Review of scientific instruments vol:67 issue:9 pages:3005-3009
The technique of electric-field-induced second-harmonic generation (EFISHG) has been extended by use of a femtosecond, quasi-cw laser pump source. The effects of ultrashort pulse widths on the coherent EFISHG process have been examined and the analysis procedure used for nanosecond pulse EFISHG measurements is found to be suitable for femtosecond measurements in off-resonant regions. A convenient method for measurement of the group velocity mismatch between the fundamental and second-harmonic pulses in solutions has also been developed to accurately describe the femtosecond EFISHG process. Phase-sensitive detection of the modulated second-harmonic signals results in improvements in accuracy and sensitivity over existing nanosecond pulse experiments. This has been demonstrated with a measurement of Gamma(-2 omega; omega, omega, 0) of an organic molecule, 4-nitroanisole. (C) 1996 American Institute of Physics.