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激光加热平台成长

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激光浮区法设备示意图

激光加热平台成长(Laser-heated pedestal growth,缩写简称LHPG)或激光浮区法(laser floating zone,缩写简称LFZ))是一种晶体成长技术。

该技术可以被视为一种精简版的区域熔炼,只不过热源改成了功率强大的二氧化碳激光或者钇铝石榴石激光

在现代众多液体/固体相变化晶体成长技术中,激光加热平台成长已成为材料科学研究中的重要技术。[1][2] 激光加热平台成长技术具有两大优势,其一为高拉取速率(高达传统柴氏拉晶法的60倍快),其二为可以生长熔点较高的材料。[3][4][5] 除此之外,激光加热平台成长不需要用到坩埚,意味着该技术可以成长几乎不受杂质及应力影响的单晶

优点

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激光浮区法可以成长线形几何形状、小半径、成本较低的晶体,因此这种技术可以用来生长单晶纤维(single-crystal fibers,简称SCF)。激光加热平台成长技术生产的单晶纤维可以用来取代许多装置(如迷你激光等)中用到的块材纤维,尤其是那些需要高熔点材料的应用。[6][7] 然而,单晶纤维的机械性质与光学性质也要比块材纤维得这些性质来得优越或至少持平,这种取代才有意义。也就是说,能否严格控管单晶纤维各种晶体成长的条件就非常重要。[8][9][10]

光学元件

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直到1980年,激光加热平台成长只用两道激光光束聚焦在待熔的材料上。[11] 只用两道激光加热的后果就是熔融区产生了极大的辐射热梯度,导致整个加热过程不稳定。就算把激光光束加到四道,虽能改善情况,但还是不能解决不稳定的难题。[12] 后来,Fejer等人对激光加热平台成长技术做出了一项突破性的改良。[13] 他们结合了一种称为"reflaxicon"的特殊光学元件,"reflaxicon"的构造由两同轴锥面反射镜所组成,一内一外将入射激光光散成无数道往不同方向的反射光。这些反射光经其它面镜反射后,最后落在晶体的柱体表面上。[14] 有了reflaxicon这项光学元件后,反射光雨露均沾地为柱体表面提供热量,进而使辐射热梯度减少了。在这项技术中,轴温度梯度可高达10000 °C/cm,相较于传统晶体成长技术的10–100 °C/cm明显高出不少。

对流速率

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激光浮区法另一项有趣的特色是,因为马伦哥尼效应的关系,所以有着速率极高的对流在熔融的液相中进行。[15] 参考文献中连结的影片纪录把一条极为细小的线伸进正被激光光加热的液相铌酸锂中,铂线快速地转动(影片0:40秒后铂线看似不动,其实仍还在以高速绕其转轴旋转),足见液相铌酸锂中对流之剧烈。[16]

参见

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参考文献

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  1. ^ Feigelson, R.S. Growth of fiber crystals. Kaldis, E (编). Crystal Growth of Electronic Materials. 1985: 127. ISBN 0-444-86919-0. 
  2. ^ Andreeta, M.R.B.; Hernandes, A.C. Laser-Heated Pedestal Growth of Oxide Fibers. Dhanaraj, G.; Byrappa, K.; Prasad, V.; Dudley, M. (编). Springer Handbook of Crystal Growth. 2010: 393. ISBN 978-3-540-74182-4. 
  3. ^ Ardila, D.R.; Andreeta, M.R.B.; Cuffini, S.L.; et al. Laser heated pedestal growth of Sr2RuO4 single-crystal fibers from SrRuO3. Journal of Crystal Growth. 1997, 177 (1–2): 52–56. Bibcode:1997JCrGr.177...52A. doi:10.1016/S0022-0248(96)00904-9. 
  4. ^ De Camargo, A.S.S; Nunes, L.A.O.; Andreeta, M.R.B.; et al. Near-infrared and upconversion properties of neodymium-doped RE0.8La0.2VO4 (RE = Y, Gd) single-crystal fibres grown by the laser-heated pedestal growth technique. Journal of Physics: Condensed Matter. 2002, 14 (50): 13889–13897. doi:10.1088/0953-8984/14/50/314. 
  5. ^ De Vicente, F.S.; Hernandes, A.C.; De Castro, A.C.; et al. Photoluminescence spectrum of rare earth doped zirconia fibre and power excitation dependence. Radiation Effects and Defects in Solids. 1999, 149 (1–4): 153–157. Bibcode:1999REDS..149..153D. doi:10.1080/10420159908230149. 
  6. ^ De Camargo, A.S.S.; Andreeta, M.R.B; Hernandes, A.C.; et al. 1.8 µm emission and excited state absorption in LHPG grown Gd0.8La0.2VO4:Tm3+ single crystal fibers for miniature lasers. Optical Materials英语Optical Materials. 2006, 28 (5): 551–555. Bibcode:2006OptMa..28..551D. doi:10.1016/j.optmat.2005.07.002. 
  7. ^ Romero, J.J.; Montoya, E.; Bausa, L.E.; et al. Multiwavelength laser action of Nd3+:YAlO3 single crystals grown by the laser heated pedestal growth method. Optical Materials英语Optical Materials. 2004, 24 (4): 643–650. Bibcode:2004OptMa..24..643R. doi:10.1016/S0925-3467(03)00179-4. 
  8. ^ Prokofiev, V.V.; Andreeta, J.P.; Delima, C.J.; et al. Microstructure of single-crystal sillenite fibers. Radiation Effects and Defects in Solids. 1995, 134 (1–4): 209–211. Bibcode:1995REDS..134..209P. doi:10.1080/10420159508227216. 
  9. ^ Prokofiev, V.V.; Andreeta, J.P.; Delima, C.J.; et al. The influence of temperature gradients on structural perfection of single-crystal sillenite fibers grown by the LHPG method. Optical Materials英语Optical Materials. 1995, 4 (4): 521–527. Bibcode:1995OptMa...4..521P. doi:10.1016/0925-3467(94)00123-5. 
  10. ^ Andreeta, M.R.B.; Andreeta, E.R.M.; Hernandes, A.C.; et al. Thermal gradient control at the solid–liquid interface in the laser-heated pedestal growth technique. Journal of Crystal Growth. 2002, 234 (4): 759–761. Bibcode:2002JCrGr.234..759A. doi:10.1016/S0022-0248(01)01736-5. 
  11. ^ Burrus, C.A.; Stone, J. Single−crystal fiber optical devices: A Nd:YAG fiber laser. Applied Physics Letters. 1975, 26 (6): 318. Bibcode:1975ApPhL..26..318B. doi:10.1063/1.88172. 
  12. ^ Haggerty, J.S. Production of fibers by a floating zone fiber drawing technique, Final Report. 1972. NASA-CR-120948. 
  13. ^ Fejer, M.M.; Byer, R.L.; Feigelson R.; Kway W. Growth and characterization of single crystal refractory oxide fibers. Proceedings of the SPIE, Advances in Infrared Fibers II 320. Bellingham, WA: SPIE: 50. 1982. ISBN 978-0-89252-355-9. 
  14. ^ Edmonds, W.R. The reflaxicon: a new reflective optical element, and some applications. Applied Optics英语Applied Optics. 1973, 12 (8): 1940 [2017-03-17]. Bibcode:1973ApOpt..12.1940E. doi:10.1364/AO.12.001940. (原始内容存档于2011-09-27). 
  15. ^ Liu, M.; Chen, J.C.; Chiang, C.H.; Hu, L.J.; Lin, S.P. Mg-doped sapphire crystal fibers grown by laser-heated pedestal growth method. Japanese Journal of Applied Physics Part I英语Japanese Journal of Applied Physics. 2006, 45: 194–199. Bibcode:2006JaJAP..45..194L. doi:10.1143/JJAP.45.194. 
  16. ^ Convection in Laser Heated Pedestal Growth technique. YouTube. 正以激光加热平台成长技术成长纤维中的铌酸锂通铂线之实验. [2017-03-17]. (原始内容存档于2016-06-17).