Until recently, the generation of super-octave continua in bulk materials at full repetition rates of femtosecond (fs) oscillators has been limited to a few special cases of Kerr lens mode-locked Ti:sapphire lasers. In 2019, we described a 3.4-octave fs source with 50 nJ pulse energy at the repetition rate of 78 MHz based on polycrystalline Cr:ZnS [Vasilyev et al., Optica 6, 126 (2019) [CrossRef] ]. Here we explain the mechanism of fs supercontinuum generation in transition-metal doped polycrystalline II-VI semiconductors at relatively low (nJ-level) pulse energy. We demonstrate that this new supercontinuum regime is enabled by a complex, yet well-reproducible, interplay between the effects arising from the third-order nonlinearity, the quadratic nonlinearities, and thermal optical effects in the medium. We also demonstrate the control of fs pulse propagation in disordered $\chi ^{ (2)}$ media via the control of the material microstructure.

中文翻译：

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多晶介质中的低阈值超连续谱生成

直到最近，在散装材料中以飞秒（fs）振荡器的完全重复速率生成超八度音阶连续体的方法仅限于Kerr透镜锁模Ti：蓝宝石激光器的一些特殊情况。在2019年，我们基于多晶Cr：ZnS描述了一个3.4倍频程的fs源，其脉冲能量为50 nJ，重复频率为78 MHz [Vasilyev等。，。光学6，126（2019）[交叉引用] ]。在这里，我们解释了在相对较低的（nJ级）脉冲能量下，过渡金属掺杂的多晶II-VI半导体中fs超连续谱产生的机理。我们证明了这种新的超连续谱体系是由复杂的，但可重现的，由三阶非线性，二次非线性和介质中的热光学效应产生的效应之间的相互作用所实现的。我们还演示了通过控制材料微观结构来控制无序$ \ chi ^ {（2）} $介质中fs脉冲传播的控制。