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(Color online) Schematic of a fully tunable microcavity for a quantum dot experiment. (a) The bottom mirror is a semiconductor distributed Bragg reflector (DBR) and the active layer contains self-assembled quantum dots. The top mirror is a miniature concave template coated with a dielectric DBR. The bottom mirror can be moved in x and y, allowing spatial tuning of the cavity anti-node with respect to a single quantum dot, and in z, allowing spectral tuning of the cavity. (b) Profile of a crater created in a silica substrate with laser ablation measured using a stylus surface profiler. The curve is a fit to a spherical section with radius of curvature, R = 120 μm. (c) Optical microscope image of the crater.
(Color online) Optical characterization of the tunable microcavity. (a) Photoluminescence (PL) from a high density ensemble of quantum dots located inside the microcavity at 77 K plotted against energy (solid line). One longitudinal mode exists within the bandwidth of the quantum dot PL; accompanying the main peak corresponding to emission into the mode with lateral mode index m + n = 0 is a series of lateral modes with m + n = 1, 2, 3. m and n are the mode indices: the number of anti-nodes in the lateral field distribution [Ref. 27]. The ensemble PL of the dots recorded from a piece of bare wafer without the top mirror cavity is also shown (dashed line). The spectral resolution of the spectrometer system is 70 μeV. (b) Cavity Q as a function of cavity length.
(Color online) Quantum dot photoluminescence (PL) as a function of microcavity detuning at 4.2 K. The PL was excited non-resonantly with a laser with wavelength 830 nm. The cavity anti-node was adjusted to coincide with the quantum dot. (a) PL vs microcavity length (background representing 0 counts, white 30 000 counts). The modes are labeled with the lateral mode index m + n. (b) PL versus microcavity length showing a pronounced resonance with one particular quantum dot. (c) PL spectra for several cavity detunings close to the resonance using the data in (b). The curves are fits to two Lorentzians.
(Color online) Lifetime measurements from a single quantum dot in the tunable microcavity at 4.2 K. The same dot and cavity setup were used as in Fig. 3(b). The PL was excited with 50 ps pulses from an 830 nm laser. Decay curves were recorded with timing resolution 500 ps using a silicon avalanche photodetector and time-correlated single photon counting. (a) Decay curve at the spatial and spectral resonance; (b) decay curve at the spatial resonance but spectrally detuned by wavelength 0.5 nm. The curves are the result of a fit taking into account the response of the detector. (c) Lifetime at the spatial resonance as a function of spectral (wavelength) detuning with a Lorentzian fit with FWHM 0.25 nm. (d) Lifetime at the spectral resonance as a function of spatial detuning with a Gaussian fit with FWHM 2.5 μm.
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