A unified treatment of ultrafast optical heterodyne detected and Z-scan spectroscopies

摘要

An analysis of femtosecond optical heterodyne detected (OHD) birefringence and dichroism i! presented within the iramework of the Z.:scan techilique previously developed for the measuremen of nonlinear refractive indices. In particular, the phase of the effective local oscillator neld, in th~ language of OHD spectroscopy, is shown to depend on the sample position (z) and thespatiall) detected portion of the signal pulse in the far field for nonresonant pump-probe responses due t( focused Gaussian beams. Consequently, this treatment shows how the contributions of Om: birefringence and dichroism, and the corresponding homodyne signals, can best be separated in thi~ simple two-beam experimental configuration and provides a description of the previously reportec technique calledposition-sensitive Kerr lens spectroscopy. The nonresonant third-order polarizatior electronic response of fused silica illustrates this apertured OHD description. Spatial and frequenc) filtering results in ultrafast Z-scan responses that are dominated by dichroic and birefringenj responses, respectively. An analysis of apertured OHD spectroscopy which incorporates a description of the optical phase fronts of the signal fields is required in order to exploit this relatively simple experimental techilique for quantitative determinations of polarization-specific electronic responses and Raman nuclear spectral densities.