Shao Mingchuan, Liang Fei, Yu Haohai, Zhang Huaijin
State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100 China.
Light Sci Appl. 2020 Mar 18;9:45. doi: 10.1038/s41377-020-0281-4. eCollection 2020.
Nonlinear frequency conversion is a ubiquitous technique that is used to obtain broad-range lasers and supercontinuum coherent sources. The phase-matching condition (momentum conservation relation) is the key criterion but a challenging bottleneck in highly efficient conversion. Birefringent phase matching (BPM) and quasi-phase matching (QPM) are two feasible routes but are strongly limited in natural anisotropic crystals or ferroelectric crystals. Therefore, it is in urgent demand for a general technique that can compensate for the phase mismatching in universal nonlinear materials and in broad wavelength ranges. Here, an additional periodic phase (APP) from order/disorder alignment is proposed to meet the phase-matching condition in arbitrary nonlinear crystals and demonstrated from the visible region to the deep-ultraviolet region (e.g., LiNbO and quartz). Remarkably, pioneering 177.3-nm coherent output is first obtained in commercial quartz crystal with an unprecedented conversion efficiency above 1‰. This study not only opens a new roadmap to resuscitate those long-neglected nonlinear optical crystals for wavelength extension, but also may revolutionize next-generation nonlinear photonics and their further applications.
非线性频率转换是一种广泛应用的技术，用于获得宽范围的激光器和超连续谱相干光源。相位匹配条件（动量守恒关系）是关键标准，但也是高效转换中一个具有挑战性的瓶颈。双折射相位匹配（BPM）和准相位匹配（QPM）是两种可行的途径，但在天然各向异性晶体或铁电晶体中受到很大限制。因此，迫切需要一种通用技术，能够在通用非线性材料和宽波长范围内补偿相位失配。在此，提出了一种由有序/无序排列产生的附加周期相位（APP），以满足任意非线性晶体中的相位匹配条件，并在从可见光区域到深紫外区域（如铌酸锂和石英）得到了验证。值得注意的是，首次在商用石英晶体中获得了177.3纳米的开创性相干输出，其转换效率达到了前所未有的千分之一以上。这项研究不仅为复苏那些长期被忽视的用于波长扩展的非线性光学晶体开辟了一条新途径，还可能彻底改变下一代非线性光子学及其进一步应用。
