Linewidth broadening and emission saturation of a resonantly excited quantum dot monitored via an off-resonant cavity mode

We report on the robustness of a detuned mode channel for reading out the relevant $s$-shell properties of a resonantly excited coupled quantum dot (QD) in a pillar microcavity. The line broadening of the QD $s$-shell is “monitored” by the mode signal with high conformity to the directly measured QD linewidth. The mode signal also monitors the saturation behavior of a near Fourier transform-limited photon emission from a resonantly excited QD. We also investigate the temperature dependence of the coupling mechanism between an off-resonant QD and a cavity mode under pure resonant excitation of the quantum emitter.

Figure 1

(Color online) Temperature dependent resonance scans: (a)–(f) frequency scans of cw laser over the $s$-shell of a QD in Pillar 1, each obtained at different sample temperatures and hence QD-mode detunings $\Delta E\left(T\right)$. The FM emission of the pillar is around 1.3578 eV for all these scans. Each plot is a color scale of the intensity of spectra taken at gradually varying laser-QD detunings $\delta$. All of the frequency scans shown were performed at a fixed laser power of $P_0=300\text{nW}$. The composite QD and laser signal along with the cavity mode emission is clearly visible in all plots. Horizontal dashed lines mark the QD exciton and cavity mode positions at the given temperatures. The discontinuities in (c) and (f) are an artifact due to the laser mode-hop.

Figure 2

(Color online) Temperature dependence of Relative Mode Intensity under $s$-shell excitation: (a) set of spectra at the exact laser-QD resonance position $\left(\delta =0\right)$ obtained from scans in Figs. 1a, 1b, 1c, 1d, 1e, 1f at different temperatures $T$. The composite QD and laser line contains the resonance fluorescence signal from the QD while the blue detuned line corresponds to the enhanced cavity mode. The detuning between the resonantly excited QD and mode signal $\Delta E\left(T\right)$ gradually increases with increasing temperature. (b) Relative mode intensity, calculated from the spectra in (a), as a function of increasing QD-cavity mode detuning $\Delta E$. The corresponding temperatures are indicated in the figure.

Figure 3

(Color online) Power-dependent linewidth analysis of resonance scans: line shapes of the resonantly excited QD in Pillar 1, derived from the full frequency scans performed over the $s$-shell of the quantum dot. Scans were performed at increasing excitation powers at a constant sample temperature of $T=26\text{K}$. (a) Composite QD and laser signal profiles derived from resonance scans at variable excitation powers. Solid lines are Lorentzian fits to the data. (b) The coupled cavity mode signal profile for the corresponding excitation powers. (c) FWHM extracted from line fits in (a) as a function of increasing excitation power. The solid line is a theoretical fit to the data. (d) FWHM calculated from (b) along with the fit (solid line) for the mode signal. (e) and (f) QD and mode emission profiles obtained from a frequency scan over the $s$-shell of another QD (Pillar 2). The corresponding frequency scan is shown in the inset of plot (e). The frequency scan in this case is performed at a constant laser excitation power of $P_0=100\text{nW}$.

Figure 4

(Color online) Saturation of nearly Fourier transform-limit photon emission from resonantly excited QD: (a) integrated intensity of the composite QD and laser emission as a function of increasing excitation power $P_0$ under $s$-shell excitation of the QD at $T=9.5\text{K}$. The inset shows the ratio of the detuned mode signal to the composite QD and laser signal at the corresponding laser powers. The red dashed line is a guide to the eyes. (b) The integrated intensity of the coupled cavity mode as a function of increasing excitation power. The solid red line is a theoretical fit to the data points using the fitting parameters of $T_1=0.81\pm 0.05\text{ns}$ and $T_2=1.55\pm 0.05\text{ns}$. (c) Time correlated photon counting (TCPC) measurement of the QD exciton under $p$-shell excitation at $T=9.5\text{K}$. (d) High resolution PL spectrum of the QD emission (red points) under $s$-shell excitation performed at $P_0=1.0\mu \text{W}$. The red line is a Lorentzian fit to the data while the black points in represents the PL of the cw laser representing the instrumental response function (IRF) of the setup i.e., $0.72\pm 0.02\mu \text{eV}$.