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Abstract
We demonstrated that gold nanowires (GNWs), as a new kind of saturable absorber (SA), could be used to construct all-fiber passively Q-switched thulium-doped fiber lasers (TDFL). The GNWs were mixed with polyvinylpyrrolidone (PVP) to form the GNWs-PVP SA film. It exhibited a broad absorption band covered from 300 nm to 2500 nm, which was induced by the surface plasmon resonance (SPR) absorption of GNWs. When the GNWs-PVP SA film was inserted into the TDFL cavity pumped by a 1570 nm fiber laser, a stable passively Q-switched laser at ∼1940nm was obtained when the threshold of pump power exceeded ∼800 mW. Furthermore, ∼2.4 µs pulses with a repetition rate of 52.75 kHz were also obtained at the pump power of ∼1500 mW.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Passively Q-switched thulium-doped fiber laser (TDFL) operating at the 2 µm wavelength region have been found a variety of applications in laser material processing, coherent laser lidar, remote sensing, biomedical diagnostics, and spectroscopy [1–5]. Compared to active ones, passive Q-switching possessed some superiorities such as low cost, compactness, and simple configuration and flexibility in design. A feasible method to realize passively Q-switched operation in a fiber laser was to use saturable absorber (SA).The common SAs were previously centralized on nonlinear polarization rotation (NPR), crystals and semiconductor saturable mirrors (SESAMs) [6–8]. However, their fabrication procedures are very complex. Moreover, they were not compatible with optical fiber, which may restrict their applications in fiber lasers. Hence, SAs possessed excellent compatibility with optical fiber systems was of great significance for all-fiber Q-switched lasers [9–14].
To date, topological insulators, carbon nanotubes, graphene and two-dimensional nanomaterials have been used as SAs to constructed all-fiber Q-switched fiber lasers [15-19]. Moreover, gold nanomaterials as a new type of SAs have already been used for constructing all-fiber Q-switched lasers owing to their broadband absorption, fast response time of few picoseconds and the large third-order nonlinearity [20]. Similar to gold nanorods, gold nanowires (GNWs) also have two surface plasmon resonance (SPR) absorption bands. One is the transverse SPR absorption band around 520 nm, the other one is longitudinal SPR absorption band covered from near-infrared to mid-infrared, which indicats that it can be used for constructing wideband pulsed fiber lasers, especially for mid-infrared pulse laser [21,22]. In the past years, the optical properties of GNWs have been extensively studied. Billot et al. first reported the surface plasmon resonance (SPR) characteristics of GNWs [23]. Pong et al. investigated the nonlinear optical properties of GNWs [24]. Li et al. demonstrated that the SPR absorption of GNWs was not only exhibited in the visible region, but also had absorption property in the near-infrared (NIR) region [25,26]. Morita et al. investigated the impact of different morphology of gold nanowires on the application. In contrast, there are no reports on employing GNWs as SAs for constructing pulsed lasers. In addition, it is still challenging to achieve high energy soliton pulse generation by using the nanomaterials as SA. Yan et al. were the first to realize high energy soliton pulse generation by using a magnetron sputtering deposition grown SA [27,28].
In this paper, we proposed and demonstrated a passively Q-switched TDFLs by using a broadband GNWs-PVP film as SA. By inserting the GNWs-PVP SA film into the TDFL cavity pumped by a 1570 nm fiber laser, stable passively Q-switched laser at ∼1940nm was obtained when the threshold of pump power exceeded ∼800 mW. ∼2.4 µs pulses with a repetition rate of 52.75 kHz were also obtained at the pump power of ∼1500 mW.
2. Preparation and characterization of GNWs and GNWs-PVP SA
GNWs were synthesized by a simple solution method. The detailed procedures were described as follows, 20 mM HAuCl4.4H2O and 0.4 M oleylamine were mixed in cyclohexane and then stirred for 3 hours, the color of the solution was changed from orange to yellow. Subsequently, 700 mg triisopropylsilane was added into the above solution and kept for 24 hours without stirring, the color of the sample became dark brown. Finally, 20 mL hexane was added to the above solution, and then left at -20°C for 8 hours [29]. The color variation of the solution during the reaction process was shown in Fig. 1(a). (I)∼(II) shows the different reaction time (0 s, 3 hours) after mixing of oleylamine, HAuCl4•4H2O and cyclohexane. (III) shows the reaction time for 24 hour after mixing of triisopropylsilane. The schematic illustration of the GNWs growth process was shown in Fig. 1 (b). When HAuCl4•4H2O and oleylamine were mixed together, the former was partially reduced by the latter to AuCl (Au+) [30]. An ordered mesostructure was formed because oleylamine wrapped the newly formed Au+ species. Oleylamine could play several functions such as a surfactant, solvent and reductant. In addition, it played a decisive role on the anisotropic growth mechanism of nanoclusters when it adsorbed in the specific crystalline surface [31].The oleylamine layers separated the charged Au+ assemblies within this mesostructure. This assembled process similar to the synthesis of mesoporous material [32]. It developed into intermediate products similar to the shape of chain by the directed attachment process. It was a neck-growing process, and it formed elongated chain-like nanoparticles along the {111} direction and eventually form GNWs with two enlarged spherical ends. The Au+ species slowly reduced to form GNWs within the mesostructured, which was a thermodynamically favorable growth direction [33]. Owing to the confined space and high regularity of the Au+-amine mesostructure, the spherical ends got smaller and smaller and eventually disappear, while the GNWs diameter got thinner and thinner [34].
Fig. 1. Color change during the synthesis of GRWs solution: (a) (I) just mixing of oleylamine, HAuCl4•4H2O and cyclohexane (II) the solution was stirred for 3 hours (III) 24 hours after addition of TIPS, (b) Schematic illustration of the GNWs growth process.
The lattice structure of GNWs was measured by using X-ray diffraction (XRD) method as shown in Fig. 2(a). The GNWs had a face-centered cubic (fcc) structure. The XRD peaks at 38.21°, 44.41°, 64.61°,77.61°and 82.3° were indexed to (111), (200), (220), (311) and (222) reflection lines respectively, which were matched the diffraction standard of Au (JCPDS 4-784). The broad absorption peaks of GNWs indicated that the GNWs are high crystallinity of nanowires [35]. Figure 2 (b) shows the TEM image of GNWs at the magnifications of 30,000. The length distribution was in the range of 100 nm to 2000nm and the average diameter of GNWs was ∼1.8 nm .The aspect ratios were in the range of 500 to 2000. It could be seen that GNWs prone to bundles because of van der Waals forces exist between layers of oleamine [36,37]. Figure 2 (c) shows the high-resolution TEM (HRTEM, JEOL JEM-2100H) image of GNWs at the magnifications of 200,000. The interfringe distance was 0.23 nm which was corresponded to {111} lattice spacing of the face-centered cubic (fcc) gold nanocrystals [38,39]. Figure 2 (d) shows the electron c-shot of GNWs. It could be seen that there were obvious concentric circular bright spots corresponding to the (111), (200), (220), (311) crystal planes and the corresponding selected area electron diffraction (SAED). The image showed a clear regular bright spot, indicating good crystallinity and orientation of the nanowires. It could be calculated that the GNWs grow along the (200) crystal orientation which was consistent with the XRD characterization results [40,41].
Fig. 2. (a) XRD patterns of GNWs, (b) TEM image of GNWs, (c) High-resolution TEM of GNWs , (d) The electron c-shot of GNWs.
In order to obtain the absorption spectrum of GNWs, the preparation process of the sample was described below. Firstly, the GNWs solution was cast on the calcium fluoride glass and then dried at room temperature, which was used to test the absorption spectrum from 300 nm to 10 µm [42]. Besides, GNWs powder was mixed with KBr and then pressed, which was used to test the absorption spectrum from10 µm to 25 µm. The absorption spectrum of GNWs was shown in Fig. 3(a). The red curve represented the UV−vis−near-IR (300 nm-3500 nm) spectrum of GNWs (UV3600 Shimadzu Corporation). The green curve showed the mid-IR (3500 nm-10000 nm) spectrum of GNWs (Shimadzu IR Prestige-21 FTIR Spectrometer) and the purple curve showed the far-IR (10 µm-25 µm) spectrum of GNWs (Shimadzu IR Prestige-21 FTIR Spectrometer), respectively [43,44]. The absorption peak at 520 nm as indicated by the downward arrows was induced by the transverse SPR of GNWs, and the broadband absorption from 2500 nm to 25 µm was induced by the longitudinal SPR of GNWs [45]. The cyclohexane solution of GNWs was blended with 10.8 wt% aqueous solution of polyvinylpyrrolidone (Molecular weight 1300000, Sigma), then it was stirred for 12 hours to form the stable suspension of GNWs-PVP. Most previous works utilized PVA to incorporate the SA materials, but in our experiment, the solvent of GNWs solution is hexane. We used PVP as film-forming agent since the PVA solution can’t dissolve into hexane. It was static for 8 h until no sediment was observed. Finally, GNWs-PVP film was made by pouring GNWs-PVP solution onto a flat substrate and then slowly drying at room temperature. Figure 3(b) shows the UV-vis-NIR absorption spectrum of the film for GNWs-PVP and pure PVP, respectively [46]. The GNWs-PVP film also exhibited transverse SPR peak at ∼520 nm. The longitudinal SPR of GNWs-PVP film induced broadband absorption from 1000 nm to 2500 nm. Pure PVP film only played a small background in the range of 500 nm∼2500 nm. The peak of the marked asterisk was caused by the vibration of the PVP molecule.
Fig. 3. (a) Absorption spectrum of GNWs in UV−vis−near infrared spectroscopy (red), mid-infrared spectroscopy (green) and far infrared spectroscopy regions (purple), (b) The absorption spectra of GNWs-PVP film and PVP film.
The relationship between the transmission ratio and the pump peak densities was measured to study the saturable absorption property of GNWs film by a 1982nm pulsed fiber laser which has a repetition rate of 37 MHz and a pulse width of 800 ps, as shown in Fig. 4(a). The following formula was used to fit the data shown in Fig. 4(a). α (I) = αs /(1 + I/Is) + αns (where α (I) is the absorption coefficient, αs and αns are the saturable and nonsaturable absorption components, and I and Is are input and saturation intensities, respectively).The modulation depth (ΔT) we measured was 12.3%, the non-bleachable loss (αns) was 32% and the saturation intensity (Is) was 140 MW/cm2. The Z-scan curve at 1982nm was shown in Fig. 4 (b). The nonlinear absorption model was employed to fit the Z-scan data we tested. The measured data was fitted by using the following equation:
Fig. 4. (a) The relationship between the transmission ratio and pump peak densities of GNWs-PVP film, (b) Z-scan curve at 1982nm.
3. Results and discussion
The experimental setup of Q-switched fiber laser was shown in Fig. 5. The as-fabricated GNWs-PVP film was inserted between two fiber connectors to integrate into a ring laser cavity. The pump source was a 1570 nm fiber laser. A 10 dB WDM coupler with 10% port allowed Q-switched laser pulse output. In addition, the pump light was launched into the laser cavity by using the 1570/2000nm wavelength division multiplexer (WDM). The length of the entire laser cavity was 6 meters. The gain medium was Tm-doped single mode fiber which had a length of 20 cm [48]. An isolator was added to the laser cavity in order to ensure light propagates in one direction in the laser cavity. The output lasers were monitored by using the optical spectrum analyzer, the digital oscilloscope and a power meter.
The continuous wave laser was started operation when the pump power exceeded 600 mW. The self-starting Q-switched was realized as the pump power exceeded 800 mW. The emission spectrum of the Q-switched laser was shown in Fig. 6 (a), the central wavelength at 1940nm. The output pulse train and single pulse profile were shown in Fig. 6 (b) and (c). The repetition rate is ∼52.75 kHz and the single pulse duration is ∼2.4µs. Figure 6 (d) presented the dependence of the repetition rate and pulse duration on the pump power. A decreasing trend from 10 µs to 1.86 µs while the repetition rate had an increasing trend from 52.75 kHz to 100.5 kHz as the pump power increased from 800 mW to 1500 mW, which represented the typical characteristics of passively Q-switched fiber lasers. The maximum pulse energy is about 0.18 µJ and the narrowest pulse duration is 1.86 µs based on the current laser cavity.
Fig. 6. Q-switched Tm-doped fiber laser: (a) Emission spectrum, (b) Output pulse train, (c) Single pulse profile with 2.4 µs FWHM pulse width,(d) Dependence of the repetition rate and pulse duration on the pump power.
Figure 7 shows the output power of the Q-switched fiber laser versus pump power. We could see that as the pump power increased, the average output power was also increased. Specifically, when the pump power increased from 800 mW to 1500 mW, the corresponding average output power increased linearly from 2.95 mW to 18.2 mW. The slope efficiency was ∼2.1%. The low slope efficiency was mainly caused by the low output ratio of the output coupler. Only 10% of the total power was extracted from the laser cavity. The modification of the output ratio of the coupler is expected to improve the slope efficiency. Long term stability is a key factor of SA for practical applications. We measured the radio-frequency (RF) spectrum of the Q-switched laser by using a high resolution RF spectrum analyzer (Agilent, E4411B), as shown in Fig. 8. The fundamental repetition rate is 67.5 kHz with a strong signal to noise ratio of 47 dB at the pump power of 980 mW, which shows that the long term stability of GNWs SA is good for real applications. If the pump power further increased more than 1500 mW, the Q-switched laser will become unstable. The optical damage threshold of GNWs SA is about 1560 mW. The magnetron sputtering deposition method could be used to fabricate GNWs SA with high quality, which is preferable for improving the optical damage threshold of SA [27,28]. In addition, mode-locked or Q-switched lasers at different wavelengths, especially at mid-infrared, could be realized by using GNWs SA with broadband saturable absorption.
4. Conclusions
In conclusion, we demonstrated that GNWs as a new kind of SA to construct all-fiber passively Q-switched TDFL. The GNWs were mixed with PVP to form the GNWs-PVP SA film. It exhibited a broad absorption band covered from 300 nm to 2500 nm, which was induced by the SPR absorption of GNWs. When the GNWs-PVP SA film was inserted into TDFL cavity pumped by a 1570 nm fiber laser, stable passively Q-switched laser at ∼1940nm was obtained when the threshold of pump power exceeded ∼800 mW. Furthermore, ∼2.4 µs pulses with a repetition rate of 52.75 kHz were also obtained at the pump power of ∼1500 mW. Our results showed that GNWs as a new SA could be used to construct the passively Q-switched TDFLs.
Funding
National Natural Science Foundation of China (NSFC) (61527823, 61378004, 61605219, 61605058, 61827821, 11774132, 11474132); State Key Laboratory on Integrated Optoelectronics (SKLIOE) (Open Fund); Tsinghua National Laboratory for Information Science and Technology (TNLIST); Youth Innovation Promotion Association of the Chinese Academy of Sciences; Key Technology Research and Development Project of Jilin Province (20180201120GX); Major Science and Technology Tendering Project of Jilin Province (20170203012GX); Joint Foundation from Equipment Preresearch and Ministry of Education (6141A02022413); Outstanding Young Talent Fund Project of Jilin Province (20180520188JH).
References
1. G. Q. Xie, J. Ma, P. Lv, W. L. Gao, P. Yuan, L. J. Qian, H. H. Yu, H. J. Zhang, J. Y. Wang, and D. Y. Tang, “Graphene saturable absorber for Q-switching and mode locking at 2 µm wavelength,” Opt. Mater. Express 2(6), 878–883 (2012). [CrossRef]
2. C. Liu, C. C. Ye, Z. Q. Luo, H. H. Cheng, D. D. Wu, Y. L. Zheng, Z. Liu, and B. Qu, “High-energy passively Q-switched 2 µm Tm3+-doped double-clad fiber laser using grapheneoxide-deposited fiber taper,” Opt. Express 21(1), 204–209 (2013). [CrossRef]
3. L. Wu, D. Li, S. Zhao, K. Yang, X. Li, R. Wang, and J. Liu, “Passive Q-switching with GaAs or Bi-doped GaAs saturable absorber in Tm:LuAG laser operating at 2 µm wavelength,” Opt. Express 23(12), 15469–15476 (2015). [CrossRef]
4. Z. Q. Luo, Y. Z. Huang, M. Zhong, Y. Y. Li, J. Y. Wu, B. Xu, H. Y. Xu, Z. P. Cai, J. Peng, and J. Weng, “1-,1.5-,and 2 µm fiber lasers Q-Switched by a broadband few-layer MoS2 saturable absorber,” J. Lightwave Technol. 32(24), 4077–4084 (2014). [CrossRef]
5. C. E. Preda, G. Ravet, and P. Mégret, “Experimental demonstration of a passive all-fiber Q-switched erbium and samarium-doped laser,” Opt. Express 37(4), 629–631 (2012). [CrossRef]
6. U. Keller, K. J. Weingarten, F. X. Kartner, D. Kopf, B. Braun, I. D. Jung, R. Fluck, C. Honninger, N. Matuschek, and J. Aus der Au, “Semiconductor saturable absorber mirrors (SESAM’s) for femtosecond to nanosecond pulse generation in solid-state laser,” IEEE J. Sel. Top. Quantum Electron. 2(3), 435–453 (1996). [CrossRef]
7. Y. X. Zhuang, J. J. Zhou, J. H. Xie, Y. Teng, and J. R. Qiu, “Temperature-dependent broadband near-infrared luminescence in silicate glass ceramics containing Li2MgSiO4:Cr4+ nanocrystals,” J. Mater. Res. 25(09), 1833–1837 (2010). [CrossRef]
8. R. Fluck, B. Braun, E. Gini, H. Melchior, and U. Keller, “Passively Q-switched 1.34-mm Nd: YVO4 microchip laser with semiconductor saturable-absorber mirrors,” Opt. Express 22(13), 991–993 (1997). [CrossRef]
9. Y. L. Tang, X. C. Yu, X. H. Li, Z. Y. Yan, and Q. J. Wang, “High-power thulium fiber laser Q switched with single-layer graphene,” Opt. Express 39(3), 614–617 (2014). [CrossRef]
10. L. Wu, D. Li, S. Zhao, K. Yang, X. Li, R. Wang, and J. Liu, “Passive Q-switching with GaAs or Bi-doped GaAs saturable absorber in Tm:LuAG laser operating at 2µm wavelength,” Opt. Express 23(12), 15469–15476 (2015). [CrossRef]
11. D. P. Zhou, L. Wei, B. Dongand, and W. K. Liu, “Tunable passively-switched erbium-doped fiber laser with carbon nanotubes as a saturable absorber,” IEEE Photonics Technol. Lett. 22(1), 9–11 (2010). [CrossRef]
12. M. Laroche, A. M. Chardon, J. Nilsson, D. P. Shepherd, W. A. Clarkson, S. Girard, and R. Moncorge, “Compact diode-pumped passively Q-switched tunable Er-Yb double-clad fiber laser,” Opt. Lett. 27(22), 1980–1982 (2002). [CrossRef]
13. T. Jiang, Y. Xu, Q. J. Tian, L. Liu, Z. Kang, R. Y. Yang, G. S. Qin, and W. P. Qin, “Passively Q-switching induced by gold nanocrystals,” Appl. Phys. Lett. 101(15), 151122 (2012). [CrossRef]
14. Z. Kang, X. Y. Guo, Z. X. Jia, Y. Xu, L. Liu, D. Zhao, G. S. Qin, and W. P. Qin, “Gold nanorods as saturable absorbers for all fiber passively Q-switched erbium-doped fiber laser,” Opt. Mater. Express 3(11), 1986–1991 (2013). [CrossRef]
15. Z. T. Wang, Y. Chen, C. J. Zhao, H. Zhang, and S. C. Wen, “Switchable Dual-Wavelength Synchronously Q-Switched Erbium-Doped Fiber Laser Based on Graphene Saturable Absorber,” IEEE Photonics J. 4(3), 869–876 (2012). [CrossRef]
16. S. B. Lu, Z. N. Guo, X. D. Xu, H. Zhang, D. Y. Tang, and D. Y. Fan, “Few-layer black phosphorus based saturable absorber mirror for pulsed solid-state lasers,” Opt. Express 23(17), 22643 (2015). [CrossRef]
17. L. M. Zhao, D. Y. Tang, X. Wu, and H. Zhang, “Dissipative soliton generation in Yb-fiber laser with an invisible intracavity bandpass filter,” Opt. Lett. 35(16), 2756–2758 (2010). [CrossRef]
18. Y. Chen, C. J. Zhao, S. Q. Chen, J. Du, P. H. Tang, G. B. Jiang, H. Zhang, S. C. Wen, and D. Y. Tang, “Large energy, wavelength widely tunable, topological insulator Q-switched erbium-doped fiber laser,” IEEE J. Sel. Top. Quantum Electron. 20(5), 315–322 (2014). [CrossRef]
19. X. T. Jiang, S. X. Liu, W. Y. Liang, S. J. Luo, Z. L. He, Y. Q. Ge, H. D. Wang, R. Cao, F. Zhang, Q. Wen, J. Q. Li, Q. L. Bao, D. Y. Fan, and H. Zhang, “Broadband Nonlinear Photonics in Few-Layer MXene Ti3C2Tx (T = F, O, or OH),” Laser Photonics Rev. 12(2), 1700229 (2018). [CrossRef]
20. H. B. Liao, R. F. Xiao, J. S. Fu, P. Yu, G. K. L. Wong, and P. Sheng, “Large third-order optical nonlinearity in Au:SiO2 composite films near the percolation threshold,” Appl. Phys. Lett. 70(1), 1–3 (1997). [CrossRef]
21. L. Billot, M. Lamy de la Chapelle, A.-S. Grimault, A. Vial, D. Barchiesi, J.-L. Bijeon, P.-M. Adam, and P. Royer, “Surface enhanced Raman scattering on gold nanowire arrays: Evidence of strong multipolar surface plasmon resonance enhancement,” Chem. Phys. Lett. 422(4-6), 303–307 (2006). [CrossRef]
22. E. Hutter and J. H. Fendler, “Exploitation of Localized Surface Plasmon Resonance,” Adv. Mater. 16(19), 1685–1706 (2004). [CrossRef]
23. Y. Kondo and K. Takayanagi, “Synthesis and Characterization of Helical Multi-Shell Gold Nanowires,” Science 289(5479), 606–608 (2000). [CrossRef]
24. C. Morita, H. Tanuma, C. Kawai, Y. Ito, Y. Imura, and T. Kawai, “Room-Temperature Synthesis of Two-Dimensional Ultrathin Gold Nanowire Parallel Array with Tunable Spacing,” Langmuir 29(5), 1669–1675 (2013). [CrossRef]
25. Y. Lu, J. Song, J. Y. Huang, and J. Lou, “Fracture of sub-20 nm ultrathin gold nanowires,” Adv. Funct. Mater. 21(20), 3982–3989 (2011). [CrossRef]
26. V. Rodrigues, T. Fuhrer, and D. Ugarte, “Signature of atomic structure in the quantum conductance of gold nanowires,” Phys. Rev. Lett. 85(19), 4124–4127 (2000). [CrossRef]
27. P. G. Yan, Z. K. Jiang, H. Chen, J. D. Yin, J. T. Lai, J. Z. Wang, T. C. He, and J. B. Yang, “α-In2Se3 wideband optical modulator for pulsed fiber lasers,” Opt. Lett. 43(18), 4417–4420 (2018). [CrossRef]
28. J. T. Wang, Z. K. Jiang, H. Chen, J. R. Li, J. D. Yin, J. Z. Wang, T. H. He, P. G. Yan, and S. C. Ruan, “High energy soliton pulse generation by a magnetron-sputtering-deposition-grown MoTe2 saturable absorber,” Photonics Res. 6(6), 535–541 (2018). [CrossRef]
29. Z. Y. Huo, C. k. Tsung, W. Y. Huang, X. F. Zhang, and P. D. Yang, “Sub-two nanometer single crystal Au nanowires,” Nano Lett. 8(7), 2041–2044 (2008). [CrossRef]
30. A. Sánchez-Iglesias, M. Grzelczak, J. Pérez-Juste, and L. M. Liz-Marzán, “Binary self-assembly of gold nanowires with nanospheres and nanorods,” Angew. Chem., Int. Ed. 122(51), 10181–10185 (2010). [CrossRef]
31. J. H. M. Maurer, L. González-García, B. Reiser, I. Kanelidis, and T. Kraus, “Templated self-assembly of ultrathin gold nanowires by nanoimprinting for transparent flexible electronics,” Nano Lett. 16(5), 2921–2925 (2016). [CrossRef]
32. X. M. Lu, M. S. Yavuz, H. Y. Tuan, B. A. Korgel, and Y. Xia, “Ultrathin gold nanowires can be obtained by reducing polymeric strands of oleylamine-AuCl complexes formed via aurophilic interaction,” J. Am. Chem. Soc. 130(28), 8900–8901 (2008). [CrossRef]
33. S. Gong, W. Schwalb, Y. Wang, Y. Chen, Y. Tang, J. Si, B. Shirinzadeh, and W. Cheng, “A wearable and highly sensitive pressure sensor with ultrathingold nanowires,” Nat. Commun. 5(1), 1–7 (2014). [CrossRef]
34. A. Halder and N. Ravishankar, “Ultrafine single-crystalline gold nanowire Arrays by oriented attachment,” Adv. Mater. 19(14), 1854–1858 (2007). [CrossRef]
35. F. Kim, K. Sohn, J. Wu, and J. X. Huang, “Chemical synthesis of gold nanowires in acidic solutions,” J. Am. Chem. Soc. 130(44), 14442–14443 (2008). [CrossRef]
36. C. Deng and F. Sansoz, “Near-ideal strength in gold nanowires achieved through microstructural design,” ACS Nano 3(10), 3001–3008 (2009). [CrossRef]
37. N. Pazos-Perez, D. Baranov, S. Irsen, M. Hilgendorff, L. A. Liz-Marzan, and M. Giersig, “Synthesis of flexible ultrathin gold nanowires in organic media,” Langmuir 24(17), 9855–9860 (2008). [CrossRef]
38. L. H. Pei, K. Mori, and M. Adachi, “Formation process of two dimensional networked gold nanowires by citrate reduction of AuCl4- and the shape stabilization,” Langmuir 20(18), 7837–7843 (2004). [CrossRef]
39. M. Chirea, A. Freitas, B. S. Vasile, C. Ghitulica, C. M. Pereira, and F. Silva, “Gold nanowire networks: synthesis, characterization, and catalytic activity,” Langmuir 27(7), 3906–3913 (2011). [CrossRef]
40. S. Y. He, Y. Zhang, Z. R. Guo, and N. Gu, “Biological synthesis of gold nanowires using extract of rhodopseudomonas capsulata,” Biotechnol. Prog. 24(2), 476–480 (2008). [CrossRef]
41. N. Pazos-Pecrez, S. Barbosa, L. Rodriguez-Lorenzo, P. Aldeanueva-Potel, J. Pecrez-Juste, I. Pastoriza-Santos, R. A. Alvarez-Puebla, and L. M. Liz-Marzacn, “Growth of sharp tips on gold nanowires leads to increased surface-enhanced raman scattering activity,” J. Phys. Chem. Lett. 1(1), 24–27 (2010). [CrossRef]
42. S. Takahata, K. Yamazoe, T. Koyasu, and Tsukuda, “Surface plasmon resonance in gold ultrathin nanorods and nanowires,” J. Am. Chem. Soc. 136(24), 8489–8491 (2014). [CrossRef]
43. H. K. Tyagi, H. W. Lee, P. Uebel, M. A. Schmidt, N. Joly, M. Scharrer, and P. S. J. Russell, “Plasmon resonances on gold nanowires directly drawn in a step-index fiber,” Opt. Lett. 35(15), 2573–2575 (2010). [CrossRef]
44. H. A. Chen, H. Y. Lin, and H. N. Lin, “localized surface plasmon resonance in lithographically fabricated single gold nanowires,” J. Phys. Chem. C 114(23), 10359–10364 (2010). [CrossRef]
45. B. K. Pong, H. I. Elim, J. X. Chong, W. Ji, B. L. Trout, and J. Y. Lee, “New insights on the nanoparticle growth mechanism in the citrate reduction of gold(III)salt: formation of the Au nanowire intermediate and its nonlinear optical properties,” J. Phys. Chem. C 111(17), 6281–6287 (2007). [CrossRef]
46. Z. Kang, M. Y. Liu, X. J. Gao, N. Li, S. Y. Yin, G. S. Qin, and W. P. Qin, “Mode-locked thulium-doped fiber laser at 1982nm by using a gold nanorods saturable absorber,” Laser Phys. Lett. 12(4), 045105 (2015). [CrossRef]
47. M. Y. Liu, D. L. Zhou, Z. X. Jia, Z. R. Li, N. Li, S. Q. Li, Z. Kang, J. Yi, C. J. Zhao, G. S. Qin, H. W. Song, and W. P. Qin, “Plasmonic Cu1.8S nanocrystals as saturable absorbers for passively Q-switched erbium-doped fiber lasers,” J. Mater. Chem. C 5(16), 4034–4039 (2017). [CrossRef]
48. Z. Kang, Q. Li, X. J. Gao, L. Zhang, Z. X. Jia, Y. Feng, G. S. Qin, and W. P. Qin, “Gold nanorod saturable absorber for passive mode-locking at 1 µm wavelength,” Laser Phys. Lett. 11(3), 035102 (2014). [CrossRef]
