Quantum Dial for High-Harmonic Generation

Abstract: High-harmonic generation (HHG) is a highly nonlinear optical process that typically requires an intense laser to trigger emissions at integer multiples of the driving field frequency. Since HHG is commonly used as a spectroscopic tool to probe material properties, it becomes impossible to extract information about a material without introducing distortions caused by the strong driving field. Recent advances in bright squeezed vacuum sources have allowed HHG to be driven by purely quantum fields alone. Our work focuses on controlling and tuning HHG emission using a weak classical driving field with energy 1000 times less than that used in conventional HHG experiments, perturbed by an even weaker quantum field, such as bright squeezed vacuum (BSV). Our technique opens new avenues for nonlinear spectroscopy of materials by minimizing issues such as laser-induced damage, distortions, and heating. Our results show that a BSV pulse, containing less than 0.5% of the driving laser energy, can serve as an optical dial for tuning nonlinear emission, electron dynamics, and ionization.