In recent years, explorations of the nonlinear optical (NLO) responses of van der Waals (vdW) crystals have proven to be integral to the study of their fundamental material symmetries, while also providing a platform to revolutionize optoelectronic and photonic devices. Here, we will discuss our recent efforts to probe the NLO properties of an emerging class of polar vdW semiconductors and extend vdW nonlinear optics to include the often-overlooked spatial degree of freedom of light. First, we will highlight our studies of bismuth telluro-halide crystals, where we observe giant second order optical nonlinearities in the telecom band and second-harmonic textures that are highly correlated to the orientation of their polar domains. We will then turn our focus to nonlinear frequency-mixing processes in vdW crystals driven by twisted light. Here, we demonstrate the harmonic scaling of orbital angular momentum and the free tuning of the wavelength, topological charge, and radial index of vortex light-fields, both supported by atomically thin semiconductors. Our work points to new materials and structured-illumination-based methods to dramatically extend the versatility of vdW materials for classical and quantum communication nanotechnologies.

Bio: Prashant Padmanabhan is a Staff Scientist and Principal Investigator at the Center for Integrated Nanotechnologies (CINT) at Los Alamos National Laboratory. His current interests include using ultrafast pulses spanning the terahertz to extreme ultraviolet regime to control spin-dependent phenomena in van der Waals magnets, explore nonlinear optical processes in topological materials, and exploit spatial mode structuring to drive emergent phenomena in quantum materials. Prashant received his Ph.D. in Applied Physics from the University of Michigan in the group of Dr. Roberto Merlin before pursuing postdoctoral research at the University of Cologne, Germany and Los Alamos National Laboratory.