Volume grating

We note from Eq. (15) that the space-charge field is shifted in space by n/2 with respect to the intensity pattern [Eq. (11)], which corresponds to a distant shift of Ag/4 in the x direction (Fig. 3d). This space-charge field induces an index volume grating via the Pockels effect (Fig. 3e). The refractive index including the fundamental component of refractive index modulation with magnitude of An can be written as... 

In order to determine whether the grating is a thin (plane) or volume grating, the following well-known quality parameter (Q) can be used [80] ... 

Acoustic (Thermal) Grating-Volume Grating. Since the acoustic signal can originate from the thermal effect as well as the volume change, the separation of these origins is not trivial. Several methods for the separation will be discussed in later sections (Section III.B-G). 

The observed TG signal in the picosecond-to-nanosecond time scale was analyzed in terms of a combination of the thermal effect (including AH), volume grating, and population grating components. 

If the reaction takes place in an aqueous solution, the temperature variation method can be used. The thermal expansion coefficient of water strongly depends on the temperature, and in particular, it vanishes at 4°C. Therefore, the signal observed at this temperature should come from the volume effect (volume grating). Of course, it also includes the population grating or other effects except for the thermal effect, and these contributions should be subtracted. When organic solvents are the media, a series of solvents or binary mixtures of solvents, which do not affect the other reaction parameters (such as the quantum yield, the volume change, the... 

The inscription of a single holographic volume grating was performed on homogeneous transparent thin films. Particularly in homopolymers and copolymers with... 

Besides the absolute value of the refractive index modulation, the stability is an important parameter, particularly for the development of a storage material. In Fig. 27 the temporal variation of the diffraction efficiency of volume gratings is plotted for films of a statistical copolymer 6 (azobenzene content 29.5 wt%) and... 

Fig. 27 Stability of volume gratings in thin films of the statistical copolymer 6 and block copolymer 7 with methoxy-azobenzene side-groups...

We have demonstrated that azobenzene-containing materials can efficiently form holographic SRGs and volume gratings for various kinds of applications. Two material classes, azobenzene-containing block copolymers and molecular glasses, were designed and synthesized and they can find applications in different fields. 

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