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![]() 44107-GB7
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liquid
crystal. A film with a composition (75% of Wacker C4745 and 25% of
MBBA )�
that results in a color change from red to blue under a deformation of
approximately 25% is shown in Fig. 3a. The color was immediately and completely
restored after deformation.
If
the film is kept stretched, then restoration of the color required six or more
hours.
Excitation of cholesteric films by Nd:YAG laser ( with laser dye Pyrromethene 597 ) results in fluorescence and lasing. The selective reflection band of the unstretched film was positioned at 640 nm (Fig.3b, upper curve).� In the unstretched, reddish film, two emission peaks were observed in the spectrum of left-handed circularly polarized light. One peak was a broad emission centered at 572 nm corresponding to the top of fluorescence band of the pyrromethene laser dye in this matrix. The peak, at c.a. 640 nm, corresponds to the high energy edge of the selective reflection band schematically shown as a step in Fig. 3b (upper part). Under conditions of stretching, the left-circularly polarized lasing emission from the polymer film shifts towards the blue end of the visible spectrum following the position of the selective reflection band (Fig.3b, lower curves). The left-handed emission in stretched film displays a number of sharp peaks with the intensity increasing at shorter wavelengths (right-handed emission does not display any sharp peaks). The intensity increases in the band edge lasing modes positioned close to 572 nm because the selective reflection band shifts toward the peak of the laser dye emission with increased quantum efficiency of emission. If there were no amplification of emission at the edge of the selective reflection band, the emission at 600 nm would have been smaller than the emission at 572 nm by a factor of c.a. 100.
The research grant from PRF had a profound effect on the scientific career of P. I. During the course of the project 5 articles co-authorized with the students were published in scientific journals and two presentations were made at scientific conferences. This grant allowed not only to conduct scientific research by P.I., but also supported research projects of 6 students. This, in turn, had an important educational impact and helped students to secure good jobs. Finally, this grant helped P.I. to get a tenured position at Fordham University.