So our paper is accepted by PRApplied! Congratulations to all, in particular to Yuxiang. His careful work leads to this quite unexpected discovery, on top of the original work by Ruijuan which appeared to be nearly perfect already, with systematic studies over the last year that are all key to this publication. Special thanks to Ruocheng and Xiao for their contributions.

More functionalities await to be unlocked for CP-AOM to modulate CW and pulsed lasers. Furthermore, this 99% efficiency makes CP-AOM a feasible choice to manipulate quantum light, with unprecedented speed and flexibility. So, there are more exciting developments ahead, and let's move forward.

A technical summary of this work:

Light sometime needs to be modulated to be useful.  Acoustic-optical modulation, with the speed and accuracy, is a uniquely important technique for advancing optical science at frontiers. We demonstrate that AOM efficiency can be perfected by composite diffraction in a resource-efficient manner without sacrificing the control bandwidth. The efficiency enhancement in our 4-F-linked composite setup arises from two effects, termed momentum echo and high-order rephasing, which can be simultaneously optimized by adjusting the relative distance between the two AOMs. Experimentally, we achieved a diffraction efficiency exceeding 99% (excluding insertion loss) and a 35 dB single-mode suppression of the 0th-order beam, demonstrating a full-contrast optical router with a switching time of less than 100~nanoseconds. Theoretically, we formulate the dynamics of CP-AOM in terms of multi-mode quantum control and discuss extensions beyond the N=2 configuration presented in this work.

More precise imaging optics would help to improve the efficiency further to the R=99.9% level, thereby also enhancing the zeroth-order rejection ratio to beyond 40~dB. With improved optics and assuming 1% level insertion loss unrelated to diffractions, iterative application of CP-AOM would support to push the free-space acoustic-optical frequency-shifting range deeply into the microwave regime. The low insertion loss combined with nearly ideal diffraction should also facilitate the application of CP-AOM as a fast two-port optical router for quantum light, or for coherently splitting/combining pulsed and CW lasers.  Similar to composite pulse quantum control, the CP-AOM functionalities expand in N-AOM systems with large N. Examples include achieving high-order Bragg diffraction, general wavefront engineering, and spatial-temporal control of ultrafast pulses. The substantially enhanced performance of CP-AOMs, coupled with reduced acoustic amplitude requirements, may significantly advance our ability to accurately control light at high speeds with low-loss acoustic-optics.

The CP-AOM technique discussed in this work is in direct analogy to composite pulse control of matterwave. Nevertheless, a distinct feature in CP-AOM is the precise 4-F imaging for the effective wavefront reversal. Aided by developments of matterwave lensing techniques, we also expect the momentum echo and high-order rephasing effects discussed in this work to be exploited in atom interferometry, to enhance the matterwave control efficiency/bandwidth.