![]() Upon interaction of the two waves, quantized as a photon and a phonon, they can scatter 24. The field of acousto-optics describes the interaction between optic and acoustic waves. To achieve this, we engineer a transmissive optical Bragg grating by periodic sinusoidal pressure modulation 23 using high-pressure ultrasound, enabling efficient AOM in ambient air. In this Article, we demonstrate a novel light control method employing highly intense ultrasound waves in air. Strikingly, more advanced gas-based schemes enabling superior control options including efficient acousto-optic modulation (AOM) have not yet entered the photonics field. Applying similar principles, gas-phase refractive elements 2 such as lenses 19, beam samplers 20 and intracavity acousto-optic (AO) loss modulators 21, as well as gratings using multiple plasma layers 22, have been developed. ![]() In nature, this phenomenon is well known: in a mirage, layers of air at different temperature levels, with Δ n on the order of only 10 −5, can substantially alter the optical path 7. However, in the limit of small incident angle (grazing incidence), light reflection can still occur even for small Δ n. In addition, creating a static refractive index boundary in gases poses a technical challenge. Their refractive index, however, is very close to 1, limiting Δ n for gas-based photonic systems. In contrast to solids, gases are immune to damage and support about three orders of magnitude higher peak powers at very little dispersion within large spectral regions. One powerful route to circumvent some of these limitations has been opened by meta-optics 17, 18, relying on nanostructured dielectric media.Īn entirely different route is the employment of gaseous photonic media. For intense or ultrashort pulses, additional restrictions arise due to dispersion and nonlinear optical effects such as self-focusing 16. ![]() Compared to gases, glasses are transmissive only in a relatively small spectral range they restrict the optical peak and average power through light-induced damage 14, as well as thermal lensing 15, and cause losses at boundary layers. However, with the rapid progress in high-peak-power laser technology 8 and applications 9, 10, 11 reaching into novel wavelength regimes 12, 13, established solid-based control schemes face severe limitations. This is a key reason why bulk media are used almost exclusively for optical elements such as lenses, mirrors, waveguides, among many others. Large refractive index differences on the order of Δ n ≈ 0.5 can be reached at the boundary between gases and transparent solids for most optical wavelengths 7. The strength of this effect depends on the difference between the refractive indices Δ n and the incident angle 6. For example, an interface between different refractive indices causes a change in propagation direction of light both in reflection and transmission 1. This ultimately leads to a change in phase and intensity. When an optical wave propagates through a medium, its phase velocity changes from c 0, the speed of light in vacuum, to c 0/ n. Tailoring n represents an important foundation for many photonic control schemes 1, 2, 3, 4, 5. The main underlying parameter governing the propagation of light in a medium is the medium’s refractive index, n. Our approach is not limited to laser pulse deflection gas-phase photonic schemes controlled by sonic waves could potentially be useful for realizing a new class of optical elements such as lenses or waveguides, which are effectively invulnerable against damage and can operate in new spectral regions. 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. We demonstrate an implementation of this approach by efficiently deflecting ultrashort laser pulses using ultrasound waves in ambient air, without the use of transmissive solid media. Here we propose to circumvent these constraints using gaseous media tailored by high-intensity ultrasound waves. Modern photonics, however, can involve parameter regimes where the wavelength or high optical powers involved restrict control due to absorption, light-induced damage or optical nonlinearity in solid media. We can solve for \(y_V\) and \(y_R\).Control over the intensity, shape, direction and phase of coherent light is essential in numerous fields, from gravitational wave astronomy, quantum metrology and ultrafast sciences to semiconductor fabrication.
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