Open Access
Add to BibSonomy
Abstract
In this paper, two-dimensional (2D) few-layer Ta2CTx nanosheets are fabricated by liquid phase exfoliation (LPE) method. The nonlinear optical absorption properties are studied by Z-scan and I-scan techniques, revealing excellent saturable absorption response with an effective nonlinear absorption coefficient of -92.2 cm/MW@1064 nm. The saturation intensity and modulation depth for 1064 nm and 1550 nm are determined to be 79 and 51 MW/cm2, 9.9% and 4.5%, respectively. Furthermore, by decorating few-layer Ta2CTx nanosheets onto microfiber, few-layer Ta2CTx saturable absorber (SA) is fabricated and applied in Yb-doped and Er-doped fiber lasers (YDFLs and EDFLs). Not only a normal mode-locked operation but also square-wave pulse (SWP) are realized by increasing the length of the laser cavity at 1.5 µm, highlighting the great potential of few-layer Ta2CTx nanosheets as an optical modulator. The maximum pulse duration of 5.56 ns is also the widest SWP width that can be realized with 2D materials without filtering device in the cavity. Our work provides a platform for exploring novel SAs materials and nonlinear phenomena in mode-locked fiber lasers.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Since the discovery of graphene, 2D materials have experienced a rapid development because of the unique photoelectronic properties and wide applications in photonics and electronics, etc. [1–4]. The light-matter interaction in 2D materials excited by strong light usually exhibits saturable absorption response in nonlinear regime, where the light transmission increases with the increase of the incident light intensity [5–7]. The nonlinear optical material that has the saturable absorption properties is called saturable absorber (SA), which is the key element of passively Q-switched and mode-locked lasers. The 2D materials based SAs effectively overcome the shortcoming of the traditional SAs and have the merits of wide operation bandwidth, tunable modulation depth, low cost, easy fabrication and integration, and so on. To date, a variety of 2D materials have been successfully applied as SAs for solid-state crystalline or fiber lasers, realizing Q-switched or mode-locked operations [8–14].
MXenes, generally referring to 2D transition metal carbides, carbonitrides and nitrides, have attracted increasing attention and set off another wave of exploration enthusiasm for advanced catalysis, optoelectronics and photonics with intriguing electronic, optical and mechanical properties, as well as the versatile chemical decoration and elemental composition [15]. MXenes has the general formula of Mn+1XnTx (n = 1-3), where M is an early transition metal (e.g. Ti, Ta, Nb, Mo, Cr, etc.), X represents carbon and/or nitrogen, and T is the surface termination groups (such as -O,-OH,-F, etc.), respectively [16]. Extensive theoretical and experimental studies have been carried on the electronic and optical properties of MXenes in terms of band structure, state density, ultrafast carrier dynamics, and linear or nonlinear optical responses [17,18]. The results have unveiled that MXenes have great potential for new generation of optoelectronic and catalysis devices. Especially, the richness of surface functional groups enables MXenes to exhibit variable and most tailorable physical properties, including the tunable bandgap, large nonlinear optical absorption coefficient, high electronic conductivity, tunable modulation depth, large modulus of elasticity, intercalating with ions, and ultrafast relaxation time, and so on [19–21]. Besides, MXenes also have been proved to be a promising SA for pulsed laser generation. For example, by using Ti3C2Tx as SA, mode-locked fiber lasers operating at 1.0 and 1.55 µm with pulse duration of 480 ps and 159 fs was reported [21]. With 2D α-MoC-SA, passive mode-locking operation of EDFLs and YDFLs with pulse width of 1.81 and 418 ps was obtained [22]. Ti2CTx was used as SA for EDFLs and YDFLs, generating 265 fs at 1.5 µm and 792 ps at 1.04 µm, respectively [23].
Ta2CTx, a new member of MXene family, has the similar optical properties like Ti2CTx and thus has strong saturable absorption response. And Ta2CTx has attracted extensive attention due to its excellent electron and ionic conductivity and long-term stability, which is even better than Tin+1CnTx. Here, 2D few-layer Ta2CTx nanosheets are fabricated by LPE method. The third-order nonlinear absorption properties are studied with open-aperture Z-scan measurement at 1.06 µm, in which the effective nonlinear absorption coefficient of -92.2 cm/MW and the imaginary part of the third-order susceptibility of -1.032 ×10−8 esu are obtained, indicating the excellent saturable absorption properties. Consequently, the saturable absorption parameters in terms of saturation intensity, modulation depth are measured by I-scan method at 1.06 and 1.5 µm. Furthermore, by decorating few-layer Ta2CTx onto microfiber, microfiber-based few-layer Ta2CTx SA is fabricated and applied for passively mode-locked YDFLs and EDFLs. Not only traditional soliton mode-locked operation but also SWP is obtained by increasing the cavity length at 1.5 µm. Our work provides a new platform for exploring complex nonlinear phenomena in mode-locked fiber lasers.
2. Results and discussion
2.1 Synthesis and characterization of few-layer Ta2CTx nanosheets
2D few-layer Ta2CTx nanosheets are fabricated by the commonly used LPE method. The commercially available high-purity Ta2CTx powder is dispersed into deionized water. In order to make the solute to be fully dissolved and form nanoscale flakes, the solvent is ultrasonicated for 5 h. Then, the solution is centrifugally treated and the supernatant is transferred onto a sapphire substrate to prepare the Ta2CTx nanosheets. The thickness of the prepared Ta2CTx nanosheets is measured to be 5-15 nm (corresponding to layer number of about 7-20 [24]) by using Atomic force microscopy (AFM), as shown in Fig. 1(a) and (b). The surface morphologies and dimensions are characterized by transmission electron microscope (TEM), as shown in Fig. 1(c). The typical TEM image indicates that few layer Ta2CTx nanosheets are uniformly dispersed on the substrate and has a local size of 200 to 350 nm. The high-resolution TEM (HRTEM) image in Fig. 1(d) clearly reveals the highly crystalline quality of Ta2CTx, in which the lattice space of 0.1 nm corresponding to (002) lattice face. The corresponding selected area electron diffraction (SAED) pattern with hexagonal spots represents the hexagonal lattice structure, as shown in Fig. 1 (e), which demonstrates high crystal quality of few-layer Ta2CTx nanosheets. Moreover, X-ray photoelectron spectroscopy (XPS) is performed to further determine the surface terminations and binding energy of Ta2CTx nanosheets. Signals from C, Ta can be observed in Fig. 1(f) and (g). The Ta 4f components centered at binding energies of ∼23.8 eV can be assigned as the strong Ta spin-orbital doublet, fitting well with the binding energies of Ta-C. What’s more, small band centered at binding energies of 283.8 eV (corresponding to Ta-C) is also observed. Figure 1(h) shows the UV-vis-NIR spectrometry of few-layer Ta2CTx nanosheets, indicating strong and relatively flat broadband absorption from 400-2000 nm.
Fig. 1. a) AFM image of few-layer Ta2CTx nanosheets. b) Height profiles along the lines in AFM image. c) Large-area TEM images of Ta2CTx nanosheets. d) High-resolution TEM images. e) Corresponding selected area electron diffraction. f) XPS spectra of few-layer Ta2CTx nanosheets in Ta 4f region and C 1s. h) Ultraviolet-visible-infrared (UV-vis-NIR) absorption spectrum.
2.2 Third-order nonlinear optical response of few-layer Ta2CTx nanosheets
The nonlinear optical response of synthesized 2D few-layer Ta2CTx nanosheets is measured by the open-aperture Z-scan technique. The laser source is a homeland Yb-doped mode-locked fiber laser operating at 1064 nm with a pulse width of 10 ps and repetition rate of 1 MHz. Figure 2 (a) shows the typical Z-scan curve of few-layer Ta2CTx nanosheets at a wavelength of 1064 nm, which displays a sharp and narrow peak at the focus position, highlighting the typical saturable absorption response of few-layer Ta2CTx nanosheets.
According to the nonlinear optical absorption theory, the nonlinear absorption coefficient βeff can be expressed as $\alpha = {\alpha _0} + {\beta _{eff}}I$, where ${\alpha _0}$ is the linear absorption coefficient, ${\beta _{eff}}$ is the nonlinear absorption coefficient, and I is the laser intensity. The open aperture Z-scan trace can be fitted by the following model:
where ${I_0}$ is the on-focus light intensity, ${L_{eff}} = ({1 - {e^{ - {\alpha_0}L}}} )/{\alpha _0}$ is the effective thickness of the sample, ${z_0} = \pi {\omega _0}^2/\lambda $ is the Rayleigh range, ${\omega _0}$ represents the waist radius of the lens, and the $\lambda $ is the center wavelength.Fig. 2. a) Z-scan measurement results. b) I-scan measurement results at 1.06 µm. c) I-scan measurement results at 1.56 µm.
By fitting the open-aperture Z-scan measurement data, ${\beta _{eff}}$ is determined to be -92.2 cm/MW. In addition, the imaginary part of the third-order nonlinear susceptibility can be obtained by the equation $\textrm{Im}({{\chi^{(3 )}}} )= \frac{{2{n_0}{\varepsilon _0}{c^2}}}{{3\omega }}{\beta _{eff}}$, where n0 and ${\varepsilon _0}$ is the linear refractive index and vacuum mediated electric constant, respectively; and c is the vacuum light speed. Thus, $\textrm{Im}({{\chi^{(3 )}}} )\; $ is determined to be -1.032 ×10−8 esu. Compared with other 2D MXenes materials or BP and TMDs [21–27], the value of ${\beta _{eff}}$ is much higher, indicating a strong saturable absorption response of few-layer Ta2CTx nanosheets. The plasmon resonance of Ta2CTx should play a great role in its overall saturable absorption, which is similar to other MXenes such as Ti3CN and Nb2C [28]. Under the condition of high laser energy, the depletion of the ground state will lead to the reduction of photon absorption, and the local electric field induced by plasma resonance could also enhance the saturable absorption by increasing the absorption cross section of the ground state [29].
The microfiber based few-layer Ta2CTx-SA is fabricated through the optical deposition method [30]. The saturable absorption parameters of the microfiber based few-layer Ta2CTx-SA is carried out by using I-scan technique. A mode-locked fiber laser operating at 1064 nm with a pulse width of 50 ps and repetition rate of 12 MHz and another mode-locked fiber laser operating at 1560 nm with a pulse width of 5 ps and repetition rate of 11 MHz are used as the excitation laser source. Figure 2(b) and (c) show the nonlinear transmittance of the microfiber based few-layer Ta2CTx-SA with respect to the incident laser intensities, indicating the typical saturation absorption response at the two wavelengths. The transmittance can be well fitted by a nonlinear transmission model:
where ΔR, Is, and αns are the modulation depth, saturation intensity and unsaturable loss, respectively. As shown in Fig. 2(b) and (c), the modulation depth and the saturation intensity of microfiber based few-layer Ta2CTx -SA are estimated to be 9.9% and 79.9 MW/cm2 at 1.0 µm and 4.5% and 50.8 MW/cm2 at 1.5 µm, respectively. Table 1 summarizes the nonlinear absorption parameters of the typical 2D MXenes. As shown in Table 1, the nonlinear absorption coefficient of few-layer Ta2CTx nanosheets is relatively large, indicating a strong saturable absorption ability and light-matter interaction in few-layer Ta2CTx nanosheets. What’s more, the lower saturation light intensity and appropriate modulation depth make it easier to realize the light modulation. All the results suggest the strong nonlinear optical response and modulation ability of few-layer Ta2CTx nanosheets, indicating the great potential as a SA for passively mode-locked fiber lasers.
Table 1. Parameters comparison between few-layer Ta2CTx and other typical 2D MXenes
2.3 Passively mode-locked fiber lasers operating at 1.03 and 1.55 µm
The strong optical nonlinearities and broadband absorption properties of Ta2CTx nanosheets presented above shows great potential to be applied as SA for mode-locked fiber lasers. The microfiber based few-layer Ta2CTx -SA is applied in YDFLs and EDFLs, and the configuration scheme is shown in Fig. 3. Here, the fiber component includes a 10.4 m single mode fiber (HI-1060) and a 0.5 m Yb-doped fiber (Yb-401). The dispersion parameter of HI-1060 and Yb-401 are -38 ps/nm/km and -60 ps/nm/km, respectively. And the total cavity dispersion is determined to be 0.254 ps2. The pump source is a LD with the maximum pump power of 450 mW and central wavelength of 976 nm. The optical coupler (OC, 90/10) is used for output of radiation light. In addition, a three-paddle type polarization controller (PC) is used to adjust the light polarization state. In order to ensure the unidirectional transmission of light, a polarization insensitive isolator (PI-ISO) is used in the cavity. For EDFLs, 9.8 m and 609.5 m cavity length is composed of 0.3 m EDF (LIEKKI Er 110-4/125), 9.5 m and 609.2 m single mode fiber (SMF-28), respectively. A 980/1560 nm WDM (wavelength division multiplexer), PI-ISO, PC and 90:10 OC with operation wavelength at 1560 nm is used in the similar ring laser cavity. The dispersion parameter of SMF-28 and Er 110-4/125 are 17 ps/nm/km and -42 ps/nm/km, respectively. And the net cavity dispersion of EDFLs is calculated to be -0.194 and -13.49 ps2. An optical power meter (THORLABS S148C), a 4 GHz digital oscilloscope (Tektronix DPO 3052) coupled with a 4 GHz photodetector, an optical spectrum analyzer (Yokogawa AQ6370C) and a 3 GHz RF spectrum analyzer (Agilent N900A) are used to record the output characteristics.
Few-layer Ta2CTx nanosheets is deposited onto microfiber through the action of an evanescent field to form the microfiber based few-layer Ta2CTx-SA, which is inserted into the YDFLs and used as modulation device. The stable mode-locked operation is obtained when the pump power is up to 105 mW by adjust the angle of PC appropriately. The corresponding pulse train with timespan of ∼1.3 µs is shown in Fig. 4 (a), the adjacent pulse interval is 54 ns, corresponding to the cavity length of 10.9 m. The dissipative soliton mode-locked operation is realized in a fully positive dispersion cavity with a pulse width of 281 ps (as shown in Fig. 4 (b)). When the pump power exceeds 360 mW, the pulse train becomes unstable no matter how changing the polarization state in the cavity. Figure 4 (c) shows the RF spectrum located at 18.5 MHz with a span of 12 MHz and the signal-to-noise ratio (SNR) of ∼63 dB, indicating good stability. The spectra of the dissipative solitons with steep edges is shown in Fig. 4 (d) and the center wavelength is located at 1036.4 nm with a 3 dB bandwidth of 1.1 nm. Figure 4 (e) represents the variation of output power respect to the pump power. The maximum average output power of 6.5 mW is obtained with a slope efficiency of 2.7%. Besides, the stability is measured and recorded over 3 hours by monitoring the output spectrum at the pump power of 300 mW, as shown in Fig. 4 (f).
Fig. 4. a) and b) Oscilloscope pulse train and single pulse profile at the pump power of 300 mW. c) The corresponding RF spectrum with a span of 12 MHz. d) Output spectrum. e) Relationship between the output power and incident pump power. f) Output spectra collected for 3 h.
To further demonstrate the broadband saturable absorption properties of few-layer Ta2CTx nanosheets, the EDFLs is constructed by incorporating the microfiber based few-layer Ta2CTx-SA into a ring cavity. The traditional fundamental frequency soliton mode-locked operation is easily realized by adjusting the PC when the pump power reaches up to 110 mW. Figure 5 (a) shows the pulse train with a time scale of 2 µs and the adjacent pulse intervals is 47.6 ns. Furthermore, the single pulse width of 350 ps is obtained and the pulse profile is shown in Fig. 5 (b). As shown in Fig. 5 (c), the typical soliton output spectrum with a 3 dB bandwidth of 3.4 nm is obtained. To assess the stability of mode-locked operation, the RF spectrum is measured with different spans of at the pump power of 250 mW. The center frequency of 20.88 MHz and SNR of 58 dB with a span of 7 MHz are obtained.
Fig. 5. a) and b) Oscilloscope pulse train and single pulse profile at the pump power of 250 mW. c) Output spectrum in fundamental mode. c) The corresponding RF spectrum with a span of 7 MHz.
Encouraged by the large nonlinear absorption coefficient of Ta2CTx nanosheets, a 600 m single-mode fiber is added into the original cavity to further explore the mode-locking phenomena. It is well known that self-phase modulation (SPM) and cross-phase modulation (XPM) are two most widely studied nonlinear effects in fiber laser, and both of them are related to the length of fiber. The longer the fiber length, the stronger the nonlinear effect in the cavity. The stable SWP is obtained at the pump power of 250 mW and the corresponding pulse train is shown in Fig. 6 (a). SWP, also known as rectangular pulse, has steep sides and flat top in time domain. Different from sech2-shaped pulse and Gaussian pulse, the energy of SWP increases as the pump energy increases while the peak power remains fixed. and SWP shows great potential in applications of high frequency clock signal generation, fiber sensing, laser display and biomedicine [33,34]. Figure 6 (b) shows the pulse evolution with the variation of the pump power. The SWP pulse duration increases from 3.5 to 5.56 ns as the pump power increases from 250 mW to 400 mW while the pulse amplitude remains almost as a constant, which is also the widest rectangular pulse width that can be realized in 2D materials without filtering device used in the cavity. As shown in Fig. 6 (c), the fundamental repetition is 0.33 MHz with SNR of 50 dB. The spectrum of SWP located at 1574.7 nm with a 3 dB spectral width of 4.8 nm is illustrated in Fig. 6 (d). When the pump power increases from 250 to 400 mW, the shape of the spectrum do not change significantly, but the intensity of the peaks increases, which is the same as the characteristics of the SWP mode-locked fiber lasers [34]. The generation of SWP is mainly due to the nonlinear polarization switching and the peak power clamping effect inside the resonator [21]. The threshold of generating SWP is reduced due to the large nonlinear coefficient of Ta2CTx nanosheets, the composite structure based on microfiber and the increase of the cavity length. On the other hand, the filter effect of the microfiber based few-layer Ta2CTx-SA is also believed to be favor for SWP generation. Interference filtering effect leads to a large loss at the central wavelength and low loss on both sides [35]. When the peak power increases to a certain extent, the part above this threshold will be suppressed, while the part below this threshold will be further amplified. And SWP with steep front and rear edges is generated finally.
Fig. 6. Experimental results of the SWP mode-locked Er-fiber laser. a) Oscilloscope pulse train at the pump power of 300 mW. b) Pulse width and single pulse energy as a function of pump power. c) The corresponding RF spectrum with a span of 250 kHz. d) Output spectrum with virous pump power.
3. Conclusion
In conclusion, Ta2CTx nanosheets and microfiber based few-layer Ta2CTx-SA are prepared by LPE method. The nonlinear optical properties are investigated by the Z-scan and I-scan technique, revealing the excellent characteristics as a nonlinear optical modulator. And the effective nonlinear absorption coefficient is determined to be -92.2 cm/MW at 1064 nm, corresponding to the imaginary part of the third-order nonlinear effects of -1.032 ×10−8 esu. Moreover, YDFLs and EDFLs are realized by inserting the microfiber based few-layer Ta2CTx-SA in the ring cavity. Here, not only the normal mode-locked operation but also SWP is obtained by increasing the length of the laser cavity at 1.5 µm, highlighting the potential as a nonlinear material in the field of photonics. Our work provides a platform to explore the complex nonlinear phenomena in mode-locked fiber lasers.
Funding
National Research Foundation of China (61975095, 61975097, 62105182); the Youth Cross Innovation Group of Shandong University (2020QNQT); the Financial Support from Qilu Young Scholar of Shandong University; Shanghai Municipal Science and Technology Major Project (2019SHZDZX01); China Postdoctoral Science Foundation (2021M691954).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, “Electric field effect in atomically thin carbon films,” Science 306(5696), 666–669 (2004). [CrossRef]
2. M. Liu, X. B. Yin, E. Ulin-Avila, B. S. Geng, T. Zentgraf, L. Ju, F. Wang, and X. Zhang, “A graphene-based broadband optical modulator,” Nature 474(7349), 64–67 (2011). [CrossRef]
3. H. Tian, M. L. Chin, S. Najmaei, Q. S. Guo, F. N. Xia, H. Wang, and M. Dubey, “Optoelectronic devices based on two-dimensional transition metal dichalcogenides,” Nano Res. 9(6), 1543–1560 (2016). [CrossRef]
4. M. N. Cizmeciyan, J. W. Kim, S. Bae, B. H. Hong, F. Rotermund, and A. Sennaroglu, “Graphene mode-locked femtosecond cr:Znse laser at 2500 nm,” Opt. Lett. 38(3), 341–343 (2013). [CrossRef]
5. X. M. Wang and S. F. Lan, “Optical properties of black phosphorus,” Adv. Opt. Photonics 8(4), 618–655 (2016). [CrossRef]
6. O. Lopez-Sanchez, E. Alarcon Llado, V. Koman, A. F. I. Morral, A. Radenovic, and A. Kis, “Light generation and harvesting in a van der waals heterostructure,” ACS Nano 8(3), 3042–3048 (2014). [CrossRef]
7. K. Wei, Z. Xu, R. Chen, X. Zheng, X. Cheng, and T. Jiang, “Temperature-dependent excitonic photoluminescence excited by two-photon absorption in perovskite CsPbBr3 quantum dots,” Opt. Lett. 41(16), 3821–3824 (2016). [CrossRef]
8. J. Li, H. Luo, B. Zhai, R. Lu, Z. Guo, H. Zhang, and Y. Liu, “Black phosphorus: A two-dimension saturable absorption material for mid-infrared q-switched and mode-locked fiber lasers,” Sci. Rep. 6(1), 30361 (2016). [CrossRef]
9. K. Wu, B. Chen, X. Zhang, S. Zhang, C. Guo, C. Li, P. Xiao, J. Wang, L. Zhou, W. Zou, and J. Chen, “High-performance mode-locked and q-switched fiber lasers based on novel 2D materials of topological insulators, transition metal dichalcogenides and black phosphorus: Review and perspective (invited),” Opt. Commun. 406, 214–229 (2018). [CrossRef]
10. Z. Xie, F. Zhang, Z. Liang, T. Fan, Z. Li, X. Jiang, H. Chen, J. Li, and H. Zhang, “Revealing of the ultrafast third-order nonlinear optical response and enabled photonic application in two-dimensional tin sulfide,” Photonics Res. 7(5), 494–502 (2019). [CrossRef]
11. G. Sobon, J. Sotor, J. Jagiello, R. Kozinski, M. Zdrojek, M. Holdynski, P. Paletko, J. Boguslawski, L. Lipinska, and K. M. Abramski, “Graphene oxide vs. Reduced graphene oxide as saturable absorbers for er-doped passively mode-locked fiber laser,” Opt. Express 20(17), 19463–19473 (2012). [CrossRef]
12. L. Ye, H. Li, Z. F. Chen, and J. B. Xu, “Near-infrared photodetector based on mos2/black phosphorus heterojunction,” ACS Photonics 3(4), 692–699 (2016). [CrossRef]
13. F. Bonaccorso, Z. Sun, T. Hasan, and A. C. Ferrari, “Graphene photonics and optoelectronics,” Nat. Photonics 4(9), 611–622 (2010). [CrossRef]
14. B. Guo, Q. L. Xiao, S. H. Wang, and H. Zhang, “2D layered materials: Synthesis, nonlinear optical properties, and device applications,” Laser Photonics Rev. 13(12), 1800327 (2019). [CrossRef]
15. A. Feng, Y. Yu, Y. Wang, F. Jiang, Y. Yu, L. Mi, and L. Song, “Two-dimensional mxene Ti3C2 produced by exfoliation of Ti3AlC2,” Mater. Des. 114, 161–166 (2017). [CrossRef]
16. M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, Y. Gogotsi, and M. W. Barsoum, “Two-dimensional transition metal carbides,” ACS Nano 6(2), 1322–1331 (2012). [CrossRef]
17. T. L. Tan, H. M. Jin, M. B. Sullivan, B. Anasori, and Y. Gogotsi, “A high-throughput survey of ordering configurations in mxene alloys across compositions and temperatures,” ACS Nano 11(5), 4407–4418 (2017). [CrossRef]
18. X. Jiang, A. V. Kuklin, A. Baev, Y. Ge, H. Agren, H. Zhang, and P. N. Prasad, “Two-dimensional mxenes: From morphological to optical, electric, and magnetic properties and applications,” Phys. Rep. 848, 1–58 (2020). [CrossRef]
19. B. Fu, J. X. Sun, C. Wang, C. Shang, L. J. Xu, J. B. Li, and H. Zhang, “Mxenes: Synthesis, optical properties, and applications in ultrafast photonics,” Small 17(11), 2006054 (2021). [CrossRef]
20. S. Huang and V. N. Mochalin, “Hydrolysis of 2D transition-metal carbides (MXenes) in colloidal solutions,” Inorg. Chem. 58(3), 1958–1966 (2019). [CrossRef]
21. X. Jiang, S. Liu, W. Liang, S. Luo, Z. He, Y. Ge, H. Wang, R. Cao, F. Zhang, Q. Wen, J. Li, Q. Bao, D. 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]
22. M. Tuo, C. Xu, H. Mu, X. Bao, Y. Wang, S. Xiao, W. Ma, L. Li, D. Tang, H. Zhang, M. Premaratne, B. Sun, H.-M. Cheng, S. Li, W. Ren, and Q. Bao, “Ultrathin 2D transition metal carbides for ultrafast pulsed fiber lasers,” ACS Photonics 5(5), 1808–1816 (2018). [CrossRef]
23. Y. Shi, N. Xu, and Q. Wen, “Ti2CTx (T = O, OH or F) nanosheets as new broadband saturable absorber for ultrafast photonics,” J. Lightwave Technol. 38(7), 1975–1980 (2020). [CrossRef]
24. A. VahidMohammadi, M. Mojtabavi, N. M. Caffrey, M. Wanunu, and M. Beidaghi, “Assembling 2D mxenes into highly stable pseudocapacitive electrodes with high power and energy densities,” Adv. Mater. 31(8), 1806931 (2019). [CrossRef]
25. S. B. Lu, C. J. Zhao, Y. H. Zou, S. Q. Chen, Y. Chen, Y. Li, H. Zhang, S. C. Wen, and D. Y. Tang, “Third order nonlinear optical property of Bi2Se3,” Opt. Express 21(2), 2072–2082 (2013). [CrossRef]
26. K. Wang, B. M. Szydlowska, G. Wang, X. Zhang, J. J. Wang, J. J. Magan, L. Zhang, J. N. Coleman, J. Wang, and W. J. Blau, “Ultrafast nonlinear excitation dynamics of black phosphorus nanosheets from visible to mid-infrared,” ACS Nano 10(7), 6923–6932 (2016). [CrossRef]
27. S. Zhang, N. Dong, N. McEvoy, M. O’Brien, S. Winters, N. C. Berner, C. Yim, Y. Li, X. Zhang, Z. Chen, L. Zhang, G. S. Duesberg, and J. Wang, “Direct observation of degenerate two-photon absorption and its saturation in WS2 and MoS2 mono layer and few-layer films,” ACS Nano 9(7), 7142–7150 (2015). [CrossRef]
28. Y. C. Dong, S. Chertopalov, K. Maleski, B. Anasori, L. Y. Hu, S. Bhattacharya, A. M. Rao, Y. Gogotsi, V. N. Mochalin, and R. Podila, “Saturable absorption in 2D Ti3C2 MXene thin films for passive photonic diodes,” Adv. Mater. 30(10), 1705714 (2018). [CrossRef]
29. J. Yi, L. Du, J. Li, L. Yang, L. Hu, S. Huang, Y. Dong, L. Miao, S. Wen, V. N. Mochalin, C. Zhao, and A. M. Rao, “Unleashing the potential of Ti2CTx MXene as a pulse modulator for mid-infrared fiber lasers,” 2D Mater. 6(4), 104395 (2019). [CrossRef]
30. Q. Wu, X. Jin, S. Chen, X. Jiang, Y. Hu, Q. Jiang, L. Wu, J. Li, Z. Zheng, M. Zhang, and H. Zhang, “MXene-based saturable absorber for femtosecond mode-locked fiber lasers,” Opt. Express 27(7), 10159–10170 (2019). [CrossRef]
31. L. Wang, X. Li, C. Wang, W. Luo, T. Feng, Y. Zhang, and H. Zhang, “Few-layer MXene Ti3C2Tx (T = F, O, or OH) for robust pulse generation in a compact er-doped fiber laser,” ChemNanoMat 5(9), 1233–1238 (2019). [CrossRef]
32. L. F. Gao, H. L. Chen, F. Zhang, S. Mei, Y. Zhang, W. L. Bao, C. Y. Ma, P. Yin, J. Guo, X. T. Jiang, S. X. Xu, W. C. Huang, X. B. Feng, F. M. Xu, S. R. Wei, and H. Zhang, “Ultrafast relaxation dynamics and nonlinear response of few-layer niobium carbide MXene,” Small Methods 4(8), 2000250 (2020). [CrossRef]
33. H. Yu, R. Tao, X. Wang, P. Zhou, and J. Chen, “240 W high-average-power square-shaped nanosecond all-fiber-integrated laser with near diffraction-limited beam quality,” Appl. Opt. 53(28), 6409–6413 (2014). [CrossRef]
34. Z. C. Cheng, H. H. Li, H. X. Shi, J. Ren, Q. H. Yang, and P. Wang, “Dissipative soliton resonance and reverse saturable absorption in graphene oxide mode-locked all-normal-dispersion yb-doped fiber laser,” Opt. Express 23(6), 7000–7006 (2015). [CrossRef]
35. N. Zhao, M. Liu, H. Liu, X.-W. Zheng, Q.-Y. Ning, A.-P. Luo, Z.-C. Luo, and W.-C. Xu, “Dual-wavelength rectangular pulse yb-doped fiber laser using a microfiber-based graphene saturable absorber,” Opt. Express 22(9), 10906–10913 (2014). [CrossRef]
