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Semiconductor materials exhibiting large optical nonlinearities and ultrafast nonlinear response have received extensive attention because of their potential applications in optical limiting, all-optical devices, optical telecommunication, and so on. As a direct-gap II-VI bulk semiconductor, ZnSe crystal has been exploited as the nonlinear optical devices in the regimes of nanoseconds and picoseconds during the past years. Owing to today's fast advance of laser sources with ultrashort femtosecond pulse duration, it is possible to investigate the ultrafast optical nonlinearities in the bulk ZnSe crystal. In this paper, we experimentally investigate the ultrafast dynamics of free-carriers induced by twophoton excitation in the bulk ZnSe crystal. By performing open-aperture Z-scan experiments with 41 fs laser pulses at the wavelength of 532 nm under the condition of low excitation intensity, the two-photon absorption coefficient is measured. As the excitation intensity exceeds a critical value, the interplay between third- and fifth-order nonlinear absorption processes is observed. To evaluate the ultrafast dynamics of free carriers, we have carried out femtosecond time-resolved degenerate pump-probe measurements with the same laser system used for Z-scan experiments in different levels of pump intensities. It is shown that the transient absorption signals peaked at the zero delay is a linearly increasing function of pump intensity, indicating that the observed instantaneous nonlinear absorption is dominated by the interband two-photon absorption process. At moderate irradiance, the transient absorption signals obviously indicate two components, arising from the two-photon absorption-induced free-carrier absorption, which is equivalent to the fifth-order nonlinear absorption process. Under the excitation of relatively high pump intensity, the magnitude of the reduction of free-carrier absorption signal becomes faster, suggesting that the ZnSe crystal exhibits a new effect and causes a transmittance change of the probe light. The presumable reasons are as follows: intense irradiances will result in the increase of carrier concentration and the rise of the lattice temperature as well as the narrowing of the band gap in the ZnSe crystal, which accelerates the electron-hole interband recombination process. Accordingly, the electron-hole recombination time decreases. Furthermore, when the carrier concentration is larger than 1018 cm-3, the occurrence of the electron-hole plasma is significant. At the same time, the enhancement of the scattering among the carriers results in the reduction of the free carrier absorption cross section. In summary, it is found that the free-carrier absorption cross section decreases whereas the electron-hole recombination time becomes shorter in ZnSe crystal as the excitation intensity increases, owing to both the narrowing of band gap and the occurrence of electron-hole plasma.
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Keywords:
- two-photon absorption /
- free carrier absorption /
- ZnSe crystal
[1] Wang S Y, Hcirsburgh G, Thompson P, Hauksson I, Mullins J T, Prior K A, Cave nett B C 1993 Appl. Phys. Lett. 63 857
[2] Zhang X, Fang H, Tang S, Ji W 1997 Appl. Phys. B 65 549
[3] Sheik-Bahae M, Said A A, Wei T H, Hagan D J, Van Stryland E W 1990 IEEE J. Quantum Elect. 26 760
[4] Wang J, Sheik-Bahae M, Said A A, Hagan D J, Stral E W 1994 J. Opt. Soc. Am. B 11 1009
[5] Bindra K S, Kar A K 2001 Appl. Phys. Lett. 79 3761
[6] Gaur A, Sharma D K, Singh K S, Singh N 2007 Solid State Commun. 141 445
[7] Yang H, Zhang T Q, Wang S F, Gong Q H 2000 Acta Phys. Sin. 49 1292 (in Chinese) [杨宏, 张铁桥, 王树峰, 龚旗煌 2000 49 1292]
[8] He J, Ji W, Ma G H, Tang S H, Kong S E W, Chow S Y, Zhang X H, Hua Z L, Shi J L 2005 Phys. Chem. B 109 4373
[9] Gu B, Fan Y X, Chen J, Wang H T, He J, Ji W 2007 J. Appl. Phys. 102 083101
[10] Fan G H, Qu S L, Guo Z Y, Wang Q, Li Z G 2012 Chin. Phys. B 21 047804
[11] Jiang Y, Yang S Y, Zhang X L, Teng F, Xu, Z, Hou Y B 2006 Acta Phys. Sin. 55 4860 (in Chinese) [姜燕, 杨盛谊, 张秀龙, 滕枫, 徐征, 侯延冰 2006 55 4860]
[12] Haripadmam P C, John H, Philip R, Gopinath P 2014 Appl. Phys. Lett. 105 221102
[13] Mita Y, Akami M, Maruyama S 2000 Appl. Phys. Lett. 76 2223
[14] Kong D G, Ao G H, Gao Y C, Chang Q, Wu W Z, Ran L L, Ye H A 2012 Physica B 407 4251
[15] Yao G X, Lv L H, M G F, Zhang X Y, Zheng X F, Ji X H, Zhang H, Cui Z F 2012 Chin. Phys. B 21 107801
[16] Major A, Yoshino F, Aitchison J S, Smith W P E, Sorokin E, Sorokina I T 2004 Ap pl. Phys. Lett. 85 4606
[17] Lami J F, Gilliot P, Hirlimann C 1996 Phys. Rev. Letters 77 1632
[18] Canto-Said E J, Hagan D J, Young J, Stryland Van E W 1991 IEEE J. Quantum Elect. 27 10
[19] Astakhov G V, Yakovlev D R 2002 Phys. Rev. B 65 165335
[20] Ku S A, Tu C M, Chu W C, Luo C W, Wu K H, Yabushita A, Chi C C, Kobayashi T 2013 Opt. Express 21 13930
[21] Sahraoui B, Chevalier R, Nguyen Phu X, Rivoire G, Bala W 1996 J. Appl. Phys. 80 4854
[22] Krauss T D, Wise F W 1994 Appl. Phys. Lett. 65 1739
[23] Jia T Q, Chen H X, Huang M, Zhao F L, Qiu J R, Li R X, Xu Z Z, He X K, Zhan g J, Kuroda H 2005 Phys. Rev. B 72 125429
[24] Noor S A M, Miyakawa A, Kawata Y, Torizawa M 2008 Appl. Phys. Lett. 92 161106
[25] Masoumeh S M, Wan M M Y, Khor S F, Zainal A T, Tamchek N 2013 Chin. Phys. B 22 117802
[26] Li X, Feng D H, He H Y, Jia T Q, Shan L F, Sun Z R, Xu Z Z 2012 Acta Phys. Sin. 61 197801 (in Chinese) [李霞, 冯东海, 何红燕, 贾天卿, 单璐繁, 孙真荣, 徐至展 2012 61 197801]
[27] He J, Mi J, Li H P, Ji W 2005 J. Phys. Chem. B 109 19184
[28] Gu B, Sun Y, Ji W 2008 Opt. Express 16 17745
[29] He J, Qu Y L, Li H P, Mi J, Ji W 2005 Opt. Express 13 9235
[30] Van Stryland E W, Vanherzeele H, Woodall M A, Soileau M J, Smirl A L, Guha S, Boggess T F 1985 Opt. Eng. 24 613
[31] Mehendale M, Sivananthan S, Andreas Schroeder W 1997 Appl. Phys. Lett. 71 1089
[32] Perna G, Capozzi V, Ambrico M 1998 J. Appl. Phys. 83 3337
[33] Wu W Z, Wang Y G 2015 Opt. Lett. 40 64
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[1] Wang S Y, Hcirsburgh G, Thompson P, Hauksson I, Mullins J T, Prior K A, Cave nett B C 1993 Appl. Phys. Lett. 63 857
[2] Zhang X, Fang H, Tang S, Ji W 1997 Appl. Phys. B 65 549
[3] Sheik-Bahae M, Said A A, Wei T H, Hagan D J, Van Stryland E W 1990 IEEE J. Quantum Elect. 26 760
[4] Wang J, Sheik-Bahae M, Said A A, Hagan D J, Stral E W 1994 J. Opt. Soc. Am. B 11 1009
[5] Bindra K S, Kar A K 2001 Appl. Phys. Lett. 79 3761
[6] Gaur A, Sharma D K, Singh K S, Singh N 2007 Solid State Commun. 141 445
[7] Yang H, Zhang T Q, Wang S F, Gong Q H 2000 Acta Phys. Sin. 49 1292 (in Chinese) [杨宏, 张铁桥, 王树峰, 龚旗煌 2000 49 1292]
[8] He J, Ji W, Ma G H, Tang S H, Kong S E W, Chow S Y, Zhang X H, Hua Z L, Shi J L 2005 Phys. Chem. B 109 4373
[9] Gu B, Fan Y X, Chen J, Wang H T, He J, Ji W 2007 J. Appl. Phys. 102 083101
[10] Fan G H, Qu S L, Guo Z Y, Wang Q, Li Z G 2012 Chin. Phys. B 21 047804
[11] Jiang Y, Yang S Y, Zhang X L, Teng F, Xu, Z, Hou Y B 2006 Acta Phys. Sin. 55 4860 (in Chinese) [姜燕, 杨盛谊, 张秀龙, 滕枫, 徐征, 侯延冰 2006 55 4860]
[12] Haripadmam P C, John H, Philip R, Gopinath P 2014 Appl. Phys. Lett. 105 221102
[13] Mita Y, Akami M, Maruyama S 2000 Appl. Phys. Lett. 76 2223
[14] Kong D G, Ao G H, Gao Y C, Chang Q, Wu W Z, Ran L L, Ye H A 2012 Physica B 407 4251
[15] Yao G X, Lv L H, M G F, Zhang X Y, Zheng X F, Ji X H, Zhang H, Cui Z F 2012 Chin. Phys. B 21 107801
[16] Major A, Yoshino F, Aitchison J S, Smith W P E, Sorokin E, Sorokina I T 2004 Ap pl. Phys. Lett. 85 4606
[17] Lami J F, Gilliot P, Hirlimann C 1996 Phys. Rev. Letters 77 1632
[18] Canto-Said E J, Hagan D J, Young J, Stryland Van E W 1991 IEEE J. Quantum Elect. 27 10
[19] Astakhov G V, Yakovlev D R 2002 Phys. Rev. B 65 165335
[20] Ku S A, Tu C M, Chu W C, Luo C W, Wu K H, Yabushita A, Chi C C, Kobayashi T 2013 Opt. Express 21 13930
[21] Sahraoui B, Chevalier R, Nguyen Phu X, Rivoire G, Bala W 1996 J. Appl. Phys. 80 4854
[22] Krauss T D, Wise F W 1994 Appl. Phys. Lett. 65 1739
[23] Jia T Q, Chen H X, Huang M, Zhao F L, Qiu J R, Li R X, Xu Z Z, He X K, Zhan g J, Kuroda H 2005 Phys. Rev. B 72 125429
[24] Noor S A M, Miyakawa A, Kawata Y, Torizawa M 2008 Appl. Phys. Lett. 92 161106
[25] Masoumeh S M, Wan M M Y, Khor S F, Zainal A T, Tamchek N 2013 Chin. Phys. B 22 117802
[26] Li X, Feng D H, He H Y, Jia T Q, Shan L F, Sun Z R, Xu Z Z 2012 Acta Phys. Sin. 61 197801 (in Chinese) [李霞, 冯东海, 何红燕, 贾天卿, 单璐繁, 孙真荣, 徐至展 2012 61 197801]
[27] He J, Mi J, Li H P, Ji W 2005 J. Phys. Chem. B 109 19184
[28] Gu B, Sun Y, Ji W 2008 Opt. Express 16 17745
[29] He J, Qu Y L, Li H P, Mi J, Ji W 2005 Opt. Express 13 9235
[30] Van Stryland E W, Vanherzeele H, Woodall M A, Soileau M J, Smirl A L, Guha S, Boggess T F 1985 Opt. Eng. 24 613
[31] Mehendale M, Sivananthan S, Andreas Schroeder W 1997 Appl. Phys. Lett. 71 1089
[32] Perna G, Capozzi V, Ambrico M 1998 J. Appl. Phys. 83 3337
[33] Wu W Z, Wang Y G 2015 Opt. Lett. 40 64
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