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中红外波段飞秒激光在超快光谱学、高分辨宽光谱光谱学、量子光学及中红外光学频率梳等方面都具有重要的应用价值[1-3]。Cr: ZnS/ZnSe增益介质的宽发射谱特性,使其成为中红外波段直接产生飞秒激光的优异材料。得益于成熟稳定的掺铒、掺铥光纤激光器,Cr:ZnS/ZnSe能够被便捷地泵浦[4-5]。宽的发射谱支持Cr:ZnS/ZnSe激光器能够实现少周期量级的飞秒脉冲输出[6-8]。Cr:ZnS/ZnSe飞秒激光能够用于产生中红外的光学频率梳和分子探测等方面[9]。同时其还可以作为优良的驱动光源,用于泵浦光参量振荡器[10]、高次谐波的产生[11]、差频产生宽光谱中红外激光[12-13]等。
可饱和吸收镜(SESAM)锁模和克尔透镜锁模(KLM)是Cr:ZnS/ZnSe中获得飞秒激光的两种主要方式[14-16]。最早在Cr:ZnS/ZnSe上实现飞秒脉冲的输出就是基于SESAM锁模的方法[14]。这种方法能够实现稳定的自启动锁模运转,但SESAM的带宽限制使得这种锁模激光器的平均功率较低,脉冲宽度很难达到少周期量级[17-18]。而克尔透镜锁模没有带宽限制,因此,基于克尔透镜锁模的Cr:ZnS/ZnSe激光器就成为了更好的选择,它的输出功率可以达到瓦级,脉冲宽度可以达到少周期量级[19-20]。表1中列举了在Cr:ZnS中实现SESAM锁模和克尔透镜锁模的国内外研究进展。
表 1 Cr:ZnS中SESAM和克尔透镜锁模输出脉冲参数
Table 1. Parameters of SESAM or Kerr-lens mode-locked output pulses in Cr:ZnS
Published year Mode-locking method Pulse width Average power Ref. 2006 SESAM 1.1 ps 125 mW [23] 2012 SESAM 130 fs 130 mW [17] 2013 KLM 68 fs 1 W [19] 2016 KLM 41 fs 1.9 W [24] 2017 KLM 125 fs 80 mW [25] 2019 KLM 45 fs 1 W [13] 2020 KLM 34 fs 0.8 W [26] 2021 KLM 23 fs 1.4 W [27] 2021 SESAM 79 fs 0.8 W [28] 2021 KLM + normal dispersion 37 fs 0.66 W This work 克尔透镜锁模系统根据腔内色散量情况,可以分为孤子锁模和全正色散锁模。孤子锁模是最为常见的一种运转方式,其相对容易实现,同时也具有很好的稳定性,但随着脉冲能量的增加,容易发生脉冲分裂,在腔内出现多脉冲的情况。相比之下,全正色散锁模由于脉冲在谐振腔内放大时为啁啾脉冲,能够获得更高的脉冲能量,输出后经过脉冲压缩得到更接近傅里叶变换极限的脉冲[9, 21-22]。
文中报道了一种Cr:ZnS的全正色散克尔透镜锁模激光器,这也是首次在Cr:ZnS激光器中实现了全正色散锁模。
Operation of femtosecond Kerr-lens mode-locked laser with all-normal dispersion at 2.4 μm (Invited)
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摘要: 2 μm波段的飞秒激光光源在高分辨分子光谱学、中红外光学频率梳产生和超宽光谱的中红外光源产生等方面都具有重要的应用价值。Cr: ZnS/ZnSe具有很宽的发射峰,使其成为该波段产生宽光谱短脉冲中红外飞秒激光的重要材料。全正色散锁模的飞秒激光由于更容易实现较短的脉冲宽度与较高的峰值功率而受到青睐。文中在Cr: ZnS上实现全正色散条件下的克尔透镜锁模运转。在5.1 W的泵浦功率下实现波长覆盖范围2.0~2.7 μm,平均功率660 mW,脉冲宽度37 fs的稳定锁模脉冲输出,这是首次在Cr: ZnS中实现全正色散锁模运转的固体激光器。Cr:ZnS 全正色散锁模的飞秒激光器在高分辨分子光谱学、宽光谱中红外光光源产生等方面具有广阔的应用前景。Abstract: Femtosecond laser sources operating at around 2 μm spectral range support a plethora of applications, especially in high-resolution molecule spectroscopy, synthesis of mid-infrared optical frequency combs, and broadband mid-infrared sources. Cr:ZnS/ZnSe with broad emission bands is an ideal material to support femtosecond pulse generation at around 2 μm spectral range. Femtosecond mode-locked lasers with all-normal dispersion have recently attracted great attention due to their short pulse duration and large output pulse peak power. An operation of femtosecond Kerr-lens mode-locked laser was demonstrated in Cr: ZnS with all-normal dispersion. The laser system delivered stable mode-locked pulses with pump power of 5.1 W, spectral range from 2.0 to 2.7 μm, average power of 660 mW, duration of 37 fs. It is the first time to realize the operation of femtosecond mode-locked solid laser with all-normal dispersion in Cr: ZnS, which have potential applications in high-resolution molecule spectroscopy and generation of broadband mid-infrared sources.
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Key words:
- all-normal dispersion /
- Kerr-lens mode-lock /
- Cr: ZnS /
- mid-infrared femtosecond laser
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表 1 Cr:ZnS中SESAM和克尔透镜锁模输出脉冲参数
Table 1. Parameters of SESAM or Kerr-lens mode-locked output pulses in Cr:ZnS
Published year Mode-locking method Pulse width Average power Ref. 2006 SESAM 1.1 ps 125 mW [23] 2012 SESAM 130 fs 130 mW [17] 2013 KLM 68 fs 1 W [19] 2016 KLM 41 fs 1.9 W [24] 2017 KLM 125 fs 80 mW [25] 2019 KLM 45 fs 1 W [13] 2020 KLM 34 fs 0.8 W [26] 2021 KLM 23 fs 1.4 W [27] 2021 SESAM 79 fs 0.8 W [28] 2021 KLM + normal dispersion 37 fs 0.66 W This work -
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