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Fig. 20.5. Photorefractive, non- a degenerate four-wave mixing time response for a 100-pim-thick film of ~

the PVK: CM: DEANST polymeric c composite as the field is turned on 53

(a) and turned off (b). From (a) -a a rise time of t, = 62 ms is ob- .2

o tained and from (b) a decay time e of Td = 46 ns is obtained for a dc £

electric field of 41 V/pim. The data 5 for the rise time is fit to a functional form [1 - exp(-//r,)|2 and for the decay time to a form exp(-2i/tlj) [20.21],

Time [milliseconds]
Time [milliseconds]

ELECTRIC FIELD [V/ptm]

Fig. 20.6. Electric field dependence of the diffraction efficiency measured on a 100-pim-thick film of the PVK-TCPrC^iDEANST polymeric composite between ITO film electrodes [20.20],

ELECTRIC FIELD [V/ptm]

Fig. 20.6. Electric field dependence of the diffraction efficiency measured on a 100-pim-thick film of the PVK-TCPrC^iDEANST polymeric composite between ITO film electrodes [20.20], in this sample) for an applied field of 41 V//xm [20.21], The rise and decay times in Fig. 20.5 for the diffracted signal based on a single carrier model were found to be rr = 62 ms and rd — 46 ms, respectively.

The diffraction efficiency for a 100-//,m-thick PVK-TCP:C60:DEANST photorefractive device is shown in Fig. 20.6 as a function of the dc electric field produced by a bias voltage V applied between the transparent ITO electrodes. High efficiencies, greater than 30% and greater than those of any known inorganic photorefractive media, were observed at electric fields of ~100 V/^im [20.21], To achieve these large £-fields in the device requires the application of a high voltage (~10 kV). In Fig. 20.7 [20.21] we display the photorefractive device performance parameters (diffraction efficiency and response speed) for the best photorefractive inorganic materials [e.g., BaTi03, SrtBa1_xNb03 (SBN), Bi12SiO20 (BSO)] [20.32], for promising photorefractive polymer composite materials (e.g., bisA-NPDA:DEH1,2 [20.22,33,34], PVK:C60:DEANST [20.35,36], PVK:FDEANST:TNF [20.37], PVK:TPY:DEANST [20.38],

'Bisphenol-A-diglycidylether (bisA) and 4-nitro-l,2-phenylenediamine (NPDA).

2Diethylamino-benzaldehyde diphenylhydrazone (DEH).

10"

PVK:C60:DEANST

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