Communications Physics ( IF 5.5 ) Pub Date : 2020-10-30 , DOI: 10.1038/s42005-020-00472-5 Hanzhe Liu , Giulio Vampa , Jingyuan Linda Zhang , Yu Shi , Siddharth Buddhiraju , Shanhui Fan , Jelena Vuckovic , Philip H. Bucksbaum , David A. Reis
Since the new millennium coherent extreme ultra-violet and soft x-ray radiation has revolutionized the understanding of dynamical physical, chemical and biological systems at the electron’s natural timescale. Unfortunately, coherent laser-based upconversion of infrared photons to vacuum-ultraviolet and soft x-ray high-order harmonics in gaseous, liquid and solid targets is notoriously inefficient. In dense nonlinear media, the limiting factor is strong re-absorption of the generated high-energy photons. Here we overcome this limitation by generating high-order harmonics from a periodic array of thin one-dimensional crystalline silicon ridge waveguides. Adding vacuum gaps between the ridges avoids the high absorption loss of the bulk and results in a ~ 100-fold increase of the extraction depth. As the grating period is varied, each high harmonic shows a different and marked modulation, indicating their waveguiding in the vacuum slots with reduced absorption. Looking ahead, our results enable bright on-chip coherent short-wavelength sources and may extend the usable spectral range of traditional nonlinear crystals to their absorption windows. Potential applications include on-chip chemically-sensitive spectro-nanoscopy.
中文翻译:
固态高谐波中的拍频吸收
自从新千年以来,相干的极端紫外线和软X射线辐射已经彻底改变了在电子自然时标上对动态物理,化学和生物系统的理解。不幸的是,众所周知,在气体,液体和固体目标中,基于激光的相干激光将红外光子上转换为真空-紫外线和软X射线高次谐波是效率低下的。在稠密的非线性介质中,限制因素是所产生的高能光子的强烈重吸收。在这里,我们通过从一维薄晶体硅脊形波导的周期性阵列中生成高次谐波来克服此限制。在脊之间增加真空间隙可避免大量物质的高吸收损失,并导致提取深度增加约100倍。随着光栅周期的变化,每个高次谐波显示出不同且明显的调制,表明它们在真空槽中的波导具有减小的吸收。展望未来,我们的结果将使明亮的片上相干短波源成为可能,并且可能将传统非线性晶体的可用光谱范围扩展到其吸收窗口。潜在的应用包括片上化学敏感光谱纳米技术。