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Abstract
The broad saturable absorption of topological insulator Bi2Te3 nanowires is presented for the first time, as well as the passively Q-switched pulse operations on both Yb-doped and Er-doped bulk laser with a bandwidth over about 1.7 μm. Uniform Bi2Te3 nanowires with a large aspect ratio have been synthesized using ultrathin Te nanowires as the template. The broad absorption spectrum from visible to middle infrared reveals a broad optical response. In a 1.0 μm Yb-doped laser, a pulse width of 303 ns with a pulse energy of 1.2 µJ is achieved. While at Er-doped mid-infrared 2.79 μm, the shortest pulse width and largest pulse energy are tested to be 444 ns and 5 µJ, respectively. Those results reveal the topological insulator Bi2Te3 nanowire to be a reliable broad optical switcher for solid state lasers in near- and mid-infrared bands. As far as we know, it is for the first time that TIs based solid state lasers at mid-infrared region are reported. Furthermore, this work can be extendable to explore TIs with other nanstructures for application as optoelectronic devices.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
During the past few decades, Bi2Te3, as one of the best Thermoelectric (TE) material, has been acknowledged and researched extensively [1–3]. While their equally applications in some other areas have been under very limited studies until BixSb1−x alloy has been predicted to be a topological insulator. Given the importance of topological insulators as new states of quantum matter with strong spin-orbital coupling effect, Bi2Te3, a layered stoichiometric crystal with simple surface states, is now a new focus theme in condensed-matter physics [4–7]. Topological insulator materials, characterized by its narrow gapped insulating bulks and Dirac dispersed surfaces, have also been continuously explored for applications as optoelectronic devices, of which saturable absorber is one. Saturable absorber is the essential technique for the generation of ultrashort pulse which has widespread applications in laser communication, remote sensing, military, lidar, imaging holography. Bernard et al. initially identified Bi2Te3 as an effective saturable absorber in 2012 [8]. Zhang et al. demonstrated the first example of photonics application of 2D TIs [9]. As a result of the small bandgap bulk (0.162 eV for Bi2Te3) and the gapless surface, TIs SAs possess a broadband spectral response ranging from terahertz to infrared [10,11]. Recently, great efforts have been done to promote the development of TIs-based saturable absorbers in Q-switching and mode-locking [12–25]. To date, mid-infrared pulses have been successfully realized with TI SAs in fiber lasers [26], while, the study in −3.0 μm mid-infrared solid state laser has seldom been reported. Compared with fiber lasers, solid-state lasers can attain higher pulse peak power and pulse energy owing to the less nonlinear pulse-splitting and the relatively large laser spot induced delay of saturable absorption effect. Thus, further investigations for entirely exploiting the saturable absorption property of TIs in solid state lasers are still very necessary.
In spite of the 3D bulk and 2D layer Bi2Te3, many nanostructures with various morphologies have been synthesized through different strategies, such as nanoparticle [27], nanowire [3], nanotube [28] and hollow nanosphere [29]. However, the influence of the morphologies on optical properties has been seldom investigated. They possess different physical and chemical properties, such as band structure, thermal conductivity and carrier density. Thus we have reasons to believe that the morphology may affect the optical properties of TIs to some extent. Compared with bulk and thin nanosheet, high quality one-dimensional (1D) nanostructure, that usually have a high specific surface area, would obviously raise the density of surface trap states. Also the low dimensionality could strongly confine the charge carriers, which provide high responsivity and thus is particularly valuable for optoelectronic devices [30–33]. Carbon nanotubes (CNTs) and gold nanorods (GNRs) are two typical 1D saturable absorbers. They are widely thought of as good SAs that can be operated in a wide wavelength region by varying the diameter or the aspect ratio [34–38]. Inspired by these ideas, it is of worth to study the saturable absorption of 1D Bi2Te3.
In this work, uniform one-dimensional Bi2Te3 nanowires had been synthesized by a two-step solution process using ultrathin Te nanowires as templates. The nonlinear optical parameters of wavelength were measured with the Z-scan method. By incorporating this optical Bi2Te3 nanowires saturable absorber inside either an Yb-doped or Er-doped bulk laser, stable Q-switched solid state pulsed laser at 1.0 and 2.79 μm were realized for the first time. The results reveal that the 1D Bi2Te3 nanostructure was a reliable broadband saturable absorber.
2. Experimental details
2.1 Synthesis proceeding
Uniform one-dimensional Bi2Te3 nanowires were synthesized using ultrathin Te nanowire as template in Ref [3]. All the chemicals used in this work were analytical grade without further purification. In the first step, 1.000 g polyvinylpyrrolidone (PVP) and 0.1 g Na2TeO3 were dissolved in 30 mL distilled water. To form a homogeneous solution, 30 min vigorous magnetic stirring was needed. Before the mixed solution was transferred into a 50 mL Teflon vessel and heated at 180°C for 3 h, 2 mL of hydrazine hydrate (85%, w/w%) and 3.5 mL of aqueous ammonia solution (25-28%, w/w%) were added. After cooling down to room temperature naturally, the as prepared Te nanowires were precipitated by adding 300 mL of acetone into the solution, and then dispersed in 30 mL triethylene glycol (TEG) with 0.600 g PVP under stirring for 1h. After that, 0.08 g BiCl3, 0.5 g NaOH and 1 mL hydrazine hydrate were added. Finally, the mixture solution was transferred into a 100 ml three-neck flask and was heated up to 200°C for 40 min at a rate of 10°C/min under magnetic stirring and argon protection. Washed by ethanol for several times, and dried at 60°C for 8 h, the final Bi2Te3 nanowires were obtained.
2.2 Materials characterization
The Bi2Te3 nanowires were characterized by XRD (XRD-7000, Shimadzu), SEM (JSM-7600F, JEOL), and HRTEM (Tecnai G2-20, FEI) equipped with an EDX detector. The room temperature absorption spectra were measured using a PerkinElmer UV–VIS–NIR Spectrometer (Lambda950).
2.3 1.0 μm Q-switched laser
The experimental setup was shown in Fig. 1(a). A plano–concave cavity with a total cavity length of 18 mm was used. A b-cut 3*3*2 sized Yb:GAB crystal with Yb3+ concentration of 10 at.% was employed as the gain medium, which was end-pumped by a fiber-coupled continuous wave diode laser at 976 nm. The input mirror (IM), a plane mirror, was antireflection (AR) coated at 976 nm and high-reflection (HR) coated at 1020-1080 nm. A concave mirror with a curvature radius of 75 mm that had 3% transmittance at 1045 nm was used as the output coupler (OC). The TIs SA spin-coated on a quartz substrate was inside between the gain crystal and the OC mirror.
Fig. 1 (a) Schematic of the 1.0 μm Q-switched laser setup based on Bi2Te3 nanowires SA, (b) Schematic of the 2.79 μm Q-switched laser setup with Bi2Te3 nanowires SAM.
2.4 2.79 μm Q-switched laser
As shown in Fig. 1(b), a compact plano-plano cavity with a length of 10 mm was used to realize the TIs 2.79 μm Q-switched laser operation. The gain medium was a 5 mm long 38% Er:YSGG. IM was antireflection (AR) coated at 967 nm and highrefiection (HR) coated for 2.79 μm. The OC mirror was used as the SA mirror with T = 2%@2.79 μm. The TI nanowires were dropped on OC mirror directly.
3. Results and discussion
3.1 Characterizations of 1D Bi2Te3 nanowires
Field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) have been used to characterize the morphologies and crystal structures of as-prepared Bi2Te3 products. Figure 2(a) shows the typical FE-SEM image that high density of nanowires with an average diameter of about 20 nm and an average length of several micrometers are obtained. The smooth surface reveals a high crystallinity of Bi2Te3 nanowires. The low magnification TEM image of a 17 nm indivadual Bi2Te3 nanowire is shown in Fig. 2(b). The corresponding EDX spectrum (bottom inset in Fig. 2(b)) clearly reveals the atomic ratio Bi/Te of 1.26:1.81, very close to the stoichiometric value of 2:3. The phase structure of the products is examined by XRD. From Fig. 2(c), it can be seen that all the diffraction peaks are in good agreement with the standard card of Bi2Te3 (JCPDS 15–0863). Top inset in Fig. 2(b) presents the high magnification TEM image. The atoms arrange themselves into the layer crystalline, while several defects are also seen. The lattice spacing is measured as 0.22 nm, corresponding to the (001) planes separation, indicating that the nanowires grow along the <001> direction.
Fig. 2 (a) SEM image of Bi2Te3 nanowires. (b) Low-magnification TEM image of Bi2Te3 nanowires. Bottom inset: the representative EDX spectrum. Top inset: High-magnification TEM image. (c) XRD patterns of the as-prepared Bi2Te3 powder. (d) Linear absorbance of Bi2Te3 nanowires solution from 300 to 2000 nm. Inset: the The linear absorption spectrum of the Bi2Te3 film at the wavelength range of 2.5-3.0 µm.
Figure 2(d) presents the linear absorption spectrum of the Bi2Te3 at the wavelength range from 300 to 2000 nm. A characteristic absorption peak is located at 739 nm which may be originated from higher-order bulk subband. Inset in Fig. 2(d) shows the mid-infrared absorption of Bi2Te3 film. The noise peeks around 2750 nm is resulted from instrumental error caused by the strong absorptions in water. The smooth absorption from visible to middle infrared indicates a broad optical response. To value the applications for pulse laser generation, the filmy Bi2Te3 nanowire SAs are used in a Yb-doped 1.0 μm and Er:YSGG 2.79 μm bulk laser operations.
3.2 1.0 μm Yb-doped Q-switched laser
To clarify the nonlinear absorption characteristics of Bi2Te3 nanowires SA, an open-aperture z-scan technology is employed. The Bi2Te3 nanowires SA in this part is prepared with a spin coating method at 500 rpm for 1 min. Inset in Fig. 3(b) display the optical image of Bi2Te3 nanowires SA on SiO2 substrate. The Bi2Te3 nanowires are dispersed in ethanol solution by ultrasonicating for 1 h. The concentration is about 0.2 mg/mL. Figure 3(a) and 3(b) present the z-scan normalized transmittance as a function of the sample position and the optical transmittances as increased excited intensity, respectively. The sharp peaks in Fig. 3(a) and the saturated trend in Fig. 3(b) confirm the good nonlinear absorption characteristic of Bi2Te3 nanowires. By fitting the corresponding optical transmittances, the saturation intensity, modulation depth, and nonsaturable loss are calculated to be 1.12 MW/cm2, 12.64%, and 2.8%, respectively. Such a low nonsaturable loss will be significantly benefical for a large pulse power.
Fig. 3 Nonlinear absorptions and Q-switched laser performances at 1.0 μm with TI SAs. (a) Open aperture Z-scan curve. (b) Nonlinear transmission. Inset: the optical image of the spin coated TI SA on SiO2 substrate. (c) Q-switched pulse train at different time scale under the average output power of 203 mW. Inset: (d) Corresponding single pulse with duration of 303 ns. Inset: the optical spectrum of the Q-switched laser operation.
The CW Yb:GAB laser operation without Bi2Te3 nanowires SA is achieved at a threshold absorbed pump power of 1.04 W. When the pump power is increased, only noise-like pulses with small amplitude are observed. Thus the self Q-switching of Yb:GAB can be elminated. When the Bi2Te3 nanowires SA is inserted into the laser cavity with careful alignment, Q-switched laser oscillation is realized as the absorbed pump power exceeded the threshold of 1.15 W. With the absorbed pump power increased to the highest 2.03 W, stable Q-switched pulses are always observed. The output power increases linearly that a maximum output value of 213 mW is obtained, corresponding to a slope efficiency of 24.7%.
We have recorded the pulse width and repetition rate with a digital oscilloscope (DSO-X 3052A, Agilent). Within the range of stable Q-switched pulse operation, the pulse width drops from 1.58 μs to a minimum data of 303 ns, while the repetition rate increases from 47.8 to 178.2 kHz. Based on the recorded repetition rate, maximum single pulse energy of 1.2 μJ is achieved under the absorbed pump power of 2.03 W. Figure 3(c,d) present the corresponding pulse trains and single pulse profile. The pulse duration and the pulse repetition rate are measured to be 303 ns and 178.2 kHz, respectively. The time scales of 5 ms in Fig. 3(c) reveal the good amplitude stability. The clock amplitude jitter (CAJ) of the pulse trains is calculated to be about 4.4%. Inset in Fig. 3(d) displays the corresponding output dual-wavelength spectrum. Note that beyond a pump power of 2.1 W, the Q-switched pulses become unstable probably because of the thermal effects and the oversaturation of nanosheets SA. No damage to the SA is observed during the laser operation since the same output pluses can recur with decreasing the pump power.
3.3 2.79 μm Er-doped Q-switched laser
Due to the strong absorptions in vapor, water, and biological tissues, solid state laser emitting 2.7-3.0 µm have attracted considerable attention for use in medical applications and laser radar measurements of atmospheric humidity. For the passively Q-switched mid-infrared (MIR) laser operations, saturable absorbers (SAs) are of especial important. Duo to the Pauli blocking of the electrons and holes, as well as the bulk narrow-band gap, TIs have been verified to have broadband saturable absorption and are suitable for passively Q-switched MIR laser operations [25]. While, to the best of our knowledge, there is no report on solid state MIR pulsed laser with TIs SAs.
Here, we investigate the nonlinear absorption and Q-switched Er:YSGG 2.79 μm pulsed laser with ID TIs nanowires for the first time. Figure 4(a) shows a typical normalized Z-scan curve of TIs nanowires. A OPO based nanosecond Er:YSGG 2.79 µm pulsed laser is selected as the laser source. The sharp peak indicates the excellent saturable absorption. Inset in Fig. 4(a) gives the corresponding nonlinear transmission of the SA at the position that Z = 0. Fitting the experimental datas, the saturable intensity and modulation depth are calculated to be 1.0MW/cm2, and 9.9%. The calculated nonsaturable loss is 6.6%. Compared to the BP and WS2 SA [39,40], the modulation depth of TIs nanowires SA in mid-infrared region is relatively larger. Thus a high laser performance in 2.79 µm will be expected.
Fig. 4 Nonlinear absorptions and Q-switched laser performances at 2.79 μm with TI SAM. (a) Open aperture Z-scan curve. Inset: nonlinear transmission. (b) Output laser spectrum. (c) Q-switched pulse train, and (d) corresponding shortest single pulse.
Figure 4(b,d) demonstrate the results of TIs nanowires based passively Q-switched Er:YSGG 2.79 µm laser. Increasing the pump power with a careful adjustment, a maxmum average output power of 344 mW is obtained with a pulse duration of 444 ns and a pulse repetition rate of 69.3 kHz. The output laser spectrum at 2.79 µm is showed in Fig. 4(b). The corresponding pulse trains and single pulse profile are displayed in Fig. 4(c) and Fig. 4(d), respectively. The calculated largest pulse energy is of 5 μJ.
3.4 Discussion
This paper firstly demonstrates the pulse operations on both Yb-doped and Er-doped bulk laser using Bi2Te3 nanowire SA with the bandwidth over about 1.7 μm. The Bi2Te3 nanowire keeps a smooth absorption from visible to middle infrared bands, which is responsible for the high performances as an excellent and broadband optical modulator.
In Table 1, a summary of some popular nano SAs-based Q-switched 1.0 μm solid state lasers are presented. Compared with the TIs-based results, this work presents a significantly improved laser performance. Particularly, compared with a solvothermal synthesized Bi2Te3 nanosheets SA in our group in [16], the laser operation here exhibits a larger output power, a shorter laser pulse and a higher pulse energy, which is consistent with the enhanced nonlinear absorption characteristics. Furthermore, our results can be considered as superior or at least comparable to the laser results based on other nano SAs, since the studies on graphene and CNT are more mature.
Table 1. Comparison of 1.0 μm Q-switched bulk lasers based on different nano SAs.
As far as we know, TIs SA based Q-switched MIR solid state lasers are reported for the first time. Table 2 displays a comparation of the Q-Switched 3.0μm solid state lasers with some other nano SAs. Inspite of the fact that the laser pulse is strongly influenced by the SAs as well as the laser parameters, the results in this work still have some advantages. The pulse widths in this work are much narrower than that with graphene and BP SA, and comparable to the MoS2 SA. The 5 μJ pulse energy is a great deal of advantage. Those results reveal that the TIs nanowire SA is reliable and suitable for Q-switched MIR solid state laser.
Table 2. Comparison of Q-switched bulk lasers at ~3 μm based on different nano SAs
Among the 1D SAs, Carbon nanotubes (CNTs) and gold nanorods (GNRs) can realize a pulse laser operation in the largest wavelength region around 2.0 μm by complexly varying the diameter or the aspect ratio. While stable Q-switched solid state pulsed lasers at 1.0 and 2.79 μm are easily obtained by the same TIs nanowires SA. This work reveal that the Bi2Te3 nanowire may be more suitable and promissing to be a reliable broad 1D saturable absorber. For higher pulse peak powers, further investigations will be focused on the improvement of the crystallinity of Bi2Te3 nanowires.
4. Conclusions
In this work, passively Q-switched solid state lasers at 1.0 and 2.79 μm with 1D Bi2Te3 nanowires as saturable absorber are presented for the first time. Uniform 1D Bi2Te3 nanowires with an average diameter of about 20 nm and an average length of several micrometers have been synthesized by a two-step solution process using ultrathin Te nanowires as templates. With an open-aperture z-scan technology, the saturating intensity of 1.12 MW/cm2 and modulation depth of 12.64% are measured at 1.0 μm; while at 2.79 μm MIR band, its saturating intensity and modulation depth were measured to be 1 MW/cm2, and 9.9%, respectively. In near-infrared region at 1.0 μm, a pulse width of 303 ns with pulse energy of 1.2 µJ is achieved. For the pulsed operation at 2.79 μm, the shortest pulse width and largest pulse energy are tested to be 444 ns and 5 µJ. Our works provide another effective broadband optical modulator and topological insulator Bi2Te3 nanowire is a reliable broad optical switcher for solid state laser from near-infrared to mid-infrared region, and has great potential in ultrafast photonics applications. Furthermore, this work can be extendable to explore TIs with other nanostructures for applications as optoelectronic devices.
Funding
National Natural Science Foundation of China (51472240, 61078076, 11764014, 11647138 and 11304313); Science & Technology Major Project of Jiangxi Province (20165ABC28010); Nature Science Foundation of Fujian Province (2015J05134), Natural Science Foundation of Jiangxi Province (20161BAB216132); PhD Research Startup Foundation of Jiangxi University of Science and Technology (jxxjbs17041).
References and links
1. B. Poudel, Q. Hao, Y. Ma, Y. Lan, A. Minnich, B. Yu, X. Yan, D. Wang, A. Muto, D. Vashaee, X. Chen, J. Liu, M. S. Dresselhaus, G. Chen, and Z. Ren, “High-Thermoelectric Performance of Nanostructured Bismuth Antimony Telluride Bulk Alloys,” Science 320(5876), 634–638 (2008). [CrossRef] [PubMed]
2. Y. Zhang, L. P. Hu, T. J. Zhu, J. Xie, and X. B. Zhao, “High yield Bi2Te3 single crystal nanosheets with uniform morphology via a solvothermal synthesis,” Cryst. Growth Des. 13(2), 645–651 (2013). [CrossRef]
3. K. Wang, H. W. Liang, W. T. Yao, and S. H. Yu, “Templating synthesis of uniform Bi2Te3 nanowires with high aspect ratio in triethylene glycol (TEG) and their thermoelectric performance,” J. Mater. Chem. 21(38), 15057–15062 (2011). [CrossRef]
4. C. L. Kane and E. J. Mele, “Z2 topological order and the quantum spin Hall effect,” Phys. Rev. Lett. 95(14), 146802 (2005). [CrossRef] [PubMed]
5. D. Hsieh, D. Qian, L. Wray, Y. Xia, Y. S. Hor, R. J. Cava, and M. Z. Hasan, “A topological dirac insulator in a quantum spin hall phase,” Nature 452(7190), 970–974 (2008). [CrossRef] [PubMed]
6. H. Zhang, C. X. Liu, X. L. Qi, X. Dai, Z. Fang, and S. C. Zhang, “Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface,” Nat. Phys. 5(6), 438–442 (2009). [CrossRef]
7. D. Pesin and A. H. MacDonald, “Spintronics and pseudospintronics in graphene and topological insulators,” Nat. Mater. 11(5), 409–416 (2012). [CrossRef] [PubMed]
8. F. Bernard, H. Zhang, S. P. Gorza, and P. Emplit, “Towards mode-locked fiber laser using topological insulators,” in Advanced Photonics Congress, OSA Technical Digest (online) (Optical Society of America, 2012), paper NTh1A.5. [CrossRef]
9. C. J. Zhao, H. Zhang, X. Qi, Y. Chen, Z. T. Wang, S. C. Wen, and D. Y. Tang, “Ultra-short pulse generation by a topological insulator based saturable absorber,” Appl. Phys. Lett. 101(201), 211106 (2012). [CrossRef]
10. Q. Chen, M. Sanderson, and C. Zhang, “Nonlinear terahertz response of HgTe/CdTe quantum wells,” Appl. Phys. Lett. 107(8), 081111 (2015). [CrossRef]
11. Q. Chen, Y. S. Ang, R. A. Lewis, X. Wang, and C. Zhang, “Photomixing in topological insulator HgTe/CdTe quantum wells in terahertz regime,” Appl. Phys. Lett. 101(21), 211109 (2012). [CrossRef]
12. Z. Luo, Y. Huang, J. Weng, H. Cheng, Z. Lin, B. Xu, Z. Cai, and H. Xu, “1.06 μm Q-switched ytterbium-doped fiber laser using few-layer topological insulator Bi2Se3 as a saturable absorber,” Opt. Express 21(24), 29516–29522 (2013). [CrossRef] [PubMed]
13. B. L. Wang, H. H. Yu, H. Zhang, C. J. Zhao, S. C. Wen, H. J. Zhang, and J. Y. Wang, “Topological insulator simultaneously Q-switched dual-wavelength Nd:Lu2O3 laser,” IEEE Photonics J. 6(3), 1501007 (2014). [CrossRef]
14. M. T. Hu, J. H. Lin, J. R. Tian, Z. Y. Dou, and Y. R. Song, “Generation of Q-switched pulse by Bi2Se3 topological insulator in Yb:KGW laser,” Laser Phys. Lett. 11(11), 115806 (2014). [CrossRef]
15. H. H. Yu, H. Zhang, Y. C. Wang, C. J. Zhao, B. L. Wang, S. C. Wen, H. J. Zhang, and J. Y. Wang, “Topological insulator as an optical modulator for pulsed solid-state lasers,” Laser Photonics Rev. 7(6), L77–L83 (2013). [CrossRef]
16. Y. J. Sun, C. K. Lee, J. L. Xu, Z. J. Zhu, Y. Q. Wang, S. F. Gao, H. P. Xia, Z. Y. You, and C. Y. Tu, “Passively Q-switched tri-wavelength Yb3+:GdAl3(BO3)4 solid-state laser with topological insulator Bi2Te3 as saturable absorber,” Photon. Res. 3(3), A97–A101 (2015). [CrossRef]
17. J. L. Xu, Y. J. Sun, J. L. He, Y. Wang, Z. J. Zhu, Z. Y. You, J. F. Li, M. M. C. Chou, C. K. Lee, and C. Y. Tu, “Ultrasensitive nonlinear absorption response of large-size topological insulator and application in low-threshold bulk pulsed lasers,” Sci. Rep. 5(1), 14856 (2015). [CrossRef] [PubMed]
18. M. Liu, N. Zhao, H. Liu, X. W. Zheng, A. P. Luo, Z. C. Luo, W. C. Xu, C. J. Zhao, H. Zhang, and S. C. Wen, “Dual-wavelength harmonically mode-locked fiber laser with topological insulator saturable absorber,” IEEE Photonics Technol. Lett. 26(10), 983–986 (2014). [CrossRef]
19. J. Sotor, G. Sobon, K. Grodecki, and K. M. Abramski, “Mode-locked erbium-doped fiber laser based on evanescent field interaction with Sb2Te3 topological insulator,” Appl. Phys. Lett. 104(25), 251112 (2014). [CrossRef]
20. C. Zhao, Y. Zou, Y. Chen, Z. Wang, S. Lu, H. Zhang, S. Wen, and D. Tang, “Wavelength-tunable picosecond soliton fiber laser with Topological Insulator: Bi2Se3 as a mode locker,” Opt. Express 20(25), 27888–27895 (2012). [CrossRef] [PubMed]
21. Y. H. Lin, C. Y. Yang, S. F. Lin, W. H. Tseng, Q. Bao, C. Wu, and G. R. Lin, “Soliton compression of the erbium-doped fiber laser weakly started mode-locking by nanoscale p-type Bi2Te3 topological insulator particles,” Laser Phys. Lett. 11(5), 055107 (2014). [CrossRef]
22. Y. Chen, C. J. Zhao, H. H. Huang, S. Chen, P. Tang, Z. Wang, S. Lu, H. Zhang, S. Wen, and D. Tang, “Self-assembled topological insulator: Bi2Se3 membrane as a passive Q-switcher in an erbium-doped fiber laser,” J. Lightwave Technol. 31(17), 2857–2863 (2013). [CrossRef]
23. P. H. Tang, X. Q. Zhang, C. J. Zhao, Y. Wang, H. Zhang, D. Y. Shen, S. C. Wen, D. Y. Tang, and D. Y. Fan, “Topological insulator: Bi2Te3 saturable absorber for the passive Q-switching operation of an in-band pumped 1645 nm Er:YAG ceramic laser,” IEEE Photonics J. 5(2), 1500707 (2013). [CrossRef]
24. M. Jung, J. Lee, J. Koo, J. Park, Y. W. Song, K. Lee, S. Lee, and J. H. Lee, “A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi2Te3 topological insulator,” Opt. Express 22(7), 7865–7874 (2014). [CrossRef] [PubMed]
25. S. Q. Chen, C. J. Zhao, Y. Li, H. H. Huang, S. B. Lu, H. Zhang, and S. C. Wen, “Broadband optical and microwave nonlinear response in topological insulator,” Opt. Mater. Express 4(4), 587–596 (2014). [CrossRef]
26. J. Li, H. Luo, L. Wang, C. Zhao, H. Zhang, H. Li, and Y. Liu, “3-μm Mid-infrared pulse generation using topological insulator as the saturable absorber,” Opt. Lett. 40(15), 3659–3662 (2015). [CrossRef] [PubMed]
27. M. Scheele, N. Oeschler, K. Meier, A. Kornowski, C. Klinke, and H. Weller, “Synthesis and Thermoelectric Characterization of Bi2Te3 Nanoparticles,” Adv. Funct. Mater. 19(21), 3476–3483 (2009). [CrossRef]
28. S. H. Kim and B. K. Park, “Solvothermal synthesis of Bi2Te3 nanotubes by the interdiffusion of Bi and Te metals,” Mater. Lett. 64(8), 938–941 (2010). [CrossRef]
29. Y. Jiang, Y. J. Zhu, and L. D. Chen, “Microwave-assisted Preparation of Bi2Te3 Hollow Nanospheres,” Chem. Lett. 36(3), 382–383 (2007). [CrossRef]
30. C. Yan, J. Wang, X. Wang, W. Kang, M. Cui, C. Y. Foo, and P. S. Lee, “An Intrinsically Stretchable Nanowire Photodetector with a Fully Embedded Structure,” Adv. Mater. 26(6), 943–950 (2014). [CrossRef] [PubMed]
31. L. Peng, L. Hu, and X. Fang, “Low-Dimensional Nanostructure Ultraviolet Photodetectors,” Adv. Mater. 25(37), 5321–5328 (2013). [CrossRef] [PubMed]
32. H. Li, X. Wang, J. Xu, Q. Zhang, Y. Bando, D. Golberg, Y. Ma, and T. Zhai, “One-Dimensional CdS Nanostructures: A Promising Candidate for Optoelectronics,” Adv. Mater. 25(22), 3017–3037 (2013). [CrossRef] [PubMed]
33. X. Zhou, Q. Zhang, L. Gan, X. Li, H. Q. Li, Y. Zhang, D. Golberg, and T. Y. Zhai, “High-Performance Solar-Blind Deep Ultraviolet Photodetector Based on Individual Single-Crystalline Zn2GeO4 Nanowire,” Adv. Funct. Mater. 26(5), 704–712 (2016). [CrossRef]
34. 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]
35. 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]
36. H. H. Liu and K. K. Chow, “Operation-Switchable Bidirectional Pulsed Fiber Laser Incorporating Carbon-Nanotube-Based Saturable Absorber,” IEEE J. Sel. Top. Quant. 20(5), 0901905 (2014). [CrossRef]
37. J. W. Kim, S. Y. Choi, D. I. Yeom, S. Aravazhi, M. Pollnau, U. Griebner, V. Petrov, and F. Rotermund, “Yb:KYW planar waveguide laser Q-switched by evanescent-field interaction with carbon nanotubes,” Opt. Lett. 38(23), 5090–5093 (2013). [CrossRef] [PubMed]
38. H. H. Liu, Y. Yang, and K. K. Chow, “Enhancement of thermal damage threshold of carbon-nanotube-based saturable absorber by evanescent-field interaction on fiber end,” Opt. Express 21(16), 18975–18982 (2013). [CrossRef] [PubMed]
39. M. Fan, T. Li, S. Zhao, G. Li, X. Gao, K. Yang, D. Li, and C. Kränkel, “Multilayer black phosphorus as saturable absorber for an Er:Lu2O3 laser at ∼3 μm,” Photon. Res. 4(5), 181–186 (2016). [CrossRef]
40. C. Luan, K. Yang, J. Zhao, S. Zhao, L. Song, T. Li, H. Chu, J. Qiao, C. Wang, Z. Li, S. Jiang, B. Man, and L. Zheng, “WS2 as a saturable absorber for Q-switched 2 micron lasers,” Opt. Lett. 41(16), 3783–3786 (2016). [CrossRef] [PubMed]
41. H. Yu, X. Chen, X. Hu, S. Zhuang, Z. Wang, X. Xu, J. Wang, H. Zhang, and M. Jiang, “Graphene as a Q-Switcher for Neodymium-Doped Lutetium Vanadate Laser,” Appl. Phys. Express 4(2), 022704 (2011). [CrossRef]
42. X. L. Li, J. L. Xu, Y. Z. Wu, J. L. He, and X. P. Hao, “Large energy laser pulses with high repetition rate by graphene Q-switched solid-state laser,” Opt. Express 19(10), 9950–9955 (2011). [CrossRef] [PubMed]
43. H. W. Chu, S. Z. Zhao, Y. F. Li, K. J. Yang, G. Q. Li, D. C. Li, J. Zhao, W. C. Qiao, T. Li, C. S. Feng, Y. G. Wang, and Y. S. Wang, “Diode-pumped passively Q-switched Nd:GGG laser with a double-walled carbon nanotube saturable absorber,” Laser Phys. Lett. 11(3), 035001 (2014). [CrossRef]
44. B. Xu, Y. Cheng, Y. Wang, Y. Huang, J. Peng, Z. Luo, H. Xu, Z. Cai, J. Weng, and R. Moncorgé, “Passively Q-switched Nd:YAlO3nanosecond laser using MoS2as saturable absorber,” Opt. Express 22(23), 28934–28940 (2014). [CrossRef] [PubMed]
45. F. Lou, R. Zhao, J. He, Z. Jia, X. Su, Z. Wang, J. Hou, and B. Zhang, “Nanosecond-pulsed, dual-wavelength passively Q-switched ytterbium-doped bulk laser based on few-layer MoS2 saturable absorber,” Photon. Res. 3(2), 25–29 (2015). [CrossRef]
46. Y. J. Sun, J. L. Xu, Z. J. Zhu, Y. Q. Wang, H. P. Xia, Z. Y. You, C. K. Lee, and C. Y. Tu, “Comparison of MoS2 nanosheets and hierarchical nanospheres in the application of pulsed solid-state lasers,” Opt. Mater. Express 5(12), 2924–2932 (2015). [CrossRef]
47. J. Ma, S. Lu, Z. Guo, X. Xu, H. Zhang, D. Tang, and D. Fan, “Few-layer black phosphorus based saturable absorber mirror for pulsed solid-state lasers,” Opt. Express 23(17), 22643–22648 (2015). [CrossRef] [PubMed]
48. C. Li, J. Liu, S. Jiang, S. Xu, W. Ma, J. Wang, X. Xu, and L. Su, “2.8 μm passively Q-switched Er:CaF2 diode-pumped laser,” Opt. Mater. Express 6(5), 1570–1575 (2016). [CrossRef]
49. L. Kong, Z. Qin, G. Xie, Z. Guo, H. Zhang, P. Yuan, and L. Qian, “Black phosphorus as broadband saturable absorber for pulsed lasers from 1 μm to 2.7 μm wavelength,” Laser Phys. Lett. 13(4), 045801 (2016). [CrossRef]
50. M. Fan, T. Li, S. Zhao, G. Li, H. Ma, X. Gao, C. Kränkel, and G. Huber, “Watt-level passively Q-switched Er:Lu2O3 laser at 2.84 μm using MoS2,” Opt. Lett. 41(3), 540–543 (2016). [CrossRef] [PubMed]
