Excitation spectra of terahertz Bloch emission in semiconductor superlattices

We present theoretical and experimental studies of the amplitude of the terahertz (THz) light emitted by biased superlattices excited by fast optical pulses as a function of the pump photon energy. The comparison of the measured transient signal and of its dependence upon the excitation photon energy with a model calculation allows a clear separation between the contributions of the dissociated carriers and bound pairs to the emitted THz field.

Figure 1

The transient THz radiation emitted by a GaAs (7.5 nm)/AlAs (0.5 nm) superlattice recorded for various central photon energies of the excitation laser.

Figure 2

Symbols: amplitude of the emitted THz electric field (as defined by the second-to-third extremas amplitude difference) versus detuning ${\delta }_L$ in the GaAs (7.5 nm)/AlAs (0.5 nm) superlattice. The amplitude of the time derivative of the total current $j_{Bloch}\left(t\right)+j_{1S}\left(t\right)$ is plotted in the same figure as a solid line. The dashed line is the band-to-band contribution and the dashed-dotted line is the total excitonic contribution.

Figure 3

Symbols: amplitude of the emitted THz electric field (as defined by the second-to-third extremas amplitude difference) versus detuning ${\delta }_L$ in the 11.8 nm/2.4 nm $\text{GaAs}/{\text{Al}}_{0.3}{\text{Ga}}_{0.7}\text{As}$ superlattice. The amplitude of the time derivative of the total current $j_{Bloch}\left(t\right)+j_{1S}\left(t\right)$ is plotted in the same figure as a solid line. The dashed line is the band-to-band contribution and the dotted line is the main excitonic contribution to the $1S$ amplitude.