Ultrafast sources in the mid-IR are indispensable research tools for spectroscopic and medical applications and can also potentially be used to generate attosecond pulses. We investigated a route to directly achieve self-compressed supercontinuum pulses with an octave-exceeding spectrum extending into the mid-IR by employing self-defocusing nonlinearities obtained through cascaded ${\chi }^{(2)}$ interactions in domain-structured ferroelectrics. A model was developed based on a single-wave nonlinear envelope equation that accounts for cascaded ${\chi }^{(2)}$ nonlinearities, the native Kerr response from the third-order nonlinear polarization, and the delayed Raman response. Experimental validation of the model was carried out by using an in-house fabricated, periodically poled, Rb-doped ${\text{KTiOPO}}_4$ crystal with a period of 36 μm. A supercontinuum spectrum spanning from 1.1 to 2.7 μm was achieved, as well as self-compression down to 18.6 fs, from a 128 fs pump pulse at 1.52 μm. Using the actual pump pulse and sample parameters, excellent agreement was reached between the model and the experimental results, thus proving the validity of the model. As periodically poled ${\text{KTiOPO}}_4$ can be obtained with large apertures, this approach is energy scalable and hence promising for future development in the field.

中文翻译：

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χ ^（2）结构的KTiOPO _4中的超连续谱生成和孤子自压缩

中红外的超快光源是光谱和医学应用必不可少的研究工具，也有可能被用于产生阿秒脉冲。我们研究了通过级联获得的自散焦非线性来直接实现具有超过倍频程的频谱扩展到中红外的自压缩超连续谱脉冲的途径${\chi }^{（\mathrm{2个}）}$畴结构铁电中的相互作用。基于单波非线性包络方程开发了一个模型，该模型考虑了级联${\chi }^{（\mathrm{2个}）}$非线性，来自三阶非线性极化的原始Kerr响应以及延迟的拉曼响应。通过使用内部制造的，周期性极化，掺Rb的模型进行模型的实验验证${\text{钛白粉}}_4$周期为36μm的晶体。从1.52μm处的128 fs泵浦脉冲获得了从1.1到2.7μm的超连续谱，以及自压缩低至18.6 fs。使用实际的泵脉冲和样品参数，模型与实验结果达到了极好的一致性，从而证明了模型的有效性。由于定期极化${\text{钛白粉}}_4$ 可以通过大孔径获得这种方法，这种方法具有能量可扩展性，因此有望在该领域进行未来的发展。