Polariton Parametric Amplifier Pump Dynamics in the Coherent Regime

We studied the pump coherent dynamics in a II-VI microcavity parametric amplifier, using angle-resolved four-wave mixing. The polariton parametric amplification is found to result in a strong quenching and saturation of the pump coherence lifetime above the threshold. For the polariton scattering processes that remain below the amplification threshold, we find an angle-dependent collision broadening associated with the efficiency of the polariton scattering towards the excitonic reservoir.

Figure 1

Calculated polariton dispersion relation vs incident angle at $\delta =+3\mathrm{m}\mathrm{e}\mathrm{V}$ (solid lines). Polariton dispersion measured by reflectivity (symbols). Dotted lines: bare cavity and exciton dispersion relations. The FWM response is measured resonantly (solid symbols) for varying incident angle at specific $(E,\mathbf{k})$. Beams in direction ${\mathbf{k}}_1$ and ${\mathbf{k}}_2$ are resonant with outgoing beam in direction $2{\mathbf{k}}_2\mathrm{\text{−}}{\mathbf{k}}_1$. Inset: integrated photoluminescence intensity vs excitation power, under excitation at the magic angle. Dashed line: stimulation threshold.

Figure 2

Ti-FWM signal as a function of the time delay for different incident angles around the magic angle, as indicated in the figure. Dotted line: Ti-FWM response at the magic angle of 18.5°. The injected carrier density is $n=5\times {10}^9{\mathrm{c}\mathrm{m}}^{-2}$.

Figure 3

Dephasing time $T_2$ vs incident angle for $n=1\times {10}^9{\mathrm{c}\mathrm{m}}^{-2}$ (open symbols) and $n=5\times {10}^9{\mathrm{c}\mathrm{m}}^{-2}$ (solid symbols; the solid line is a guide for the eye) in the strong coupling regime. The resonance appears at the magic angle.

Figure 4

Measured dephasing time $T_2$ vs incident power for incident angle $\theta =0°$, $18.5°$, $20°$ and $22.5°$. Detuning $\delta =+3\mathrm{m}\mathrm{e}\mathrm{V}$.

Figure 5

Normalized collision broadening vs excitation angle. Symbols: experimental data (open: $n=1\times {10}^9{\mathrm{c}\mathrm{m}}^{-2}$; solid: $n=5\times {10}^9{\mathrm{c}\mathrm{m}}^{-2}$). Lines: theory (dash-dotted: $n=5\times {10}^9{\mathrm{c}\mathrm{m}}^{-2}$; dotted: $n=1\times {10}^{10}{\mathrm{c}\mathrm{m}}^{-2}$).