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采用有机半导体发光材料聚[2-甲氧基-5-（2-乙基己氧基）-1，4-苯乙炔]作为增益介质，低官能度光敏单体制备的液晶/聚合物光栅作为外部反馈谐振腔，制备出参数可独立控制的分离式结构的有机半导体激光器.液晶/聚合物光栅中液晶分子的取向影响光栅折射率调制量，从而影响光栅的反馈能力，最终影响激光器出射激光的性能.通过研究发现决定液晶分子取向的主要有两种与光栅周期有关的作用力，利用这一原理制备不同周期的光栅，光栅周期小于450 nm时，相分离出的液晶分子取向由光栅矢量方向变为光栅沟槽方向，此时光栅的折射率调制量增加，光反馈能力增强.采用周期为395 nm的液晶/聚合物光栅制备二级布拉格散射的有机半导体激光器，相较于大周期光栅（593 nm）制备的激光器，激光阈值由0.70 μJ/pulse降低至0.18 μJ/pulse，转化效率由2.5%提高到6.4%，且出射激光垂直于基板表面发射，有利于后续的处理及应用.In this paper, we report a high-conversion-efficiency organic semiconductor distributed feedback laser. The gain layer of the laser device is made from poly (2-methoxy-5-(20-ethylhexyloxy) p-phenyl-enevinylene) (MEH-PPV), and the holographic polymer dispersed liquid crystal (HPDLC) grating is used as the external light feedback layer. Thus the parameters of the laser device can be modulated independently. The solution of MEH-PPV in xylene (6 mg·mL-1) is deposited on the bottom glass substrate by spin-coating (2000 r/min). The MEH-PPV layer thickness is controlled at (80±2) nm by the spin-coating rate and confirmed by the Dektak profilometer. The HPDLC is made by the photo-induced phase separation method. To determine the orientations of LC molecules, the diffraction efficiency of each sample is measured by a He-Ne laser. The diffraction efficiency is defined as the diffracted light intensity in the first order divided by the incident light intensity. If p light diffraction efficiency (ηp) is much larger (smaller) than s light diffraction efficiency (ηs), it can be thought of as a symbol of a fairly good alignment of LC along the grating vector (grating grooves). When the period of HPDLC grating is larger than 450 nm, ηp is greater than ηs, and the averaged orientation of liquid crystal molecules is aligned along the grating vector direction, i.e., orthogonal to the holographic plane. For feedback light propagating along the grating vector, the refractive index modulation is dependent on the difference between the polymer refractive index np and the ordinary refractive index no of phase-separated LC. These two values are very close to each other, thus the effective light feedback for lasing output is not high. However, when the period of HPDLC grating is smaller than 450 nm, ηs is greater than ηp, and the orientation of phase-separated LC is altered. The refractive index modulation of feedback light originates from the difference between the polymer refractive index np and the extraordinary refractive index ne of phase-separated LC, thus the refractive index modulation can be improved and the HPDLC layer can provide better light feedback. The lasing threshold is 0.70 μJ/pulse, and the conversion efficiency is 2.5% for the sample with a grating period of 593 nm. However, the lasing threshold is lowered to 0.18 μJ/pulse, and the conversion efficiency increases to 6.4% for the sample with a grating period of 395 nm. These results show that the output lasing performance can be improved by using small period grating, since it has bigger refractive index in the grating vector direction (the lasing feedback direction). The laser performance of sample with small grating period is improved in some aspects such as threshold energy, conversion efficiency to some extent compared with those reported previously.
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Keywords:
- organic semiconductor laser /
- holographic polymer dispersed liquid crystal /
- refractive index difference /
- conversion efficiency
[1] Moses D 1992 Appl. Phys. Lett. 60 3215
[2] Samuel I D W, Turnbull G A 2007 Chem. Rev. 107 1272
[3] Chenais S, Forget S 2012 Polym. Int. 61 390
[4] Grivas C, Pollnau M 2012 Laser Photon. Rev. 6 419
[5] Chen Y, Herrnsdorf J, Guilhabert B, Kanibolotsky A L, Mackintosh A R, Wang Y, Pethrick R A, Gu E, Turnbull G A, Skabara P J, Samuel I D W, Laurand N, Dawson M D 2011 Org. Electron. 12 62
[6] Heliotis G, Xia R, Bradley D D C, Turnbull G A, Samuel I D W, Andrew P, Barnes W L 2003 Appl. Phys. Lett. 83 2118
[7] Heliotis G, Xia R, Bradley D D C, Turnbull G A, Samuel I D W, Andrew P, Barnes W L 2004 J. Appl. Phys. 96 6959
[8] Liu L J, Huang W B, Diao Z H, Zhang G Y, Peng Z H, Liu Y G, Xuan L 2014 Acta Phys. Sin. 63 194202 (in Chinese) [刘丽娟, 黄文彬, 刁志辉, 张桂洋, 彭增辉, 刘永刚, 宣丽 2014 63 194202]
[9] Deng S P, Li W C, Huang W B, Liu Y G, Lu X H, Xuan L 2011 Acta Phys. Sin. 60 056102 (in Chinese) [邓舒鹏, 李文萃, 黄文彬, 刘永刚, 鲁兴海, 宣丽 2011 60 056102]
[10] Mele E, Camposeo A, Stabile R, Del Carro P, Di Benedetto F, Persano L, Cingolani R, Pisignano D 2006 Appl. Phys. Lett. 89 131109
[11] Pisignano D, Persano L, Mele E, Visconti P, Anni M, Gigli G, Cingolani R, Favaretto L, Barbarella G 2005 Synth. Met. 153 237
[12] Ramirez M G, Boj P G, Navarro-Fuster V, Vragovic I, Villalvilla J M, Alonso I, Trabadelo V, Merino S, Díaz-García M A 2011 Opt. Express 19 22443
[13] Butler J J, Malcuit M S, Rodriguez M A 2002 J. Opt. Soc. Am. B 19 183
[14] Huang W B, Deng S P, Liu Y G, Peng Z H, Yao L S, Xuan L 2012 Acta Phys. Sin. 61 094208 (in Chinese) [黄文彬, 邓舒鹏, 刘永刚, 彭增辉, 姚丽双, 宣丽 2012 61 094208]
[15] Deng S P, Huang W B, Liu Y G, Diao Z H, Peng Z H, Yao L S, Xuan L 2012 Acta Phys. Sin. 61 126101 (in Chinese) [邓舒鹏, 黄文彬, 刘永刚, 刁志辉, 彭增辉, 姚丽双, 宣丽 2012 61 126101]
[16] Diao Z H, Huang W B, Deng S P, Liu Y G, Peng Z H, Yao L S, Xuan L 2013 Acta Phys. Sin. 62 034202 (in Chinese) [刁志辉, 黄文彬, 邓舒鹏, 刘永刚, 彭增辉, 姚丽双, 宣丽 2013 62 034202]
[17] Hsiao V K S, Lu C, He G S, Pan M, Cartwright A N, Prasad P N 2005 Opt. Express 13 3787
[18] Turnbull G A, Andrew P, Barnes W L, Samuel I D W 2003 Appl. Phys. Lett. 82 313
[19] Huang W, Liu Y, Diao Z, Yang C, Yao L, Ma J, Xuan L 2012 Appl. Opt. 51 4013
[20] Vardanyan K K, Qi J, Eakin J N, Sarkar M D, Crawford G P 2002 Appl. Phys. Lett. 81 4736
[21] Kim Y T, Hwang S, Hong J H 2006 Appl. Phys. Lett. 89 173506
[22] Kogelnik H, Shank C V 1972 J. Appl. Phys. 43 2327
[23] Montemezzani G, Zgonik M 1997 Phys. Rev. E 55 1035
[24] Turnbull G A, Andrew P, Jory M J, Barnes W L, Samuel I D W 2001 Phys. Rev. B 64 125122
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[1] Moses D 1992 Appl. Phys. Lett. 60 3215
[2] Samuel I D W, Turnbull G A 2007 Chem. Rev. 107 1272
[3] Chenais S, Forget S 2012 Polym. Int. 61 390
[4] Grivas C, Pollnau M 2012 Laser Photon. Rev. 6 419
[5] Chen Y, Herrnsdorf J, Guilhabert B, Kanibolotsky A L, Mackintosh A R, Wang Y, Pethrick R A, Gu E, Turnbull G A, Skabara P J, Samuel I D W, Laurand N, Dawson M D 2011 Org. Electron. 12 62
[6] Heliotis G, Xia R, Bradley D D C, Turnbull G A, Samuel I D W, Andrew P, Barnes W L 2003 Appl. Phys. Lett. 83 2118
[7] Heliotis G, Xia R, Bradley D D C, Turnbull G A, Samuel I D W, Andrew P, Barnes W L 2004 J. Appl. Phys. 96 6959
[8] Liu L J, Huang W B, Diao Z H, Zhang G Y, Peng Z H, Liu Y G, Xuan L 2014 Acta Phys. Sin. 63 194202 (in Chinese) [刘丽娟, 黄文彬, 刁志辉, 张桂洋, 彭增辉, 刘永刚, 宣丽 2014 63 194202]
[9] Deng S P, Li W C, Huang W B, Liu Y G, Lu X H, Xuan L 2011 Acta Phys. Sin. 60 056102 (in Chinese) [邓舒鹏, 李文萃, 黄文彬, 刘永刚, 鲁兴海, 宣丽 2011 60 056102]
[10] Mele E, Camposeo A, Stabile R, Del Carro P, Di Benedetto F, Persano L, Cingolani R, Pisignano D 2006 Appl. Phys. Lett. 89 131109
[11] Pisignano D, Persano L, Mele E, Visconti P, Anni M, Gigli G, Cingolani R, Favaretto L, Barbarella G 2005 Synth. Met. 153 237
[12] Ramirez M G, Boj P G, Navarro-Fuster V, Vragovic I, Villalvilla J M, Alonso I, Trabadelo V, Merino S, Díaz-García M A 2011 Opt. Express 19 22443
[13] Butler J J, Malcuit M S, Rodriguez M A 2002 J. Opt. Soc. Am. B 19 183
[14] Huang W B, Deng S P, Liu Y G, Peng Z H, Yao L S, Xuan L 2012 Acta Phys. Sin. 61 094208 (in Chinese) [黄文彬, 邓舒鹏, 刘永刚, 彭增辉, 姚丽双, 宣丽 2012 61 094208]
[15] Deng S P, Huang W B, Liu Y G, Diao Z H, Peng Z H, Yao L S, Xuan L 2012 Acta Phys. Sin. 61 126101 (in Chinese) [邓舒鹏, 黄文彬, 刘永刚, 刁志辉, 彭增辉, 姚丽双, 宣丽 2012 61 126101]
[16] Diao Z H, Huang W B, Deng S P, Liu Y G, Peng Z H, Yao L S, Xuan L 2013 Acta Phys. Sin. 62 034202 (in Chinese) [刁志辉, 黄文彬, 邓舒鹏, 刘永刚, 彭增辉, 姚丽双, 宣丽 2013 62 034202]
[17] Hsiao V K S, Lu C, He G S, Pan M, Cartwright A N, Prasad P N 2005 Opt. Express 13 3787
[18] Turnbull G A, Andrew P, Barnes W L, Samuel I D W 2003 Appl. Phys. Lett. 82 313
[19] Huang W, Liu Y, Diao Z, Yang C, Yao L, Ma J, Xuan L 2012 Appl. Opt. 51 4013
[20] Vardanyan K K, Qi J, Eakin J N, Sarkar M D, Crawford G P 2002 Appl. Phys. Lett. 81 4736
[21] Kim Y T, Hwang S, Hong J H 2006 Appl. Phys. Lett. 89 173506
[22] Kogelnik H, Shank C V 1972 J. Appl. Phys. 43 2327
[23] Montemezzani G, Zgonik M 1997 Phys. Rev. E 55 1035
[24] Turnbull G A, Andrew P, Jory M J, Barnes W L, Samuel I D W 2001 Phys. Rev. B 64 125122
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