Direct observation of orientation limit in a fast photorefractive polymer composite

Abstract

We report on a photorefractive polymer with a 4-ms-response time in transient four-wave mixing experiments at 0.5 W/cm2 writing irradiance, 95 V/μm applied electric field, and a grating period of 3.1 μm. Complementary transient ellipsometry, however, reveals orientational birefringence response which leads the four-wave mixing response all the way to its saturation, despite complex dynamics in these processes. Orientation does not limit the dynamic formation of photorefractive gratings in this polymer, which suggests that even faster photorefractive responses are possible for polymer composites with improved charge generation and transport properties.

Photorefractive Performance of Poly[methyl-3-(9-carbazolyl) propylsiloxane] Based Composites Sensitized with Poly(3-hexylthiophene) in a 0.2-1wt % Range

“…21 The transmittance (T) as a function of the applied electric field for six samples is shown in Figure 7. The birefringence (∆nBR) of samples was determined from the variation of the transmitted intensity through crossed polarizers upon the external electric field, as described by the following equation:…”

Materials Design and Physics of Organic Photorefractive Systems

“…[31,32] Moreover, only tentative theoretical descriptions are available. [33,34] Thus, different analytical functions are used, ranging from single- [35] and doubleexponential, [31,32,36] and to stretched exponential [37] fits. This is often motivated by assuming that the first time constant t 1 describes the build-up of the space-charge field, whereas at later times chromophore reorientation and other effects dominate.…”

“…Among them are poly(phenylenevinylene) (PPV) derivatives such as DBOP-PPV, [50] acrylates with tetraphenyldiaminobiphenyl [49] units in the monomer (TPDac), and polyfluorenes, of which TFB is an example, [32] is shown in Scheme 1. A TFBbased host ± guest system is also currently the fastest organic PR material (see Figure 6); [32] yet it is remarkable that the large difference in mobility of more than two orders of magnitude between PVK and TFB composites only corresponds to a holographic response of TFB that is four times faster (1 [32] versus 4 ms [36] ).…”

“…[32,36,46] A significant disadvantage, however, is their lack of compositional stability: The highly polar chromophores, which are mobile in low T g systems, tend to crystallize over a time span between hours and a couple of months in the apolar photoconductive host material. [52,53] Therefore, the issue of limited shelf lifetime has to be addressed, for example by using eutectic [53] and isomeric [54] dye mixtures or by improving the compatibility of the components.…”

A femtosecond Raman generator for long wavelength two-photon and third harmonic generation imaging

“…This type of linear interaction between coherent light beams has been shown to operate on a femtosecond time scale by Refs. 19 and 20, and it is thus much faster than techniques based on the slow microsecond to second scale photorefractive nonlinearity, [21][22][23][24][25][26] which also allow all-optical dynamic wavefront shaping. In contrast to nonlinear techniques in general, our approach is linear and therefore does not have fundamental minimum intensity requirements.…”