Optical heterodyne detected spectrograms of ultrafast nonresonant electronic responses

Abstract

The dispersed optical heterodyne detected (OHD) birefringence and dichroism that result from the electronic response of nonresonant materials are described for a number of ultrafast pulse shapes. The OHD spectrograms that correspond to these dispersed instantaneous electronic responses display detuning oscillations along both the interpulse delay and the probe frequency dimensions. The frequency of these oscillations depends only on the detuning of the selected Fourier component of the probe pulse from the carrier frequency and the pulse shapes. This effect is demonstrated for Gaussian, sech2, and one-sided exponential probe pulses. For each of these pulse shapes the OHD spectrograms exhibit a characteristic dependence on detuning frequency. The effects of linear chirp on these OHD spectrograms are also considered. Experimentally observed nonresonant electronic spectrograms are compared with theory. These OHD spectrograms are also compared with the well-known frequency-resolved optical gating traces. Analysis of the OHD spectrograms may provide a more useful approach for the characterization of ultrafast pulses because of the phase-specific, amplitude level origin of these responses.