Extreme Space-Time Optics

In the dynamic field of optics, extreme nonlinear and space-time subtopics stand out for their rapid evolution and broad applicability. Here, I discuss recent developments in extreme nonlinear optics, from harnessing extreme intensities through single-cycle optical modulation to pushing the boundaries of modulations induced by a single photon.<br/><br/><b>The road to Photonic Time Crystals: </b>Transparent conducting oxides (TCOs) and other near zero index (NZI) materials demonstrate exceptional optical properties, particularly enhancing optical nonlinearities. Leveraging TCOs' rapid optical response from optically driven electronic transitions, they prove valuable for optical modulators and beyond. This study examines how a single-cycle pulse modulates a probe beam, paving the way for exploring photonic time crystals—an intriguing new phase of photonic matter.<br/><br/>In standard <i>spatial</i> photonic crystals (PCs), periodic modulations in material and optical properties lead to interesting optical behavior including frequency bandgaps, modification spontaneous emission, and nontrivial topologies. Importantly, PCs require sharp spatial interfaces. A photonic time crystal (PTC) is a spatially-homogeneous medium that changes periodically in time leading to predicted bandgaps in momentum and lasing in the bandgap. As in the spatial case, there must be sharp temporal changes placing stringent requirements on implementation in the optical domain. Our results demonstrate that TCOs unexpectedly have an ultrafast relaxation time accompanying the ultrafast rise-time making them ideal candidates for PTCs.<br/><br/><b>All-optical Modulation with Single-photon Intensities:</b> The manipulation of light by light lies at the core of numerous photonic applications spanning telecommunication, microscopy, computing, and quantum optics. However, achieving such effects at a single photon level, where one photon significantly influences another macroscopic beam, remains a formidable challenge. Demonstrations of nonlinearity at a single photon level have been realized in optical/photonic cavities strongly linked to atoms, quantum dots, and other types of single-photon emitters. Progress in achieving single-photon nonlinearities has been demonstrated with polaritons. However, achieving high-speed single-photon all-optical modulation at room temperatures and for a broad range of wavelengths remains a challenging problem.<br/><br/>Here, we use electron avalanche multiplication process to modulate a beam of light by another beam with a single-photon intensities. The single photon produces a cascade up to millions of new electrons into a conduction band of silicon, that is typically detected electrically. We show the detection these changes through another probe laser beam at a near-infrared (NIR) wavelength and successfully demonstrated the modulation of the telecom light using an 810-nm light pulse with an average photon count of approximately 0.0005-0.1 per pulse. Our approach has a high efficiency operation across a broad wavelength range (from 400nm to 1000nm for silicon SPAD) at room temperature. We believe that our approach has great potential for achieving strong optical nonlinearity at the single-photon level and at THz rates, which could significantly advance the field of photonics and enable a variety of applications at the single-photon level.