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20 refractive index △n is related to space charge field Esc by equation △n = − n3 re 2 Esc (2.4) where re is the effective electro-optic coefficient. Another effect which leads to the refractive index field dependence in polymer composites is Kerr orientational effect (χ (3) ). This orientational effect called “orientational enhancement” is present in PR polymer composites in contrast to both inorganic and organic crystals. The physical mechanism responsible for orientational enhancement is the orientation of NLO chromophores which are the necessary constituents of a PR polymer composite by the local spatially varying space charge field Esc. This effect will be considered in more detail later in Section 2.4. At this point, the spatially modulated index of refraction and thus, the diffraction grating, is created. Now, as the PR effect has been introduced, it is time to consider experimental geometries under which it is observed. 2.1.3 Experimental methods for photorefractive studies The two main experimental techniques used for study of the photorefractive performance of a material are two-beam coupling (2BC) and four-wave mixing (FWM). In this section, we consider the physical grounds for both 2BC and FWM geometries to be employed as PR effect probes.
2 1' 2' 1 1 Detector 2 d 2 E a 2 Detector 1 1 1 Polymer composite ITO-covered glass Figure 2.3: Experimental geometry for the two-beam coupling experiment. Two-beam coupling As already mentioned before, the two-beam coupling experiment is the first experiment to perform when a new material is tested for PR performance. The geometry of a typical experiment is shown in Figure 2.3. A typical PR polymer sample consists of two ITO-covered glass slides with a PR polymer film of 30 −100 µm thickness in between. To the best of my knowledge, no PR effect can be observed in polymer composites without an external electric field (typically ∼ 1−150 V/µm) applied. Op- tical beams 1 and 2 are incident at angles θ1 and θ2 respectively, and interfere in the PR material, creating a nonlocal (Φ = 0) diffraction grating. Then the same beams 1 and 2 partially diffract from the grating they have just created (beams 1’ and 2’ in 21
Page 1 and 2: Nonlinear Optical Probes and Proces
Page 3 and 4: Table of Contents Table of Contents
Page 5 and 6: References . . . . . . . . . . . .
Page 7 and 8: List of Figures 2.1 Schematic exper
Page 9 and 10: 3.31 Time evolution of the diffract
Page 11 and 12: Nonlinear Optical Probes and Proces
Page 13 and 14: Chapter 1 Introduction From ancient
Page 15 and 16: of the polarization density is [2]
Page 17 and 18: degenerate four-wave mixing and the
Page 19 and 20: (Section 3.3) as well as photorefra
Page 21 and 22: References [1] R. Boyd. Nonlinear o
Page 23 and 24: the optics of nonlinear devices bas
Page 25 and 26: materials. The figure-of-merit may
Page 27 and 28: generation of charge carriers, tran
Page 29 and 30: after the interference pattern is c
Page 31: transport is mostly due to drift ra
Page 35 and 36: coincide. However, due to refractio
Page 37 and 38: The equation to be solved is the wa
Page 39 and 40: It is obvious that the differential
Page 41 and 42: the symmetry group of the crystal a
Page 43 and 44: much weaker than the writing beams
Page 45 and 46: where d is the thickness of the sam
Page 47 and 48: ability to reorient in the space ch
Page 49 and 50: energy levels (ionization potential
Page 51 and 52: ficiency is the external applied fi
Page 53 and 54: photogeneration efficiency φ then
Page 55 and 56: where α is the absorption coeffici
Page 57 and 58: Energy 0 g( ) i Figure 2.6: Schem
Page 59 and 60: charge carrier mobility arises from
Page 61 and 62: 2.2.3 Charge trapping and detrappin
Page 63 and 64: Eqs. 2.29 and so, we will assume be
Page 65 and 66: However, Eq. 2.44 was derived under
Page 67 and 68: So, in this case the form of the so
Page 69 and 70: independent ζ0 [17]. We substitute
Page 71 and 72: on the both photoconductivity and p
Page 73 and 74: Trap-unlimited regime In this secti
Page 75 and 76: m xa 1 0.8 0.6 0.4 0.2 1 -1 TMT1
Page 77 and 78: simplify these to: ˜ λ1 ≈ 1; ˜
Page 79 and 80: - 6 0 , 10 40 30 20 10 simulated d
Page 81 and 82: and ˜γ, the correct estimate of i
Page 83 and 84:
is no longer valid, so the followin
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tion 2.3.2, we show how the ionized
Page 87 and 88:
numerical simulation of the dynamic
Page 89 and 90:
The first order system of equations
Page 91 and 92:
where C, ˜ C are constants determi
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Diffr.eff. , arb.units 1 0.8 0.6 0.
Page 95 and 96:
Figure 2.15: PR speed ν calculated
Page 97 and 98:
a real system the effect from a cha
Page 99 and 100:
ρ0(t) ≈ ˜ρ0 and ionized accept
Page 101 and 102:
the PR performance, in particular d
Page 103 and 104:
2.4.1 “Simple” electro-optic ef
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Eq. 2.71 and compared to the measur
Page 107 and 108:
For one-dimensional molecules whose
Page 109 and 110:
applied electric field Ea, but also
Page 111 and 112:
or, in terms of microscopic quantit
Page 113 and 114:
The photoconductivity part of the P
Page 115 and 116:
[14] Y. Cui, B. Swedek, N. Cheng, J
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[41] P. Gunter and J.-P. Huignard,
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Next, in Section 3.4, we will discu
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a) NC O O C 60 NC O NC O NC PVK c)
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transport is only conducted through
Page 125 and 126:
NA of the C60 molecules (see Figure
Page 127 and 128:
3.3 Photoconductivity experiments I
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photogenerated in the bulk during a
Page 131 and 132:
voltage V , but the voltage V0 at w
Page 133 and 134:
Figure 3.4: Electric field dependen
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320nm Nd:YAG laser with Raman shift
Page 137 and 138:
zero. In these equations, q is the
Page 139 and 140:
non-Gaussian charge transport. In t
Page 141 and 142:
30 V/ m 30 C 0 40 C 0 50 C 0 Figure
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Figure 3.9: Dependence of the mobil
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a) b) Figure 3.10: Current transien
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Conventionally, in the DC photocond
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a) b) 40 V/ m 100 mW/cm 2 Figure 3.
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1 0= 770 s -1 -1 = 4.35 s B = 1.66
Page 153 and 154:
Figure 3.14: Trapping parameter γT
Page 155 and 156:
Figure 3.15: Long time scale photoc
Page 157 and 158:
Figure 3.16: Example of the photocu
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He-Ne laser Beam Splitter Polarizat
Page 161 and 162:
Figure 2.3. Then, the ratio of the
Page 163 and 164:
to explore experimentally which mec
Page 165 and 166:
In most of the PR polymer composite
Page 167 and 168:
disappeared, we opened the other wr
Page 169 and 170:
Now we describe the general trends
Page 171 and 172:
ciency is an increasing function of
Page 173 and 174:
are defined in Eqs. 2.58). Eq. 3.23
Page 175 and 176:
state diffraction efficiency was th
Page 177 and 178:
Figure 3.26: Dependence of the fast
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E a) b) Applied electri
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Figure 3.28: Dependence of the fast
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(i) calculate the PR speed as deter
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h h C 60 (N A ) s T 1 E PVK PDCST
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ferences that affect dissociation r
Page 189 and 190:
serve that the addition of all chro
Page 191 and 192:
is simplified. Knowing the availabl
Page 193 and 194:
the free hole with the ionized acce
Page 195 and 196:
Figure 3.30: Intensity dependence o
Page 197 and 198:
3.5.2 Plasticized composites This c
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the recombination rate γ and the s
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h h h h h h C 60 (N (NA) A) s s s
Page 203 and 204:
Figure 3.33: Concentration dependen
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mophore may contain a large error d
Page 207 and 208:
ather requires knowing trapping rat
Page 209 and 210:
Figure 3.36: Time evolution of diff
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and for low concentrations of AODCS
Page 213 and 214:
concentration x10 %. For the lower
Page 215 and 216:
3.6 Summary of Chapter 3 In Chapter
Page 217 and 218:
References [1] W. E. Moerner and S.
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[27] J. Schildkraut and Y. Cui. Zer
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[51] A. Blythe. Electrical Properti
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E = 0 E 0 Fi
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chromophores are randomly oriented
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where the local field factors are g
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system, and k is Boltzmann’s cons
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Ar Laser + Ti:Sapphire Laser Spectr
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Figure 4.4: Typical data in the EFI
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and the birefringence ∆n(t) is pr
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experiment is the applied field. Ho
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nature. For the transient shown in
Page 241 and 242:
Figure 4.7: Illustration of the HeN
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the screening of the external elect
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is accompanied by the reduction in
Page 247 and 248:
References [1] W. E. Moerner, S. M.
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Chapter 5 Second harmonic generatio
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2 d 2 0 L Figure 5.1: Schematic
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of the nonlinear susceptibilities i
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x z E p E s Figure 5.2:
Page 257 and 258:
(a) (b) (c)
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to βz ′ z ′ z ′ as follows [
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d31 = N 2 〈cos θ sin2 θ〉〈co
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Thus, SHG measurements of the azimu
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a) b) 10 5 -10 -5 5 10 15 -5 -10 c)
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Nd:YAG “Reference” PMT 2 F Quar
Page 269 and 270:
( ) ( ) H3C Si (CH2) 11 O NO2 H 3C
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Figure 5.11: Maker fringes observed
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We observed light-induced alignment
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polarized UV light. The intensity o
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and then d31 = d sub 31 + N 4 cos
Page 279 and 280:
The angular dependence of the secon
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= ⎛ ⎜ ⎝ sin Φ d25cos 2 Φ s
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S-input polarization The case of s-
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pf,y = 0 pf,x = 1 ω nf bf,x = pf,
Page 287 and 288:
References [1] M. B. Feller, W. Che
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Chapter 6 Summary In this, final, C
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anticipated from the theoretical mo
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Bibliography Abkowitz, M., Bassler,
Page 295 and 296:
Daubler, T. K., Bittner, R., Meerho
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Kuzyk, M. G., and Dirk, C. W., Eds.
Page 299 and 300:
Reznikov, Y., Ostroverkhova, O., Si
Page 301:
Zilker, S. J., Grasruck, M., Wolff,
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