Possible features of observing the shock processes in Relaxed Optics are analyzed and discussed. Along with acoustic shock processes, electromagnetic shock processes are also observed. The formal analogy between acoustic and electromagnetic shock processes follows from the specifics of the propagation of shock acoustic waves and Cherenkov radiation. The first process is limited by the speed of sound in the medium, while the second is limited by the phase speed of light in the medium. The speed of sound in a medium characterizes the speed of propagation of thermal vibrations of the medium, while the phase speed of light in a medium characterizes the speed of propagation of electromagnetic vibrations of the medium. In other words, these are characteristics of the collective motion of atoms, electrons, and ions of the medium. For the case of intense laser irradiation in the saturation regime of excitation, these considerations are also transferred to irreversible processes (instead of microvoids, nanovoids are observed in the experiment). If acoustic shock processes are characterized by the speed of processes that are greater than the speed of sound in the medium, then electromagnetic shock processes are characterized by the speed that is greater than the phase speed of light in the medium. Both the speed of sound and the phase speed of light in the medium are characteristics of collective acoustic and electromagnetic processes of the medium, respectively. From this point of view, there is a certain analogy, although the experimental implementations of these processes differ significantly. Two types of model are discussed: two-cascade acoustic and five-cascade electro magnetic. That is why we analyzed the specifics of modeling and observing these processes in different media: solids, liquids, and gases. For this purpose, a cascade model of optical breakdown of the medium was used, which includes a modified Rayleigh model (five-cascade model). The feasibility of using this model to describe and explain the presented experimental results is analyzed. It is shown that, by the size of the voids, we can judge the nature of laser-induced shock processes: acoustic or electromagnetic.
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