Freewheeling across laser’s wonderland: from mid-infrared filaments to neurophotonics (Prof. A. Zheltikov)

Its first part will offer a brief overview of our recent experiments on laser filamentation using ultrashort high-peak-power mid-infrared pulses. These studies reveal unique properties of optical nonlinearities in the mid-infrared and unusual scenarios of ultrafast nonlinear dynamics. Generation of few- and even single-cycle mid-infrared field waveforms with peak powers ranging from a few megawatts to hundreds of gigawatts has been demonstrated within a broad range of central wavelengths. We will show that the Wigner and Gabor chronocyclic maps of ultrashort mid-infrared laser probes can help reveal new, often unexpected aspects of the ultrafast optical response of complex molecular mixtures. Below-the-bandgap high-order harmonics generated by ultrashort mid-infrared laser pulses are shown to be ideally suited to probe the nonlinearities of electron bands, enabling an all-optical mapping of the electron band structure in bulk solids.

In the second part of the talk, as a dramatic plot twist, fiber-optic neurointerfaces for opto- and thermogenetics will be discussed. Our experiments in this area of research show that specifically designed and carefully optimized fiber-optic interfaces can help to extend optogenetic methods to deeper brain regions. We demonstrate implantable fiber-optic interfaces enabling parallel long-term optogenetic interrogation of distinctly separate, functionally different sites in the brain of freely moving mice. Fiber probes developed by our group can induce a localized, precisely controlled heating of individual cells expressing heat-sensitive genetically encoded thermosensitive channels. A diamond microcrystal attached to the tip of the fiber and heated by laser radiation transmitted through the fiber provides a local heating of the cell culture, enabling a well-controlled thermal activation of cells. Moreover, this fiber probe can simultaneously measure the temperature of a cell through a temperature-dependent frequency shift of optically detected magnetic resonance, which is induced by coupling the microwave field to the spin of nitrogen–vacancy centers in diamond on the tip of the fiber probe.