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Ultrafast THz Spectroscopy and Nonlinear Optics of Semiconductor

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Ultrafast THz Spectroscopy and Nonlinear Optics of Semiconductor Powered By Docstoc
					Ultrafast THz Spectroscopy and
Nonlinear Optical Properties of
Semiconductor Nanostructures
Zhen-Yu ZHAO
17 July 2008


   Laboratoire Pierre Aigrain - Ecole Normale Supérieure, Paris
   State Laboratory of Precise Spectroscopy - East China Normal University, Shanghai




                                                                                        1
Outline
   Section 1:
   Development of THz Time Domain Spectroscopy (THz-TDS)
•   Optical Rectification
•   Micro-Photoconductive Emitter


   Application of THz - TDS
•   Gain Measurement of Quantum Cascade Laser (QCL)



   Section 2:
   Nonlinear Optical Properties of AgCl Nanocrystals doped Tellurite
    Glasses
•   Fabrication
•   Characterization
•   Nonlinear Optical Measurement


                                                                        2
    Section 1
Development & Application of
THz Time Domain Spectroscopy



                               3
THz Radiation                                                         Section 1




            1THz↔300μm↔1picosecond↔4.1meV↔10K


     Application THz spectroscopy : Semiconductor nanostructures


                                                      http://www.thznetwork.org
                                                                                  4
                                                                                                Section 1
     THz Time domain Spectroscopy

     M1
                                     Ti : sapphire laser




                                                                             Balanced
                                                                             photodiodes
                                         S
                                                                ZnTe      WP
          Pump
          beam
BS
                                                                                           Δτ

                 Emitter                                           λ/4
                                       τ
                                                                 Electro-Optic Sampling

                                             Probe beam
     M2                    M3   M4                         M5

                                      Free Space Electro-Optic Sampling

            THz emitter:
            Optical Rectification
            Photoconductive antenna



                                                                                                        5
                                                                             Section 1
Optical Rectification                                            THz radiation



                                       Lens




                        Laser pulse,
                        Δτ :100fs,      Z
                        λ :800nm              ZnTe
                                              crystals
                                                         SHG & Transmitted
                                                         beam




                             FFT




                                                                                     6
                                                    Section 1
Optical Rectification
                                     Picarin Lens
                        Z
                            Teflon



                                                      Bolometer




                        Z   Filter      Lens


                                                        PMT




                        Z              Lens


                                                      Photodiode




                                                              7
                                                                                  Section 1
Optical Rectification
                              Nonlinear Optical Processes

       1. Optical Rectification                     2. Second Harmonic Generation


                                                     ħω                        2ħω


       Nonlinear Crystals                                 Nonlinear Crystals

      3. Two Photon Absorption                        4. Free Carrier Absorption
                            high state
                                                                                Conduction band

        ħω

                                                      2ħω
        ħω                    β: TPA coefficient


                            low state                                           Valence band


                                                                                           8
                                                                             Section 1
Optical Rectification

                                                          [001]
                                                      θ             Laser
                                                                    polarization
                                      ZnTe




                               X.-C. Zhang et al. J. Opt. Soc. Am. B 18 : 823 (2001)




                        D.C. Hutchings and B.S. Wherrett, J. Opt. Mod. 41: 1141 (1994)


                                                                                         9
                                                                                     Section 1
Optical Rectification


                                15mm
                                                             Two Color Experiments
             Lens :f=4cm

                             BBO      ZnTe

Laser beam                                   THz radiation




                           Rotation




                                                                                             10
                                                         Section 1
Interdigitated photoconductive antenna



                      +




              Laser pulse,          Hemisphere Si lens
              Δτ :100fs, λ :800nm




Conventional
Photoconductive       —
antenna




                                                                 11
   Interdigitated photoconductive antenna




                                          stripline gap1.5µm


500µm                                               Electrods
                                                    Opaques




                             +-
   A. Dreyhaupt et al. Appl. Phys. Lett. 86 :121114 (2005)
   A. Dreyhaupt et al. Opt. Lett. 31 :1546 (2006)               Nathan Jukam, UCSB




                                                                                     12
                                         Section 1
Interdigitated photoconductive emitter

           Bias dependence




                                                 13
                                                                                            Section 1
Interdigitated photoconductive emitter
                     Γ→L Intervalley scattering




                         C. Ludwig and J. Kuhl, Appl. Phys. Lett. 69 (9), 1194 (1996)
                         J.-H. Son, T. B. Norris, and J. F. Whitaker, J. Opt. Soc. Am. B 11, 2519 (1994)



                                                                                                       14
                                                                   Section 1
Interdigitated photoconductive emitter




                   Optimization by change the exciting intensity
                                                                           15
                                                                                  Section 1
Interdigitated photoconductive emitter

                     Space Charge Screenings Effect


            Low Optical Flux                                  High Optical Flux


                                                          -
                                                                     -




        +                    —                        +                       —
                          Bias Field

                        Coulomb Field


                                                                                          16
 Interdigitated photoconductive emitter                                          Section 1



                                         Temperature Dependence of THz emitter




J. S.Blakemore, J. Appl. Phys. 53: R123-R181 (1982)



                                                                                         17
Comparison of 2 THz emitters                                     Section 1



                    ZnTe Crystals   Interdigitated Photoconductive antenna

THz Amplitude       10V/cm          100V/cm

Central Frequency   2THz            1THz~~1.4THz

Bandwidth           0.5~~2.7THz     0~~3.5THz

S/N                 500~1000        5000~~10000




                                                                         18
                                                                                                Section 1
THz Quantum Cascade Laser

                                   Concept

    Semiconductor Laser                                            Quantum Cascade Laser




      ħω



     Interband transition                                          Inter-subband transition

                                   Milestone
     1970                   1980   1990                           2000
        1971                                   1994                      2002        2004     2006
                                                                                                        Years

    First Idea                            First QCL @ Bell Labs          THz        2.9 THz   1.9 THz
                                                                         QCL        QCL 77k   QCL 95k



                                                                                                         19
                                                                   Section 1
THz Quantum Cascade Laser

        Bound to Continuum Active-injection Region of 2.9THz QCL




                                                                           20
                                                                           Section 1
THz Quantum Cascade Laser

            Surface Plasmon Waveguide of 2.9 THz QCL


                 220µm
                                           (a)            Metal 220µm        Metal
                                                                             Contact

                                           12µm


                                                                            Bottom
                                                 Active                     n+ layer
                                                 Region




                                                                        SI Substrate




                            MPQ-Paris VII

                                                                                       21
                                                                  Section 1
THz Quantum Cascade Laser

                                Characterization of 2.9 THz QCL



          V




QCL            THz



              THz Collimation      Pyroelectric
                                   Detector
      A




                                                                          22
                                                                                    Section 1
THz Gain Measurement

            M1
                                       Ti : sapphire laser




                                            S                                   D
                                                                  A   B C
                 Pump
                 beam
       BS

                        ETHz
                                        τ
                                                                        FSEOS
                                                Probe beam
            M2                 M3 M4                         M5




                                                                                            23
                                                                                      Section 1
THz Gain Measurement
                 Amplified THz transmission by gain of quantum cascade laser




                                                                       2.9THz




  THz Gain at different injection current                 THz Gain at different temperature




                                                                                              24
                                   Section 1
THz Gain Measurement

                   Gain Clamping




                                           25
                                                                Section 1
Summary 1

 Development of THz-TDS


  THz performance of ZnTe crystal.
  THz output of interdigitated photoconductive antenna


  Application of THz-TDS


  First measurement of Gain of 2.9 THz Quantum Cascade Laser




                                                                        26
   Section 2
Nonlinear Optical Properties of
AgCl NCs doped Tellurite Glasses




                                   27
   Introduction                                                                                              Section 2




                                                 Photonic Glasses




                                                  Tellurite Glasses


                Optical Switching                                                   Optical limiting
                 Glass               Χ(3) ~ 1014esu
                 SiO2                      2.4                                  Er+ Doped TeO2-Nb2O5-
      46PbO–42Bi2O3–12Ga2O3                42                                         ZnO Glass
           20Nb2O5–80TeO2                  72

------J. Lin et al. J. Non-Cryst. Solids 336 : 189–194 (2004)   ------Y.Q. LI et al. J. Rare Earth 25 : 412 – 415 (2007)



                                  Nanocrystals doped Tellurite Glasses


                                                                                                                       28
Fabrication                             Section 2




•   Melting:
   80TeO2:20Nb2O5 & 1%wt AgCl powder
   800°C / 15minutes.



•   Quenching:
   Annealed at 300°C




•   Thermal treatment:
   At 360°C
   30min, 60min, 90min, 120min




                                                 29
Characterization                                               Section 2




          Nanocrystals FESEM Image vs Termal treatment time




  (a) 30min thermal treated             (b) 60min thermal treated


                                                                        30
Characterization                                               Section 2




          Nanocrystals FESEM Image vs Termal treatment time




  (c) 90min thermal treated            (d) 120min thermal treated


                                                                        31
Characterization                                                    Section 2




         Size distribution function vs thermal treatment time

                       12nm / 30 min               17nm / 60 min




                       26nm / 90 min               35nm / 120 min




                                                                             32
Characterization                                                                        Section 2


                                                      Jahn-Teller effect : Lattice deformation


                                                         Cl-

                                                         Ag+




                                                  Reaction: 2Cl- →Cl2 + 2e- & 2Ag++2e-→2Ag




                                                                  Cl- colour center

H. Vogelsang, Phys. Rev. B 61: 1847-1852 (2000)                                                  33
Characterization                                                      Section 2




                                                Urbach law:




                                  Trapped
                                  state

      Eg                                    Samples           Eg (eV)
                          Eg                undoped             3.1
                                             0 min              2.9
                                            30 min              2.9
                                            60 min              2.3
                                            90 min              1.9
Bandgap of glass   Bandgap redshift of      120 min             1.7
    matrix           treated glass


                                                                               34
Nonlinear Optical Properties                          Section 2




                       lens       lens   Powermeter
            50% BS



   Attenutation
                          Sample

                     Powermeter




                                                               35
Nonlinear Optical Properties                                       Section 2




                                   PC       Open Aperture Z-scan
M      Ti :sapphire
1      Laser


                  Z              Lock
                                 -In

M
      L           S    L     L          D
2




    β: 1GW/cm ~~ 1.8 GW/cm




                                                                            36
  Nonlinear Optical Properties                                                              Section 2




 Ti :sap
 phire
 Laser     Δτ
                                                PC



                                      Lock-In

BS                     M5                   2K1-K2
                                                      D
                        M4
                                                     K1
                                                     K2
                M3                L      S 2K2-K1

                                         Samples          Eg (eV)   n0    χ(3) (10-13esu)    n2 (10-11esu)
 M1                          M2

                                          undoped           3.1     2.0        7.2               1.2
                                           0 min            2.9     2.1        7.3               1.3

                DFWM                      30 min            2.6     2.2        7.8               1.4
                experiment                60 min            2.3     2.2         14               2.3
                                          90 min            1.9     2.2         11               1.9
                                          120 min           1.7     2.2        9.5               1.6


                                                                                                       37
Summary 2                                                                    Section 2




 Nonlinear optical properties of AgCl NCs doped tellurite glass


•   Samples were Prepared by Melt-Quenching and Thermal Treatment Methods

•   Characterization with Microscopic and Spectroscopic Methods

•   Nonlinear Optical Properties were Measured by Z-scan, Optical Limiting and
    DFWM




                                                                                     38
Conclusion

   Section 1:
   Development of THz Time Domain Spectroscopy (THz-TDS)
•   Competition OR TPA FCA, Azimuthal dependence
•   Intervally scattering, Space charging screening, Electron mobility
   Application of THz – TDS
•   Gain Measurement of 2.9THz QCL




   Section 2:
   Nonlinear Optical Properties of AgCl Nanocrystals doped Tellurite Glasses
•   Fabrication
•   Optical limiting performance and Two-photon absorption
•   Enhancement of χ(3)




                                                                                39
Acknowledgement

    THz group (LPA-ENS)
 Advisor:          Jérôme Tignon
 Staff members:    Sophie Hameau, Sukhdeep Dhillon et al.
 Postdoc:          Nathan Jukam;
 Ph.D student:     Dimitri Oustinov;
 Master student:   Julien Amijo, Geog Dürr;
 Techniciens:      Pascal Morfin, Phillipe Pace et al.
 Collaborators:    Carlo Sirtori et al.


    Sun’s Group (East China Normal University)
 Co-Advisor:       Zhenrong Sun,
 Staff members:    Tianqing Jia, Xiaohua Yang et al.
 Collaborators:    Jian Lin, et al.

				
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