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Quantum Dots in Photonic Structures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL.04.01.02-00-034/11 współfinansowany przez Unię Europejską

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Prezentacja na temat: "Quantum Dots in Photonic Structures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL.04.01.02-00-034/11 współfinansowany przez Unię Europejską"— Zapis prezentacji:

1 Quantum Dots in Photonic Structures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL /11 współfinansowany przez Unię Europejską ze środków Europejskiego Funduszu Społecznego w ramach Programu Operacyjnego Kapitał Ludzki Lecture 14: Implemenatations, perspeectives

2 Plan for today 1. Reminder 2. QD lasers 3. Other…

3 H V H V The source of polarization entangled photons Linear polarizer

4 Obstacle: anisotropy The method: biexciton – exciton cascade The energy carries the information on the polarization of the photon Biexciton Exciton Empty dot Enangled photons from a QD

5 An obstacle: anisotropy The method: biexciton – exciton cascade The energy carries the information on the polarization of the photon Biexciton Exciton Empty dot Entangled photons from a QD (in circular polarization basis:)

6 Fine structure of neutral exciton X X X dark Isotropic exchange Anisotropic exchange

7 Entanglement test STOP (H) START (H) START STOP XX X time 0 XX-X cascade

8 Influence of the in-plane electric field on the photoluminescence of individual QDs InAs/GaAs Quantum Dots Kowalik et al., APL2005

9 Evolution of the anisotropy exchange splitting with the applied voltage Kowalik et al., APL2005

10 Magnetic Field [T] [meV] Angle [rad] model K. Kowalik et al., PRB 2007 Increase or decrease of the anisotropy splitting, depending on the magnetic field direction Influence of the in-plane magnetic field on the photoluminescence of individual QDs

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12 QD in a pillar molecule: an ultrabright source of entangled photons

13 The idea: obtain polarization entangled photon pairs from biexciton-exciton cascade Main obstacle: anisostropy of the QD exciton level splitting Hindrance: low collection efficiency (a few %) QD as an entangled photons source XX The solution: coupling of the X and XX to the modes of the photonic molecule When exciton level homogeneous linewidth larger than exciton anisotropy splitting: polarization entangled photons emitted in XX-X cascade Increased extraction efficiency due to photon funneling into cavity mode Energy X Ground state

14 Pillar molecules Distance R Electronic lithography Distance Radius 1,3151,3201,3251,3301,335 PL Intensity (arb. units) Energy (eV) Photon Energy (meV)

15 Experimental realization Purcell effect evidenced on X and XX transitions The proof of entanglement: polarization resolved second order XX-X crosscorrelations A. Dousse, at al. Nature 2010

16 Characterization of the source - entanglement Entanglement criteria fullfilled Density matrix of the two- photon state 67 % degree of entanglement

17 Quantum Dot Lasers

18 mirror cavity mirror A laser – basic characteristics

19 Active material mirror cavity mirror A laser – basic characteristics

20 Active material mirror pumping emission cavity mirror A laser – basic characteristics

21 Two reflectors: – to reflect the light in phase – multipass amplification Components of a laser An energy pump source An active medium to create population inversion by pumping mechanism: - photons at some site stimulate emission at other sites while traveling

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23 Potential Advantages for Quantum Dot Semiconductor Lasers Wavelength of light determined by the energy levels not by bandgap energy: – improved performance & increased flexibility to adjust the wavelength

24 Potential Advantages for Quantum Dot Semiconductor Lasers Wavelength of light determined by the energy levels not by bandgap energy: – improved performance & increased flexibility to adjust the wavelength

25 Potential Advantages for Quantum Dot Semiconductor Lasers Wavelength of light determined by the energy levels not by bandgap energy: – improved performance & increased flexibility to adjust the wavelength Small volume: – low power high frequency operation – large modulation bandwidth – small dynamic chirp – small linewidth enhancement factor Superior temperature stability of I threshold I threshold (T) = I threshold (T ref ).exp ((T-(T ref ))/ (T 0 )) – High T 0 decoupling electron-phonon interaction by increasing the intersubband separation. – Undiminished room-temperature performance without external thermal stabilization

26 QDs as an active medium in lasers: the first theoretical predictions M. Asada et al., IEEE J. Quantum Electron. 22, 1915 (1986). Y. Arakawa et al., Appl. Phys. Lett. 40, 939 (1982). Increased gain Extremely low current treshhold

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28 Increased maximum material gain

29 Potential Advantages for Quantum Dot Semiconductor Lasers Lower Threshold Higher Modulation Speed Smaller Linewidth Less Temperature Sensitivity Reduced Auger Recombination Mid-Infrared Semiconductor Lasers

30 Q. Dot Laser vs. Q. Well Laser In order for QD lasers compete with QW lasers: A large array of QDs since their active volume is small An array with a narrow size distribution has to be produced to reduce inhomogeneous broadening Array has to be without defects – may degrade the optical emission by providing alternate nonradiative defect channels The phonon bottleneck created by confinement limits the number of states that are efficiently coupled by phonons due to energy conservation – Limits the relaxation of excited carriers into lasing states – Causes degradation of stimulated emission – Other mechanisms can be used to suppress that bottleneck effect (e.g. Auger interactions)

31 QDL – Application Requirements Same energy level – Size, shape and alloy composition of QDs close to identical – Inhomogeneous broadening eliminated real concentration of energy states obtained High density of interacting QDs – Macroscopic physical parameter light output Reduction of non-radiative centers – Nanostructures made by high-energy beam patterning cannot be used since damage is incurred Electrical control – Electric field applied can change physical properties of QDs – Carriers can be injected to create light emission

32 Electrically pumped Quantum Dot Laser Fujitsu Temperature Independent QD laser (2004)

33 Temperature Independent QD laser Fujitsu (2004)

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35 QD laser already on the market

36 Stable operation up to 60C without a cooler Modulation rates up to 500MHz 2VDC operation 532nm output ( mW power level, with frequency doubling) Tiny TO-56 package (5.6mm diameter)

37 Lasing in a QD-microdisc system InAs/GaAs QDs cavity Q exceeds

38 Lasing in a QD-microdisc system In most of our samples lasing persists when the sample is tuned from 6 to 55 K (a QD tuning range of 1.5 nm). This indicates the lasing is not based exclusively on observable QD states resonantly coupled to the mode.

39 Lasing in a QD-microdisc system However, the relative spectral tuning of observed QDs emission states and cavity modes does influence the L-I curve. Z. G. Xie et al., PRL2007

40 A recipy for a good QD laser To achieve single state lasing the processes associated with the loss must be suppressed and more efficient lasing via the single-emitter state (i.e., higher effective oscillator strength and higher Q), must be implemented. Z. G. Xie et al., PRL … a good QD-cavity mode spatial matching

41 The investigations clearly visualize a smooth transition from spontaneous to predominantly stimulated emission which becomes harder to determine for high beta. S. M. Ulrich et al., PRL2007

42 = t 2 – t 1 t 1 = 0 t 2 = 20 wejście START wejście STOP Karta do pomiaru korelacji Dioda START Dioda STOP Liczba skorelowanych zliczeń n( ) Od źródła fotonów

43 S. M. Ulrich et al., PRL2007 Increased g (2) ( ) at lasing treshold

44 S. M. Ulrich et al., PRL2007 of a mode = the ratio of SE into that mode divided by the total SE into all modes

45 Wiersig et al., Nature2009 Measured second-order photon correlation function at zero delay time (top) and output intensity versus input pump power, P exc (bottom), for three different microcavity lasers. Q = QDs Q = QDs Q = QDs

46 k-space imaging Fourier plane

47 k-space imaging Fourier plane imaging

48 Real-space imaging

49 Angle resolved emission from QDs in planar cavity Photon Energy GaAs/InGaAs planar cavity

50 Angle resolved emission from QDs in planar cavity

51 QD in micropillar microcavity– angular dependences Each mode characterizied by a specific emission pattern

52 QD in micropillar microcavity – angular dependences

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54 Mode 01 Mode 21

55 Mode 01 Mode 21

56 QDs in bio-physics Foto: Felice Frankelwww.felicefrankel.com

57 Zalety QD jako źródeł światła: -Duża wydajność kwantowa -Duża wartość molowego współczynnika ekstynkcji (przekroju czynnego na oddziaływanie ze światłem) -Szerokie pasmo wzbudzenia -Wąskie pasmo emisji (FWHM ~25-40 nm) -Duże przesunięcie Stokesa -Duża odporność na fotowybielanie -Długi czas życia stanu wzbudzonego Remigiusz Worch, IF PAN

58 Medintz et al., 2005, Nature Materials Porównanie z klasycznymi fluoroforami Związek organiczny: rhodamine red Białko fluorescencyjne: DsRed2 QDs: Remigiusz Worch, IF PAN

59 Przykład obrazowania komórek Medintz et al., 2005, Nature Materials Barwienie organelli komórkowych za pomocą QD: -Cyan- 655 nm- jądra komórkowe -Magenta- 605 nm- białko Ki-67 (obecne w jądrze, marker proliferacji) -Pomarańczowy- 525 nm- mitochondria -Zielony- 565 nm – mikrotubule -Czerwony – 705 nm – filamenty aktynowe Remigiusz Worch, IF PAN

60 INVITROGEN: Qdot Nanocrystal Multicolor immunofluorescence imaging with Qdot® secondary antibody conjugates. Laminin in a mouse kidney section was labeled with an anti-laminin primary antibody and visualized using green-fluorescent Qdot® 565 IgG. PECAM (platelet/endothelial cell adhesion molecule; CD31) was labeled with an anti– PECAM-1 primary antibody and visualized using red-fluorescent Qdot® 655 IgG. Nuclei were stained with blue-fluorescent Hoechst

61 INVITROGEN: Qdot Nanocrystal

62 W bio-aplikacjach QD stosowane są jako koloidy (najczęściej core-shell CdSe-ZnS). Pasywacja ZnS służy stabilności, jak również tworzy platformę do dalszych modyfikacji chemicznych. Kapowanie molekułami bi-funkcyjnymi zapewnia rozpuszczalność w środowisku wodnym, jak również różne grupy chemiczne umożliwiają dołączanie biomolekuł. Medintz et al., 2005, Nature Materials Remigiusz Worch, IF PAN

63 Istnieje potrzeba sprawdzania stabilności tak uzyskanych struktur koloidalnych oraz znajomości promienia hydrodynamicznego w roztworze. Jedną z technik wykorzystywanych w tym celu jest spektroskopia korelacji fluorescencji (Fluorescence Correlation Spectroscopy, FCS) E. P. Petrov and P. Schwille, Springer Ser Fluoresc (2008) Remigiusz Worch, IF PAN

64 Monitorujemy natężenie fluorescencji F(t) w objętości utworzonej przez skupione światło laserowe. FCS – idea techniki Obserwowane fluktuacje są, w najprostszej sytuacji, wynikiem, swobodnej dyfuzji fluorescencyjnych (luminescencyjnych) obiektów. Stosujemy formalizm autokorelacji. F(t) -> G(tau) Remigiusz Worch, IF PAN

65 FCS – funkcja autokorelacji Dla swobodnie dyfundujących cząstek w 3-D funkcja ma postać: Z dopasowania dostajemy: tau_d (charakterystyczny czas dyfuzji przez ognisko), a z amplitudy G(0) -1 = średnią liczbę cząstek Przy znanej wielkości ogniska, możemy obliczyć współczynnik dyfuzji D oraz stężenie. W przypadku kropek, z D można oszacować promień hydrodynamiczny (z relacji Einsteina-Stokesa). Remigiusz Worch, IF PAN

66 FCS i QD – przykład zastosowania Różne związki chemiczne dołączone do ZnS – wpływ na wielkość i stabilność koloidalną Murcia et al., 2008, Optics Commun Remigiusz Worch, IF PAN

67 FCS i QD – przykład zastosowania – IF PAN (R. Worch) QD z dołączonym białkiem roślinnym o własnościach enzymatycznych (FNR) Technika FCS użyta do oceny zmian promienia hydrodynamicznego: QD 5503,7±1,3 nm QD 550+FNR10,4±2,1 nm QD 65013,1±4,1 nm QD 650+FNR19,8±4,2 nm Szczepaniak, Worch, Grzyb, J. Phys.: Condens. Matter, w recenzji Remigiusz Worch, IF PAN

68 Nanoparticles of cadmium selenide (quantum dots) glow when exposed to ultraviolet light. When injected, they seep into cancer tumors. The surgeon can see the glowing tumor, and use it as a guide for more accurate tumor removal.

69 February 2003 The Industrial Physicist Magazine Quantum Dots for Sale Nearly 20 years after their discovery, semiconductor quantum dots are emerging as a bona fide industry with a few start-up companies poised to introduce products this year. Initially targeted at biotechnology applications, such as biological reagents and cellular imaging, quantum dots are being eyed by producers for eventual use in light-emitting diodes (LEDs), lasers, and telecommunication devices such as optical amplifiers and waveguides. The strong commercial interest has renewed fundamental research and directed it to achieving better control of quantum dot self-assembly in hopes of one day using these unique materials for quantum computing. Semiconductor quantum dots combine many of the properties of atoms, such as discrete energy spectra, with the capability of being easily embedded in solid-state systems. "Everywhere you see semiconductors used today, you could use semiconducting quantum dots," says Clint Ballinger, chief executive officer of Evident Technologies, a small start-up company based in Troy, New York...

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