Electric field induced second harmonic generation with and without fringes

Electric field induced second harmonic generation (EFISH) is a well-known t echnique to measure the first hyperpolarizability (beta) of organic molecul es in solution. The characteristic experimental output is observation of os cillatory fringes of second harmonic radiation as the solution path length is changed and evaluation of beta from the fringe amplitude. We present two different cases where even in the absence of these characteristic fringes beta may still be evaluated: first, when using absorbing materials, and sec ond, when using broadband laser sources. The ability to determine beta by E FISH under these conditions greatly enhances the ability of this technique to measure beta values over a wide range of laser frequencies. Measurements of the same molecule's beta values at different frequencies are reported, verifying the two-level model for the dispersion of beta. (C) 2000 American Institute of Physics. [S0034- 6748(00)02709-X].