Giant enhancement of higher-order harmonics of an optical-tweezer phonon laser

TL;DR

This paper demonstrates a three-order magnitude enhancement in the brightness and coherence of higher-order harmonics in levitated micro-sphere phonon lasers through electronic control, advancing their potential applications.

Contribution

The study introduces a simple electronic control method that significantly boosts the lasing strength, linewidth, and frequency stability of higher-order harmonics in levitated phonon lasers.

Findings

Achieved three orders of magnitude increase in phonon laser brightness.

Significant improvements in linewidth and frequency stability.

Enhanced higher-order phonon coherence.

Abstract

Phonon lasers, as mechanical analogues of optical lasers, are unique tools for not only fundamental studies of phononics but also diverse applications such as acoustic imaging and force sensing. Very recently, by levitating a micro-size sphere in an optical tweezer, higher-order mechanical harmonics were observed in the phonon-lasing regime, as the first step towards nonlinear levitated optomechanics [Nat. Phys. 19, 414 (2023)]. However, both the lasing strengths and the quality factors of the observed harmonics are typically very low, thus severely hindering their applications. Here we show that, by applying a simple but powerful electronic control to such a levitated micro-sphere, three orders of magnitude enhancement are achievable in the brightness of the phonon lasers, including both the fundamental mode and all its higher-order harmonics. Also, giant improvements of their linewidth and frequency stability are realized in such an electro-optomechanical system, together with further improved higher-order phonon coherence. These results, as a significant step forward for enhancing and controlling micro-object phonon lasers, can be readily used for a wide range of applications involving nonlinear phonon lasers, such as acoustic frequency comb, ultra-sound sensing, atmospherical monitoring, and even bio-medical diagnosis of levitated micro-size objects.