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 quasiphase 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 3 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.
Manipulation of the light phase lies at the heart of the investigation of light-matter interactions, especially for efficient nonlinear optical processes. Here, we originally propose the angular engineering strategy of the additional periodic phase (APP) for realization of tunable phase matching and experimentally demonstrate the widely tunable phase-matched second harmonic generation (SHG) which is expected for dozens of years. With an APP quartz crystal, the phase difference between the fundamental and frequency-doubled light is continuously angularly compensated under this strategy, which results the unprecedented and efficient frequency doubling at wavelengths almost covering the deep-UV spectral range from 221 to 332 nm. What’s more, all the possible phase-matching types are originally realized simultaneously under the angular engineering phase-matching conditions. This work should not only provide a novel and practical nonlinear photonic device for tunable deep-UV radiation but also be helpful for further study of the light-matter interaction process.
Second harmonic generation (SHG) is the nonlinear response of electrons to high‐intensity light and has been successfully applied in basic scientific research and modern optoelectronics. However, constrained by stringent but essential phase‐matching conditions, efficient vacuum ultraviolet (VUV) SHG is still a challenge in solid‐state lasers. Here, this work employs a spatial frequency manipulation strategy to realize artificially structured phase‐matching conditions in ordinary quartz crystals for efficient frequency doubling in the VUV range. Phase‐matched VUV SHG at wavelengths of 177.3 and 167.8 nm is realized with unprecedented output power and conversion efficiency. The design strategy releases the phase‐matching condition for nonlinear optics and provides a way to study light–matter nonlinear interactions, and the present sources should be helpful for the development of VUV photonics, including high‐resolution angle‐resolved photoemission spectroscopy and Al+ optical clocks.
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