters, radiative and radiationless quantum yields as well as photochemically produced transients. Design criterion of the experiment and experimental results for solutions of a series of methyl substituted benzenes in cyclohexane will be discussed.