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标题：Electrically tunable laser based on oblique heliconical cholesteric liquid crystal
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作者：Jie Xiang ; Andrii Varanytsia ; Fred Minkowski 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：46
页码：12925-12928
DOI：10.1073/pnas.1612212113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceLiquid-crystal lasers based on micrometer-scale self-organization of organic molecules into the so-called cholesteric liquid crystal are simple to manufacture; they are small in size and low in cost and power consumption. Their potential applications range from sensing and imaging to informational displays and miniature "lab-on-a-chip" devices. We report a cholesteric structure used as the lasers resonator cavity that enables a continuous real-time tuning of the emitted wavelength in a very broad range by applying an electric field. The structure is heliconical, with the molecules rotating around a helical axis and being tilted toward this axis. The electric field controls the tilt and the pitch, thus changing the wavelength by at least 100 nm. A cholesteric liquid crystal (CLC) formed by chiral molecules represents a self-assembled one-dimensionally periodic helical structure with pitch [IMG]f1.gif" ALT="Formula" BORDER="0"> in the submicrometer and micrometer range. Because of the spatial periodicity of the dielectric permittivity, a CLC doped with a fluorescent dye and pumped optically is capable of mirrorless lasing. An attractive feature of a CLC laser is that the pitch [IMG]f1.gif" ALT="Formula" BORDER="0"> and thus the wavelength of lasing [IMG]f2.gif" ALT="Formula" BORDER="0"> can be tuned, for example, by chemical composition. However, the most desired mode to tune the laser, by an electric field, has so far been elusive. Here we present the realization of an electrically tunable laser with [IMG]f2.gif" ALT="Formula" BORDER="0"> spanning an extraordinarily broad range (>100 nm) of the visible spectrum. The effect is achieved by using an electric-field-induced oblique helicoidal (OH) state in which the molecules form an acute angle with the helicoidal axis rather than align perpendicularly to it as in a field-free CLC. The principal advantage of the electrically controlled CLCOH laser is that the electric field is applied parallel to the helical axis and thus changes the pitch but preserves the single-harmonic structure. The preserved single-harmonic structure ensures efficiency of lasing in the entire tunable range of emission. The broad tuning range of CLCOH lasers, coupled with their microscopic size and narrow line widths, may enable new applications in areas such as diagnostics, sensing, microscopy, displays, and holography.
关键词：cholesteric liquid crystals ; lasing ; electric tunability ; heliconical structure