Deep-ultraviolet second harmonic generation in a conventional crystal quartz by freeing phase-matching in nonlinear optics

Abstract

Nonlinear frequency conversion in optics can originate the coherent light at the wavelength where it is hard or unlikely to achieve by directly lasing and is a fundamental topic in science and engineering covering both classical and quantum regions. The critical requirement for efficient nonlinear frequency conversion is phase-matching, a momentum conservation relation between the fundamental and harmonic light. It is dreaming of a technique for compensating the phase-mismatching in universal nonlinear materials and wavelength ranges, since the phase-matching was proposed in 1962. Here, an additional periodic phase (APP) concept was proposed for the phase-matching in nonlinear optics and experimentally demonstrated the APP phase-matched second harmonic generation with a conventional crystal quartz at the wavelength deep to vacuum-ultraviolet 177.3 nm. This study may not only develop a universal way to resuscitate the nonlinear optical materials for efficient nonlinear frequency conversion, but also may revolutionize the nonlinear photonics and their further applications.