Anisotropic Laser Performance in an Optically Isotropic Crystal by Phonon Engineering

Symmetry is an eternal motif in understanding the characteristics of nearly all the laws and courses of science. The symmetry‐breaking in the optical crystal will generate a rich variety of unprecedented physical phenomena and create new functional properties. Herein, the symmetry‐breaking in a photon–phonon collaboratively pumped laser, dominated by the anisotropic lattice vibrations is investigated. Using an optically isotropic Nd:YAG crystal as an example, the phonon‐assisted electronic transitions accompanied by anisotropic fluorescence emission are observed, beyond the intrinsic structural symmetry ruled by Neumann's principle. For the first time, the phonon‐assisted new‐wavelength lasers at 1151 and 1166 nm are achieved in Nd:YAG with divergent light polarization, determined by the vibrational direction of involved phonons. These results provide a flexible degree of freedom for photonics by phonon engineering and pave the way to new frontiers in the field of laser generation and manipulation.