Control of the molecular alignment inside liquid-crystal droplets by use of laser tweezers
Control of the molecular alignment inside liquid-crystal droplets by use of laser tweezers
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DOI：
10.1002/smll.200500038
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发表时间：
2005-05-01
期刊：
影响因子：
13.3
通讯作者：
Misawa, H
中科院分区：
文献类型：
--
作者：
Murazawa, N;Juodkazis, S;Misawa, H
在这里，我们演示了由于液滴内向列液晶的偶极分子重排和各向异性偏振性而引起的光致双折射如何将液滴的径向（从而光学各向同性）结构改变为双折射结构。这种双折射的强度相关变化可以用各向异性偏振率和取向光学非线性效应来理解。激光镊子引起的双折射改变了通过的光的动量。反过来，对于圆偏振镊子来说，这种变化会产生足够大的角动量变化，足以旋转微米大小的液滴。对于线性偏振镊子，分子排序会产生动量，从而横向移动液滴。结果表明，光学非线性可以“大”到足以产生机械（有质动力）影响，也就是说，它允许以亚微米分辨率控制微观物体的运动和位置。由激光镊子的偏振和功率控制的光诱导分子排列允许人们驱动、旋转和平移比组成分子本身大 10(3)-10(4) 倍的物体。
Here, we demonstrate how the light-induced birefringence due to the dipole molecular realignment and anisotropic polarizability of a nematic liquid crystal inside a droplet changes the droplet's radial (and thus optically isotropic) structure into a birefringent one. This intensity-dependent change of birefringence can be understood in terms of the anisotropic polarizability and orientational optical nonlinear effect. Birefringence induced by laser tweezers changes the momentum of the passing light. In turn, for the circularly polarized tweezers, this change generates an angular momentum change large enough to spin micrometer-sized droplets. For the linearly polarized tweezers, the molecular ordering generates momentum, which laterally displaces the droplet. It is shown that the optical nonlinearity can be "large" enough to have mechanical (ponderomotive) implications, that is, it allows control of the movement and position of micro-objects with submicrometer resolution. The optically induced molecular alignment controlled by the polarization and power of the laser tweezers allows one to actuate, rotate, and translate objects which are up to 10(3)-10(4) times larger than the constituent molecules themselves.