LD泵浦Er3+/Yb3+:Lu2Si2O7 晶体kHz微型激光器

韩雪; 吕游; 彭嘉宁; 郭嘉祥; 惠勇凌; 朱占达; 雷訇; 李强

doi:10.3788/IRLA20220811

LD泵浦Er³⁺/Yb³⁺:Lu₂Si₂O₇ 晶体kHz微型激光器

doi: 10.3788/IRLA20220811

韩雪^1,,
吕游¹,
彭嘉宁¹,
郭嘉祥¹,
惠勇凌^{1, 2, 3, 4},
朱占达^{1, 2, 3, 4},
雷訇^{1, 2, 3, 4,},
李强^{1, 2, 3, 4, ,}

1.
北京工业大学材料与制造学部激光工程研究院，北京 100124
2.
跨尺度激光成型制造技术教育部重点实验室，北京 100124
3.
北京市激光应用技术工程技术研究中心，北京 100124
4.
激光先进制造北京市高等学校工程研究中心，北京 100124

基金项目: 国家自然科学基金项目(62075003、62275007)；北京市自然科学基金项目（4202007）；教委科研计划项目（KZ202110005010）

详细信息

作者简介:
韩雪，女，硕士生，主要从事固体激光器方面的研究

通讯作者: 李强，男，教授，博士，主要从事固体激光技术及加工系统方面的研究。

中图分类号: TN248.1

Er³⁺/Yb³⁺: Lu₂Si₂O₇ crystal microchip laser pumped by LD at kHz

Han Xue^1
,,
Lv You¹,
Peng Jianing¹,
Guo Jiaxiang¹,
Hui Yongling^{1, 2, 3, 4},
Zhu Zhanda^{1, 2, 3, 4},
Lei Hong^{1, 2, 3, 4
,},
Li Qiang^{1, 2, 3, 4
, ,}

1.
Institute of Laser Engineering, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China
2.
Key Laboratory of Trans-scale Laser Manufacturing Technology, Ministry of Education, Beijing 100124, China
3.
Beijing Engineering Research Center of Laser Technology, Beijing 100124, China
4.
Beijing Higher Institution Engineering Research Center of Advanced Laser Manufacturing, Beijing 100124, China

Funds: National Natural Science Foundation of China (62075003, 62275007); Beijing Natural Science Foundation Project (4202007); Education Commission Scientific Research Project (KZ202110005010)

摘要: 目前1.5 μm LD泵浦的铒镱共掺玻璃/晶体被动调Q微型激光器广泛应用于激光测距、激光雷达等领域。随着激光器输出能量和重频的增加，玻璃面临突出的热效应问题，晶体的热导率是玻璃的10倍以上，有望能够实现比玻璃基质更大脉冲能量和更高重频的激光输出。文中报道了一种采用LD脉冲端面泵浦、铒镱共掺焦硅酸镥晶体为增益介质的1 537 nm被动调Q微型激光器。通过优化泵浦光斑大小、输出镜透过率与调Q晶体初始透过率相匹配，实现激光输出重频与泵浦重频一致。最终实现了输出重频为1 kHz、单脉冲能量35 μJ、脉冲宽度7 ns、峰值功率为5 kW、光束质量因子M²=1.33的激光输出。以及输出重频为10 kHz、单脉冲能量10 μJ、脉冲宽度10 ns、峰值功率为1 kW、光束质量因子M²=1.51的激光输出。结果表明，Er³⁺/Yb³⁺:Lu₂Si₂O₇ 晶体是实现高重频1.5 μm激光输出的优良介质。文中研究结果对LD脉冲端面泵浦的kHz铒镱共掺晶体被动调Q人眼安全微片激光器具有重要的参考意义。
- 微片激光器 /
- 被动调Q /
- 高重频 /
- Er³⁺/Yb³⁺:Lu₂Si₂O₇晶体 /
- 脉冲泵浦
Abstract: Objective The 1.5 μm laser which has an excellent transparency in atmosphere and is in the eye safety wavelength region, has been widely used in range finders, LiDAR, optical communication, medicine and other fields. LD end-pumped Er³⁺/Yb³⁺ co-doped glass/crystal laser is an effective way to obtain 1.5 μm wavelength output micro laser because it meets the requirements of small volume, peak power, low cost and high efficiency. When using laser for ranging, the higher the laser repetition frequency is, the greater the single pulse energy is, the narrower the pulse width is, the faster the measurement speed is, the higher the accuracy is, and the farther the distance is. However, due to the low thermal conductivity of Er³⁺/Yb³⁺: glass and the increase of laser output energy and repetition frequency, the gain medium faces the prominent thermal effect problem, which makes it easier to reach the damage threshold of dielectric coating and glass, affecting the lifetime of the laser. For Lu₂Si₂O₇ (LPS) crystal, its upper level fluorescence lifetime can be compared with that of glass, and its thermal conductivity is more than 10 times higher than that of the glass. It is an excellent gain medium for realizing 1.5 μm pulsed laser with large energy and high repetition frequency. At present, LPS crystal is mainly pumped continuously. Continuous pumping will cause heat accumulation inside the crystal and reduce the output energy and beam quality of laser output. In this paper, the pulse pumping mode and Er³⁺/Yb³⁺:LPS are used as the gain medium to achieve a 1.5 μm laser output with repetition frequency stabilized at 1 kHz and 10 kHz. Methods In this study, the factors that affect the output of LD end pumped passively Q-switched laser include crystal doping concentration and length, pump beam diameter, initial transmittance of saturable absorber and output coupling mirror (OC) transmittance. Under the theoretical simulation, the general optimization range of the above parameters was obtained, and the optimal parameters were obtained through the experiment. The optimal doping concentration of Yb³⁺ and length of Lu₂Si₂O₇ crystal was obtained by comparing the free oscillating output power at different OC transmittance. In order to achieve the repetition frequency of 1 kHz and 10 kHz Q-switched pulse laser output, we used the control variable method to optimize the pump beam diameter, initial transmittance of saturable absorber and OC transmittance, and obtained the best experimental parameters by comparing the output frequency and single pulse energy. Results and Discussions The results of free oscillating were shown (Fig.2(a)), the output power of 0.5at.%Er³⁺/4.0at.%Yb³⁺:LPS was always higher than 0.5at.%Er³⁺/5.0at.%Yb³⁺:LPS with the transmittance of the OCs changing from 4% to 30%. And when the length of medium increased, the output power of free oscillation also decreased. According to the experimental result, 2.85-mm-thick 0.5at.%Er³⁺/4.0at.%Yb³⁺:LPS was selected for passive Q-switched experiment. The slope efficiency of 2.85-mm-thick 0.5at.%Er³⁺/4.0at.%Yb³⁺:LPS was further studied. The optimal slope efficiency of 5.8% was obtained by optimizing the pump beam diameter and the transmittance of OCs (Fig.2(b)-(d)). In order to achieve the repetition frequency of 1 kHz and 10 kHz Q-switched pulse laser output, we compared the repetition frequency, energy, pulse width of three sets of control variable experiments, the results were shown (Tab.1-6). Finally, the laser output with repetition frequency of 1 kHz, single pulse energy of 35 μJ, pulse width of 7 ns, peak power of 5 kW and M²=1.33 was obtained when the pump beam diameter is 300 μm, the initial transmittance of Co²⁺:MgAl₂O₄ is 94.5% and transmittance of OC is 15%. And the laser output with repetition frequency of 10 kHz, single pulse energy of pulse energy of10 μJ, pulse width of 10 ns, peak power of 1 kW and M²=1.51 was obtained when the pump beam diameter is240 μm, initial transmittance of Co²⁺:MgAl₂O₄ is 98.6% and transmittance of OC is 10%. Conclusions LD pulse end-pumped passively Q-switched 1537 nm laser with Er³⁺/Yb³⁺:Lu₂Si₂O₇ crystal at 1 kHz and 10 kHz was reported. In this experiment, the doping concentration of LPS crystal was optimized by the free oscillation experiment and the 2.85-mm-thick 0.5at.%Er³⁺/4.0at.%Yb³⁺:LPS was selected for passive Q-switching experiment. Secondly, the Q-switching experiment was conducted to optimize the pump beam diameter, the initial transmittance of Co²⁺:MgAl₂O₄ and the transmittance of the output coupling mirror. Finally, the laser output with repetition frequency of 1 kHz, single pulse energy of 35 μJ, pulse width of 7 ns, peak power of 5 kW and M²=1.33 and repetition frequency of 10 kHz, single pulse energy of 10 μJ, pulse width of 10 ns, peak power of 1 kW and M²=1.51 were realized. The results show that Er³⁺/Yb³⁺:Lu₂Si₂O₇ crystal is an excellent medium for 1.5 μm laser output with high repetition frequency.
- microchip laser /
- passively Q-switched /
- high repetition rate /
- Er³⁺/Yb³⁺:Lu₂Si₂O₇ crystal /
- pulse pumped
图 1 实验装置图

Figure 1. Experimental device

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图 2 自由振荡优化结果。(a)不同输出镜透过率下的自由振荡输出功率；(b)不同泵浦光斑下的输出功率； (c)不同输出镜透过率下的输出功率；（d）斜效率拟合图

Figure 2. Free oscillation optimization results.（a） Free oscillating output power at different transmittance of output mirrors; （b） Comparison of output power under different pump spots; （c） Output power at different transmittance of output mirrors; （d） Fitting plot of slope efficiency

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图 3 输出激光光谱

Figure 3. Output laser spectra

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图 4 1 kHz下的脉冲特性。（a）脉宽图；（b）泵浦光和激光脉冲的波形图；（c）输出激光脉冲序列图；（d）远场光斑及光束质量测量图

Figure 4. Pulse performance for 1 kHz. （a） Pulse width figure; （b） Pump waveform and output laser pulse train;（c） Output laser pulse train; （d） Far field facula and beam quality measurement diagram

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图 5 10 kHz下的脉冲特性。（a）脉宽图；（b）泵浦光和激光脉冲的波形图；（c）输出激光脉冲序列图；（d）远场光斑及光束质量测量图

Figure 5. Pulse performance for 10 kHz. （a） Pulse width figure; （b） Pump waveform and output laser pulse train; （c） Output laser pulse train; （d） Far field facula and beam quality measurement diagram

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表 1 1 kHz泵浦光斑优化

Table 1. Optimization of pump beam diameter for 1 kHz

F_focus/
mm ω_p/
μm f_p/
kHz T_Q T_OC τ_p/
μs E_p/
mJ f_o/
kHz E_o/
μJ

3 240 1 95.8% 15% 700 3.5 1 20
4 300 24
5 350 20

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表 2 1 kHz Co²⁺:MgAl₂O₄的初始透过率优化

Table 2. Optimization of initial transmittance of Co²⁺:MgAl₂O₄ for 1 kHz

f_p/kHz T_Q ω_p/μm T_OC τ_p/μs E_p/mJ f_o/kHz E_o/μJ

1 94.5% 300 15% 700 3.5 1 27
95.8% 24

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表 3 1 kHz 输出耦合镜透过率优化

Table 3. Optimization of transmittance of output coupling mirror for 1 kHz

f_p/kHz T_OC T_Q ω_p/μm τ_p/μs E_p/mJ E_o/μJ τ_o/ns

1 15% 94.5% 300 700 3.5 27 7.8
20% 35 7
30% 30 7.3

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表 4 10 kHz泵浦光斑优化

Table 4. Optimization of pump beam diameter for 10 kHz

F_focus/
mm ω_p/
μm f_p/
kHz T_Q T_OC τ_p/
μs E_p/
mJ f_o/
kHz E_o/
μJ

3 240 10 98.6% 15% 70 0.35 10 7
4 300 10 5
5 350 <10 -

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表 5 10 kHz Co²⁺:MgAl₂O₄的初始透过率优化

Table 5. Optimization of initial transmittance of Co²⁺:MgAl₂O₄ for 10 kHz

f_p/kHz T_Q ω_p/μm T_OC τ_p/μs E_p/mJ f_o/kHz E_o/μJ

10 98.6% 240 15% 70 0.35 10 7
99% >10 -

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表 6 10 kHz 输出耦合镜透过率优化

Table 6. Optimization of transmittance of output coupling mirror for 10 kHz

f_p/kHz T_OC T_Q ω_p/μm τ_p/μs E_p/mJ E_o/μJ τ_o/ns

10 8% 240 70 0.35 8 10
10% 98.6% 10 10
15% 7 12

下载: 导出CSV

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[14]	张健, 于永吉, 姜承尧, 王子健, 王彬, 陈薪羽, 金光勇. 高重频Nd:YVO₄声光调Q与RTP电光调Q激光器实验对比分析 . 红外与激光工程, 2017, 46(2): 205002-0205002(5). doi: 10.3788/IRLA201746.0205002
[15]	皇甫军强, 贾海旭, 杨丽丽, 丁双红. LD泵浦被动调Q腔内和频拉曼激光器速率方程 . 红外与激光工程, 2016, 45(6): 606006-0606006(7). doi: 10.3788/IRLA201645.0606006
[16]	张帅, 刘志国, 王仕成, 赵乾. 高重频激光干扰制导武器建模与仿真评估研究 . 红外与激光工程, 2016, 45(3): 306008-0306008(6). doi: 10.3788/IRLA201645.0306008
[17]	王子健, 金光勇, 于永吉, 翟睿智. 高重频声光调Q Nd:YVO₄激光器2.1μm光参量振荡器 . 红外与激光工程, 2015, 44(9): 2638-2642.
[18]	岱钦, 崔建丰, 毛有明, 吴凯旋, 张濛. LD 脉冲泵浦被动调Q 窄脉冲大能量全固态激光器 . 红外与激光工程, 2014, 43(7): 2066-2069.
[19]	苏艳丽, 罗旭, 张学辉, 姜梦华, 惠勇凌, 雷訇, 李强. 重复频率连续可调谐的Cr⁴⁺:YAG被动调Q微片激光器 . 红外与激光工程, 2014, 43(2): 355-359.
[20]	汤伟, 邵俊峰, 赵帅, 王挺峰, 郭劲. 高重频CO₂激光对Hg_0.826Cd_0.174Te晶体的损伤 . 红外与激光工程, 2013, 42(10): 2663-2668.

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0. 引　言

1.5 μm波段激光位于大气传输窗口，对大气穿透能力强，处于人眼安全波段，对人眼的损伤阈值高，成为人们研究人眼安全激光器的热点波段^[1]。LD直接泵浦的铒镱共掺玻璃/晶体激光器具有体积小、结构简单、成本低等优点，广泛应用于激光测距、激光雷达、光通信、医学等领域^[2-5]。对于LD端面泵浦的Er³⁺/Yb³⁺共掺磷酸盐玻璃激光器，增益介质上能级寿命长，Er³⁺、Yb³⁺离子之间能量转移效率高，能够同时满足高峰值功率、转换效率高等要求，是获得1.5 μm波长输出微型激光器的有效方式^[6-8]。国内外对LD端面泵浦Er³⁺/Yb³⁺共掺磷酸盐玻璃被动调Q激光器进行了不断地开发探索。2016年，俄罗斯 Vitkin 等人实现了重复频率1 Hz，单脉冲能量 0.7 mJ，脉宽 10.5 ns的脉冲激光输出^[9]。2017年，蔡瑾鹭等人得到重复频率为10 Hz，单脉冲能量约为210 μJ，脉宽2.8 ns，光束质量因子M ²=1.2的1 535 nm 激光输出^[10]。2018 年，北京工业大学郭娜等人采用增益预泵浦方式，实现重频1 kHz，单脉冲能量40 μJ，脉宽 5.09 ns，峰值功率7.85 kW，光束质量因子 M²=1.4，波长1 535 nm的激光输出^[11]。目前Er³⁺/Yb³⁺:glass作为增益介质的LD端面泵浦微型激光器重频最高可达kHz量级。在利用激光进行测距时，激光的重频越高、单脉冲能量越大，测量速度越快、精度越高、距离越远^[11]。但是Er³⁺/Yb³⁺:glass的热导率低，随着激光器输出能量和重频的增加，增益介质面临突出的热效应问题，容易到达介质膜及玻璃的损伤阈值，影响激光器的使用寿命。与玻璃基质对比，晶体材料具备良好的热性质，易于实现较高重复频率。但是目前常用于产生1.5 μm激光的晶体由于声子能量较小，Er³⁺离子⁴I_11/2能级的寿命相对较短，荧光量子效率低等问题，使得此种激光器存在泵浦利用率低，阈值较高，输出单脉冲能量小，激光器整体转换效率低等缺点^[12]。Lu₂Si₂O₇（LPS）晶体的上能级荧光寿命可以与玻璃相比拟，热导率比玻璃高10倍以上，是实现大能量高重频1.5 μm脉冲激光的优良增益介质^[13]。2020年，陈雨金等人用LD连续泵浦Y-切Er/Yb:LPS，在泵浦功率为6.1 W时，获得了重频为1.32 kHz，单脉冲能量为45.5 μJ，脉宽25 ns的1 537 nm波段激光输出^[14]。同年该课题组连续泵浦Z-切LPS晶体，在泵浦功率3.4 W时，获得重频0.84 kHz，单脉冲能量26.9 μJ，脉宽4.3 ns的1 537 nm激光输出^[15]。目前，LPS晶体的泵浦方式主要为连续泵浦，输出重频会随泵浦功率和热效应变化，重频不稳定不利于测距等实际应用；另外，连续泵浦造成的晶体内部的热积累，会降低激光输出的能量及光束质量。为了获得稳定的输出重频，并且减小热效应带来的影响，文中采用脉冲泵浦方式，Er³⁺/Yb³⁺:LPS晶体作为增益介质，通过优化泵浦光斑大小、输出镜透过率与调Q晶体相匹配，实现激光输出重频与泵浦重频一致，获得输出重频稳定在1 kHz和10 kHz的1.5 μm激光输出。

3. 结　论

文中首先通过自由振荡实验，优化了增益介质的长度及Yb³⁺离子的掺杂浓度，最终选择长度为2.85 mm，Er³⁺离子掺杂浓度为0.5 at.%、Yb³⁺离子掺杂浓度为4.0 at.%的Z切LPS晶体进行调Q实验。在调Q实验中，采用脉冲泵浦方式，通过优化泵浦光斑及输出镜透过率的大小，使其与调Q晶体初始透过率相匹配，实现激光输出重频与泵浦重频一致。最终实现了输出重频为1 kHz、单脉冲能量35μJ、脉冲宽度7 ns、峰值功率为5 kW、光束质量因子M²=1.33以及输出重频为10 kHz、单脉冲能量10 μJ、脉冲宽度10 ns、峰值功率为1 kW、光束质量因子M²=1.51的1 537 nm激光输出。实验结果表明，Er³⁺/Yb³⁺:Lu₂Si₂O₇ 晶体是实现1 kHz和10 kHz高重频1.5 μm激光输出的优良介质，并且重频越高，晶体热导率高的优势越突出。文中研究结果对LD脉冲端面泵浦的kHz铒镱共掺晶体被动调Q微片激光器具有重要的参考意义。

参考文献 (15)

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LD泵浦Er³⁺/Yb³⁺:Lu₂Si₂O₇ 晶体kHz微型激光器

doi: 10.3788/IRLA20220811

作者简介:
韩雪，女，硕士生，主要从事固体激光器方面的研究

通讯作者: 李强，男，教授，博士，主要从事固体激光技术及加工系统方面的研究。

Er³⁺/Yb³⁺: Lu₂Si₂O₇ crystal microchip laser pumped by LD at kHz

计量

LD泵浦Er³⁺/Yb³⁺:Lu₂Si₂O₇ 晶体kHz微型激光器

doi: 10.3788/IRLA20220811

作者简介:
韩雪，女，硕士生，主要从事固体激光器方面的研究

通讯作者: 李强，男，教授，博士，主要从事固体激光技术及加工系统方面的研究。

English Abstract

Er³⁺/Yb³⁺: Lu₂Si₂O₇ crystal microchip laser pumped by LD at kHz

全文HTML

2.1. 增益介质掺杂浓度及长度优化

2.2. 调Q实验结果

目录

F_focus/ mm	ω_p/ μm	f_p/ kHz	T_Q	T_OC	τ_p/ μs	E_p/ mJ	f_o/ kHz	E_o/ μJ
3	240	1	95.8%	15%	700	3.5	1	20
4	300							24
5	350							20

f_p/kHz	T_Q	ω_p/μm	T_OC	τ_p/μs	E_p/mJ	f_o/kHz	E_o/μJ
1	94.5%	300	15%	700	3.5	1	27
1	95.8%	300	15%	700	3.5	1	24

F_focus/ mm	ω_p/ μm	f_p/ kHz	T_Q	T_OC	τ_p/ μs	E_p/ mJ	f_o/ kHz	E_o/ μJ
3	240	10	98.6%	15%	70	0.35	10	7
4	300						10	5
5	350						<10	-

留言板

LD泵浦Er3+/Yb3+:Lu2Si2O7 晶体kHz微型激光器

doi: 10.3788/IRLA20220811

作者简介: 韩雪，女，硕士生，主要从事固体激光器方面的研究

通讯作者: 李强，男，教授，博士，主要从事固体激光技术及加工系统方面的研究。

Er3+/Yb3+: Lu2Si2O7 crystal microchip laser pumped by LD at kHz

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出版历程

LD泵浦Er3+/Yb3+:Lu2Si2O7 晶体kHz微型激光器

doi: 10.3788/IRLA20220811

作者简介: 韩雪，女，硕士生，主要从事固体激光器方面的研究

通讯作者: 李强，男，教授，博士，主要从事固体激光技术及加工系统方面的研究。

English Abstract

Er3+/Yb3+: Lu2Si2O7 crystal microchip laser pumped by LD at kHz

全文HTML

2.1. 增益介质掺杂浓度及长度优化

2.2. 调Q实验结果

目录

LD泵浦Er³⁺/Yb³⁺:Lu₂Si₂O₇ 晶体kHz微型激光器

作者简介:
韩雪，女，硕士生，主要从事固体激光器方面的研究

Er³⁺/Yb³⁺: Lu₂Si₂O₇ crystal microchip laser pumped by LD at kHz

LD泵浦Er³⁺/Yb³⁺:Lu₂Si₂O₇ 晶体kHz微型激光器

作者简介:
韩雪，女，硕士生，主要从事固体激光器方面的研究

Er³⁺/Yb³⁺: Lu₂Si₂O₇ crystal microchip laser pumped by LD at kHz