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Abstract
The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of Nd:Ca0.7La0.3Mg0.3Al11.7O19 (CLnA) crystal were recorded at room temperature. The Judd-Ofelt parameters Ω2, Ω4 and Ω6 were calculated to be 0.80×10−20 cm2, 3.83×10−20 cm2 and 2.71×10−20 cm2, respectively. The spontaneous transition rates, branching ratios and the radiative lifetime were calculated for the 4F3/2 excited state. The emission cross section is 4.01×10−20 cm2 at 1052 nm for σ-polarization and 0.96×10−20 cm2 at 1052 nm for π-polarization, respectively. Continuous-wave (CW) laser operations of a-cut and c-cut Nd:Ca0.7La0.3Mg0.3Al11.7O19 crystals have been demonstrated.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Nd3+-doped laser crystals provide an efficient way to generate high-power and low-threshold laser around 1 µm, which can be applied in various fields including medicine, industry, military and scientific researches [1–3]. Compared with Yb3+-doped crystals, Nd3+-doped crystals have relative narrow emission band-width, which limits the application in ultra-short pulse generation [4]. However, Nd3+-doped disordered crystals are promising in realizing ultrafast mode-locked laser due to the inhomogeneous broadening of the emission spectra. Up to now, a great deal of Nd3+ lasers has been developed based on various host disordered crystals, such as CNGG [5], CLNGG [6], CaYAlO4 [7], CaGdAlO4 [8], Y3ScAl4O12 [9], Ca2Ga2SiO7 [10], LaMgAl11O19 [11], Sr0.7La0.3Mg0.3Al11.7O19 [12], SrLaGa3O7 [13], Ca3La2(BO3)4 [14] and so on.
Nd3+-doped calcium-lanthanum-aluminate (Nd:Ca1-xLaxMgxAl12-xO19, CLnA), which is formed from calcium (CaAl12O19) and lanthanide (LaMgAl11O19) hexaaluminates, has a magnetoplumbite structure PbFe12O19 (space group P63/mmc) where Mg2+ ions substitute for Al3+ ions for charge compensation [15,16]. In CLnA crystal, Nd3+ ions are occupied in two different sites, which leads to inhomogeneous broadening of the fluorescence spectra. In 1988, Gbehi et al. [15] reported the growth of CLnA crystal using the melting zone technique and found that the fluorescence spectra of CLnA crystal and Nd:LaMgAl11O19 crystal are very similar. However, no any detailed report about the polarized spectral properties can be found in [15].
In this paper, we studied the polarized absorption and emission spectra of CLnA crystal. Using Judd-Ofelt theory, the spectral parameters of Nd3+ ions in CLnA crystal were obtained. The CW laser operation of CLnA crystal was demonstrated by LD pumping.
2. Experiments
The CLnA crystal was grown by the Czochralski method. On the basis of spectral properties previously performed on Nd:LaMgAl11O19 [17] and Nd:Sr0.7La0.3Mg0.3Al11.7O19 [18] crystals, the Nd3+ concentration of 5 at.% has been selected in CLnA crystal. High purity (>99.999%) La2O3, MgO, CaCO3, Al2O3 and Nd2O3 powders were used as raw materials. They were dried and weighed according to the formula Ca0.7La0.25Nd0.05Mg0.3Al11.7O19. After the compounds were ground and thoroughly mixed, they were pressed into pieces and then sintered at 1300 °C for 24 h in the air. The charge was loaded into an iridium crucible for crystal growth. A LaMgAl11O19 crystal with a <100> orientation was used as the seed.
The crystal sample for spectroscopic measurements was cut from the as-grown CLnA crystal, and the surfaces perpendicular to the <100> growth axis were polished. The Nd3+ ions concentration in the sample was 1.44×10−20 ions/cm3. The polarized absorption spectra was measured by a UV–VIS–NIR spectrophotometer (Model Cary-5000, Varian, USA) with a spectral interval of 1 nm at room temperature. The fluorescence spectra with a spectral interval of 0.5 nm, as well as the decay curve of the 4F3/2 multiplet, were recorded using a FLS980 spectrometer (Edinburgh) under 796 nm excitation. All the measurements were taken at room temperature.
Laser experimental setup of LD-pumped continuous-wave CLnA crystal lasers is shown schematically in Fig. 1. Two laser gain media were CLnA crystals cut along a and c crystalline axis with dopant concentration of 5% and dimensions of 3 × 3 × 6 mm3. The pump source in our experiment was a fiber-coupled laser diode (LD) centered around 800 nm with a core diameter of about 200 µm and a numerical aperture of 0.22. The pump light delivered from the fiber was firstly paralleled by a convex lens with focal length of 50 mm, and then was focused into the laser crystal with a spot radius of ∼150 µm by a f = 150 mm convex lens. The input mirror M1 was coated with high reflectivity for laser wavelength and high transmission for the pump light. Three different output couplers (OCs), with transmissions of 5%, 10% and 15% at 1053 nm, were used in the experiments. The cavity length was about 15 mm.
3. Results and discussion
The polarized absorption cross section spectra of CLnA crystal in the wavelength region of 300-1000 nm were recorded at room temperature and shown in Fig. 2. Nine absorption bands are corresponding to transitions from the ground state 4I9/2 to the various excited states of Nd3+ ions. Owing to the anisotropy of the crystal, the absorption spectra show strong polarization dependence and the σ-polarization absorption cross section is much larger than that of π-polarization. From the Fig. 2, we can see that the prominent absorption peaks around 583, 729, and 792 nm correspond to the transitions of 4I9/2→4G5/2 + 2G7/2, 4I9/2→4F7/2 + 4S3/2, and 4I9/2→4F5/2 + 2H9/2, respectively. The absorption cross-sections were calculated to be 2.18×10−20 cm2 at 792 nm for σ polarization and 0.40×10−20 cm2 at 795 nm for π polarization, with full width at half maximum (FWHM) of 11.2 nm and 20.4 nm. The absorption cross section for σ polarization is larger than the value of La0.95Nd0.05MgAl11O19 (1.7×10−20 cm2 at 795 nm [17]) and Sr0.7La0.25Nd0.05Mg0.3Al11.7O19 (8.6×10−21 cm2 at 792 nm [18]). The FWHMs of CLnA crystal are larger than that of Nd:CaGdAlO4 crystal (5 nm for σ polarization, 4 nm for π polarization [19]) and Nd:CaYAlO4 crystal (both 5 nm for σ and π polarization [20]). The broad bandwidth means that CLnA crystal is more suitable for diode pumping and indicates an inhomogeneous broadening behavior, which is probably due to the disordered structure of CLnA crystal.
Fig. 2. Polarized absorption cross-sections of CLnA crystal at room temperature. (1 - 2L15/2+4D1/2+2I11/2+4D5/2+4D3/2, 2 - 2P1/2, 3 - 2K15/2+2D3/2+4G11/2+2G9/2, 4 - 4G9/2+4G7/2+2K13/2, 5 - 4G5/2+2G7/2, 6 - 4F9/2, 7 - 4F7/2+4S3/2, 8 - 2H9/2+4F5/2, 9 - 4F3/2).
The Judd-Ofelt theory [21,22] was applied to analyze the polarized absorption spectra, and then the branching ratios of the transitions from the upper laser level 4F3/2 and the radiative lifetime of the level can be evaluated. The detailed calculation procedures are the same as Ref. [23,24]. The reduced matrix elements used for absorption and emission transitions can be consulted in [23] and [25], respectively. In Table 1, average wavelength of different transition, the line strength of experiment and calculation, and RMS deviation of Nd3+ ion in CLnA crystal are given. The value of RMS deviations is 0.277×10−20 cm2 and 0.182×10−20 cm2 for σ-polarization and π-polarization, which indicates a good agreement between the experimental and the calculated spectral intensities.
Table 1. The average wavelength of different transition, the line strength of experiment and calculation, and RMS deviation of Nd3+ ion in CLnA crystal
Three J-O intensity parameters of different Nd3+ doped crystals are listed in Table 2. For CLnA crystal, the effective JO intensity parameters were calculated by Ω= (2Ωσ+ Ωπ)/3, and the Ω2,4,6 were obtained to be 0.80×10−20 cm2, 3.83×10−20 cm2, and 2.71×10−20 cm2, respectively. In general, Ω2 is related to the chemical bonding, structural change and symmetry of the ligand field around Nd3+ ion site. The result indicates that the covalency of CLnA is larger than that of Nd:YAG, but lower than that of Nd3+ doped LaMgAl11O19, Sr0.7La0.3Mg0.3Al11.7O19, LuVO4, Ca2Ga2SiO7 and Ca2Ga2SiO7 crystal. Ω4/Ω6 is the spectroscopic quality factor which depends on the rigidity of the host matrix [29]. The spectroscopic quality Ω4/Ω6 of CLnA crystal is 1.41 (more than 1), suggesting that CLnA crystal is a promising medium for efficient laser operation.
Table 2. The J-O intensity parameters of different Nd3+ doped crystals.
Based on the obtained intensity parameters, the calculated radiative transition rates, branching ratios and the radiative lifetimes of 4F3/2→4I9/2, 4F3/2→4I11/2, 4F3/2→4I13/2 and 4F3/2→4I15/2 transitions of CLnA crystal are given in Table 3. We can see that the branching ratio of the 4F3/2→4I9/2 transition is larger than that of the 4F3/2→4I11/2 transition for each polarization. The radiative lifetime of 4F3/2 energy level was calculated to be 364 µs, which is smaller than the value of La0.95Nd0.05MgAl11O19 (401 µs [17]) and Sr0.7La0.25Nd0.05Mg0.3Al11.7O19 (500 µs [18]), but much larger than the value of other oxide crystals, such as Nd:CaNb2O6 (167 µs [30]), Nd:CaYAlO4 (114 µs [20]), Nd:Bi4Ge3O12 (293 µs [31]) and Nd:GdNbO4 (194 µs [32])). The results indicate that CLnA crystal owns a higher energy storage ability.
Table 3. Calculated radiative transition rates, branching ratios, radiative lifetimes for different transition levels of CLnA crystal.
The polarized fluorescence spectra of the CLnA crystal in the range of 850-1450 nm were measured under 796 nm excitation. The stimulated emission cross section, which is one of the most important parameters affecting the potential laser performance, can be calculated from the fluorescence spectra using the Füchtbauere Ladenburg (F–L) formula [33], as presented in Fig. 3. Three emission bands centered at 850-940 nm, 1040-1160 nm and 1320-1440 nm are assigned to the transitions of 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2, respectively. The most intense emission appears at 1052 nm and the experimental 4F3/2→4I11/2 branching ratios were calculated to be 50.64% for σ polarization and 45.78% for π polarization. The intrinsic uncertainty of Judd-Ofelt calculation (±20%) [34] is large enough to explain the deviation observed between the experimental and calculated branching ratios. The calculated emission cross section is 4.01×10−20 cm2 for σ-polarization and 0.96×10−20 cm2 for π-polarization both at 1052 nm, respectively, with FWHM of 7.5 and 7.3 nm. The FWHM is little larger than the value of Nd:LaMgAl11O19 (6.6 nm for σ polarization [17]). The broad bandwidth confirms an inhomogeneous broadening behavior, which accounts for the disordered structure of CLnA crystal. In 2000, Yang et al. [35] reported a self-mode locked Nd:LaMgAl11O19 laser pumped by a laser diode with the transform-limited pulses of 631 fs duration. Considering the spectral parameters of CLnA crystal, one can estimate the tunable laser operation with tunable region of tens of nanometers and mode-locked femtosecond laser operation from CLnA crystal.
Figure 4 shows the fluorescence decay curve of 4F3/2 multiplet. The fluorescence lifetime was calculated to be 333 µs by a single exponential fitting, which is comparable with the value of La0.95Nd0.05MgAl11O19 (321 µs [17]), Sr0.7La0.25Nd0.05Mg0.3Al11.7O19 (372 µs [18]) and Nd:SrLaGa3O7 (318 µs [36]) but much longer than that of Nd:YAG (248 µs [37]), Nd:YVO4 (87 µs [38]), Nd:CaGdAlO4 (123 µs [19]) and Nd:CaYAlO4 (129 µs [20]). According to the radiative lifetime from J-O theory, the luminescent quantum efficiency of the 4F3/2 level was calculated to be 91.5% by the equation of η=τ/τrad. The results show that CLnA crystal is a promising gain medium for solid-state laser generation.
The output power characteristics with respect to absorbed pump power of a-cut CLnA laser is shown in Fig. 5(a). The highest output power of 5.40 W was obtained with a OC of T = 5% under the absorbed pump power of 11.51 W, corresponding to an optical-to-optical efficiency of about 46.9% and a slope efficiency of 47.7%. The laser threshold was measured to be 107 mW of absorbed power. When the transmission of output coupler was 10% and 15%, the maximum output power changed to 5.08 W and 4.79 W, while the corresponding slope efficiency became 45.2% and 43.0%, respectively. The maximum output power and slope efficiency of CLnA are larger than those of Nd:LaMgAl11O19 (1.71 W, 40.4% [17]), but lower than those of Nd:Sr0.7La0.3Mg0.3Al11.7O19 (6.9 W, 50% [18]). At maximum, the peak wavelength was measured to be 1052.76 nm (see Fig. 5(b)). There was no pump saturation in our experiments, which indicates the output power can be further scaled with high pump power.
Fig. 5. (a) The dependence of output power on absorbed pump power of a-cut CLnA laser and (b) The corresponding laser spectrum with peak at 1052.76 nm.
The experimental results of the c-cut CLnA crystal are shown in Fig. 6(a). Using the output coupler with transmission of 10%, a maximum output up to 4.78 W was achieved with threshold of 429 mW of absorbed power, which led to a slope efficiency of about 30.5% by linear fit. Using the output coupler with transmission of 15%, the maximum output power decreased to be 4.75 W and the corresponding slope efficiency was linearly fitted to be about 31.2%. Using the output coupler with transmission of 5%, the maximum output power further decreased to be 4.26 W with a slope efficiency of about 27.1%. From the output power curves in Fig. 5(a) and Fig. 6(a), one can find the a-cut CLnA crystal has better laser performance than the c-cut CLnA crystal. The saturation effect at high pump power of c-cut CLnA crystal should be explained by thermal lensing effect inside the c-cut CLnA crystal, which led to the laser operation at stability limit or even unstable any more. Figure 6(b) shows the laser wavelength registered at maximum output power with a peak at 1052.84 nm.
Fig. 6. (a)The dependence of output power on absorbed pump power of c-cut CLnA laser and (b) The corresponding laser spectrum with peak at 1052.84 nm.
4. Conclusion
In summary, the polarized absorption spectra, the polarized fluorescence spectra, and the fluorescence decay curve of CLnA crystal were recorded at room temperature. The absorption cross-sections are 2.18×10−20 cm2 at 792 nm for σ polarization and 0.40×10−20 cm2 at 795 nm for π polarization with FWHM of 11.2 nm and 20.4 nm. The effective Judd-Ofelt parameters Ω2, Ω4 and Ω6 were calculated to be 0.80×10−20 cm2, 3.83×10−20 cm2 and 2.71×10−20 cm2, respectively. The spontaneous transition rates, branching ratios and the radiative lifetime were calculated for the 4F3/2 excited state. The emission cross section is 4.01×10−20 cm2 for σ-polarization and 0.96×10−20 cm2 for π-polarization both at 1052 nm with FWHM of 7.5 and 7.3 nm, respectively. The fluorescence lifetime is 333 µs, and the luminescent quantum efficiency of the 4F3/2 level is 70.1%. Continuous-wave laser operation of the a- and c-cut samples under 800 nm laser diode has been demonstrated. Maximum output powers of 5.40 W and 4.78 W were obtained for the a-cut and c-cut samples, corresponding to a slope efficiency of 47.7% and 30.5%, respectively. Improving the laser performance could be realized by optimizing the quality of CLnA crystal.
Funding
National Natural Science Foundation of China (61621001).
Disclosures
The authors declare no conflicts of interest.
References
1. T. J. Kane, W. J. Kozlovshy, and R. I. Byer, “Coherent laser radar at 1.06 µm using Nd:YAG lasers,” Opt. Lett. 12(4), 239–241 (1987). [CrossRef]
2. K. Washio, “Neodymium-doped solid-state lasers and their applications to materials processing,” Mater. Chem. Phys. 31(1-2), 57–66 (1992). [CrossRef]
3. R. Moncorge, B. Chambon, J. Y. Rivoire, N. Garnier, E. Descroix, P. Laporte, H. Guillet, S. Roy, J. Mareschal, D. Pelenc, J. Doury, and P. Farge, “Nd doped crystals for medical laser applications,” Opt. Mater. 8(1-2), 109–119 (1997). [CrossRef]
4. E. Sorokin, M. H. Ober, I. Sorokina, E. Wintner, and A. J. Schmidt, “Femtosecond solid-state lasers using Nd3+-doped mixed scandium garnets,” J. Opt. Soc. Am. B 10(8), 1436–1442 (1993). [CrossRef]
5. A. Agnesi, S. Dell’Acqua, A. Guandalini, G. Reali, F. Cornacchia, A. Toncelli, M. Toncelli, K. Shimamura, and T. Fukuda, “Optical spectroscopy and diode-pumped laser performance of Nd3+ in the CNGG crystal,” IEEE J. Quantum Electron. 37(2), 304–313 (2001). [CrossRef]
6. Z. B. Shi, X. Fang, H. J. Zhang, Z. P. Wang, J. Y. Wang, H. H. Yu, Y. G. Yu, X. T. Tao, and M. H. Jiang, “Continuous-wave laser operation at 1.33 µm of Nd:CNGG and Nd:CLNGG crystals,” Laser Phys. Lett. 5(3), 177–180 (2008). [CrossRef]
7. H. R. Verdun and L. M. Thomas, “Nd:CaYAlO4 – a new crystal for solid-state lasers emitting at 1.08 µm,” Appl. Phys. Lett. 56(7), 608–610 (1990). [CrossRef]
8. A. A. Lagatskii, N. V. Kuleshov, V. G. Shcherbitskii, V. F. Kleptsyn, V. P. Mikhailov, V. G. Ostroumov, and G. Huber, “Lasing characteristics of a diode-pumped Nd3+:CaGdAlO4 crystal,” Quantum Electron. 27(1), 15–17 (1997). [CrossRef]
9. C. Feng, H. N. Zhang, Q. P. Wang, and J. X. Fang, “Dual-wavelength synchronously mode-locked laser of a Nd:Y3ScAl4O12 disordered crystal,” Laser Phys. Lett. 14(4), 045804 (2017). [CrossRef]
10. A. A. Kaminskii, V. A. Karasev, V. D. Dubrov, V. P. Yakunin, B. V. Mill’, and A. V. Butashin, “New disordered Ca2Ga2SiO7:Nd3+ crystal for high-power solid-state lasers,” Quantum Electron. 22(2), 97–98 (1992). [CrossRef]
11. K. S. Bagdasarov, L. M. Dorozhkin, A. M. Kevorkov, Y. I. Krasilov, A. V. Potemkin, A. V. Shestakov, and I. I. Kuratev, “Continuous lasing in La1-xNdxMgAl11O19 crystas,” Quantum Electron. 13(5), 639–640 (1983). [CrossRef]
12. O. Musset, L. Fouquin, and J. P. Boquillon, “Laser emission under flashlamp pumping of a new crystal: Nd-doped strontium-lanthanum-aluminate (Nd:ASL),” Appl. Phys. B 68(2), 181–185 (1999). [CrossRef]
13. A. V. Terentiev, P. V. Prokoshin, K. V. Yumashev, and V. P. Mikhailov, “Passive mode locking of a Nd3+:SrLaGa3O7 laser,” Appl. Phys. Lett. 67(17), 2442–2444 (1995). [CrossRef]
14. Z. B. Pan, H. J. Cong, H. H. Yu, L. Tian, H. Yuan, H. Q. Cai, H. J. Zhang, H. Huang, J. Y. Wang, Q. Wang, Z. Y. Wei, and Z. G. Zhang, “Growth, thermal properties and laser operation of Nd:Ca3La2(BO3)4: A new disordered laser crystal,” Opt. Express 21(5), 6091–6100 (2013). [CrossRef]
15. T. Gbehi, J. Thery, D. Vivien, R. Collongues, G. Dhalenne, and Revcolevschi, “Neodymium sites in Calcium Lanthanide Hexaaluminates, potential laser materials,” J. Solid State Chem. 77(2), 211–222 (1988). [CrossRef]
16. S. Alablanche, A. Kahn-Harari, J. Thery, B. Viana, and D. Vivien, “Structural and optical properties of Calcium Neodymium Hexaaluminates single crystals, potential laser materials,” J. Solid State Chem. 98(1), 105–120 (1992). [CrossRef]
17. Y. X. Pan, S. D. Zhou, J. W. Wang, B. Xu, J. Liu, Q. S. Song, J. Xu, D. Z. Li, P. Liu, X. D. Xu, and J. Xu, “Growth, spectral properties, and diode-pumped laser operation of a Nd3+-doped LaMgAl11O19 crystal,” Appl. Opt. 57(32), 9657–9661 (2018). [CrossRef]
18. L. H. Zheng, P. Loiseau, and G. Aka, “Diode-pumped laser operation at 1053 and 900 nm in Sr1−xLax−yNdyMgxAl12−xO19 (Nd:ASL) single crystal,” Laser Phys. 23(9), 095802 (2013). [CrossRef]
19. J. Q. Di, X. H. Sun, X. D. Xu, C. T. Xia, Q. L. Sai, H. H. Yu, Y. C. Wang, L. Zhu, Y. Gao, and X. Y. Guo, “Growth and spectral characters of Nd:CaGdAlO4 crystal,” Eur. Phys. J.: Appl. Phys. 74(1), 10501 (2016). [CrossRef]
20. D. Z. Li, X. D. Xu, S. S. Cheng, D. H. Zhou, F. Wu, Z. W. Zhao, C. T. Xia, J. Xu, H. M. Zhu, and X. Y. Chen, “Polarized spectral properties of Nd3+ ions in CaYAlO4 crystal,” Appl. Phys. B 101(1-2), 199–205 (2010). [CrossRef]
21. B. R. Judd, “Optical absorption intensities of rare-earth ions,” Phys. Rev. 127(3), 750–761 (1962). [CrossRef]
22. G. S. Ofelt, “Intensities of crystal spectra of rare-earth ions,” J. Chem. Phys. 37(3), 511–520 (1962). [CrossRef]
23. A. A. Kaminskii, G. Boulon, M. Buoncristiani, B. Di Bartolo, A. Kornienko, and V. Mironov, “Spectroscopy of a new laser garnet Lu3Sc2Ga3O12:Nd3+. Intensity luminescence characteristics, stimulated emission, and full set of squared reduced-matrix elements | ‹‖U(t)‖› | for Nd3+ ions,” Phys. Stat. Sol. (a) 141(2), 471–494 (1994). [CrossRef]
24. X. Y. Chen, Z. D. Luo, D. Jaque, J. J. Romero, J. G. Sole, Y. D. Huang, A. D. Jiang, and C. Y. Tu, “Comparion of opticsl spectra of Nd3+ in NdAl3(BO3)4 (NAB), Nd:GdAl3(BO3)4 (NGAB) and Nd:Gd0.2Y0.8Al3(BO3)4 (NGYAB) crystals,” J. Phys.: Condens. Matter 13(5), 1171–1178 (2001). [CrossRef]
25. W. T. Carnall, P. R. Fields, and K. Rajnak, “Energy levels in the Trivalent Lanthanide Aqua Ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+,” J. Chem. Phys. 49(10), 4424–4442 (1968). [CrossRef]
26. J. Dong, A. Rapaport, M. Bass, F. Szipocs, and K. Ueda, “Temperature-dependent stimulated emission cross section and concentration quenching in highly doped Nd3+:YAG crystals,” Phys. Stat. Sol. (a) 202(13), 2565–2573 (2005). [CrossRef]
27. S. R. Zhao, H. J. Zhang, Y. B. Lu, J. H. Liu, J. Y. Wang, X. G. Xu, H. R. Xia, and M. H. Jiang, “Spectroscopic characterization and laser performance of Nd:LuVO4 single crystal,” Opt. Mater. 28(8-9), 950–955 (2006). [CrossRef]
28. C. Y. Shen, D. L. Wang, H. H. Xu, Z. B. Pan, H. J. Zhang, J. Y. Wang, and R. I. Boughton, “Bulk crystal growth and thermal, spectroscopic and laser properties of disordered Melilite Nd:Ca2Ga2SiO7 single crystal,” J. Alloys Compd. 727, 8–13 (2017). [CrossRef]
29. W. F. Krupke, “Optical absorption and fluorescence intensities in several rare-earth-doped Y2O3 and LaF3 single crystals,” Phys. Rev. 145(1), 325–337 (1966). [CrossRef]
30. Y. Cheng, X. D. Xu, J. Xu, Z. Xin, and S. M. Zhou, “Spectroscopic properties of Nd3+:CaNb2O6 crystal,” Appl. Phys. B 96(1), 43–50 (2009). [CrossRef]
31. N. Li, Y. Y. Xue, D. H. Wang, B. Liu, C. Guo, Q. S. Song, X. D. Xu, J. F. Liu, D. Z. Li, J. Xu, Z. A. Xu, and J. Y. Xu, “Optical properties of Nd:Bi4Ge3O12 crystals grown by the micro-pulling-down method,” J. Lumin. 206, 412–416 (2019). [CrossRef]
32. S. J. Ding, F. Peng, Q. L. Zhang, J. Q. Luo, W. P. Liu, D. L. Sun, R. Q. Dou, J. Y. Gao, G. H. Sun, and M. J. Cheng, “Crystal growth, spectral properties, and continuous wave laser operation of Nd:GdNbO4,” J. Alloys Compd. 693, 339–343 (2017). [CrossRef]
33. B. Aull and H. Jenssen, “Vibronic interactions in Nd:YAG resulting in nonreciprocity of absorption and stimulated emission cross sections,” IEEE J. Quantum Electron. 18(5), 925–930 (1982). [CrossRef]
34. F. Cornacchia, A. Toncelli, M. Tonelli, E. Cavalli, E. Bovero, and N. Magnani, “Optical spectroscopy of SrWO4:Nd3+ single crystals,” J. Phys.: Condens. Matter 16(39), 6867–6876 (2004). [CrossRef]
35. H. R. Yang, D. Y. Shen, S. C. Tam, Y. L. Lam, J. G. Liu, K. Ueda, W. J. Xie, and J. H. Gu, “Femtosecond self-mode-locked La1-xMgNdxAl11O19 laser pumped by a laser diode,” Jpn. J. Appl. Phys. 39(Part 1, No. 12A), 6542–6545 (2000). [CrossRef]
36. Y. Y. Zhang, H. J. Zhang, H. H. Yu, S. Q. Sun, J. Y. Wang, and M. H. Jiang, “Characterization of disordered melilite Nd:SrLaGa3O7 crystal,” IEEE J. Quantum Electron. 47(12), 1506–1513 (2011). [CrossRef]
37. S. Singh, R. G. Smith, and L. G. Van Uitert, “Stimulated-emission cross section and fluorescent quantum efficiency of Nd3+ in yttrium aluminum garnet at room temperature,” Phys. Rev. B 10(6), 2566–2572 (1974). [CrossRef]
38. Y. Sato and T. Taira, “Comparative study on the spectroscopic properties of Nd:GdVO4 and Nd:YVO4 with hybrid process,” IEEE J. Sel. Top. Quantum Electron. 11(3), 613–620 (2005). [CrossRef]
