-
主动锁模激光技术通过腔内主动调制器产生的周期性损耗和相位位移实现激光调制,输出与外部触发信号同步的超快激光脉冲序列。受制于调制器开关时间,主动锁模激光脉冲宽度通常为几十至几百皮秒,难以产生飞秒量级超短脉冲激光,但可以获得较高的振荡激光功率。1991年,世界上首台2 μm波段主动锁模激光器诞生于美国海军实验室[8],Pinto等利用钛宝石激光泵浦Tm:YAG晶体,基于声光调制器的调控实现了脉冲宽度35 ps的主动锁模激光输出。2003年,意大利光子学和纳米技术研究所Galzerano等利用Z型腔结构替代了美国海军实验室的直线型谐振腔,搭建了如图1所示的Tm3+、Ho3+共掺声光调制主动锁模固体激光器,获得了平均功率20 mW、脉冲宽度97 ps的超快激光输出[9]。此后,随着半导体激光技术的蓬勃发展,2 μm波段主动锁模激光器迅速发展。2011年,法国Saint-Louis研究所Philipp等利用二极管激光泵浦掺Tm3+双包层石英光纤,调制元件为声光调制器,在37.88 MHz重复频率下获得了脉冲宽度为38 ps的脉冲激光输出,平均输出功率达到11.8 W,脉冲能量315 nJ[10]。2014年,哈尔滨工业大学Yao等利用如图2所示的8镜折叠Z型腔中实现了声光主动锁模Ho:YAG激光器,锁模脉冲激光重复频率为82.76 MHz,单脉冲能量12.57 nJ,脉冲宽度为102 ps[11]。2015~2016年,哈尔滨工业大学Yao等先后实现了基于Ho:LuAG晶体[12]、Ho:LuVO4 晶体[13]、Ho:YAG 陶瓷[14] 等固体介质的声光调制主动锁模固体激光器,其中基于Ho:LuVO4晶体实现了最高功率3.04 W、重复频率82.7 MHz、脉冲宽度363.3 ps的超快激光输出。2018年,长春理工大学Ma等采用电光调制器取代声光调制器,利用长4 m的Tm3+、Ho3+共掺增益光纤实现了重频高达2.2 GHz、脉冲宽度约200 ps的超快激光输出,并通过可调谐窄带宽光滤波器实现了1907~1927 nm光谱范围内的波长调谐超快激光运转[15]。
表1列出了2 μm波段主动锁模激光器主要研究进展。从表中可以看出,2 μm波段主动锁模激光器平均功率已实现数瓦至十数瓦,但是脉冲宽度大部分集中在皮秒量级,难以产生飞秒脉冲激光。此外,主动锁模光纤激光器需要在光纤结构中加入空间调制器件,大大占用了空间体积,无法发挥光纤激光器体积小、结构紧凑的优势,因此在2 μm波段光纤激光器中主动锁模技术应用较少。
表 1 Tm3+/ Ho3+掺杂2 μm波段主动锁模激光研究进展
Table 1. Development on the actively mode-locked Tm3+/ Ho3+ doped 2 μm lasers
Doped ions Material type Gain materials Pump sourse Saturable absorber Repetition
rate/MHzPulse duration/
psWavelength/
nmOutput power Pulse energy/nJ Year Ref. Tm3+ Solid Tm:YAG 786.5 nm Ti:
sapphire laserAO 300 35 2 010 70 mW 0.23 1991 [8] Tm:YLF 793 nm LD AO 149.3 170 1 910 2.6 W 17.4 2015 [16] Fiber TDF 792 nm LD AO 37.88 38 1 978 11.8 W 314 2011 [10] TDF 792 nm LD AO 0.06 - - 5 W ~8000 2012 [17] TDF 1.57 μm laser EO 11.884/
12.099816/
4461 950 14.3 mW ~0.0012 2013 [18] TDF 1550 nm fiber laser EO 21.4 58 1 980 ~10 mW - 2014 [19] TDF LD AO 66 200 1 950-2130 53 W 800 2015 [20] TDF 1.55 μm laser EO 40000 1.29 2053 - - 2017 [21] Ho3+ Solid Ho:YLF 1940 nm Tm:
fiber laserAO 81.36 290 2 050 4 W 49 2013 [22] Ho:YAG 1.9 μm Tm:
YLF laserAO 82.76 102 2097 1.04 W 12.57 2015 [11] Ho:LuAG 1910 nm Tm:
fiber laserAO 82.48 333.4 2 010 2.7 W 32.7 2015 [12] Ho:YAG 1.9 μm Tm:
fiber laserAO 81.92 294 2 022 3.41 W 41.6 2016 [23] Ho:LuVO4 1940 nm Tm:
fiber laserAO 82.7 363.3 2073.8 3.04 W 36.8 2016 [13] Ho:YAG ceramic 1910 nm Tm:
fiber laserAO 82.15 241.5 2122.1 1.84 mW 0.022 2016 [14] Ho:Sc2SiO5 1940 nm Tm:
fiber laserAO 81.88 282.4 2112.1 2.72 W 33.2 2018 [24] Tm3+/
Ho3+Solid Tm,Ho:
BaYF780 nm LD AO 100 97 2066 20 mW 0.2 2003 [9] Fiber THDF 1570 nm LD EO 2200 200 1 907-1 927 - - 2018 [15] 注:TDF: Tm-doped fiber,Tm3+掺杂光纤;THDF: Tm-Ho co-doped fiber,Tm3+/ Ho3+共掺光纤 -
被动锁模激光器是利用可饱和吸收效应对谐振腔内的损耗进行调制实现超快激光输出的一类激光器,相比主动锁模激光器可以实现更短的脉冲激光输出,并且具有腔型结构更加简单、效率更高等优点。可饱和吸收效应的来源可以是半导体可饱和吸收镜、低维纳米材料等饱和吸收体,也可以是基于非线性光学效应的类饱和吸收体,包括克尔透镜效应、非线性偏振旋转、非线性光环形镜和非线性多模干涉等。
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SESAM由于结构紧凑、可靠性高以及工作波长、非饱和吸收损耗、饱和恢复时间等参数可调,嵌入分布式布拉格反射层(Distributed Bragg Reflectors, DBRs)设计可实现几十到几百nm范围的高反射率,是产生高稳定性、高功率超快激光的理想锁模元件,在1 μm波段具有成熟而广泛的应用。1993年,德国莱特实验室Schepler 等首次利用基于GaAs衬底的InGaAs量子阱结构SESAM实现了基于Tm3+、Ho3+共掺晶体的被动锁模激光输出[25]。然而,与GaAs衬底晶格匹配的波长扩展型GaInAs量子阱材料最佳工作波长处于1 µm波段,而2 µm波段接近GaInAs量子阱的截止波长。应用于2 µm激光波段时,需要大幅提高In元素的比例,如锁模激光工作波长从1.0 μm~1.3 μm~2.0 μm,相应的SESAM量子阱材料InxGa1−xAs中 In 的组分x从0.25~0.38~0.53,势必引起晶格常数失配,接近临界状态,导致非饱和吸收损耗增大和抗损伤阈值降低。同时,这也将严重限制SESAM参数的设计自由度,并导致饱和恢复时间在十几到上百皮秒。为降低饱和恢复时间,通常需要借助低温生长、离子掺杂或注入等方法引入缺陷,不仅增加了生长制备难度,而且导致非饱和吸收损耗进一步增大。1996年,美国雷神公司Sharp等利用InP衬底的InGaAs量子阱结构SESAM,实现了脉宽190 fs的掺Tm3+光纤锁模激光输出,重复频率50 MHz,脉冲能量20 pJ[26]。然而,与InP晶格匹配的高折射率和宽反射带DBR半导体材料较少[27]从而在可饱和吸收层量子阱参数设计方面受到诸多限制。此后,极少见到InP衬底SESAM材料用于2 µm波段超快激光的报道。
锑化物历来是中红外波段激光器、探测器的首选材料,其中又以基于GaSb衬底的III-V族锑化物材料居多,首先是因为室温下GaSb的禁带宽度为726 meV,完全覆盖2~3 μm中红外波段,而且可以作为势垒材料。其次,与GaSb匹配的GaxIn1−xAsySb1−y、A1xGa1−xAsySb1−y半导体化合物的禁带宽度对应波长可以覆盖1.7~4.4 μm波段的光谱范围,而且AlSb、GaSb、InAs的晶格常数又非常接近,相互之间晶格失配很小,有利于制备高质量材料。因此,随着MBE等薄层外延生长技术的进步,基于GaSb衬底的GaxIn1−xAsySb1−y/A1xGa1−xAsySb1−y/GaSb量子阱/垒结构SESAM近年来逐渐成为产生2 μm波段超快激光的理想锁模元件。2009年,英国St. Andrews大学Lagatsky等以GaSb为衬底制备了InGaAsSb-SESAM,通过钛宝石激光泵浦Tm,Ho:KY(WO4)2晶体,实现了脉宽3.3 ps的2057 nm锁模脉冲激光输出[28]。该量子阱结构SESAM可以显著抑制载流子的俄歇复合效应,但饱和恢复时间却增加至100 ps以上,难以通过色散补偿等手段实现脉宽进一步压缩。2010年,该课题组提出了离子注入的方法来降低GaSb-SESAM饱和恢复时间,通过在SESAM中注入N+或者As+离子,有效减少了载流子复合时间,最终基于离子注入的GaSb-SESAM获得了脉宽191 fs的2 μm波段Tm,Ho:KY(WO4)2超短脉冲激光[29]。然而,离子注入等缺陷工程方法会降低SESAM反射率,增大非饱和吸收损耗,导致激光效率下降,而且对生长条件的要求苛刻,增加了制备难度。
窄禁带半导体GaSb具有强烈的俄歇复合效应,可有效增加快速无辐射损耗,从而导致载流子寿命降低。2012年,芬兰Tampere科技大学Guina等利用常规MBE外延生长技术,在不采用低温生长、离子注入等缺陷工程方法的情况下,制备出基于GaSb衬底的Ga0.71In0.29Sb/GaSb量子阱/垒结构SESAM,其快饱和恢复时间仅为0.5 ps,慢饱和恢复时间为10 ps左右,满足了产生飞秒超快激光的需求[30]。2013年,德国Konstanz大学Yang等利用Ga0.71In0.29Sb/GaSb量子阱SESAM,首次在全固态Tm,Ho:YAG激光中实现了2 μm波段超快激光运转,获得了21 ps的锁模脉冲,比GaInAs/GaAs-SESAM以及ISBTs量子阱半导体锁模获得的脉冲宽度压缩了2倍[31]。2020年,德国Max Born研究所Zhao等基于GaSb-SESAM实现了重复频率78 MHz、平均功率51 mW、脉冲宽度54 fs的超短脉冲激光输出,这也是目前SESAM锁模2 μm超快激光产生的最短脉冲宽度[32]。
上述半导体SESAM的饱和吸收特性来源于导带和价带之间的带间跃迁,其工作波长取决于半导体量子阱的能隙宽度,虽然可以通过调节半导体量子阱的成分和厚度控制其工作波长,但是改变的范围有限。此外,带间跃迁量子阱半导体饱和光强也不能随意调节。在量子阱结构中,量子阱导带沿着生长方向会离散成数个子带,当相应波长入射光的电场在沿量子阱生长方向上产生分量时,电子从基态激发到上能级,产生子带间跃迁(Intersubband Transitions, ISBTs)。由于各子带之间的相对位置可以通过改变量子阱的结构、阱宽、杂质的掺杂浓度及位置等参数来控制,而且子带间存在的大量非辐射声子参与各子带能级上电子的弛豫过程,从而使子带间跃迁具有驰豫时间快(典型的驰豫时间为1 ps左右)、跃迁波长可调等优点,在量子级联激光器、光电探测、全光开关等领域具有重要的应用。然而,要实现2 μm中红外波段(~0.6 eV)子带间跃迁,半导体量子阱和势垒的导带能级间隔需要大于1 eV,实际上只有少数半导体量子阱系统具有这么大的导带能级间隔。截止目前,人们已在GaAs/AlGaAs[33]、InGaAs/AlAs[34]、InGaAs/AlAsSb[35-36]等半导体量子阱系统中发现2 μm中红外波段子带间跃迁,利用fs激光泵浦探测技术测得子带间跃迁的典型弛豫时间在亚皮秒量级,而且该弛豫时间可以通过改变量子阱的宽度和杂质掺杂浓度进行调整。2008年,德国康斯坦茨大学Yang等首次利用基于InP衬底的InGaAs/AlAsSb子带间跃迁半导体量子阱实现了2 μm波段饱和吸收锁模固体激光运转,获得了脉宽60 ps的超快激光输出[37],为2 μm波段超快激光发展提供了一种新的技术途径。表2总结了SESAM被动锁模2 μm超快激光研究进展。从表2可以看出,目前基于SESAM锁模的2 μm超快激光最短脉冲宽度为54 fs[32],最高单脉冲能量可达4.75 nJ[37]。
表 2 基于SESAM Tm3+/ Ho3+ 掺杂2 μm波段锁模激光器研究进展
Table 2. Development on the SESAM mode-locked Tm3+/ Ho3+ doped 2 μm lasers
Doped ions Material type Gain materials Pump sourse Saturable absorber Repetition rate/MHz Pulse duration/fs Waveleng-th/nm Output power/mW Pulse energy/nJ Year Ref. Tm3+ Solid Tm:GPNG 792 nm Ti: sapphire laser InGaAsSb-SESAM 222 410 1 997 84 0.38 2010 [39] Tm:KYW 801 nm Ti: sapphire laser InGaAsSb-SESAM 105 386 2 030 235 2.24 2011 [40] Tm:Sc2O3 796 nm Ti:sapphire laser InGaAsSb-SESAM 124.3 218 2107 325 2.6 2012 [41] Tm:Lu2O3 ceramic 796 nm Ti:sapphire laser InGaAsSb-SESAM 121.2 180 2076 400 3.3 2012 [42] Tm:LuYSiO5 Ti:sapphire laser InGaAsSb-SESAM 100 19600 1944.3 64.5 0.645 2012 [43] Tm:YAG ceramic 785 nm Ti:sapphire laser InGaAs-SESAM 88.9 6300 2 012 125 1.4 2013 [44] Tm:LuAG 789 nm LD InGaAs-SESAM 129.2 38000 2 022 1210 9.37 2015 [45] Tm:CaYAlO4 790 nm LD SESAM 145.4 35300 1958.9 &
1960.6830 5.7 2015 [46] Tm:YAG ceramic 786 nm Ti:sapphire laser GaAs-SESAM 89 3000 2 012 150 1.68 2015 [47] Tm:LuAG ceramic 787 nm Ti:sapphire laser GaSb-SESAM 92 2700 2 022 232 2.52 2017 [48] Tm LuScO ceramic 795 nm Ti:sapphire laser GaAsSb-SESAM 78.9 63 2057 175 2.22 2018 [49] Tm:YLF 793 nm LD GaAs-SESAM 94 31000 1 909 95 1.01 2018 [50] Tm:LuYO3 ceramic 795 nm Ti:sapphire laser GaSb-SESAM 78 54 2040.5 51 0.65 2020 [32] Tm:YAG 790 nm LD GaAs-SESAM 97.7 47900 2 012 117 1.2 2020 [51] Tm:CaF2 792 nm LD SESAM 96.35 >1500 1886.8 132 1.37 2020 [52] Fiber TDF 783 nm Ti: sapphire laser InGaAs-SESAM 50 190 1 900 - 0.02 1996 [26] TDF 793 nm LD SESAM 39.8 815000 1978 150 3.8 2012 [53] TDF - SESAM 52.6 230 1 860-
1 930106 2 2012 [54] TDF 1550 nm fiber laser SESAM 108 712 1 945 70 0.65 2015 [55] TDF 1.59 μm Er,Yb:fiber laser SESAM 535 7900 1 938 50 0.09 2016 [56] TDF 793 nm LD SESAM 1600 7200 1959.7 4.5 0.003 2018 [57] Ho3+ Solid Ho:YLiF4 1 940 nm Tm: fiber laser InGaAsSb-SESAM 122 1100 2064 580 4.75 2011 [38] Ho:YAG ceramic 1908nm Tm:fiber laser GaSb-SESAM 82.1 2100 2064 230 2.8 2016 [58] Fiber HDF 1150 nm LD SESAM 7.8 2230 2094 28 3.7 2016 [59] Tm3+/Ho3+ Tm,Ho:KY(WO4)2 802 nm Ti: sapphire laser InGaAsSb-SESAM 132 3300 2057 315 2.38 2009 [28] Solid Tm,Ho:TZN 792 nm Ti: sapphire laser InGaAsSb-SESAM 143 630 2 012 38 0.27 2010 [39] Tm,Ho:KY(WO4)2 802 nm Ti: sapphire laser InGaAsSb-SESAM 118 570 2055 130 1.1 2010 [60] Tm,Ho:NaY(WO4)2 795 nm Ti: sapphire laser InGaAsSb-SESAM 144 191 2058 82 0.57 2010 [29] Tm,Ho:YAP 791 nm Ti:sapphire laser InGaAs-SESAM 107 40400 2064.5 132 1.23 2013 [61] Tm,Ho:YAG 726-859 nm Ti:sapphire laser GaSb-SESAM 106.9 21300 2091 63 0.59 2013 [31] Tm,Ho:KLu(WO4)2 802 nm Ti:sapphire laser InGaSb-SESAM 93 7200 2058 155 1.67 2015 [62] Tm,Ho:CaYAlO4 795 nm Ti:sapphire laser InGaAsSb-SESAM 80.45 87 2024.6 27 0.34 2018 [63] Tm,Ho:CNGG - GaSb-SESAM 89.3 73 2061 36 0.4 2020 [64] Tm,Ho:LiLuF4 Ti:sapphire laser GaAs-SESAM 98.04 12000 1895 350 3.51 2020 [65] Fiber THDF - InGaSb -SESAM 50 750 1 972 20 0.4 2007 [66] THDF 799 nm LD InGaSb-SESAM 24.4 1100 2060 10 0.4 2011 [67] THDF 1.56 μm LD SESAM 38.75 600 1 980 15 0.4 2011 [68] 注:HDF: Ho-doped fiber,Ho3+掺杂光纤 SESAM虽然已实现2 μm波段亚百飞秒超短脉冲激光输出,但仍然存在工作波长受限、封装工艺复杂、制备成本高昂等缺点。近年来,伴随着低维纳米材料研究热潮的兴起,科研人员发现低维纳米材料不仅种类繁多、制作简单、成本低廉,而且具有吸收带宽、弛豫快速、参数可调等优点,广泛应用于光纤和固体激光中的饱和吸收被动锁模器件。目前,已经成功应用于Tm3+/Ho3+掺杂2 μm波段的低维纳米材料主要有碳纳米管(Carbon Nanotubes, CNTs)、石墨烯(Graphene)、拓扑绝缘体(Topological Insulators, TIs)、过渡金属硫化合物(Transition Metal Dichalcogenides, TMDs)、黑磷(BP)等。
最早被用作可饱和吸收体的低维纳米材料是具有优异光学和电学特性的一维碳纳米管,其中单壁碳纳米管(Single Walled Carbon Nanotubes, SWCNTs)由于饱和阈值低、恢复时间短、化学稳定性高等优点,在2 μm波段被动锁模激光器中应用较多。2008年,俄罗斯科学院Solodyankin等人利用电弧放电法合成了SWCNTs,并用于Er3+离子1.57 μm光纤激光泵浦Tm3+光纤激光中,首次实现了脉宽1.32 ps的2 μm超快激光运转,平均输出功率为3.4 mW[69]。然而,碳纳米管存在损伤阈值较低问题,而且长时间工作会出现漂白现象。
石墨烯是一种蜂窝状晶格的单层碳原子薄片,具有零带隙、恢复时间超快、饱和通量低等优点,是一类理想的宽带可饱和吸收材料。2011年,山东师范大学Liu等首次利用石墨烯实现了2 μm波段Tm3+:YAP激光锁模运转,获得了平均功率268 mW、重复频率71.8 MHz、最大脉冲能量3.7 nJ的超快激光输出,脉宽约为10 ps[70]。2012年,北京工业大学Liu等利用石墨烯锁模2 μm波段Tm3+掺杂光纤激光,获得了重复频率3.17 MHz、脉冲能量0.56 nJ、脉宽3.6 ps的超快激光[71]。同年,上海交通大学Ma等利用石墨烯实现了Tm:CLNGG晶体锁模激光运转,通过CaF2棱镜对进行腔内色散补偿,获得了脉宽729 fs、重复频率98.7 MHz、平均功率60.2 mW的超快激光,证明了石墨烯具有实现2 μm波段飞秒脉冲的能力[72]。2015年,该课题组实现了石墨烯被动锁模Tm:YAG陶瓷超快激光运转,获得了平均功率158 mW、脉宽2.8 ps、重频98.7 MHz的超短脉冲激光[73]。2016年,韩国亚洲大学Jeong等利用石墨烯实现了Tm3+掺杂全光纤孤子锁模激光运转,产生了脉冲宽度773 fs、重复频率19.31 MHz、最大输出功率115 mW、脉冲能量6 nJ的超快激光输出[74]。
TIs是一类不同于普通绝缘体的材料,其内部绝缘,而表面因狄拉克型电子态具有良好的导电特性,并展现出独特的量子特性,其中由泡利阻塞效应引起的饱和吸收效应呈现出恢复时间快、调制深度高等特点。此外,TIs同时具有窄带隙体结构(0.2 ~0.3 eV)和零带隙表面态结构,因此具有超宽带的可饱和吸收特性。2014年,韩国首尔大学Jung等通过在Tm3+、Ho3+共掺光纤端面上沉积一层由机械剥离方法制备的Bi2Te3,首次实现了TIs饱和吸收体在2 μm波段超快激光中的应用,获得了脉宽795 fs的超短脉冲激光输出[75]。2016年,波兰弗罗茨瓦夫技术大学Tarka等基于Sb2Te3锁模实现了Tm3+掺杂超快光纤激光运转,脉冲宽度为890 fs,单脉冲能量为30 pJ[76]。然而,TIs抗光损伤阈值不高,而且电子弛豫速率较低,对饱和恢复时间造成不利影响,从而限制了其在2 μm波段锁模激光中的应用。
以MoS2、MoSe2、WS2、WSe2等为代表的TMDs具有很强的三阶非线性光学特性,可用于2 μm波段超快可饱和吸收体。2015年,上海交通大学Tian等利用液相剥离方法获得了多层MoS2,并将其沉积在金镜上制备了可饱和吸收体,首次实现了Tm3+掺杂光纤锁模激光运转,获得了单脉冲能量15.5 nJ、脉宽843 ps的2 μm波段超快激光输出[77]。然而,截止目前基于TMDs材料实现的Tm3+/Ho3+掺杂2 μm波段固体和光纤锁模激光脉宽绝大多数都在皮秒量级,可能是由于TMDs饱和吸收体本身较大的非线性饱和吸收损耗所致。
黑磷的结构与石墨烯类似,层间通过微弱的范德瓦尔斯力结合,其带隙可以从0.3 eV扩展到2 eV。2015年,波兰弗罗茨瓦夫理工大学Sotor等利用黑磷作为可饱和吸收体,在掺Tm3+光纤激光器中实现了中心波长1910 nm、脉冲宽度739 fs的超快激光输出[78],证实了黑磷在中红外波段的饱和吸收特性。然而,尽管黑磷是磷同素异形体中最稳定的一种,但在空气中易发生氧化,遇水会发生较强的反应,造成制备难度较高、使用寿命较短等问题,限制了其应用。
表3总结了基于低维纳米材料可饱和吸收体锁模的Tm3+/Ho3+掺杂2 μm波段超快激光主要进展情况。从表中可以看出,适用于2 μm波段的低维纳米材料可饱和吸收体种类丰富,目前基于低维纳米材料锁模的2 μm超快激光脉冲宽度可达飞秒量级,然而其损伤阈值较低,且插入损耗较大,致使超快激光输出功率普遍在毫瓦量级,严重制约了超快激光功率和能量。
表 3 基于低维纳米材料可饱和吸收体锁模的Tm3+/ Ho3+掺杂2 μm波段超快激光研究进展
Table 3. Development on the ultrafast Tm3+/ Ho3+ doped 2 μm lasers based on the low-dimension nanomaterial saturable absorber mode-locking
Doped ions Material type Gain materials Pump sourse Saturable absorber Repetition rate/MHz Pulse duration/fs Wavelength/nm Output power/mW Pulse energy/nJ Year Ref. Tm3+ Solid Tm:YAP 795 nm LD Graphene 71.8 ~10000 2 023 268 3.7 2011 [70] Tm:YLF Ti:sapphire laser SWCNT - 19000 1 888 55 - 2011 [79] Tm:Lu2O3 798 nm Ti:sapphire laser SWCNT 88 175 2070 36 0.41 2012 [80] Tm:KLuW 802 nm Ti:sapphire laser SWCNT 88 141 2 037 26 0.3 2012 [81] Tm:CLNGG 790 nm LD Graphene 98.7 729 2 018 60.2 0.61 2012 [72] Tm:YAP 800 nm Ti:sapphire laser Graphene 71.8 10000 2 023 268 3.7 2012 [82] Tm:Lu2O3 796 nm Ti:sapphire laser Graphene 110 410 2067 270 0.13 2013 [83] Tm:YAG ceramic 790 nm LD Graphene 98.7 2800 2 016 158 0.08 2015 [73] Tm:MgWO4 796 nm Ti:sapphire laser Graphene 87 86 2 017 96 1.1 2017 [84] Tm:CNNGG 785 nm Ti:sapphire laser SWCNT 90 84 2 018 22 0.24 2018 [85] Tm:CLNGG 785 nm Ti:sapphire laser SWCNT 86 78 2 017 54 0.63 2018 [86] Tm:LuYO3 795 nm Ti:sapphire laser SWCNT 72.6 57 2 045 63 0.87 2019 [87] Tm:YAG 792 nm LD MoS2 232.2 280000 2 011 & 2 017 200 0.86 2020 [88] Fiber TDF 1.57 μm Er fiber laser SWCNT 37 1320 1 930 3.4 0.09 2008 [69] TDF 1.57 μm Er fiber laser SWCNT 45 750 1 885 25 0.5 2009 [89] TDF 790 nm LD Graphene 3.17 - 2 007 1.8 0.56 2012 [71] TDF - Graphene 6.46 3600 1 940 2 0.4 2012 [90] TDF Er fiber laser Graphene 506 58 - - 1 2012 [91] TDF 1.56 μm Er fiber laser SWCNT 6.71 2300 1 947 3 0.45 2013 [92] TDF 1.57 μm Er,Yb:fiber laser Graphene 20.5 1200 1 884 1.35 0.06 2013 [93] Tm3+ Fiber TDF 1.55 μm Er fiber laser Graphene 16.93 2100 1953.3 1.41 0.08 2013 [94] TDF 1.55 μm Er,Yb:fiber laser MoS2 9.67 843000 1 905 150 15.5 2015 [77] TDF 1568 nm LD BP 36.8 739 1 910 1.5 0.0407 2015 [78] TDF 1.57 μm Er fiber laser CNT 25.76 152 1 972 4.85 0.19 2016 [95] TDF 1.56 μm Er fiber laser Graphene 19.31 773 1 910 115 6 2016 [74] TDF 1.56 μm LD TIs-Sb2Te3 39.5 890 1 945 1.2 0.03 2016 [76] TDF 1.56 μm Er,Yb:fiber laser Graphene 58.87 205 1 945 13 0.22 2017 [96] TDF 1.55 μm LD WTe2 18.72 1250 1915.5 39.9 2.13 2017 [97] TDF 1.55 μm LD MoTe2 15.37 1300 1934.85 212 13.8 2018 [98] TDF 1.55 μm LD SWCNT 21.4 211 - 36 1.68 2019 [99] TDF 1.55 μm LD CNT - 910-6430 1733-2 033 - - 2019 [100] Ho3+ Fiber HDF 1 940 nm Tm fiber laser BP 29.1 1300 2094 11 0.379 2017 [101] HDF 1 940 nm Tm fiber laser Graphene 21.13 190 2060 54 2.55 2018 [102] HDF Tm fiber laser CNT 22.13 212 2080 84 3.79 2019 [103] Tm3+/ Ho3+ Solid Tm, Ho:KLu(WO4)2 802 nm Ti:sapphire laser SWCNT 91 2800 2060 97 1.07 2014 [104] Tm,Ho:CNGG 786 nm Ti:sapphire laser SWCNT 102 76 2081 67 0.66 2018 [105] Tm,Ho:CLNGG 796 nm Ti:sapphire laser SWCNT 99.28 67 2083 - - 2019 [106] Fiber THDF 1.55 μm LD TIs-Bi2Te3 27.9 795 1 935 1 - 2014 [75] THDF 1570 nm fiber laser TIs-Bi2Te3 21.5 1260 1909.5 - - 2015 [107] THDF 1.55 μm LD WS2 34.8 1300 1 941 0.6 0.017 2015 [108] THDF 1566 nm LD VSe2 11.6 1400 1 912 - - 2021 [109] -
类饱和吸收体是指能够诱导出类似可饱和吸收效应的非线性光学过程。固体激光器中的类饱和吸收体主要基于克尔透镜效应,是由非线性折射率变化引起的谐振腔内自聚焦效应,无需其他元件可实现自锁模。2017年,德国Max-Planck量子光学研究所Zhang等实现了基于Ho:YAG薄片增益介质的克尔透镜锁模激光运转,实验装置如图3所示,获得了脉冲宽度270 fs、平均输出功率28 W、单脉冲能量0.36 μJ的超快激光脉冲[110]。同年,土耳其Koç大学Canbaz等利用780 nm钛宝石激光泵浦Tm:YLF晶体,实现了脉冲宽度514 fs、重复频率41.5 MHz、平均输出功率14.4 mW的克尔透镜锁模激光输出[111]。2018年,天津工业大学Zhang等实现了Tm:YAP自锁模激光运转,利用两镜直线型谐振腔获得了重复频率468 MHz的脉冲激光,最大平均输出功率为1.65 W,中心波长为1943 nm,脉宽为~621 ps[112]。2020年,日本电子通信大学Suzuki等实现了Tm:Sc2O3晶体克尔透镜锁模激光运转,利用如图4所示的四镜Z型腔结构,通过色散补偿,获得了平均功率130 mW、脉冲宽度72 fs的2108 nm超短脉冲激光输出,展示了克尔透镜锁模技术产生中红外2 μm波段超短脉冲激光的能力[113]。2021年,该课题组在同一谐振腔内同时利用Tm:Lu2O3和Tm:Sc2O3单晶,获得了1850~2200 nm的宽带增益光谱,通过腔内色散补偿和腔外脉冲压缩实现了41 fs的超短脉冲激光输出,平均功率为42 mW[114]。然而,与其他波段固体激光介质类似,Tm3+/ Ho3+掺杂2 μm波段克尔透镜锁模激光器也存在难以自启动的问题,通常需要谐振腔处于介稳状态并通过外部扰动来触发,增大了谐振腔设计难度。
与晶体和陶瓷固体介质不同,光纤介质中存在丰富的非线性效应,可用于实现类饱和吸收锁模。其中,NPR是光纤中最为常用的类饱和吸收效应,早在1995年美国麻省理工学院Nelson等已实现小于500 fs的2 μm波段超快激光输出[115]。尽管NPR饱和恢复时间仅有约几飞秒,可以实现稳定的飞秒脉冲激光输出,但是光纤介质内光的偏振旋转极易受到外界环境以及光纤本身状态的影响,这就导致了NPR锁模光纤激光器具有环境稳定性差的缺点。此外,NPR通常与SAM配合使用,以实现有效自启动。2017年,德国电子加速器Li等利用NPR和SAM相结合,实现了Ho3+掺杂锁模光纤激光自启动运转,获得了脉宽920 fs的超短脉冲激光输出,同时发现SAM可以将锁模激光运转阈值降低约20%[116]。
NLMMI利用了单模光纤-多模光纤-单模光纤相互耦合时产生的非线性模式损耗调制。2017年,中国计量大学Li等首次利用NLMMI锁模技术实现了1570 nm光纤激光泵浦Tm3+离子掺杂光纤介质的2 μm波段超快激光运转,实验中SMF-SIMF-GIMF-SMF结构处于弯曲状态,当泵浦功率达180 mW时,激光器工作在稳定的锁模状态,实现了脉冲宽度1.4 ps、光谱宽度3.6 nm、重复频率19.82 MHz的1888 nm超快激光输出[117]。然而,NLMMI锁模激光结构复杂、调节困难,环境稳定性较差。
NOLM主要是基于Sagnac干涉环原理产生非线性相移差实现激光锁模。如果与强度有关的非线性相移差来源于增益光纤放大环路,则称为非线性光放大镜(Nonlinear Amplifier Loop Mirror, NALM),如果非线性相移差来自于增益光纤的吸收则为非线性光吸收镜(Nonlinear Absorber Loop Mirror, NAbLM)。与NPR锁模技术相比,NOLM锁模技术更容易实现全光纤化。2020年,马来西亚马来亚大学Ahmad等报道了一种全光纤类噪声双包层掺铥光纤锁模激光器,基于NOLM技术实现了脉宽384 fs、光谱带宽14.8 nm、脉冲能量252.6 nJ的超快激光输出[118]。
表4总结了基于类饱和吸收体锁模的Tm3+/Ho3+掺杂2 μm波段超快激光研究进展。从表4可以看出,基于克尔透镜锁模的固体激光可实现迄今2 μm波段超快激光的最窄脉冲宽度41 fs[114],而凭借优异的大比表面积散热特性,Ho3+掺杂克尔透镜锁模薄片激光和Tm3+掺杂NALM锁模光纤激光分别已实现28 W/270 fs、32.8 W/317 fs的大功率、窄脉宽超快激光输出,为获得高性能2 μm波段超快激光提供了有效的技术途径。
表 4 基于类饱和吸收体锁模的Tm3+/ Ho3+掺杂2 μm波段超快激光研究进展
Table 4. Development on the mode-locked Tm3+/Ho3+ doped ultrafast 2 μm lasers based on artificial SA nonlinear optical effects
Doped ions Material type Gain materials Pump sourse Artificial SA Repetition rate/MHz Pulse duration/fs Wavelength/nm Output power/mW Pulse energy/nJ Year Ref. Tm3+ Solid Tm:YLF 780 nm Ti:sapphire laser Kerr-lens 41.5 514 2303 14.4 0.35 2017 [111] Tm:Sc2O3 1.59 μm Er,Yb:fiber laser Kerr-lens 93.8 72 2108 130 1.38 2020 [113] Tm:Lu2O3 &
Tm:Sc2O31611 nm Er:Yb MOPA Kerr-lens 93.3 41 2094 42 0.45 2021 [114] Ho3+ Solid Ho:YAG TD 1.908 µm TDFL Kerr-lens 77 270 2090 28000 363 2017 [110] Tm3+ Fiber TDF 783 nm Ti:sapphire laser NPR - 350-500 1798-1 902 0.24 13.74 1995 [115] TDF 793 nm LD NPR 41.4 173 1 974 167 4 2008 [119] TDF 793 nm LD NPR 41.4 1200 1 976 178 4.3 2008 [120] TDF 1.5 μm Er fiber laser NPR 9.78 770 1 982 1.5 0.15 2011 [121] TDF 1575 nm laser NPR & SAM 19.7 482 1 927 13.2 0.67 2012 [122] TDF 1575 nm Er fiber laser NPR 45.42 119 1 912 7.8 0.17 2012 [123] TDF 1561 nm Er fiber laser NPR 6.37 - 1942.2 110 17.3 2013 [124] TDF 1550 nm Er fiber laser NPR & SAM 22.9 200 1 950 16 0.7 2014 [125] TDF 793 nm LD NPR 1.902 2200 1992.7 0.142 0.0746 2014 [126] TDF 793 nm Ti:sapphire laser NPR 67.5 45 1 880 13 0.19 2014 [127] TDF 793 nm LD NPR 2.68 3100 1 862 3 1.12 2015 [128] TDF 1569 nm Er fiber laser NPR 20-30 130 - - 7.6 2015 [129] TDF 793 nm LD NPR 6.32 406 2003.2 - 12.342 2016 [130] TDF 1550 nm Er fiber laser NPR 11.6 350 1 890 90 7.8 2017 [131] TDF - NPR - 142.8 1 950 370 31 2018 [132] TDF 1610 nm EYDFL NPR 10.62 534 1 988 189 17.8 2019 [133] Ho3+ Fiber HDF 1 950 nm Tm fiber laser NPR & SAM 65 920 2 040-2070 - 0.8 2017 [116] HDF 1 950 nm fiber laser NPR 13.2 370000 2133 68.6 5.2 2018 [134] Tm3+ Fiber TDF 1570 nm fiber laser NLMMI 19.82 1400 1 888 - - 2017 [117] Tm3+ Fiber TDF 786 nm laser NALM 4.75 682 - 41 8.75 2012 [135] TDF 786 nm LD NALM 10.4 1500 2 034 0.66 0.063 2013 [136] TDF 793 nm LD NOLM 1.514 341 2 017 377.3 249.32 2014 [137] TDF 793 nm LD NALM 9.1 460 1 990 301 32.72 2015 [138] TDF 793 nm LD NPR & NOLM 2.66 258 2 007 112 42.11 2017 [139] TDF 793 nm LD NOLM 2.85 384 1988.8 720 252.6 2020 [118] TDF 1550 nm Er fiber laser NALM 3.228 317 1946.4 32800 10100 2021 [140] Ho3+ Fiber HDF 1.9 μm TDFL NAbLM 7.765 - 2058 - - 2020 [141] HDF Tm laser NALM 41.7 - 2 050 4 0.095 2020 [142] 注:SA: Saturable absorber,可饱和吸收体;TD: Thin disk,薄片;MOPA: Master oscillator power-amplifier,主振荡功率放大;TDFL: Tm-doped fiber laser,Tm3+掺杂光纤激光器;EYDFL: Er-Yb co-doped fiber laser,Er3+/Yb3+离子共掺光纤激光器 -
受制于光纤非线性效应或固体激光增益,目前直接振荡产生的2 μm超快激光脉冲能量较低。例如,基于主动锁模技术的Tm3+/ Ho3+掺杂光纤超快激光最高脉冲能量为0.8 μJ,相应的输出功率为53 W[20];基于NOLM锁模技术的2 μm超快光纤激光最高单脉冲能量为10.1 μJ[140]。对于2 μm固体激光振荡器,基于克尔透镜锁模技术的Ho:YAG薄片超快激光已实现平均功率28 W、脉冲宽度270 fs的超短脉冲激光输出,然而最高脉冲能量仅为363 nJ[110],这已是目前Tm3+/ Ho3+掺杂固体锁模激光器直接振荡产生的最高脉冲能量。为进一步提高Tm3+/ Ho3+掺杂2 μm波段超快激光脉冲能量,需要采用放大技术。
再生放大器(Regenerative Amplifiers, RA)采用种子光多次通过增益介质的方式实现较大的增益倍数,可有效提高Tm3+/ Ho3+掺杂介质的能量提取效率,并维持种子光的光束质量,成为当前2 μm波段超快激光放大的常用方式。2013年,奥地利光子学研究所Malevich等首次实现了Ho:YAG飞秒激光再生放大,结构如图8所示。种子源激光由基于I型BBO和II型KTA晶体的光学参量放大获得,脉冲宽度为180 fs,脉冲能量约为0.7 μJ,光谱宽度为40 nm。种子激光经啁啾脉冲放大(Chirped Pulse Amplification, CPA)部分的脉冲展宽器展宽进入Ho:YAG再生放大器,最后由压缩器压缩输出,获得了超快激光脉冲能量为3 mJ,脉冲宽度440 fs,重复频率5 kHz[143]。2015年,德国自由电子激光科学中心Kroetz等实现了Ho:YLF超快激光再生放大,通过降低重复频率、控制晶体温度,使激光晶体工作在增益饱和状态,克服了脉冲分叉不稳定性,实现了脉冲分裂现象的完全抑制,在1 kHz重复频率下获得了单脉冲能量6.9 mJ、脉冲宽度1.9 ps[144]。
进一步地将再生放大技术与其他放大技术结合,可以产生更高的脉冲能量。2015年,德国Max Born研究所Grafenstein等基于如图9(a)所示的实验装置,采用Ho:YLF再生放大和单通放大技术实现了1 kHz重频的34 mJ皮秒脉冲激光输出,激光能量稳定性RMS低于0.9%,结果如图9(b)所示[145]。
以上介绍的Tm3+/Ho3+掺杂2 μm波段超快激光放大器都采用了CPA技术,虽然获得了大能量的激光输出,但光光转换效率不高。2018年,德国汉诺威激光中心Hinkelmann等提出了直接放大方式的Ho:YLF多通放大器(Multipass Amplifier, MPA),结构如图10 所示,包括种子源、声光调制器和多程放大系统。种子源为Ho3+掺杂光纤激光器,脉冲宽度为5 ps。多通放大器采用长度为20 mm的1.5 at.%掺杂Ho:YLF晶体,并利用TEC(Thermoelectric Cooler,半导体制冷器)冷却,最终实现了重复频率10 kHz、脉冲能量100 μJ大能量超快激光输出[146]。
2020年,德国Max Born研究所Grafenstein等实现了脉冲宽度2.4 ps、脉冲能量52.5 mJ、峰值功率17 GW的大能量2 μm波段超快激光输出[147],脉冲间RMS只有0.23%,表现出优异的稳定性能。种子光通过高增益的环形腔再生放大器发射出脉冲能量为12 mJ的激光,通过两个功率放大级进一步提高脉冲能量,最终达到52.5 mJ,为了防止激光吸收水蒸气,再生放大器和功率放大级都封装在充满氮气的密封装置中。在实验中,Grafenstein等人增加了铥掺杂光纤预放大装置,减少了种子脉冲的非线性相位,降低了B积分,克服了高增益、高效率激光放大系统中的一个技术难点。
表5总结了Tm3+/ Ho3+掺杂2 μm波段超快激光放大技术的研究进展情况。Ho3+掺杂激光介质由于发射波长超过2 μm,对大气中水蒸气的吸收更少,易在空气中传输,降低了激光器稳定运转要求,简化了激光器设计,而且具有支持超短脉冲产生的宽带发射光谱,加上量子亏损小、上能级寿命长,因此在大能量2 μm波段超快激光放大器中应用居多。其中,Ho3+离子掺杂YLF和YAG晶体更加适合大能量超短脉冲激光放大,例如Ho:YLF晶体已实现最大脉冲能量52.5 mJ的皮秒激光放大。此外,在大能量固体激光放大器中,增益介质的热管理是限制功率和能量提升的技术难点之一,除了基质材料本身热导率高有益于放大器能量和功率提升外,对增益介质的高效制冷也必不可少。从表5中可以看出,目前Tm3+/Ho3+掺杂2 μm波段超快激光放大器主要采用水冷、TEC、液氮冷却等方式,均能实现十数到数十mJ的脉冲能量放大,但是脉冲宽度大都在ps量级,而且重复频率也不尽相同,其中采用液氮冷却可以实现100 kHz/39 mJ的高重频、大能量2 μm波段皮秒激光放大。
表 5 Tm3+/ Ho3+掺杂2 μm波段超快激光放大技术研究进展
Table 5. Development of Tm3+/ Ho3+ doped 2 μm ultrafast laser amplification techniques
Doped ions Material type Gain materials Repetition rate/kHz Pulse duration/ps Pulse energy/mJ Cooling type Year Ref. Tm3+ Solid Tm:YAP 1 0.38 0.7 - 2015 [148] Tm:YAP 1 0.36 0.015 TEC 2018 [149] Ho3+ Solid Ho:YAG 5 0.44 3 Water cooling 2013 [143] Ho:YLF 10 300 11 TEC 2013 [150] Ho:YLF 10 50 1.1 Water cooling 2015 [151] Ho:YLF 1/0.01 1.9 6.9/13 TEC 2015 [144] Ho:YLF 100 10 39 Liquid nitrogen 2015 [152] Ho:YLF 1 37 34 Water cooling 2015 [145] Ho:YLF 0.7 - 16 Water cooling 2016 [153] Ho:YLF 10/500 8.3/5.5 0.145/0.0112 TEC 2018 [146] Ho:YLF 10 6.3 0.1 TEC 2018 [154] Ho:YLF 1 2.4 52.5 Water cooling 2020 [147] Ho:YLF 1 6.8 28 Water cooling 2020 [155] Ho:YAG 10 3.2 1.6 - 2021 [156]
Research development on Tm3+/ Ho3+ ions doped mid-infrared ultrafast lasers (Invited)
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摘要: 稀土离子Tm3+/ Ho3+ 掺杂中红外2 μm波段超快激光由于广泛的应用前景成为近十余年来激光领域的研究热点之一。文中首先综述了稀土离子Tm3+/Ho3+掺杂固体/光纤2 μm波段超快激光锁模技术进展,包括主动锁模技术以及饱和吸收、克尔透镜、非线性偏振旋转、非线性光环形镜、非线性多模干涉等被动锁模技术;其次,结合激光增益介质及色散管理技术回顾了Tm3+/ Ho3+掺杂固体和光纤锁模激光脉冲宽度压缩进展;再次,总结了Tm3+/ Ho3+大能量/高功率超快激光技术及进展;最后,对2 μm波段超快激光发展趋势进行了总结和展望。
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关键词:
- Tm3+/ Ho3+ /
- 2 μm波段 /
- 锁模激光 /
- 主动锁模 /
- 被动锁模
Abstract: Due to the wide applications, rare earth ions Tm3+/ Ho3+ doped mid-infrared 2 μm ultrafast laser has become one of the hot research topics in the laser field in the past decade. In this paper, the development progress of mode-locking techniques at 2 μm was firstly reviewed, including active mode-locking techniques and passive mode-locking techniques based on the effects of saturation absorption, Kerr lens, nonlinear polarization rotation, nonlinear optical loop mirror, nonlinear multimode interference. Secondly, the development on Tm3+/ Ho3+ doped solid and fiber mode-locked laser pulse compressions was reviewed from the sides of the laser gain media and dispersion management techniques. Thirdly, the technical routes of realizing Tm3+/ Ho3+ high-power and high-energy ultrafast lasers were summarized. Finally, the development trends for 2 μm ultrafast lasers were concluded and outlooked.-
Key words:
- Tm3+/ Ho3+ /
- 2 μm wave band /
- mode-locked laser /
- active mode-locking /
- passive mode-locking
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表 1 Tm3+/ Ho3+掺杂2 μm波段主动锁模激光研究进展
Table 1. Development on the actively mode-locked Tm3+/ Ho3+ doped 2 μm lasers
Doped ions Material type Gain materials Pump sourse Saturable absorber Repetition
rate/MHzPulse duration/
psWavelength/
nmOutput power Pulse energy/nJ Year Ref. Tm3+ Solid Tm:YAG 786.5 nm Ti:
sapphire laserAO 300 35 2 010 70 mW 0.23 1991 [8] Tm:YLF 793 nm LD AO 149.3 170 1 910 2.6 W 17.4 2015 [16] Fiber TDF 792 nm LD AO 37.88 38 1 978 11.8 W 314 2011 [10] TDF 792 nm LD AO 0.06 - - 5 W ~8000 2012 [17] TDF 1.57 μm laser EO 11.884/
12.099816/
4461 950 14.3 mW ~0.0012 2013 [18] TDF 1550 nm fiber laser EO 21.4 58 1 980 ~10 mW - 2014 [19] TDF LD AO 66 200 1 950-2130 53 W 800 2015 [20] TDF 1.55 μm laser EO 40000 1.29 2053 - - 2017 [21] Ho3+ Solid Ho:YLF 1940 nm Tm:
fiber laserAO 81.36 290 2 050 4 W 49 2013 [22] Ho:YAG 1.9 μm Tm:
YLF laserAO 82.76 102 2097 1.04 W 12.57 2015 [11] Ho:LuAG 1910 nm Tm:
fiber laserAO 82.48 333.4 2 010 2.7 W 32.7 2015 [12] Ho:YAG 1.9 μm Tm:
fiber laserAO 81.92 294 2 022 3.41 W 41.6 2016 [23] Ho:LuVO4 1940 nm Tm:
fiber laserAO 82.7 363.3 2073.8 3.04 W 36.8 2016 [13] Ho:YAG ceramic 1910 nm Tm:
fiber laserAO 82.15 241.5 2122.1 1.84 mW 0.022 2016 [14] Ho:Sc2SiO5 1940 nm Tm:
fiber laserAO 81.88 282.4 2112.1 2.72 W 33.2 2018 [24] Tm3+/
Ho3+Solid Tm,Ho:
BaYF780 nm LD AO 100 97 2066 20 mW 0.2 2003 [9] Fiber THDF 1570 nm LD EO 2200 200 1 907-1 927 - - 2018 [15] 注:TDF: Tm-doped fiber,Tm3+掺杂光纤;THDF: Tm-Ho co-doped fiber,Tm3+/ Ho3+共掺光纤 表 2 基于SESAM Tm3+/ Ho3+ 掺杂2 μm波段锁模激光器研究进展
Table 2. Development on the SESAM mode-locked Tm3+/ Ho3+ doped 2 μm lasers
Doped ions Material type Gain materials Pump sourse Saturable absorber Repetition rate/MHz Pulse duration/fs Waveleng-th/nm Output power/mW Pulse energy/nJ Year Ref. Tm3+ Solid Tm:GPNG 792 nm Ti: sapphire laser InGaAsSb-SESAM 222 410 1 997 84 0.38 2010 [39] Tm:KYW 801 nm Ti: sapphire laser InGaAsSb-SESAM 105 386 2 030 235 2.24 2011 [40] Tm:Sc2O3 796 nm Ti:sapphire laser InGaAsSb-SESAM 124.3 218 2107 325 2.6 2012 [41] Tm:Lu2O3 ceramic 796 nm Ti:sapphire laser InGaAsSb-SESAM 121.2 180 2076 400 3.3 2012 [42] Tm:LuYSiO5 Ti:sapphire laser InGaAsSb-SESAM 100 19600 1944.3 64.5 0.645 2012 [43] Tm:YAG ceramic 785 nm Ti:sapphire laser InGaAs-SESAM 88.9 6300 2 012 125 1.4 2013 [44] Tm:LuAG 789 nm LD InGaAs-SESAM 129.2 38000 2 022 1210 9.37 2015 [45] Tm:CaYAlO4 790 nm LD SESAM 145.4 35300 1958.9 &
1960.6830 5.7 2015 [46] Tm:YAG ceramic 786 nm Ti:sapphire laser GaAs-SESAM 89 3000 2 012 150 1.68 2015 [47] Tm:LuAG ceramic 787 nm Ti:sapphire laser GaSb-SESAM 92 2700 2 022 232 2.52 2017 [48] Tm LuScO ceramic 795 nm Ti:sapphire laser GaAsSb-SESAM 78.9 63 2057 175 2.22 2018 [49] Tm:YLF 793 nm LD GaAs-SESAM 94 31000 1 909 95 1.01 2018 [50] Tm:LuYO3 ceramic 795 nm Ti:sapphire laser GaSb-SESAM 78 54 2040.5 51 0.65 2020 [32] Tm:YAG 790 nm LD GaAs-SESAM 97.7 47900 2 012 117 1.2 2020 [51] Tm:CaF2 792 nm LD SESAM 96.35 >1500 1886.8 132 1.37 2020 [52] Fiber TDF 783 nm Ti: sapphire laser InGaAs-SESAM 50 190 1 900 - 0.02 1996 [26] TDF 793 nm LD SESAM 39.8 815000 1978 150 3.8 2012 [53] TDF - SESAM 52.6 230 1 860-
1 930106 2 2012 [54] TDF 1550 nm fiber laser SESAM 108 712 1 945 70 0.65 2015 [55] TDF 1.59 μm Er,Yb:fiber laser SESAM 535 7900 1 938 50 0.09 2016 [56] TDF 793 nm LD SESAM 1600 7200 1959.7 4.5 0.003 2018 [57] Ho3+ Solid Ho:YLiF4 1 940 nm Tm: fiber laser InGaAsSb-SESAM 122 1100 2064 580 4.75 2011 [38] Ho:YAG ceramic 1908nm Tm:fiber laser GaSb-SESAM 82.1 2100 2064 230 2.8 2016 [58] Fiber HDF 1150 nm LD SESAM 7.8 2230 2094 28 3.7 2016 [59] Tm3+/Ho3+ Tm,Ho:KY(WO4)2 802 nm Ti: sapphire laser InGaAsSb-SESAM 132 3300 2057 315 2.38 2009 [28] Solid Tm,Ho:TZN 792 nm Ti: sapphire laser InGaAsSb-SESAM 143 630 2 012 38 0.27 2010 [39] Tm,Ho:KY(WO4)2 802 nm Ti: sapphire laser InGaAsSb-SESAM 118 570 2055 130 1.1 2010 [60] Tm,Ho:NaY(WO4)2 795 nm Ti: sapphire laser InGaAsSb-SESAM 144 191 2058 82 0.57 2010 [29] Tm,Ho:YAP 791 nm Ti:sapphire laser InGaAs-SESAM 107 40400 2064.5 132 1.23 2013 [61] Tm,Ho:YAG 726-859 nm Ti:sapphire laser GaSb-SESAM 106.9 21300 2091 63 0.59 2013 [31] Tm,Ho:KLu(WO4)2 802 nm Ti:sapphire laser InGaSb-SESAM 93 7200 2058 155 1.67 2015 [62] Tm,Ho:CaYAlO4 795 nm Ti:sapphire laser InGaAsSb-SESAM 80.45 87 2024.6 27 0.34 2018 [63] Tm,Ho:CNGG - GaSb-SESAM 89.3 73 2061 36 0.4 2020 [64] Tm,Ho:LiLuF4 Ti:sapphire laser GaAs-SESAM 98.04 12000 1895 350 3.51 2020 [65] Fiber THDF - InGaSb -SESAM 50 750 1 972 20 0.4 2007 [66] THDF 799 nm LD InGaSb-SESAM 24.4 1100 2060 10 0.4 2011 [67] THDF 1.56 μm LD SESAM 38.75 600 1 980 15 0.4 2011 [68] 注:HDF: Ho-doped fiber,Ho3+掺杂光纤 表 3 基于低维纳米材料可饱和吸收体锁模的Tm3+/ Ho3+掺杂2 μm波段超快激光研究进展
Table 3. Development on the ultrafast Tm3+/ Ho3+ doped 2 μm lasers based on the low-dimension nanomaterial saturable absorber mode-locking
Doped ions Material type Gain materials Pump sourse Saturable absorber Repetition rate/MHz Pulse duration/fs Wavelength/nm Output power/mW Pulse energy/nJ Year Ref. Tm3+ Solid Tm:YAP 795 nm LD Graphene 71.8 ~10000 2 023 268 3.7 2011 [70] Tm:YLF Ti:sapphire laser SWCNT - 19000 1 888 55 - 2011 [79] Tm:Lu2O3 798 nm Ti:sapphire laser SWCNT 88 175 2070 36 0.41 2012 [80] Tm:KLuW 802 nm Ti:sapphire laser SWCNT 88 141 2 037 26 0.3 2012 [81] Tm:CLNGG 790 nm LD Graphene 98.7 729 2 018 60.2 0.61 2012 [72] Tm:YAP 800 nm Ti:sapphire laser Graphene 71.8 10000 2 023 268 3.7 2012 [82] Tm:Lu2O3 796 nm Ti:sapphire laser Graphene 110 410 2067 270 0.13 2013 [83] Tm:YAG ceramic 790 nm LD Graphene 98.7 2800 2 016 158 0.08 2015 [73] Tm:MgWO4 796 nm Ti:sapphire laser Graphene 87 86 2 017 96 1.1 2017 [84] Tm:CNNGG 785 nm Ti:sapphire laser SWCNT 90 84 2 018 22 0.24 2018 [85] Tm:CLNGG 785 nm Ti:sapphire laser SWCNT 86 78 2 017 54 0.63 2018 [86] Tm:LuYO3 795 nm Ti:sapphire laser SWCNT 72.6 57 2 045 63 0.87 2019 [87] Tm:YAG 792 nm LD MoS2 232.2 280000 2 011 & 2 017 200 0.86 2020 [88] Fiber TDF 1.57 μm Er fiber laser SWCNT 37 1320 1 930 3.4 0.09 2008 [69] TDF 1.57 μm Er fiber laser SWCNT 45 750 1 885 25 0.5 2009 [89] TDF 790 nm LD Graphene 3.17 - 2 007 1.8 0.56 2012 [71] TDF - Graphene 6.46 3600 1 940 2 0.4 2012 [90] TDF Er fiber laser Graphene 506 58 - - 1 2012 [91] TDF 1.56 μm Er fiber laser SWCNT 6.71 2300 1 947 3 0.45 2013 [92] TDF 1.57 μm Er,Yb:fiber laser Graphene 20.5 1200 1 884 1.35 0.06 2013 [93] Tm3+ Fiber TDF 1.55 μm Er fiber laser Graphene 16.93 2100 1953.3 1.41 0.08 2013 [94] TDF 1.55 μm Er,Yb:fiber laser MoS2 9.67 843000 1 905 150 15.5 2015 [77] TDF 1568 nm LD BP 36.8 739 1 910 1.5 0.0407 2015 [78] TDF 1.57 μm Er fiber laser CNT 25.76 152 1 972 4.85 0.19 2016 [95] TDF 1.56 μm Er fiber laser Graphene 19.31 773 1 910 115 6 2016 [74] TDF 1.56 μm LD TIs-Sb2Te3 39.5 890 1 945 1.2 0.03 2016 [76] TDF 1.56 μm Er,Yb:fiber laser Graphene 58.87 205 1 945 13 0.22 2017 [96] TDF 1.55 μm LD WTe2 18.72 1250 1915.5 39.9 2.13 2017 [97] TDF 1.55 μm LD MoTe2 15.37 1300 1934.85 212 13.8 2018 [98] TDF 1.55 μm LD SWCNT 21.4 211 - 36 1.68 2019 [99] TDF 1.55 μm LD CNT - 910-6430 1733-2 033 - - 2019 [100] Ho3+ Fiber HDF 1 940 nm Tm fiber laser BP 29.1 1300 2094 11 0.379 2017 [101] HDF 1 940 nm Tm fiber laser Graphene 21.13 190 2060 54 2.55 2018 [102] HDF Tm fiber laser CNT 22.13 212 2080 84 3.79 2019 [103] Tm3+/ Ho3+ Solid Tm, Ho:KLu(WO4)2 802 nm Ti:sapphire laser SWCNT 91 2800 2060 97 1.07 2014 [104] Tm,Ho:CNGG 786 nm Ti:sapphire laser SWCNT 102 76 2081 67 0.66 2018 [105] Tm,Ho:CLNGG 796 nm Ti:sapphire laser SWCNT 99.28 67 2083 - - 2019 [106] Fiber THDF 1.55 μm LD TIs-Bi2Te3 27.9 795 1 935 1 - 2014 [75] THDF 1570 nm fiber laser TIs-Bi2Te3 21.5 1260 1909.5 - - 2015 [107] THDF 1.55 μm LD WS2 34.8 1300 1 941 0.6 0.017 2015 [108] THDF 1566 nm LD VSe2 11.6 1400 1 912 - - 2021 [109] 表 4 基于类饱和吸收体锁模的Tm3+/ Ho3+掺杂2 μm波段超快激光研究进展
Table 4. Development on the mode-locked Tm3+/Ho3+ doped ultrafast 2 μm lasers based on artificial SA nonlinear optical effects
Doped ions Material type Gain materials Pump sourse Artificial SA Repetition rate/MHz Pulse duration/fs Wavelength/nm Output power/mW Pulse energy/nJ Year Ref. Tm3+ Solid Tm:YLF 780 nm Ti:sapphire laser Kerr-lens 41.5 514 2303 14.4 0.35 2017 [111] Tm:Sc2O3 1.59 μm Er,Yb:fiber laser Kerr-lens 93.8 72 2108 130 1.38 2020 [113] Tm:Lu2O3 &
Tm:Sc2O31611 nm Er:Yb MOPA Kerr-lens 93.3 41 2094 42 0.45 2021 [114] Ho3+ Solid Ho:YAG TD 1.908 µm TDFL Kerr-lens 77 270 2090 28000 363 2017 [110] Tm3+ Fiber TDF 783 nm Ti:sapphire laser NPR - 350-500 1798-1 902 0.24 13.74 1995 [115] TDF 793 nm LD NPR 41.4 173 1 974 167 4 2008 [119] TDF 793 nm LD NPR 41.4 1200 1 976 178 4.3 2008 [120] TDF 1.5 μm Er fiber laser NPR 9.78 770 1 982 1.5 0.15 2011 [121] TDF 1575 nm laser NPR & SAM 19.7 482 1 927 13.2 0.67 2012 [122] TDF 1575 nm Er fiber laser NPR 45.42 119 1 912 7.8 0.17 2012 [123] TDF 1561 nm Er fiber laser NPR 6.37 - 1942.2 110 17.3 2013 [124] TDF 1550 nm Er fiber laser NPR & SAM 22.9 200 1 950 16 0.7 2014 [125] TDF 793 nm LD NPR 1.902 2200 1992.7 0.142 0.0746 2014 [126] TDF 793 nm Ti:sapphire laser NPR 67.5 45 1 880 13 0.19 2014 [127] TDF 793 nm LD NPR 2.68 3100 1 862 3 1.12 2015 [128] TDF 1569 nm Er fiber laser NPR 20-30 130 - - 7.6 2015 [129] TDF 793 nm LD NPR 6.32 406 2003.2 - 12.342 2016 [130] TDF 1550 nm Er fiber laser NPR 11.6 350 1 890 90 7.8 2017 [131] TDF - NPR - 142.8 1 950 370 31 2018 [132] TDF 1610 nm EYDFL NPR 10.62 534 1 988 189 17.8 2019 [133] Ho3+ Fiber HDF 1 950 nm Tm fiber laser NPR & SAM 65 920 2 040-2070 - 0.8 2017 [116] HDF 1 950 nm fiber laser NPR 13.2 370000 2133 68.6 5.2 2018 [134] Tm3+ Fiber TDF 1570 nm fiber laser NLMMI 19.82 1400 1 888 - - 2017 [117] Tm3+ Fiber TDF 786 nm laser NALM 4.75 682 - 41 8.75 2012 [135] TDF 786 nm LD NALM 10.4 1500 2 034 0.66 0.063 2013 [136] TDF 793 nm LD NOLM 1.514 341 2 017 377.3 249.32 2014 [137] TDF 793 nm LD NALM 9.1 460 1 990 301 32.72 2015 [138] TDF 793 nm LD NPR & NOLM 2.66 258 2 007 112 42.11 2017 [139] TDF 793 nm LD NOLM 2.85 384 1988.8 720 252.6 2020 [118] TDF 1550 nm Er fiber laser NALM 3.228 317 1946.4 32800 10100 2021 [140] Ho3+ Fiber HDF 1.9 μm TDFL NAbLM 7.765 - 2058 - - 2020 [141] HDF Tm laser NALM 41.7 - 2 050 4 0.095 2020 [142] 注:SA: Saturable absorber,可饱和吸收体;TD: Thin disk,薄片;MOPA: Master oscillator power-amplifier,主振荡功率放大;TDFL: Tm-doped fiber laser,Tm3+掺杂光纤激光器;EYDFL: Er-Yb co-doped fiber laser,Er3+/Yb3+离子共掺光纤激光器 表 5 Tm3+/ Ho3+掺杂2 μm波段超快激光放大技术研究进展
Table 5. Development of Tm3+/ Ho3+ doped 2 μm ultrafast laser amplification techniques
Doped ions Material type Gain materials Repetition rate/kHz Pulse duration/ps Pulse energy/mJ Cooling type Year Ref. Tm3+ Solid Tm:YAP 1 0.38 0.7 - 2015 [148] Tm:YAP 1 0.36 0.015 TEC 2018 [149] Ho3+ Solid Ho:YAG 5 0.44 3 Water cooling 2013 [143] Ho:YLF 10 300 11 TEC 2013 [150] Ho:YLF 10 50 1.1 Water cooling 2015 [151] Ho:YLF 1/0.01 1.9 6.9/13 TEC 2015 [144] Ho:YLF 100 10 39 Liquid nitrogen 2015 [152] Ho:YLF 1 37 34 Water cooling 2015 [145] Ho:YLF 0.7 - 16 Water cooling 2016 [153] Ho:YLF 10/500 8.3/5.5 0.145/0.0112 TEC 2018 [146] Ho:YLF 10 6.3 0.1 TEC 2018 [154] Ho:YLF 1 2.4 52.5 Water cooling 2020 [147] Ho:YLF 1 6.8 28 Water cooling 2020 [155] Ho:YAG 10 3.2 1.6 - 2021 [156] -
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