Open Access
Add to BibSonomy
Abstract
We demonstrate a Yb:LuPO4 miniature crystal laser that is formed with a 5 mm long plane-parallel resonator, and is passively Q-switched by a few-layer MoS2 saturable absorber. With 6.53 W of pump power absorbed, an average output power of 2.06 W at 1020.8 nm is generated at a pulse repetition rate of 429 kHz with a slope efficiency of 50%; the resulting pulse energy, duration, and peak power are respectively 4.8 μJ, 83 ns, and 57.8 W. While operating at 1010.5 nm, the laser is capable of producing an average output power of 1.53 W at a repetition rate of 870 kHz, with pulse duration being shortened to 61 ns. These results represent a significant progress in the development of Yb- or Nd-ion lasers passively Q-switched by two-dimensional MoS2.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
In recent years MoS2, one member of the transition metal dichalcogenides (MX2, M can be Mo or W; while X stands for S, Se, or Te), has attracted a great deal of attention in different research fields like material science, solid-state physics, optoelectronics, and laser technology. Bulk MoS2 is an indirect band-gap semiconductor, whereas two-dimensional layered MoS2 is of band structures that depend on its thickness or number of layers [1]. Moreover, the band structure is also affected by defects or strains existing in layered MoS2, making it possible to make broadband saturable absorbers from such kind of multi-layer MoS2 [2, 3].
The saturable nature of absorption in few-layer MoS2 was first confirmed in the 0.8 μm spectral region with a femtosecond laser beam [4]. Shortly thereafter, it was demonstrated that such broadband few-layer MoS2 saturable absorbers could be utilized for passive Q-switching of solid-state lasers in the 1−2 μm region [3]. Thus far, passively Q-switched operation induced by MoS2 saturable absorber has been realized in a wide variety of solid-state lasers, including Nd-ion lasers [3, 5–7], Yb-ion lasers [8–12], Tm-ion lasers [12–14], and Er-ion lasers [15].
Despite the much work mentioned above, the passive Q-switching laser performance achieved with MoS2 still remains much inferior to that attainable by use of the traditional saturable absorbers such as Cr4+:YAG, Cr2+:ZnS, or SESAM, in terms of average output power, pulse duration as well as pulse energy. In fact, up to now, only with a Tm:KLuW laser at 1.93 μm or with an Er:Lu2O3 laser at 2.84 μm, could average output power in 1-W level be produced by MoS2 passive Q-switching [12, 15]. For Yb- or Nd-ion lasers operating in the more common 1-μm spectral region, apart from an Yb:LGGG mixed garnet laser that was passively Q-switched by a MoS2 saturable absorber mirror (SAM), and that was capable of generating an output power of 0.6 W (pulse energy of 1.8 μJ and duration of 182 ns) [8], the pulsed output power produced is still limited to a 0.3-W level (pulse energy of ~1 μJ, and pulse duration longer than 200 ns) [7, 12].
To evaluate the capability of multi-layer MoS2 in passively Q-switching solid-state lasers in the 1-μm region to produce high-power, short-duration pulsed radiation, it is necessary to explore other laser materials that are more suitable for passive Q-switching with such two-dimensional layered MoS2 acting as saturable absorber. In this paper we report on the passive Q-switching performance of an Yb:LuPO4/MoS2 laser. This relatively new Yb-ion crystal has exhibited very promising performance in Cr4+:YAG or GaAs passively Q-switched laser operation [16–19]. The miniature laser was built with a 5 mm long plane-parallel cavity, consisting of an 1.0 mm thick Yb:LuPO4 crystal plate and a sapphire-based few-layer MoS2 absorber. We demonstrated that the passively Q-switched miniature laser was able to operate efficiently over a wide output coupling range from T = 5% to T = 60%; and was capable of generating an average output power in excess of 2 W with a slope efficiency of 50%; the largest pulse energy and shortest pulse duration were 4.8 μJ and 61 ns, while the highest pulse repetition rate could reach 870 kHz. These results represent a significant progress in the development of solid-state lasers in the 1-μm region that are passively Q-switched with multi-layer MoS2 saturable absorber. The results demonstrated here also reveal the great potential of exploring new saturable absorbers in these two-dimensional transition metal dichalcogenides.
2. Description of experiment
The few-layer MoS2 sample utilized was commercially available (Sixcarbon Tech, Shenzhen, China). It was prepared on a 0.35 mm thick sapphire substrate by the CVD method. The Yb:LuPO4 crystal plate, which was 1.0 mm in thickness (along the a crystallographic axis), having an Yb-ion concentration of 15 at. % (1.85 × 1021 cm−3), was grown from spontaneous nucleation in high-temperature solution. The Yb:LuPO4/MoS2 laser was fabricated employing a 5 mm long plane-parallel cavity, formed with a plane reflector that was coated for high reflectance at 1010−1200 nm (≥ 99.8%) and for high transmittance at 975 nm (> 95%), and a plane output coupler whose transmittance (output coupling) could be chosen in a range from T = 5% to T = 60%. In the resonator the Yb:LuPO4 crystal plate, which was fixed on a copper heat-sink, was placed close to the reflector, while the MoS2 sample was positioned between the laser crystal and the output coupler. The laser was pumped by a 975-nm fiber-coupled diode laser (fiber core diameter of 105 μm and NA of 0.22). The pumping beam was first focused and then was coupled through the reflector mirror into the laser crystal with a beam spot radius of about 70 μm.
Yb:LuPO4 crystal possesses some desirable spectroscopic properties, making it very attractive in applications for making efficient continuous-wave (cw) or passively Q-switched compact lasers longitudinally pumped by popular InGaAs diode lasers emitting around 975 nm. Its strongest absorption peak is found locating at 975.0 nm for σ polarization, with an absorption cross-section amounting to 2.7 × 10−20 cm2; whereas for π polarization the strongest absorption, having a cross-section of 2.1 × 10−20 cm2, occurs at 985.0 nm, but the absorption cross-section at 975.0 nm drops to about 0.70 × 10−20 cm2 [20]. This yields an averaged absorption cross-section of 1.7 × 10−20 cm2 for unpolarized pumping radiation at 975 nm that is usually encountered in practice, as was the case in the current experiment. Differing from the case of absorption, the strongest emission peak occurs for π polarization at 985.0 nm (cross section of 3.0 × 10−20 cm2), compared to that at 975 nm for σ polarization (cross section of 2.4 × 10−20 cm2) [20]. It should be stressed that for usual laser action the strongest emission peak, for either π or σ polarization, is of little significance because of the presence of extremely large resonant absorption losses; what is important is the emission band peaked at about 1001 nm with a maximum cross-section of 2.0 (or 1.9) × 10−20 cm2 for π (or σ) polarization, and what is more important for π-polarized laser operation under high output coupling conditions, just as the case of the current experiment, proves to be the emission sideband ranging roughly from 1010 to 1020 nm, with emission cross-section decreasing from 1.3 to 0.7 × 10−20 cm2 [20]. Stimulated emission cross-sections of such magnitudes, along with a fluorescence lifetime of 0.83 ms [21], make this crystal very suitable for applications in passively Q-switched lasers.
3. Results and discussion
Figure 1(a) shows the transmission spectrum in the 1000−1200 nm region for the sapphire based few-layer MoS2 sample (MoS2/Sapphire), a sapphire plate (0.35 mm thick), and the MoS2 film. The intrinsic transmission of the few-layer MoS2 film was determined by use of the relationship T (MoS2) = T (MoS2/Sapphire)/T (Sapphire) [12]. Illustrated as the inset to Fig. 1(a) is the Raman spectrum measured for the MoS2/Sapphire sample, from which the two characteristic Raman active vibration modes for bulk MoS2, viz., the in-plane E12g mode at 383.5 cm−1 and the out-of-plane A1g mode at 408.6 cm−1 [22], are seen to appear with a slight red-shift. The small deviation in mode frequency arises from the structural modification of the few-layer MoS2 compared to the bulk material. From the intrinsic transmission spectrum of the MoS2 film, one obtains that for the range of 1010−1040 nm over which the pulsed laser action occurred, the initial transmission was T0 = 92.5%.
Fig. 1 (a) Transmission spectra for the MoS2/Sapphire sample, a sapphire plate, and the MoS2 film. Inset: Raman spectrum for the MoS2/Sapphire sample. (b) Transmission versus incident intensity measured by z-scan method for the MoS2/Sapphire. (c) AFM image of the MoS2 film. (d) Surface height variation of the MoS2 film along a straight line marked in (c).
Figure 1(b) shows the transmission (T) versus incident intensity (I) measured for the MoS2/Sapphire by the standard z-scan technique, employing a mode-locked ps Nd fiber laser at 1064 nm. Fitting the measured data to the relation [23], T(I) = 1 − ΔTexp(−I/Isat) − Ans yields a modulation depth of ΔT = 3.1%; a saturation intensity of Isat = 1.08 kW/cm2; and a non-saturable absorption loss of Ans = 27.7% . Presented in Fig. 1(c) is an AFM (atomic force microscope) image of the few-layer MoS2, the surface height variation along the straight line marked is shown in Fig. 1(d), the difference in film thickness being less than 2.5 nm.
Employing the very compact 5-mm-long plane-parallel resonator, we achieved efficient passively Q-switched operation of the Yb:LuPO4/MoS2 laser, with the output coupling changed over a wide range from T = 5% to T = 60%. This turns out to be rather unusual, given the fact that in all previous work on Yb-ion lasers passively Q-switched with MoS2, the output couplings used were limited to T ≤ 10% [8–12]. As is known, a greater output coupling is in general more desirable for passively Q-switched lasers; it cannot only benefit the generation of higher-energy, shorter-duration pulses, but can also prevent possible optical damage to the intracavity elements. The optimal output coupling was found to be T = 30%, which resulted in the most efficient pulsed laser operation. In all cases the laser oscillation obtained was π-polarized (E//c axis).
Figure 2 depicts the average output power versus absorbed pump power (Pabs), produced from the passively Q-switched Yb:LuPO4/MoS2 laser operating under different output coupling conditions of T = 10%, 30%, and 50%. The amount of Pabs is determined from the incident pump power by Pabs = ηaPin, here ηa designates the small-signal absorption, it was measured to be 0.90 for the 1.0 mm thick laser crystal. In the case of T = 10%, the Q-switched lasing threshold was 1.17 W; it increased to 1.80 W and 2.24 W for T = 30% and T = 50%, respectively. Under the optimal output coupling of T = 30%, an average output power of 2.06 W was produced at Pabs = 6.53 W, the optical-to-optical efficiency was 31.5%, while the slope efficiency was 50%. One sees that even under an output coupling as high as T = 50%, very efficient Q-switched operation could be realized, generating a maximum output power of 1.53 W with a slope efficiency of 42%.
Fig. 2 Average output power as a function of Pabs, measured for the Yb:LuPO4/MoS2 laser under output coupling conditions of T = 10%, 30%, and 50%.
The wavelengths at which the passively Q-switched laser action occurred was found to depend critically on the output coupling, but only varied slightly with pumping level. Illustrated in Fig. 3 are the lasing spectra measured at Pabs = 4.0 W for the three different output couplings. In the case of T = 10%, the laser could oscillate simultaneously at several wavelengths ranging from 1036.0 to 1041.0 nm, due to the gain competition as well as the relatively low overall losses. Increasing the output coupling (and hence the overall losses) would force the laser to oscillate at shorter wavelengths where higher gain is available. In the case of T = 30%, the laser action occurred at 1020.8 nm; while for T = 50%, the laser oscillation shifted to 1010.5 nm.
As is expected for usual passive Q-switching, the pulse repetition rate increased with pumping level. The variation of repetition rate with pump power is depicted in Fig. 4(a) for different output couplings. In the case of T = 10%, the repetition rate increased from 167 kHz measured not far above threshold, to 735 kHz at Pabs = 6.53 W, the highest pump level applied in the experiment. Under the optimum output coupling of T = 30%, the repetition rate rising became much slower at high pumping level, reaching 429 kHz at the same highest pump power. In the case of T = 50%, the repetition rate increased rapidly from 250 kHz just above threshold to 870 kHz at Pabs = 6.53 W. One notices that at a certain pump power, the repetition rate reached under the largest output coupling (T = 50%) proved to be the highest. Such a seemingly unusual behavior might be attributed to the fact that the π-polarized emission cross-section at 1010.5 nm (lasing wavelength for T = 50%) is roughly two times greater than at 1021 nm or at 1040 nm [20], where laser action occurred in the case of T = 30% or T = 10%.
Fig. 4 Pulse repetition rate (a) and pulse energy (b) versus Pabs for passively Q-switched operation under different output coupling conditions.
From the measured results of average output power (Fig. 2) and of repetition rate, the pulse energy could be calculated. The results are illustrated in Fig. 4(b). The pulse energies achievable under conditions of T = 50% were low, which was connected to the high repetition rates. One notes that the pulse energy generated in the case of T = 10% or of T = 50% would become roughly fixed, as the pump power exceeded a certain level. This behavior is common for passively Q-switched lasers. However, the situation for T = 30% seemed quite different; the pulse energy increased continually with pump power, reaching 4.8 μJ at the highest pump power applied in the experiment.
Figure 5 shows the dependence of pulse duration (FWHM) on absorbed pump power, measured for Q-switched operation under different output couplings. Upon increasing the pump power from threshold, the pulse duration became shortened rapidly at the initial stage; then dropped slowly; and eventually reached a certain value that remained nearly unchanged. This variation behavior is typical of passive Q-switching by “fast” saturable absorbers, as found in Yb lasers passively Q-switched with MoS2 [10–12]. The shortest pulse duration measured in the cases of T = 10%, 30%, and 50% were, respectively, 131, 83, and 61 ns.
Fig. 5 Pulse duration versus Pabs for passively Q-switched operation under different output coupling conditions.
We recorded a pulse train at Pabs = 6.53 W (the highest pumping level) for T = 30% or T = 50%, and at Pabs = 3.31 W for T = 10%, which are presented in Fig. 6(a); while their corresponding individual pulse profiles are depicted in Fig. 6(b) (the pulse profile for T = 10% was measured at Pabs = 6.53 W). We found in our experiment that the stability of Q-switched operation achieved under a lower output coupling, e.g., T = 5% or T = 10%, was poorer than obtained under higher output coupling conditions. Interestingly, it was also found that the optimum output coupling, T = 30%, under which the lasing efficiency and output power were the highest, seemed to result in the most stable passively Q-switched action. This point is clearly seen in Fig. 6(a); the pulse amplitude fluctuations were estimated to be about ± 3% (for T = 10%), ± 3% (for T = 30%), and ± 5% (for T = 50%), with the percent difference between the maximum and minimum amplitudes being about 6% (for T = 10%), 6% (for T = 30%), and 10% (for T = 50%); whereas the timing jitters were about ± 14% (for T = 10%), ± 7% (for T = 30%), and ± 8% (for T = 50%).
Fig. 6 Pulse trains (a) and pulse profiles (b) recorded at the highest pump level (Pabs = 6.53 W) for passively Q-switched operation under different output coupling conditions (the pulse train for T = 10% was recorded at Pabs = 3.31 W).
The quality of the laser beam was examined. Figure 7 illustrates the variation of spot radius with propagation distance, measured at Pabs = 4.4 W (output power of 1.0 W) in the case of T = 30%. The inset shows a laser beam pattern. The beam quality factor, M2, was determined to be 1.16 in the horizontal direction (x), and 1.25 in the vertical direction (y).
Fig. 7 Spot radius of the laser beam as a function of propagation distance, measured at Pabs = 4.4 W in the case of T = 30%. Inset: the beam pattern.
Table 1 lists the primary parameters characterizing the performance of a passively Q-switched laser, for the current Yb:LuPO4/MoS2 laser and for those Yb-ion lasers that have been demonstrated so far with MoS2 as saturable absorber. The results for the Yb:YAG/MoS2 laser are not included, because of its exceptionally long pulse duration (minimum of 12 μs) [9]. The notations appearing in the table are: Pmax, the maximum average output power; PRR, the highest pulse repetition rate; Ep, the maximum pulse energy; tp, the shortest pulse duration; Pp, the maximum peak power; η, slope efficiency; and λ, lasing wavelength. One can notice that in terms of nearly all the major characteristic parameters, the performance of the current Yb:LuPO4/MoS2 laser turns out to be much superior to those Yb-ion lasers reported previously [8–12]. It may also be worth pointing out that the passively Q-switched operation under high output coupling conditions (T ≥ 30%) could remain stable, with the pump power raised over the highest level applied (Pabs = 6.53 W), enabling further scaling of both output power and pulse energy, as suggested by the results shown in Figs. 2 and 6(a).
Table 1. Comparison of Performance for Yb-ion Lasers Passively Q-switched by MoS2 Saturable Absorber
With the help of a theoretical model for passively Q-switched lasers using semiconductor saturable absorbers [24], we made an attempt to estimate the pulse energy and pulse duration attainable in the case of T = 30%. The parameters and their numbers used in the calculation are (using the same symbols as in [24]): lout = −ln(1−T) = 0.36; lp = −2ln(1−Ans) = 0.65; TR = 2Lc/c = 0.04 ns (the optical length of the cavity: Lc = 6 mm); q0 = ΔT = 0.031; the photon energy hν = 1.96 × 10−19 J (lasing wavelength of 1021 nm); for a quasi-three-level laser, σL = σem + σabs = 0.8 × 10−20 cm2 at 1021 nm [20]; and the lasing mode radius wL = 50 μm. The calculated pulse energy Ep ≈15 μJ, while the pulse duration tp ≈5 ns. One sees a large deviation between the theoretical prediction and the experimental results, which might imply that a more appropriate model needs to be built, taking into account the quasi-three-level nature of the Yb-ion laser as well as the fast recovery feature of the saturable absorber.
Compared with the traditional saturable absorbers such as Cr4+:YAG and SESAMs, which can result in few-ns or even sub-ns pulses in compact lasers, the pulse duration achieved with few-layer MoS2 in the current experiment proves to be still fairly long, leaving much room for further improvement. The passive Q-switching performance of Yb- or Nd-ion lasers, achievable with MoS2 or other transition metal dichalcogenides, will be further improved, with pulse duration shortened to few-ns and with output power scaled to multi-watt level, by optimizing the resonator parameters; by properly choosing or searching for more suitable laser materials; by improving the optical quality as well as the thermal properties of 2D materials; and more importantly, by carefully choosing the modulation depth (layer numbers).
4. Summary
In conclusion, an Yb:LuPO4 miniature crystal laser that was formed with a 5 mm long plane-parallel cavity, and was passively Q-switched by a few-layer MoS2 saturable absorber, was demonstrated. An average output power of 2.06 W at 1020.8 nm was generated at a pulse repetition rate of 429 kHz, with an optical-to-optical efficiency of 31.5% and a slope efficiency of 50%; the resulting pulse energy, duration, and peak power were 4.8 μJ, 83 ns, and 57.8 W, respectively. While operating at a shorter wavelength of 1010.5 nm, the laser could produce an average output power of 1.53 W at a repetition rate as high as 870 kHz, with a pulse duration amounting only to 61 ns. In comparison with the MoS2 passively Q-switched Yb- or Nd-ion lasers operating in the 1-μm region developed thus far, the passive Q-switching performance demonstrated with the Yb:LuPO4/MoS2 laser represents a substantial improvement, in terms of nearly all the major parameters characterizing a passive Q-switching laser action. The results achieved in our experiment also reveal the great potential of two-dimensional MoS2 and other transition metal dichalcogenides for applications in developing multi-Watt, high-repetition-rate, pulsed solid-state lasers.
Funding
National Natural Science Foundation of China (NSFC) (11574170).
References and links
1. K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, “Atomically thin MoS2: a new direct-gap semiconductor,” Phys. Rev. Lett. 105(13), 136805 (2010). [CrossRef] [PubMed]
2. K. He, C. Poole, K. F. Mak, and J. Shan, “Experimental demonstration of continuous electronic structure tuning via strain in atomically thin MoS2.,” Nano Lett. 13(6), 2931–2936 (2013). [CrossRef] [PubMed]
3. S. Wang, H. Yu, H. Zhang, A. Wang, M. Zhao, Y. Chen, L. Mei, and J. Wang, “Broadband few-layer MoS2 saturable absorbers,” Adv. Mater. 26(21), 3538–3544 (2014). [CrossRef] [PubMed]
4. K. Wang, J. Wang, J. Fan, M. Lotya, A. O’Neill, D. Fox, Y. Feng, X. Zhang, B. Jiang, Q. Zhao, H. Zhang, J. N. Coleman, L. Zhang, and W. J. Blau, “Ultrafast saturable absorption of two-dimensional MoS2 nanosheets,” ACS Nano 7(10), 9260–9267 (2013). [CrossRef] [PubMed]
5. 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]
6. T. Lin, H. Sun, X. Wang, D. Mao, Y. Wang, L. Li, and L. Duan, “Passively Q-switched Nd:YAG laser with a MoS2 solution saturable absorber,” Laser Phys. Lett. 25(12), 125805 (2015). [CrossRef]
7. H. Liu, Z. Sun, X. Wang, Y. Wang, and G. Cheng, “Several nanosecond Nd:YVO4 lasers Q-switched by two dimensional materials: tungsten disulfide, molybdenum disulfide, and black phosphorous,” Opt. Express 25(6), 6244–6252 (2017). [CrossRef] [PubMed]
8. 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), A25–A29 (2015). [CrossRef]
9. Y. Zhan, L. Wang, J. Y. Wang, H. W. Li, and Z. H. Yu, “Yb:YAG thin disk laser passively Q-switched by a hydro-thermal grown molybdenum disulfide saturable absorber,” Laser Phys. 25(2), 025901 (2015). [CrossRef]
10. Y. Sun, J. Xu, S. Gao, C. Lee, H. Xia, Y. Wang, Z. You, and C. Tu, “Wavelength-tunable, passively Q-switched Yb3+:Ca3Y2(BO3)4 solid state laser using MoS2 saturable absorber,” Mater. Lett. 160, 268–270 (2015). [CrossRef]
11. Y. Sun, J. Xu, Z. Zhu, Y. Wang, H. Xia, Z. You, C. Lee, and C. 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]
12. J. M. Serres, P. Loiko, X. Mateos, H. Yu, H. Zhang, Y. Chen, V. Petrov, U. Griebner, K. Yumashev, M. Aguiló, and F. Díaz, “MoS2 saturable absorber for passive Q-switching of Yb and Tm microchip lasers,” Opt. Mater. Express 6(10), 3262–3273 (2016). [CrossRef]
13. P. Ge, J. Liu, S. Jiang, Y. Xu, and B. Man, “Compact Q-switched 2 μm Tm:GdVO4 laser with MoS2 absorber,” Photon. Res. 3(5), 256–259 (2015). [CrossRef]
14. L. C. Kong, G. Q. Xie, P. Yuan, L. J. Qian, S. X. Wang, H. H. Yu, and H. J. Zhang, “Passive Q-switching and Q-switched mode-locking operations of 2 μm Tm:CLNGG laser with MoS2 saturable absorber mirror,” Photon. Res. 3(2), A47–A50 (2015). [CrossRef]
15. 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]
16. J. Liu, L. Wang, W. Han, H. Xu, D. Zhong, and B. Teng, “Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers,” Opt. Mater. 60, 114–118 (2016). [CrossRef]
17. L. Wang, W. Han, H. Xu, D. Zhong, B. Teng, and J. Liu, “Passively Q-switched oscillation at 1005−1012 nm of a miniature Yb:LuPO4 crystal rod laser,” Laser Phys. Lett. 14(4), 045807 (2017). [CrossRef]
18. X. Dou, L. Wang, Y. Ma, W. Han, H. Xu, D. Zhong, B. Teng, and J. Liu, “Generation of pulsed laser radiation at 1002 nm with a quantum defect of 2.6%,” IEEE Photonics J. 9(3), 1503208 (2017). [CrossRef]
19. X. Dou, L. Wang, W. Han, H. Xu, D. Zhong, B. Teng, and J. Liu, “Near-IR 1-μm high-repetition-rate pulsed radiation generated with an Yb:LuPO4 miniature crystal rod laser,” Opt. Commun. 420, 90–94 (2018). [CrossRef]
20. J. Liu, W. Han, X. Chen, D. Zhong, B. Teng, C. Wang, and Y. Li, “Spectroscopic properties and continuous-wave laser operation of Yb:LuPO4 crystal,” Opt. Lett. 39(20), 5881–5884 (2014). [CrossRef] [PubMed]
21. L. D. DeLoach, S. A. Payne, L. L. Chase, L. K. Smith, W. L. Kway, and W. F. Krupke, “Evaluation of absorption and emission properties of Yb3+ doped crystals for laser applications,” IEEE J. Quantum Electron. 29(4), 1179–1191 (1993). [CrossRef]
22. P. Tonndorf, R. Schmidt, P. Böttger, X. Zhang, J. Börner, A. Liebig, M. Albrecht, C. Kloc, O. Gordan, D. R. T. Zahn, S. Michaelis de Vasconcellos, and R. Bratschitsch, “Photoluminescence emission and Raman response of monolayer MoS2, MoSe2, and WSe2,” Opt. Express 21(4), 4908–4916 (2013). [CrossRef] [PubMed]
23. B. Chen, X. Zhang, K. Wu, H. Wang, J. Wang, and J. Chen, “Q-switched fiber laser based on transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2.,” Opt. Express 23(20), 26723–26737 (2015). [CrossRef] [PubMed]
24. G. J. Spühler, R. Paschotta, R. Fluck, B. Braun, M. Moser, G. Zhang, E. Gini, and U. Keller, “Experimentally confirmed design guidelines for passively Q-switched microchip lasers using semiconductor saturable absorbers,” J. Opt. Soc. Am. B 16(3), 376–388 (1999). [CrossRef]
