Page 192 - Photoreactive Organic Thin Films

5. CH1RAL POLYMERS WITH PHOTOAFFECTED PHASE BEHAVIOR FOR OPTICAL DATA STORAGE J "J |

FIG. 5.27 Sketch of the photorecording setup.

FIG. 5.28 Examples of LCPT-recorded images in a ~ I0-fxm-thick SK8 film, observed in (A) the
scattering mode and (B) the transmission mode.

the copolymer film; and appears then as a dark graph on the transparent
background, as illustrated in Figure 5.28B. We should emphasize here that
no polarized light is necessary for either LCPT recording or reading of the
image. Third, if crossed polarizers are used, the image can be read out as a
white graph on the black background.
In contrast to photoinduced birefringence, the mesophase patterns in
Figure 5.28 cannot be erased by light irradiation with UV light or with circu-
larly polarized visible light, and only heating above the transition tempera-
ture erases the pattern. After such a thermal treatment, a new image can be
written in the same film, up to 10 cycles of LCPT recording have been tested
with a 10-um-thick SK8 film without any loss in image quality.
To summarize, the LCPT effect allows a novel recording technique to be
implemented. The technique is very simple to realize and allows for recording
large-area images using nonpolarized light of low intensity.