Study On The Wide Dynamic Range Of Liquid Crystal Soft Photonic Materials In Response To External Field Stimulus

The liquid crystal responsive to external stimulus is studied and the relevant photonic devices based on the material are prepared respectively in this research.By doping the azo chiral molecules into the chiral nematic liquid crystal(N*LC),the helical pitch of spiral N*LC structure can be changed and the shift of Bragg reflection band of N*LC occurs consequently,attributed to the photoisomerization process of azo material under UV exposure that decrease the helical twisting power(HTP)from the trans configuration to the cis state with less HTP.Distributed with periodic different reflection color,the N*LC grating made by using a photomask has the character of waveband selectivity to the incident light,enabled by the amplitude modulation of light wavefront across the grating.The responsive waveband can be optically controlled within the range up to?140nm.Compared with the polymer LC grating,the photosensitive azo grating is accessible to electrical modulation for diffraction efficiency,and quite flexible by virtue of the erasable and rewritable patterns.Furthermore,for another type of LC photonic device i.e.the N*LC lasing film system,the lasing wavelength could also be tuned under some external excitation.To improve the emission performance of N*LC lasing film,the concentration ratio of three compositions is studied in terms of evaluating the lasing performance among the whole film sample.From the experimental results,the number of N*LC micro-droplets capable of lasing emission would get the maximum when the ratio between N*LC and polymer PVA is kept between 1:10 and 1:9,implying the optimal property of lasing film.In addition,the average diameter of micro-droplets is also quite relevant to the concentration ratio that the higher ratio of N*LC or the lower ratio of polymer PVA enlarges the diameter generally.While for the lasing behavior,the pumping threshold is confirmed to be linearly correlated to the area of N*LC micro-droplets,convinced by the equal density of pumping threshold independent on the size of N*LC micro-droplets.