https://www.scientificamerican.com/article/time-crystals-made-of-light-could-soon-escape-the-lab/

Inside its crystalline bounce house, the laser light became a parade of “chunks”, each more like a single wave crest that never loses shape rather than a broad, wide ripple on the surface of a perturbed lake. These so-called solitary waves, or solitons, emerged and formed the parade with a predictable periodicity, marching perfectly on beat, consequently building a time crystal. The physicists caught on to this “crystallization” by carefully studying the light that trickled out of the cavity.