Acousto-Optic Modulation in Ambient Air

Abstract: Control over intensity, shape, direction, and phase of coherent light is essential in numerous fields, reaching from gravitational wave astronomy over quantum metrology and ultrafast sciences to semi-conductor fabrication. Modern laser optics, however, frequently demands parameter regimes where either the wavelength or the optical power restricts control due to linear absorption, light-induced damage or optical nonlinearity. The properties of solid media, upon which most photonic control schemes rely, impose these limitations. We propose to circumvent these constraints using gaseous media tailored by high-intensity ultrasound waves. We demonstrate a first implementation of this approach by deflecting ultrashort laser pulses using ultrasound waves in ambient air, entirely omitting transmissive solid media. At optical peak powers of 20 GW exceeding previous limits of solid-based acousto-optic modulation by about three orders of magnitude, we reach a deflection efficiency greater than 50% while preserving excellent beam quality. Our approach is not limited to laser pulse deflection via acousto-optic modulation: gas-phase photonic schemes controlled by sonic waves can prospectively be translated to various optical methods, e.g., lenses or waveguides, rendering them effectively invulnerable against damage and opening up new spectral regions.