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Solar energy has become one of the new types of energy sources for humanity in the future due to its abundant recourse, clean use and huge reserve. Solar-pumped laser has potential applications in free space optical communications, remote sensing and other fields. However, the research on solar-pumped laser is limited to 1 μm band with neodymium-doped material as a gain medium. To expand the output wavelength range of solar-pumped solid-state lasers, thereby expanding their application fields is one of the goals pursued by researchers in the field. According to the analysis of the absorption spectra of existing solid laser materials, we find that the thulium-doped crystals also have strong absorption peaks in visible light band where solar radiation is strong. Therefore, it is possible that solar-pumped laser could also generate output at 2 μm eye-safe wavelength. In this paper, the absorption spectrum and spectral matching of two common laser crystals—Tm:YAG and Tm:YAP with solar spectrum are analysed and calculated. According to the quasi-three-level transition rate equation of thulium ion and the model of solar-pumped laser system, we obtain the theoretical threshold pump power densities of these two crystals to be 1.14 kW/cm3 and 1.434 kW/cm3, respectively. We choose the Tm:YAG crystal with lower threshold pump power density as the gain medium and built a two-stage pumping model with TracePro software. In our model, Fresnel lens is the primary solar light concentrator, and a conical cavity with diffusion reflection surface is used as a secondary concentrator to couple the solar energy to laser crystal. Laser setup parameters such as the distance between the Fresnel lens and the window of conic cavity, length of crystal, taper of conic cavity are optimized with the model. The work in this paper offers a valuable reference for future experimental research of 2 μm solar-pumped laser. Finally, we point out the challenge of the future work. Special attention needs to be paid to the huge thermal effect caused by a large amount of sunlight shining on the Tm:YAG crystal. We could find a new kind of diffuse reflection coolants or use thermally bonded crystals to mitigate thermal effects. It will be the focus of future work.
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Keywords:
- eye-safe /
- solar-pumped laser /
- threshold pump power /
- Tm:YAG/Tm:YAP
[1] Shi J, Wang H, Qian J, He X 2016 Opt. Commun. 363 21
Google Scholar
[2] Zhu X, Lu Z, Wang Y 2015 Laser Part. Beams 33 11
Google Scholar
[3] Kavaya M J, Beyon J Y, Koch G J, Petros M, Petzar P, Singh U N, Trieu B C, Yu J 2014 J. Atmos. Ocean. Tech. 31 826
Google Scholar
[4] Wagener T J, Demma N, Kemetec J D, Kubo T S 1995 IEEE Aero. El. Sys. Mag. 10 23
[5] Marano M, Galzerano G, Svelto C, Laporta P 2004 IEEE T. Instrum. Meas. 53 571
Google Scholar
[6] Koch G J, Beyon J Y, Petzar P, Petros M, Yu J, Trieu B C, Kavaya M J, Singh U N, Modlin E A, Bames B W, Demoz B B 2010 J. Appl. Remote Sens. 4 043512
Google Scholar
[7] Koch G J, Beyon J Y, Bames B W, Petros M, Yu J, Amzajerdian F, Kavaya M J, Singh U N 2007 Opt. Eng. 46 16201
[8] Geisthoff U W, Zenk J, Steinhart H, Iro H 2001 HNO 49 194
Google Scholar
[9] Ma Q L, Bo Y, Zong N, Pan Y B, Peng Q J, Cui D F, Xu Z Y 2011 Opt. Commun. 284 1645
Google Scholar
[10] Young C G 1966 Appl. Opt. 5 993
Google Scholar
[11] Thompson G A, Krupkin V, Yogev A 1992 Opt. Eng. 31 2644
Google Scholar
[12] Yabe T, Ohkubo T, Uchida S, Yoshida K, Nakatsuka M, Funatsu T, Mabuti A, Oyama A, Nakagawa K, Oishi T, Daito K, Behgol B, Naayama Y, Yoshida M, Motokoshi S, Sato Y, Baasandash C 2007 Appl. Phys. Lett. 90 261120
Google Scholar
[13] Saiki T, Funahashi K, Motokoshi S, Imasaki K, Fujioka K, Fujita H, Nakatsuka M, Yamanaka C 2009 Opt. Commun. 282 614
Google Scholar
[14] Saiki T, Motokoshi S, Imasaki K, Nakatsuka M, Yamanaka C, Fujioka K, Fujita H 2009 Opt. Commun. 282 936
Google Scholar
[15] 杨扬 2007 博士毕业论文 (上海: 上海交通大学)
Yang Y 2007 Ph. D. Dissertation (Shanghai: Shanghai Jiao Tong University) (in Chinese)
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Google Scholar
[17] Beyatli E, Sumpf B, Demirbas U 2019 Appl. Opt. 58 2973
Google Scholar
[18] 赵彬, 赵长明, 何建伟, 杨苏辉 2007 光学学报 27 1797
Google Scholar
Zhao B, Zhao C M, He Z W, Yang S H 2007 Acta Opt. Sin. 27 1797
Google Scholar
[19] 方容川 2001 固体光谱学 (合肥: 中国科学技术大学出版社) 第4页
Fang R C 2001 Solid State Spectroscopy (Vol. 1) (Hefei: Press of University of Science and Technology of China) p4 (in Chinese)
[20] 赵立伟 2010 硕士毕业论文 (北京: 北京理工大学)
Zhao L W 2010 M. S. Dissertation (Beijing: Beijing Institute of Technology) (in Chinese)
[21] 徐鹏 2019 博士毕业论文 (北京: 北京理工大学)
Xu P 2019 Ph. D. Dissertation (Beijing: Beijing Institute of Technology) (in Chinese)
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图 1 太阳光谱曲线
Figure 1. Curve of solar spectrum.
图 2 太阳光谱与Tm:YAP, Tm:YAG吸收谱 (a) Tm:YAG; (b) Tm:YAP
Figure 2. Matching curve of crystals and solar spectrum: (a) Tm:YAG; (b) Tm:YAP.
图 3 Tm3+离子能级跃迁示意图
Figure 3. Schematic diagram of Tm3+ ion level transition.
图 4 (a) TracePro软件建立的太阳光抽运激光器二级抽运模型; (b)锥形腔结构图
Figure 4. (a) Two-stage pumping model; (b) structure diagram of conical cavity.
图 5 锥形腔窗口位置与接受光功率关系图
Figure 5. Curve of the relationship between the position of conical cavity and the received solar power.
图 6 100 mm晶体棒侧面抽运光分布图
Figure 6. Distribution map of side pump power on 100 mm-length crystal rod.
图 7 不同晶体长度下晶体棒轴向光辐照度分布
Figure 7. Axial irradiance distribution of different-length crystals.
图 8 不同锥度下晶体棒轴向光辐照度分布图
Figure 8. Axial irradiance distribution of different-taper crystals.
表 1 晶体光谱匹配分析结果
Table 1. Spectral matching analysis results of crystals.
Active
mediumDoping density/cm3 Absorption
band/nmIrradiance in absorption
band/W·m–2Percentage of solar
radiance/%Tm:YAG 1.261×1020 (1 at.%) 360—410 21.91041 22.9 456—480 38.78578 656—720 84.80076 747—812 69.35269 Tm:YAP 1.965×1020 (1 at.%) 360—394 19.52938 29.8 450—494 68.23487 643—726 108.88686 744—836 95.81626 
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表 2 晶体参数
Table 2. Crystal parameters.
Tm:YAG Tm:YAP Doping density/cm3 1.26×1020
(1 at.%)1.965×1020
(1 at.%)Upper level lifetime/ms 10.5 4.4 Boltzmann factor
in upper level0.46 0.29 Boltzmann factor
in lower level0.017 0.015 Emission cross section/cm2 2.5×10–21 3.81×10–21 Quantum efficiency 1.8 1.9 Calculation results of
absorption coefficient
curve: $\sum\nolimits_i { {\eta _i}\overline { {a_i} } {\lambda _i} } $/cm46.0069×10–7 51.5739×10–7 Refractive index 1.82 1.91
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[1] Shi J, Wang H, Qian J, He X 2016 Opt. Commun. 363 21
Google Scholar
[2] Zhu X, Lu Z, Wang Y 2015 Laser Part. Beams 33 11
Google Scholar
[3] Kavaya M J, Beyon J Y, Koch G J, Petros M, Petzar P, Singh U N, Trieu B C, Yu J 2014 J. Atmos. Ocean. Tech. 31 826
Google Scholar
[4] Wagener T J, Demma N, Kemetec J D, Kubo T S 1995 IEEE Aero. El. Sys. Mag. 10 23
[5] Marano M, Galzerano G, Svelto C, Laporta P 2004 IEEE T. Instrum. Meas. 53 571
Google Scholar
[6] Koch G J, Beyon J Y, Petzar P, Petros M, Yu J, Trieu B C, Kavaya M J, Singh U N, Modlin E A, Bames B W, Demoz B B 2010 J. Appl. Remote Sens. 4 043512
Google Scholar
[7] Koch G J, Beyon J Y, Bames B W, Petros M, Yu J, Amzajerdian F, Kavaya M J, Singh U N 2007 Opt. Eng. 46 16201
[8] Geisthoff U W, Zenk J, Steinhart H, Iro H 2001 HNO 49 194
Google Scholar
[9] Ma Q L, Bo Y, Zong N, Pan Y B, Peng Q J, Cui D F, Xu Z Y 2011 Opt. Commun. 284 1645
Google Scholar
[10] Young C G 1966 Appl. Opt. 5 993
Google Scholar
[11] Thompson G A, Krupkin V, Yogev A 1992 Opt. Eng. 31 2644
Google Scholar
[12] Yabe T, Ohkubo T, Uchida S, Yoshida K, Nakatsuka M, Funatsu T, Mabuti A, Oyama A, Nakagawa K, Oishi T, Daito K, Behgol B, Naayama Y, Yoshida M, Motokoshi S, Sato Y, Baasandash C 2007 Appl. Phys. Lett. 90 261120
Google Scholar
[13] Saiki T, Funahashi K, Motokoshi S, Imasaki K, Fujioka K, Fujita H, Nakatsuka M, Yamanaka C 2009 Opt. Commun. 282 614
Google Scholar
[14] Saiki T, Motokoshi S, Imasaki K, Nakatsuka M, Yamanaka C, Fujioka K, Fujita H 2009 Opt. Commun. 282 936
Google Scholar
[15] 杨扬 2007 博士毕业论文 (上海: 上海交通大学)
Yang Y 2007 Ph. D. Dissertation (Shanghai: Shanghai Jiao Tong University) (in Chinese)
[16] O'Hare J M, Donlan V L 1976 Pyhs. Rev. B 14 3732
Google Scholar
[17] Beyatli E, Sumpf B, Demirbas U 2019 Appl. Opt. 58 2973
Google Scholar
[18] 赵彬, 赵长明, 何建伟, 杨苏辉 2007 光学学报 27 1797
Google Scholar
Zhao B, Zhao C M, He Z W, Yang S H 2007 Acta Opt. Sin. 27 1797
Google Scholar
[19] 方容川 2001 固体光谱学 (合肥: 中国科学技术大学出版社) 第4页
Fang R C 2001 Solid State Spectroscopy (Vol. 1) (Hefei: Press of University of Science and Technology of China) p4 (in Chinese)
[20] 赵立伟 2010 硕士毕业论文 (北京: 北京理工大学)
Zhao L W 2010 M. S. Dissertation (Beijing: Beijing Institute of Technology) (in Chinese)
[21] 徐鹏 2019 博士毕业论文 (北京: 北京理工大学)
Xu P 2019 Ph. D. Dissertation (Beijing: Beijing Institute of Technology) (in Chinese)
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