Post-writing Evolution and Erasure Characteristics

Even after the writing lasers had been turned off, in several cases considerable evolution of the gratings was observed. This occurred in samples thermally treated after writing SRGs, during erasure experiments, or even when samples were simply left to rest. When the writing beams are switched off, 

In SRGs inscribed on LC polymer films, time evolution has also been reported in reference 13. The depth of the SRG was seen to increase from 70 nm up to 300 nm, 16 h after the writing process was completed. During this period, the samples were left to rest under dark conditions. Ozaki et at also showed that the SRG formation progresses even after terminating the laser light irradiation on a composite film of an azopolymer and a conducting polymer derived from poly(p-phenylene vinylene). 

SRGs recorded with circularly polarized beams showed an even more interesting erasure behavior. The SRG can be erased by beams polarized parallel to the grooves and circularly polarized, as in the previous cases, but when erasing was tried with a beam polarized perpendicularly to the grating grooves an increase in diffraction efficiency and amplification of the surface modulation occurred (44% increase in the amplitude of the SRG, consistent with doubling of the diffraction efficiency). 

Geue et al. investigated the thermal erasure of SRGs obtained via light-driven mass transport, at various temperatures, which allowed them to estimate the activation energy for erasure to be 2.6 eV. For erasing at T Tg, the SRG was erased by flow of polymer material perpendicular to the initial surface, accompanied by the formation of an intrinsic density grating, as commented on in the work of reference 95. At T Tg, the lateral density modulation was equalized by a lateral flow of material. 

5 OPEN QUESTIONS AND CHALLENGES FORTHE NEAR FUTURE 

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Post-writing Evolution and Erasure Characteristics OPEN QUESTIONS AND CHALLENGES FORTHE NEAR FUTURE... 

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