High-frequency phonons have gained attention in the fields of quantum technology and nanophononics. Their small wavelengths make them compatible with quantum nano-devices and their frequencies can surpass modern computation speeds. This potential makes phonons useful for qubits, quantum memories, hybrid systems, and elements in quantum computing networks. The project focuses on using a novel experimental method based on the optical open cavity to excite and detect coherent phonons in nanostructures from the II-VI group of semiconductors. The project involves growth of the samples with an acoustic cavity enclosed in Distributed Bragg Reflectors (DBR), which support the cavity acoustic mode. By placing the sample inside the open optical cavity and adjusting its length, we can sweep the energy of the excitation photon, allowing comprehensive studies on the influence of photon energy on phonon generation efficiency [1,2]. Additionally, one can achieve resonant excitation in time domain, by implementing a high repetition rate laser [3] that matches a frequency of the mode supported in the acoustic cavity. This experimental scheme allows us to enhance the efficiency of phonon excitation by exploiting four resonances for coherent phonon generation: acoustic cavity resonance, optical cavity resonance, excitonic resonance, and in-phase (temporal) resonant excitation  . As a result of the project, we expect to provide a comprehensive study on the efficiency of the high-frequency coherent phonon generation in the II-VI semiconductor nanostructures obtained by pump-probe experimental technique exploiting optical open cavity. Initial results include manufacturing and assembling an open optical cavity based on titanium mechanical parts and attocube positioners. Stable light source and active stabilization realized with Red Pitaya controller allowed us to control the cavity so it is continuously supporting particular optical mode. Various samples of Al and Ni thin films were deposited on Tungsten and Silicon substrates and investigated at the pump-probe set-up where we have obtained phonon echo signal. In this work we present the concept of enhancing efficiency of coherent phonon generation along initial results and simulations.

[1] B. Jusserand at al. Polariton Resonances for Ultrastrong Coupling Cavity Optomechanics in GaAs / AlAs Multiple Quantum Wells, Phys. Rev. Lett. 115, 267402 (2015).

[2] M. Kobecki at al. Giant Photoelasticity of Polaritons for Detection of Coherent Phonons in a Superlattice with Quantum Sensitivity, Phys. Rev. Lett. 128, 157401 (2022).

[3] M. Kobecki et al. Picosecond ultrasonics with miniaturized semiconductor lasers, Ultrasonics 106, 106150 (2020).