Light interaction with random linear or nonlinear media is always an interesting scheme to study Anderson localization of photons and phase-matching-free nonlinear optics. The previous random laser scheme provided a new laser mode to achieve a local signal enhancement, but it needed an active medium with a good photoresponse via a four-level or Raman-level transition process [11,12]. The response wave band was also limited by the inherent energy-level structure of the material.

Here, a cavity-enhanced second-harmonic generation (SHG) process in a random nonlinear material was experimentally demonstrated. Compared to the conventional random laser action based on the photoluminescence (PL) effect, this cavity-enhanced SHG indicates a possible Anderson localization of the nonlinear signals by ring cavities and widens the response wave band due to the flexible frequency conversion in the nonlinear process. The combination of the random cavity scheme and the random quasi-phase-matching scheme will provide us another way to break phase-matching limitations, with locally high conversion efficiency. This work suggests important progress on nonlinear Anderson localization and indicates many potential applications, such as a band-tunable random nonlinear laser, phase-matching-free nonlinear optics, and even focusing or imaging through random nonlinear media with a nice conversion efficiency.

This research was published in “Yanqi Qiao, Fangwei Ye, Yuanlin Zheng, and Xianfeng Chen, Cavity-enhanced second-harmonic generation in strongly scattering nonlinear media, Physical Review A, 99, 043844 (2019)”.