Introduction to Nonlinear Optical (NLO) Polymerical Materials

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Introduction to Nonlinear Optical (NLO)
Polymerical Materials

• Wu Chengxun
• College of Material Sci. Tech. Dong Hua Univ.

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• 21?????????????????????????,????????????????
  ???????,??????????????????????????????????,???????
  ?????,???????(??????????)????(?????)????????????(?
  ????)??????????
• ????????????????????????

3
? ?????
1.1 ????????????

• 1.1 .1 ?????????????????????????????????????????
  ??????????????????????
• ??????????????????
• 1.2 .2 ??????????
• ????????
• ??????????????
• ??????????
• ????
• ????

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• 1960 Laser
• Criteria necessary for NLO materials
• Large nonlinear susceptibilities (?(2) or?(3)
  )
• Ease of processing
• Low absorption losses
• High optical damage threshold, etc.

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• ?????(nonlinear optics, NLO)??????????????????
  ??????????
• ????????,????????P?????????E????????,???????
• P ?(1)E ?(2)EE ?(3)EEE
• ???(2)????????? ,?????????????

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NLO?????

• NLO???????????????????????????????????????
  ???,??????????????????????????????????????????????
  ,???????????????????????????
• NLO??????????????????????NLO??????????????
  ?

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• Nonlinear optics
• P P(0) ?(1)E 1/2?(2)E E 1/6?(3)E E
  E ...
• P --- the induced polarization
• P(0)--- the permanent polarization
• E --- electric field strength
• ?(1)--- the linear susceptibility
• ?(2) and?(3)--- the second- and third-order
  susceptibility( or the first and second order
  nonlinear susceptibility)

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• Molecular polarizabilities
• µiµg,i aijEi ßijk EjEk ?ijklEjEkEl ...
• µi --- induced dipole
• µg,i ___ the ground state dipole moment
• aij--- the linear polarizability tensor
• ßijk --- the second-order polarizability or
  first-order hyper-polarizability
• ?ijkl--- the third-order polarizability or
  second hyper-polarizability.

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• ???????
• ???????

• ??a?ß???????????????????????,ß?????????????????
  ?(1)??(2)??(2)???????????????????????
• ??????????????????????????????????????(2)??????,?
  ??????,??????????????,??????????????????
• ?????????????????

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• First order NLO effects
• Second Harmonic
• Optical parametric Oscillation
• Linear electric-optic effect ( n n0 n2I)
• Sum and difference freq. Generation
• Optical rectification.

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• Second order NLO effects
• Frequency tripling
• Two-photon absorption
• Coherent spectroscopy
• Quadratic electro-optic
• Four wave mixture

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• Optical Kerr effect( n2 3?(3)/4cn02)
• Self-focusing
• Self-phase modulation
• The photo-refractive effect
• Cascading of first order NLO effects for
  applications in second order NLO.

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1.2 ?????????????
???? ?? ??
???(1) ??? ??,???
???(2 ??????(? ? 2? ) ???
???(2 ???( ? ? 0 )
???(2 ???( ?1 ?2 ?3 ) ?????
???(2 ????( ? ?1 ?2 ) ?????
???(2 Pockets??( ? 0 ? ) ?????
???(2) ??????( ? ? ? 3? ) ?????
???(2) ????????(? ?0 2? ) ???????????
???(2) Kerr??( ? 00 ? ) ??????
???(2) ?????( ? ? ? ? ) ????????????
???(2) ???( ?1 ?2 ?3 ?4 ) ????
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1.3 ??????????
1.3.1 ??????

• ?LiNbO3?KDP????????????
• ????????????
• ????????????-???????
• ?????????

1.3.2 ??????

• ?????
• ??????
• ???????????

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• Materials for?(2)
• Noncentro-symmetry is required, otherwise?(2)
  0.
• It has proved difficult to find materials
  with large NLO combined with low-enough linear
  and nonlinear losses.

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• Systematic studies have shown that conjugated
  organic molecules with large delocalized electron
  system show very large nonlinear optical effects.
• The attachment of functional groups with
  electro-accepting and donating character at
  opposite ends of the conjugation bridge leads to
  an essentially one-dimensional charge transfer,
  which will give a very dominating value
  ßzzz(z-direction refers to the charge transfer
  direction), and all other tensor elements in ß
  can be neglected.

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• Basic molecular units and structures essential
  for NLO organic materials
• The electron density of pbonds is much more
  mobile than that of the s bonds. The electron
  distribution can also be skewed by substituents,
  resulting in the hyper-polarizability in response
  to an externally applied electric field.

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• Two-level approx. Model
• Highest occupied molecular orbit(HOMO) and
  lowest occupied molecular orbit (LOMO).
• The resulting ßCT (CT --- Charge transfer)
  is a function of the energy gap between the two
  states, the oscilator strength of the CT
  transition, the dipole moment associated with
  that transition and the fundamental laser photo
  energy.

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• The equivalent internal field model of a free
  electron gas corresponding to the delocalized
  electron density of a conjugated system of length
  L ß L 3
• An optimized NLO chromophore can then be expected
  to have an extended conjugated system (large L),
  a low-energy transition (long wavelength
  absorption) with a high extinction coefficient,
  and a large dipole moment between the excited and
  ground state electronic configurations (charge
  asymmetry) introduced by donor and acceptor
  groups.

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• The charge transfer molecules have a very
  asymmetric response to an applied electronic
  field. However, the presence of conjugation and
  donor an acceptor groups generally introduces a
  undesirable effect, the so-called transparency
  efficiency trade-off, also leads to a shift of
  the absorption edge towards longer wavelengths
  (red).

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• There are few rational strategies for
  optimizing?ijkl. Well-defined structure-properties
  relations for chromophores are still absent,
  although bond length alteration has recently been
  identified as one structural parameter for?ijkl.
• Large ?(2) require noncentrosymmetric packing of
  the organic molecules.

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• Technological approaches
• Polar arrangement of the molecules in single
  crystals or Langmuir-Blodgett films.
• Chromophores as guests and polymers as hosts or
  sol-gels
• Poling process
• Films formed by molecular beam epitaxy (MBE)

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• ? Bridge benzene analogs
• Donor
• Amino,dialkylamine,diphenylamino,methoxy, ketone
  dithioacetal,julolidinyl,etc.
• Acceptor
• Nitro, cyano, dicyano-ethenyl,tricyanoethayl,3-(di
  cyanomethylidene)-2,3-dihydrobenzothiophen-2-ylide
  ne-1,1-dioxide,etc.

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• Molecular assembly
• The symmetry reduction during crystal growth
  can be accomplished by either the introduction of
  molecular asymmetry or the incorporation of
  steric substituents into chromophore.

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• The incorporation of NLO molecules in polymers
• Mixing, covalent linking (side chain, cross
  linked, main chain)
• Corona poling, electrode poling.

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• Reqirements
• High electro-optic coef.
• No orientational relaxation at 80 Co over a few
  years.
• No orientational relaxation at 250 Co over a
  short time
• No degradation up to 350 Co
• Low optical loss (lt 2dB/cm)
• Good thin-film processability
• Broadband transparency and low costs

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1.4 ??????????

• ???????????????????????,?80??????20?????????????
• ???????????????????12????????????,??????????,????
  ????????????????,??????????????????????????

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1.5 ?????

• 1.5.1 ???????????????? ???,?????????????????????
  ?????????????
• 1.5.2 ???????????????????,??????????
• 1.5.3 ????????
• 1. ?-?????
• 2. ?????
• 3. ???

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• ??????????????????????????????????????????????
  ???????,??????????????,????????????????,??????????
  ??,??????????
• ??Tg??250??????????????????????

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?????

• NLO????????????????????????????????
• ?????????????????????

???????????
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???????
32
??????????????

• ???????????????????????????,?????????NLO??
  ???????????????
• ???????????????????,??????????????????????
  ???????????????????,?????????????????????????????
  

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??????????????

• ?????????(PI-NLO)??????NLO????????,????????
  ?????????????????????? ?
• ????????????????????????????????????????????
  ???????????????????

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X??????????
X?????????
35
X???????

• X??????????????????,?????????,????????,??
  ??p??????????????????????

• ????????????????????,?????????ß?????????,?
  ???X?????????????????????? ?

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1,2-???-4,5-?????????
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????(PAA)???????

• ????????????????????????????????????????????
  ???,????????????????????????????????
• ???????????????PAA????????????????????

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PAA?????
PAA??????????
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PAA?????????

• ????????,??PAA???????????
• (1) ?????????,????????????
• (2) ???????????
• (3) ?????(PMDAMPDA)?1.011.02?
• (4) ?????1520??
• (5) ?????4???

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PI-NLO??????
????PI-1?????
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????PI-2?????
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PI-1?DSC?? PI-2?DSC??

• ???????
• PI-1?0.63dL/g
• PI-2?0.75dL/g
• Tg???

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????PI-2?????
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? ?????????

• 2.1 ??????????
• 1??????????
• 2??????????
• (1)Y??? (2)X???
• 3? ????
• 2.2 ??????????
• 1? ????? 2??????
• 3? ???
  4????????

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? ?????????????

• 3.1 ?????????????? ??
• ????????????,??????????????,??????????
• 3.2 ????????????
• ???????????(PU/PI)????????????????
• 3.3 ???????
• ??????????,?????????
• 3.4 ????????????
• ?????????,?????????,????????????????

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? ???????
4.1 ??????????????
?? ???????? ???????????
?????
????? ?????????? (EFISH) ????? ????? ??? ???????
????? ?????(HRS) ?????(ATR)??
?????? ????? ?????
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???????

• ???????F?????????????????
• F 1-(AP/A0)
• A0 ?AP??????????????????????
• 1.?????,????F????????,???F???????????
  ???
• 2. ??????????,???F???????????,???F???
  ???????????,?????????????

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Thank you