Yongquan Zeng

Suppressing spatiotemporal lasing instabilities with wave-chaotic microcavities

Taming laser instabilities Broad-area and high-power lasers often suffer from instabilities owing to the chaotic interference of multiple modes within the cavity. Such instabilities can ultimately limit the operation of the laser or damage the cavity. The usual approach to minimizing such instabilities is to limit the number of modes in the cavity. Bittner et al. designed a chaotic cavity that disrupts the formation of self-organized structures that lead to instabilities (see the Perspective by Yang). This approach of fighting chaos with chaos by using the boundary condition of the cavity shape may provide a robust route to stabilizing lasers at high operating powers. Science, this issue p. 1225; see also p. 1201 A chaotic cavity design is used to suppress the spatiotemporal instabilities in lasers. Spatiotemporal instabilities are widespread phenomena resulting from complexity and nonlinearity. In broad-area edge-emitting semiconductor lasers, the nonlinear interactions of multiple spatial modes with the active medium can result in filamentation and spatiotemporal chaos. These instabilities degrade the laser performance and are extremely challenging to control. We demonstrate a powerful approach to suppress spatiotemporal instabilities using wave-chaotic or disordered cavities. The interference of many propagating waves with random phases in such cavities disrupts the formation of self-organized structures such as filaments, resulting in stable lasing dynamics. Our method provides a general and robust scheme to prevent the formation and growth of nonlinear instabilities for a large variety of high-power lasers.

Amorphous random lasing at terahertz frequency

Multi-mode random terahertz lasing with strongly localized modes has been realized for the first time, by fabricating two dimensional randomly distributed quantum cascade pillars with a small short-range order.

Integrated 2D materials and metasurfaces for multifunctional semiconductor lasers in Terahertz (Conference Presentation)

Quantum cascade laser (QCL) is a semiconductor based laser in a superlattice structure based on intersubband transitions. Although QCLs have been achieved with high performance such as Watt-level emission, it is always highly desired to further improve the device performance with multiple functions , for example, achieving high beam collimation, arbitrary polarization control, and high speed modulation. It is also desired that those performance could be achieved through an integrated approach for miniaturalization, easy alignment and reducing cost. In this presentation, we will use Terahertz (THz) QCL as a demonstration example to obtain high collimated THz QCLs through plasmonic collimation designs with a record beam divergence, electrically tunable THz polarizations by designing integrated THz metasurfaces on a hybrid dielectric-plasmonic waveguides, and broadband graphene-based integrated THz modulators with a fast modulating speed.

Terahertz emission in one-dimensional disordered systems

Multimode terahertz (THz) laser emission around 3.2 THz in one-dimensional (1-D) disordered systems with 20% disorder. Simulation and experimental work provide evidence for spatial localization of light of defect modes within the bandgap frequency window.