Phase Evolution of Solitonlike Optical Pulses during Excitonic Rabi Flopping in a Semiconductor

We demonstrate that the temporal pulse phase remains essentially unaltered before separate phase characteristics are developed when propagating high-intensity pulses coherently on the exciton resonance of an optically thick semiconductor. This behavior is a clear manifestation of self-induced transmission and pulse breakup into solitonlike pulses due to Rabi flopping of the carrier density. Experiments using a novel fast-scan cross-correlation frequency-resolved optical gating (XFROG) method are in good agreement with numerical calculations based on the semiconductor Bloch equations.

Figure 1

(a) Fast-scan XFROG setup. (b),(c) Linear absorption spectra of an optically thin and a thick CdSe sample at $T=8\mathrm{K}$. (d) XFROG trace of a pulse after breakup.

Figure 2

(a) Experimental temporal and (b) spectral normalized intensity (dashed line) and phase (solid line) for the input pulse (bottom) and after linear propagation through the sample with $\alpha L=1.3$ at $I=0.6\mathrm{M}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ (top). (c),(d) Results of the corresponding numerical calculations.

Figure 3

(a) Experimental temporal and (b) spectral normalized intensity (dashed line) and phase (solid line) for the input pulse (bottom) and after nonlinear propagation through the sample with $\alpha L=6.7$ at $I=780\mathrm{M}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ (middle) and $1.2\mathrm{G}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ (top). (c),(d) Results of the corresponding numerical calculations for a pulse area $\theta =2.0\pi$ (middle) and $2.6\pi$ (top).

Figure 4

(a)–(c) Theoretical plots of temporal intensity (dashed line) and phase (solid line) for the 400 fs Gaussian input pulse (top) and after nonlinear propagation according to the experiment with a pulse area $\theta =2.6\pi$ (bottom). (a) Chirp-free, (b) positive chirp, and (c) negative chirp.