Time-resolved photoluminescence and photoluminescence excitation spectroscopy on single quantum systems
Semiconductor nanocrystals with dimensions below approximately 10 nm confine charge carriers in all three spatial directions. This size is in the order of the de Broglie wavelength, leading to quantum effects and discretized energy spectra of the electronic states (Fig. 1). Therefore, these artificial atoms are termed quantum dots (QD) [1, 2, 3, 4, 5, 6].
The systems studied in our group are chemically synthesized CdSe/CdS quantum dots provided by the chair of Stefan Mecking in the Department of Chemistry. These nanocrystals are available in colloidal suspension.They can easily be spin-coated onto a substrate and manipulated with an atomic force microscope, e.g. to place them into photonic structures [7, 8, 9].
To protect the quantum dots against external influences like e.g. photo-oxidization, they are coated with a thick polymer shell  (see Figure 2).
The interaction of QDs with light is investigated in a micro-photoluminescence setup (Figure 3). It is a confocal microscope with sub-micrometer spatial resolution and sub-nanometer spectral resolution. For excitation, a mode locked Erbium-doped fiber laser (link Faserlasergruppe) [11, 12, 13, 14, 15, 16, 17] is used. After frequency doubling, the wavelength is tunable from 430 nm to 700 nm with a pulse duration around one picosecond.
For high resolution spectroscopy of single nanocrystals, the colloidal suspension is highly diluted and spin-coated onto a substrate. A Hanbury-Brown and Twiss setup allows us to study the photon statistics of the emitter. Individual quantum dots can be addressed with an xy translation stage at temperatures ranging from 4 K to 300 K. High-resolution spectra are recorded with an electronically magnified CCD camera. The luminescence lifetime is determined with an avalanche photodiode. To measure lifetimes longer than 12 ns, the repetition rate of the fiber laser can be adjusted from 40 MHz down to 2.5 MHz with the help of a fiber-coupled electro-optic modulator located between the oscillator and the amplifier.
 R. Bratschitsch und A. Leitenstorfer
"Quantum dots: Artificial atoms for quantum optics"
Nature Mat. 5, 855 (2006)
 M. Kahl, T. Thomay, V. Kohnle, K. Beha, J. Merlein, M. Hagner, A. Halm, J. Ziegler, T. Nann, Y. Fedutik, U. Woggon, M. Artemyev, F. Perez-Willard, A. Leitenstorfer und R. Bratschitsch
"Colloidal quantum dots in all-dielectric high-Q pillar microcavities"
Nano Lett. 7, 2897 (2007)
 T. Thomay, T. Hanke, M. Tomas, F. Sotier, K. Beha, V. Knittel, M. Kahl, K. M. Whitaker, D. R. Gamelin, A. Leitenstorfer und R. Bratschitsch
"Colloidal ZnO quantum dots in ultraviolet pillar microcavities"
Opt. Express 16, 9791 (2008)
 F. Sotier, T. Thomay, T. Hanke, J. Korger, S. Mahapatra, A. Frey, K. Brunner, R. Bratschitsch und A. Leitenstorfer
"Femtosecond few-fermion dynamics and deterministic single-photon gain in a quantum dot"
Nature Phys. 5, 352 (2009)
 W.-M. Schulz, T. Thomay, M. Eichfelder, M. Bommer, M. Wiesner, R. Roßbach, M. Jetter, R. Bratschitsch, A. Leitenstorfer und P. Michler
"Optical properties of red emitting self-assembled InP/ (Al0.20Ga0.80)0.51In0.49P quantum dot based micropillars"
Opt. Express 18, 12543 (2010)
 G. Kiliani, R. Schneider, D. Litvinov, D. Gerthsen, M. Fonin, U. Rüdiger, A. Leitenstorfer und R. Bratschitsch
"Ultraviolet photoluminescence of ZnO quantum dots sputtered at room-temperature"
Opt. Express 19, 1641 (2011)
 J. Merlein, M. Kahl, A. Zuschlag, A. Sell, A. Halm, J. Boneberg, P. Leiderer, A. Leitenstorfer und R. Bratschitsch
"Nanomechanical control of an optical antenna"
Nature Photon. 2, 230 (2008)
 T. Hanke, G. Krauss, D. Träutlein, B. Wild, R. Bratschitsch und A. Leitenstorfer
"Efficient nonlinear light emission of single gold optical antennas driven by few-cycle near-infrared pulses"
Phys. Rev. Lett. 103, 257404 (2009)
 A. Schell, G. Kewes, T. Hanke, A. Leitenstorfer, R. Bratschitsch, O. Benson und T. Aichele
"Single defect centers in diamond nanocrystals as quantum probes for plasmonic nanostructures"
Opt. Express 19, 7914 (2011)
 Y. Gao, S. Reischmann, J. Huber, T. Hanke, R. Bratschitsch, A. Leitenstorfer und S. Mecking
"Encapsulating of single quantum dots into polymer particles"
Colloid Polym. Sci. 286, 1329 (2008)
 F. Tauser, A. Leitenstorfer und W. Zinth
"Amplified femtosecond pulses from an Er:fiber system: Nonlinear pulse shortening and self-referencing detection of the carrier-envelope phase evolution"
Opt. Express 11, 594 (2003)
 F. Tauser, F. Adler und A. Leitenstorfer
"Widely tunable sub-30-fs pulses from a compact erbium-doped fiber source"
Opt. Lett. 29, 516 (2004)
 F. Adler, K. Moutzouris, A. Leitenstorfer, H. Schnatz, B. Lipphardt, G. Grosche und F. Tauser
"Phase-locked two-branch erbium-doped fiber laser system for long-term precision measurements of optical frequencies"
Opt. Express 12, 5872 (2004)
 F. Adler, A. Sell, F. Sotier, R. Huber und A. Leitenstorfer
"Attosecond relative timing jitter and 13 fs tunable pulses from a two-branch Er:fiber laser"
Opt. Lett. 32, 3504 (2007)
 A. Sell, G. Krauss, R. Scheu, R. Huber und A. Leitenstorfer
"8-fs pulses from a compact Er:fiber system: quantitative modeling and experimental implementation"
Opt. Express 17, 1070 (2009)
 G. Krauss, S. Lohss, T. Hanke, A. Sell, S. Eggert, R. Huber und A. Leitenstorfer
"Synthesis of a single cycle of light with compact erbium-doped fibre technology"
Nature Photon. 4, 33 (2010)
 G. Krauss, D. Fehrenbacher, D. Brida, C. Riek, A. Sell, R. Huber und A. Leitenstorfer
"All-passive phase locking of a compact Er:fiber laser system"
Opt. Lett. 36, 540 (2011)