光鉗，乃是利用光束作為鉗子來抓取微米等級的顆粒，只是這個抓取的力臂並不是實體化的，它是利用被抓取物的光學性質搭配強聚焦的雷射光，利用動量轉移的方式限制微粒的位置，其輸入的光場與微粒的性質變化，能使微粒的操控具有多樣的效果，由於其非接觸與非破壞式的特點，光鉗在生醫及材料科學方面皆多有應用。本論文之實驗主要目的是研究染料摻雜液晶微球內部之液晶結構於紫外光照前後有所轉變，期間分別以具有自旋角動量(spin angular momentum, SAM)與具有軌道角動量(orbital angular momentum, OAM)光鉗作用下研究微球轉動行為之變化。
本實驗主要使用可調製光相位的特殊元件q-plate (QP)來產生光渦流場，並將此光渦流場與光鉗技術結合，使光鉗光斑強度具環性分布且同時帶有SAM與OAM。再以此光鉗光束抓取液晶微球，而微球內乃使用摻有光敏材料(偶氮染料)之向列型液晶，在照射紫外光下，會調製微球軌道轉動速度。另外，本實驗亦使用能對微球內液晶分子產生垂直和水平配向之界面活性劑，藉以製作出雙極型與輻射對稱型之液晶微球，此兩種結構之液晶微球受紫外光調制轉動結果不同。
實驗結果顯示，在具有SAM與OAM光鉗作用下可成功將角動量轉移給微球。在照射紫外光之下，輻射對稱型液晶微球軌道轉速會有所改變，這主要是因為光致染料產生異構化，從棒狀的trans態轉變至彎曲狀的cis態，使得液晶微球從輻射對稱型變成isotropic態，這時微球軌道轉速會增加，此改變乃與光鉗具有的圓偏振分量經過具有類似q-plate效果的輻射對稱型液晶微球所間接獲得的OAM有關；此外，光照後微球轉速增加幅度還與照射強度及微球尺寸有關。實驗亦發現，上述輻射對稱型液晶微球獲得的間接OAM，在使用雙極型液晶微球時，並不存在，這表示雙極液晶微球不具備類q-plate的特性。

Optical tweezers, a kind of forceps made of light, can be used to trap μm-scale particles. The trapping arms are not solid but a highly focused laser beam. It can manipulate small particles through transfer of momentum from light to particles. The changes of the properties of the optical tweezers and MSs can diversify the manipulation of microspheres. Due to its non-contact and nondestructive way in control of the MSs, optical tweezers is widely used in biomedical and materials sciences. This thesis aims to investigate the orbital rotation of the dye-doped nematic liquid crystal (DDNLC) MSs and its changes under the UV irradiation under the manipulation of the optical vortex tweezers (OVTs) with spin angular momentum (SAM) and orbital angular momentum (OAM).
This study uses a particular optical device called q-plate (QP), which is often used for modulating phase of optical field, to generate optical vortex tweezers (OVTs). The OVTs beam has an annulus light spot with both SAM and OAM. We use the OVTs beam to induce orbital rotation of MSs and use one UV light to modulate the rotation speed of the MSs which is made by doping optically sensitive dyes (azo dyes) into the NLCs. In addition, the result for the UV-irradiation-induced modulation in the rotation of the MSs is different based on radial-like and bipolar DDNLC MSs.
Experimental results show that the SAM and OAM of the OVTs beam can be successfully transferred to the MSs. The speed for the orbital rotation of the radial-like MSs can increase under the UV irradiation because of the change of the MSs structure from radial-like to isotropic state through the disturbance of the curve cis isomers on the LCs after trans-cis photoisomerization of the azo dyes. The UV-induced increase of rotation speed of the MSs is associated with the indirectly transferred OAM when the circular component of the OVTs passes through the q-plate-like MSs with radial-like texture. In addition, the UV-irradiation modulation for the orbital rotation of the MSs is dependent on the UV intensity and the size of the MSs. We also found that the indirect OAM abovementioned cannot appear when the MSs is bipolar, which result shows that the bipolar MSs has no q-plate-like ability.

1. D. S. Miller, X. Wang, and N. L. Abbott, “Design of functional materials based on liquid crystalline droplets,” Chem. Mater. 26, 496–506 (2013).
2. X. Wang, D. S. Miller, J. J. de Pablo, and N. L. Abbott, “Reversible switching of liquid crystalline order permits synthesis of homogeneous populations of dipolar patchy microparticles,” Adv. Funct. Mater. 24, 6219–6226 (2014).
3. E. Tjipto, K. D. Cadwell, J. F. Quinn, A. P. R. Johnston, N. L. Abbott, and F. Caruso, “Tailoring the interfaces between nematic liquid crystal emulsions and aqueous phases via layer-by-layer assembly,” Nano Lett. 6, 2243–2248 (2006).
4. J. Zou, J. Fang, “Director configuration of liquid-crystal droplets encapsulated by polyelectrolytes,” Langmuir 26, 7025–7028 (2010).
5. J. K. Gupta, J. S. Zimmerman, J. J. de Pablo, F. Caruso, and N. L. Abbott, “Characterization of adsorbate-induced ordering transitions of liquid crystals within monodisperse droplets,” Langmuir 25, 9016–9024 (2009).
6. R. J. Carlton, Y. M. Zayas-Gonzalez, U. Manna, D. M. Lynn, and N. L. Abbott, “Surfactant-Induced Ordering and Wetting Transitions of Droplets of Thermotropic Liquid Crystals “Caged” Inside Partially Filled Polymeric Capsules,” Langmuir 30 14944–14953 (2014).
7. D. Sec, T. Porenta, M. Ravnik, and S. Zumer, “Geometrical frustration of chiral ordering in cholesteric droplets,” Soft Matter 8, 11982–11988 (2012).
8. F. Xu and P. P. Crooker, “Chiral nematic droplets with parallel surface anchoring,” Phys. Rev. E 56, 6853–6860 (1997).
9. M. Heppenstall‐Butler, A.‐M. Williamson, and E. M. Terentjev, “Selection of droplet size and the stability of nematic emulsions,” Liq. Cryst. 32, 77–84 (2005).
10. O. O. Prishchepa, V. Ya. Zyryanov, A. P. Gardymova, and V. F. Shabanov, “Optical textures and orientational structures of nematic and cholesteric droplets with heterogeneous boundary conditions,” Mole. Cryst. Liq. Cryst. 489, 84–93 (2008).
11. V. Ya. Zyryanov, M. N. Krakhalev, O. O. Prishchepa, and A. V. Shabanov, “Inverse regime of ionic modification of surface anchoring in nematic droplets,” JETP Letters 88, 597–601 (2008).
12. J. A. Moreno-Razo, E. J. Sambriski, N. L. Abbott, J. P. Hernandez-Ortiz, and J. J. de Pablov, “Liquid-crystal-mediated self-assembly at nanodroplet interfaces,” Nature 48, 86–89 (2012).
13. O. O. Prischepa, A. V. Shabanov, and V. Ya Zyryanov, “Director configurations within nematic droplets doped by lecithin,” Mole. Cryst. Liq. Cryst. 438, 141–150 (2005).
14. S. Sivakumar, K. L. Wark, J. K. Gupta, N. L. Abbott, and F. Caruso, “Liquid crystal emulsions as the basis of biological sensors for the optical detection of bacteria and viruses,” Adv. Funct. Mater. 19, 2260–2265 (2009).
15. I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. de Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332, 1297–1300 (2011).
16. V. J. Alino, J. Pang, and K.-L. Yang, “Liquid crystal droplets as a hosting and sensing platform for developing immunoassays,” Langmuir 27, 11784–11789 (2011).
17. X. Niu, D. Luo, R. Chen, F. Wang, X. Sun, H. Dai, “Optical biosensor based on liquid crystal droplets for detection of cholic acid,” Opt. Commun. 381, 286–291 (2016).
18. M. Humar, and I. Musevic, “3D microlasers from self-assembled cholesteric liquid-crystal microdroplets,” Opt. Express 18, 26995–27003 (2010).
19. D. J. Gardiner, S. M. Morris, P. J. W. Hands, C. Mowatt, R. Rutledge, T. D. Wilkinson, and H. J. Coles, “Paintable band-edge liquid crystal lasers,” Opt. Express 19, 2432–2439 (2011).
20. P. J. W. Hands, D. J. Gardiner, S. M. Morris, C. Mowatt, T. D. Wilkinson, and H. J. Coles, “Band-edge and random lasing in paintable liquid crystal emulsions,” Appl. Phys. Lett. 98, 141102 (2011).
21. J.-D. Lin, M.-H. Hsieh, G.-J. Wei, T.-S. Mo, S.-Y. Huang, and C.-R. Lee, “Optically tunable/switchable omnidirectionally spherical microlaser based on a dye-doped cholesteric liquid crystal microdroplet with an azo-chiral dopant,” Opt. Express 21, 15765–15776 (2013).
22. S. Juodkazis, M. Shikata, T. Takahashi, S. Matsuo, and H. Misawa, “Fast optical switching by a laser-manipulated microdroplet of liquid crystal,” Appl. Phys. Lett. 74, 3627–3629 (1999).
23. S. Juodkazis, S. Matsuo, N. Murazawa, I. Hasegawa, and H. Misawa, “High-efficiency optical transfer of torque to a nematic liquid crystal droplet,” Appl. Phys. Lett. 82, 4657–4659 (2003).
24. N. Murazawa, S. Juodkazis, S. Matsuo, and H. Misawa, “Control of the molecular alignment inside liquid-crystal droplets by use of laser tweezers,” Small 1, 656–661 (2005).
25. N. Murazawa, S. Juodkazis, and H. Misawa, “Characterization of bipolar and radial nematic liquid crystal droplets using laser-tweezers,” J. Phys. D: Appl. Phys. 38, 2923–2927 (2005).
26. N. Murazawa, S. Juodkazis, and H. Misawa, “Laser manipulation based on a light-induced molecular reordering,” Opt. Express 14, 2481–2486 (2006).
27. E. Brasselet, N. Murazawa, S. Juodkazis, and H. Misawa, “Statics and dynamics of radial nematic liquid-crystal droplets manipulated by laser tweezers,” Phys. Rev. E 77, 041704 (2008).
28. Y. Yang, P. D. Brimicombe, N. W. Roberts, M. R. Dickinson, M. Osipov, and H. F. Gleeson, “Continuously rotating chiral liquid crystal droplets in a linearly polarized laser trap,” Opt. Express 16, 6877–6882 (2008).
29. M. Mosallaeipour, Y. Hatwalne, N. V. Madhusudana, and S. Ananthamurthy, “Laser induced rotation of trapped chiral and achiral nematic droplets,” J. Mod. Opt. 57, 395–399 (2010).
30. J. Hernandez, C. Provenzano, P. Pagliusi, and G. Cipparrone, “Optical manipulation of liquid crystal droplets through holographic polarized tweezers: Magnus effect,” Mol. Cryst. Liq. Cryst. 558, 72–83 (2012).
31. S. Phanphak, A. Pattanaporkratana, J. Limtrakul, and N. Chattham, “Precession mechanism of nematic liquid crystal droplets under low power optical tweezers,” Ferroelectrics 468,114–122 (2014).
32. R. A. Beth, “Mechanical detection and measurement of the angular momentum of light,” Phys. Rev. 50, 115–125 (1936).
33. M. W. Beijersbergen, L. Allen, H. Vanderveen, and J. P. Woerdman, “Astigmatic laser mode convertors and transfer of orbital angular momentum,” Opt. Commun. 96, 123–132 (1993).
34. A. Cerjan and C. Cerjan, “Orbital angular momentum of Laguerre–Gaussian beams beyond the paraxial approximation,” OSA Proc. 28, 2253–2260 (2011).
35. L. Aolita and S. P. Walborn, “Quantum communication without alignment using multiple-qubit single-photon states,” Phys. Rev. Lett. 98, 100501 (2007).
36. F. Tamburini, G. Anzolin, G. Umbriaco, A. Bianchini, and C. Barbieri, “Overcoming the rayleigh criterion limit with optical vortices,” Phys. Rev. Lett. 97, 163903 (2006).
37. H. He, M. E. J. Friese, N. R. Heckenberg, and H. Rubinszteindunlop, “Direct observation of transfer of angular-momentum to absorptive particles from a laser-beam with a phase sigularity,” Phys. Rev. Lett. 75, 826–829 (1995).
38. N. B. Simpson, K. Dholakia, L. Allen, and M. J. Padgett, “Mechanical equivalence of spin and orbital angular momentum of light: An optical spanner,” Opt. Lett. 22, 52–54 (1997).
39. M. J. Padgett, and L. Allen, “The poynting vector in Laguerre-Gaussian laser modes,” Opt. Commun. 121, 36–40 (1995).
40. A. T. O'Neil, I. MacVicar, L. Allen, and M. J. Padgett, “Intrinsic and extrinsic nature of the orbital angular momentum of a light beam,” Phys. Rev. Lett. 88, 053601 (2002).
41. V. Garces-Chavez, D. McGloin, M. J. Padgett, W. Dultz, H. Schmitzer, and K. Dholakia, “Observation of the transfer of the local angular momentum density of a multiringed light beam to an optically trapped particle,” Phys. Rev. Lett. 91, 093602 (2003).
42. A. Ashkin, “Acceleration and trapping of particles by radiation pressure,” Phys. Rev. Lett. 24, 156–159 (1970).
43. A. Ashkin, “Optical trapping and manipulation of neutral particles using lasers,” P Natl. Acad. Sci. USA 94, 4853–4860 (1997).
44. A. Ashkin, “History of optical trapping and manipulation of small-neutral particle, atoms, and molecules,” IEEE J. Sel. Top. Quant. 6, 841–856 (2000).
45. A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm, and S. Chu, “Observation of a single-beam gradient force optical trap for dielectric particles,” Opt. Lett. 11, 288–290 (1986).
46. S. P. Smith, S. R. Bhalotra, A. L. Brody, B. L. Brown, E. K. Boyda, and M. Prentiss, “Inexpensive optical tweezers for undergraduate laboratories,” Am. J. Phys. 67, 26–35 (1999).
47. 陳永昇, “光鉗的製作及其特性的了解,” 國立成功大學物理研究所碩士論文, 5–14 (民國90年7月).
48. M. E. J. Friese, T. A. Nieminen, N. R. Heckenberg, and H. Rubinsztein-Dunlop, “Optical alignment and spinning of laser-trapped microscopic particles,” Nature 394, 348–350 (1998).
49. L. Marrucci, C. Manzo, and D. Paparo, “Optical spin-to-orbital angular momentum conversion in inhomogeneous anisotropic media,” Phys. Rev. Lett. 96, 163905 (2006).
50. Z. Bouchal, V. Kollarova, P. Zemanek, and T. Cizmar, “Orbital angular momentum of mixed vortex beams,” Proc. of SPIE 6609, 660901–660908 (2007).
51. L. Allen and M. J. Padgett, “The Poynting vector in Laguerre-Gaussian beams and the interpretation of their angular momentum density,” Opt. Commun. 184, 67–71 (2000).
52. M. Massari, G. Ruffato, M. Gintoli, F. Rici, and F. Romanato, “Fabrication and characterization of high-quality spiral phase plates for optical applications,” Appl. Opt. 54, 4077–4083 (2015)
53. L. Marrucci, C. Manzo, and D. Paparo, “Pancharatnam-Berry phase optical elements for wave front shaping in the visible domain: Switchable helical mode generation,” Phys. Rev. Lett. 88, 221102 (2006).
54. L. Marrucci, E. Karimi, S. Slussarenko, B Piccirillo, E. Santamato, E. Nagali, and F. Sciarrino, “Spin-to-orbital optical angular momentum conversion in liquid crystal “q-plate”: classical and quantum applications,” Mol. Cryst. Liq. Cryst. 561, 48–56 (2012).
55. L. Marrucci, “Generation of helical modes of light by spin-to-orbital angular momentum conversion in inhomogeneous liquid crystals,” Mol. Cryst. Liq. Cryst. 488, 148–162 (2008).
56. H. Bouas-Laurent and H. DÜRR, “Organic photochromism” Pure Appl. Chem. 73, 148–162 (2001).
57. W. M. Gibbons, P. J. Shannon, S. T. Sun, and B. J. Swetlin, “Surface-mediated alignment of nematic liquid-crystals with polarized laser-light,” Nature 351, 49–50 (1991).
58. C.-R. Lee, J.-D. Lin, Y.-J. Huang, S.-C. Huang, S.-H. Lin, and C.-P. Yu, “All-optically controllable dye-doped liquid crystal infiltrated photonic crystal fiber,” Opt. Express 19, 9676–9689 (2011).
59. E. Brasselet, N. Murazawa, H. Misawa, and S. Juodkazis, “Optical vortices from liquid crystal droplets,” Phys. Rev. Lett. 103, 103903 (2009).
60. E. Brasselet, and S. Juodkazis, “Optical angular manipulation of liquid crystal droplets in laser tweezers,” J. Non. Opt. Phys. Mater. 18, 167–194 (2009).
61. John D. Current, M.D., Physics related to anesthesia, 2nd ed. (PediaPress, 2011).