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Effect of Thick Anisotropic NLC Layer on Lasing in Polymeric Cholesteric Liquid Crystals
송명훈,Hideo Takezoe,Byoungchoo Park,Junji Watanabe,Ken Ihikawa,Ki-Chul hin,uzuhi Nihimura,Takehiro Toyooka,Timothy M. wager,Yoichi Takanihi,Zhengguo Zhu 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.2
We have studied the lasing characteristics from a dye-doped nematic liquid crystal layer sandwiched by two polymeric cholesteric liquid crystal films as photonic band gap materials. The nematic layer possessing birefringence brings about the following remarkable optical characteristics: (1) reflectance in the photonic band-gap (PBG) region exceeds 50 %, due to the retardation effect,being unpredictable from a single CLC film; (2) efficient lasing occurs at the notch of PBG; (3) the lasing emissions contain both right- and left-circular polarizations. In this study, we demonstrate that a 100-μm-thick nematic liquid crystal layer system shows several dips, resulting in multi-modelasing actions just at the dips within PBG.
Rewritable, light-driven recordings in a full-colour fluorescent polydimethylsiloxane elastomer
Song, Seongkyu,Takezoe, Hideo,Jeong, Soon Moon The Royal Society of Chemistry 2018 Journal of materials chemistry. C, Materials for o Vol.6 No.40
<P>Current approaches to demonstrate light-driven writing enabling multiple “write-erase” cycles are mostly based on photochromic materials requiring complex synthesis processes. Here, we show a new approach to realize rewritable, light-driven recordings in conventional dye-incorporating poly(dimethylsiloxane) (PDMS) by using a laser-induced photobleaching technique. Upon selective photobleaching of red dyes, the PDMS film emits patterned letters of different colours (blue or green) from their backgrounds. We also found that the diffusion of dye molecules into the bleached region promoted a self-healing characteristic that could erase the patterned letters, which enables us to rewrite different letters using the same PDMS. This novel method of light-driven writing can be applied effectively in many research fields, including secure printing and optical storage devices, and will significantly advance future writing applications.</P>
Choi, Hyunhee,Takezoe, Hideo The Royal Society of Chemistry 2016 Soft matter Vol.12 No.2
<P>We demonstrate circular flow formation at a surface in homeotropically oriented nematic liquid crystals with a free surface using focused laser beam irradiation. Under a weak laser power, a pit together with an associated circular bulge is formed: the Marangoni effect. Here a diverging molecular flow from the pit (thermocapillary flow) also induces director tilt in the radial direction. Upon increasing the laser power, the pit becomes deeper, and eventually evolves into a circular flow associated with a deeper pit and a subsidiary circular bulge or valley structure. This phenomenon is induced by escaping from excess deformation energy due to a bend deformation of the director. Actually, we confirmed that the circular flow is never formed in the isotropic phase. The handedness of the vortex cannot be controlled by circular polarisation, but is controllable by doping with chiral molecules. This rotational motion (a nematic microrotor) is a unique phenomenon only exhibited by anisotropic liquids, and is expected to be applied for novel devices.</P>
Choi, Suk-Won,Takezoe, Hideo The Royal Society of Chemistry 2016 SOFT MATTER Vol.12 No.38
<P>We found possible chirality enhancement and reduction in chiral domains formed by photoresponsive W-shaped molecules by irradiation with circularly polarized light (CPL). The W-shaped molecules exhibit a unique smectic phase with spontaneously segregated chiral domains, although the molecules are nonchiral. The chirality control was generated in the crystalline phase, which shows chiral segregation as in the upper smectic phase, and the result appeared to be as follows: for a certain chiral domain, right-CPL stimuli enhanced the chirality, while left-CPL stimuli reduced the chirality, and vice versa for another chiral domain. Interestingly, no domain-size change could be observed after CPL irradiation, suggesting some changes in the causes of chirality. In this way, the present system can recognize the handedness of the applied chiral stimuli. In other words, the present material can be used as a sensitive chiral-stimuli-recognizing material and should find invaluable applications, including in chiroptical switches, sensors, and memories as well as in chiral recognition.</P>
Choi, Hyunhee,Nishimura, Suzushi,Toyooka, Takehiro,Ishikawa, Ken,Takezoe, Hideo WILEY‐VCH Verlag 2011 Advanced Functional Materials Vol.21 No.18
<P><B>Abstract</B></P><P>Detailed optical lasing characteristics in liquid crystal (LC) microlasers consisting of multiple polymer cholesteric LC (PCLC) layers are presented as broadband resonators sandwiching a layer of thick gain media, dye‐containing nematic LC (NLC) or isotropic liquid, in between. Multiple lasing emission peaks due to Fabry‐Perot cavity modes are observed for both gain media, and their polarization characteristics investigated. To analyze lasing characteristics, specified eigen modes are defined, the polarization states of which are maintained before and after passing through the broadband resonator, and obtained for the present full system by using the Berreman 4 × 4 matrix method. Using these specified eigen modes, the optical density for each mode is calculated and compared with the experimental results, and shows good agreement. Finally, lasing characteristics between the resonators with NLC and isotropic gain media are compared, and the advantages of adopting dye‐doped NLC gain medium are shown for tunable red, green, blue lasing in a microlaser system with a broadband resonator.</P>