1. Bhanu P. Singh Department Of Physics Indian Institute of Technology Bombay, Mumbai- 400076

2. Nonliear optical systems, Nonlinearity & Its influence on opto - electronic response in low-d quantum confined systems

3. Patterns in nature

4. Spatial pattern in a fluid heated from below

5. Kerr slice with feedback mirror Theoretical model

8. Pattern generation in saturable absorber where  is given by following equation Threshold intensity is given by

9. Artificial design of complexity Nonlinear optical system to simulate 2-component reaction-diffusion system dynamics System with 2 Kerr slices and bounded feedback loops Variety of patterns

10. Some observed patterns Application to information processing

11. Isolated States as memories

12.  Conjugated Polymers  Semiconductors Capacity for tailoring the optical properties such as  (3)  E g -n and   r -3 Property relationship with structure, interactions and ensuing processes

13. Microscopic origin of nonlinearity

15. B.P.Singh et al,JCP109,685(1998)

16. B.P.Singh et al,Europhys.lett.45,456(1999)

18. B.P.Singh et al,JNOPM,7,571(1998)

19. Quantum confined 0-d semiconductors + - R Quantum dot transition probability  spatial restriction Surface states in semiconductor nanoparticles Surface states provide highly efficient nonradiative channels and significantly quench the photoluminescence yield non- radiative transition HOMO PL emission primary absorption surface states LUMO

20. Nanocomposites of CdS and ZnO CdS (molar %) ZnO (molar %) nano CdS:ZnO-14555 nano CdS:ZnO-24060 nano CdS:ZnO-33367 EDAX and TEM - Approximately stoichiometric CdS and ZnO (Cd:S = 1:1.20 and Zn:O = 1:1.18)

21. RF magnetron sputtering - Experimental setup LN 2 -COOLED SUBSTRATE HOLDER SHUTTER GAS FLOW TURBO PUMP PRESSURE GAUGE SCRAPER VIEW PORT MAGNETRON GUN

22. Linear absorption spectroscopy Tunable source Detector Sample I tr = I in e -  t

23. Comparative study of PL in CdS and CdS:ZnO nanocomposite films Vasa, Singh and Ayyub (in preparation) sample exc  onochromator + PMT

24. Decay-time measurement Faster decay  higher PL yield

25. Coherent PL from nanocomposite thin films exc = 458 nm Multiple beam interference observed in PL spectra film exc emi Vasa, Singh and Ayyub (submitted) J. Phys. Cond. Mat

26. Double slit experiment - Setup Slit separation = 178  m Slit width = 30  m Sample-slit = 6.15 cm Slit-detector = 88.6 cm PMT slit width ~ 1 mm Ti:Sapphire Laser System 100 MHz, 800 nm, 80 fs Lock-in Amplifier BBO 400 nm Sample Double slit 121 Hz GG475 PMT

27. Experimental results Vasa, Singh and Ayyub J. Phys. Cond. Mat17,189(2005)

28. Photocurrent spectroscopy Vasa, Singh, Taneja, Ayyub et. al, J. Phys. Cond. Mat, 14, 281 (2002) Tunable source Powers upply Lockin sample

29. IR Photocurrent spectroscopy Vasa, Singh and Ayyub (in preparation) Measurement against dark background  Higher sensitivity

30. ARINS - Experimental setup 50% PD2 Data acquisition Ti:Sapphire Laser System 774 nm, 68 fs, 100 MHz ARR Pockels cell Variable attenuator 50% /2 polarizer PD1 R = 0.04 68 fs, 3 Hz 774 nm sample R = 0.04 HR mirror

31. ARINS - Experimental setup

32. CdS thin film (thickness = 1.3  m)  Wavelength = 776 nm  Pulse width = 82 fs  Pulse rep. Rate = 3 Hz  I sample (max) ~ 0.8 GW/cm 2  = 48 cm/ GW  (CdS Single crystal) = 6.4 cm/GW at 780 nm

33. Vasa, Singh and Ayyub (in preparation)  Presence of mid bandgap states  Free carrier absorption  Significant one photon, photo-current observed in IR Dispersion of  for a CdS:ZnO nano- composite thin film 129CdS:ZnO-2 48nano CdS 6.4 CdS (Single X´tl)  776nm (cm/GW) sample

34. Quantitative measurement of One photon resonant nonlinearity Vasa, Singh and Ayyub (in preparation)

35. detector sample chopper Ti:Sapphire + BBO 391nm 100MHz Ar + oscilloscope Carrier dynamics by pump-probe spectroscopy - Setup

36. Pump-probe spectroscopy - Results Carrier generation and relaxation time measurement

37. Origin of photo-darkening Free carrier absorption Excited state absorption Photo-induced chemical and/or structural changes LUMO PL emission primary absorption of pump HOMO non radiative transition PL emission primary absorption of pump secondary absorption of PL or probe non radiative transition LUMO HOMO

38. Proposed 4-level model Vasa, Singh and Ayyub (in preparation) non-radiative transition (~10ps,  b ) fast non-radiative transition (~ps) N1N1 N2N2 secondary absorption of pump/PL/ probe (~ps) N3N3 HOMO LUMO pl. emission (~100ps,  a ) primary absorption of pump (~ps,  ) N4N4 slow non-radiative transition (~2ms,  c ) Solutions of rate equations

39. Carrier generation and relaxation - data fitting

40. PL as a function of intensity - z scan

41. PL spectra as a function of incident intensity

43. IITB  Prof. T. Kundu  A.V.V. Nampoothiri  Subal Sahani  Biswajit Pradhan  Binay Bhushan  Rajeev Sinha Acknowledgement TIFR  Parinda Vasa  Prof. P. Ayyub Department of Science and Technology