Richtmyer-Meshkov instability (RMI) occurs when a perturbed interface separating two fluids of different densities is accelerated by a shock wave [1-2]. It plays a critical role in various engineering applications and natural phenomena [3], such as inertial confinement fusion (ICF). RMI at a small-amplitude single-mode light-heavy interface is the fundamental RMI scenario: free from high-order initial modes, phase inversion, and high-initial-amplitude effect. This makes its research the basis for all related studies. Currently, this phenomenon has been extensively studied under weak shock conditions [3]. However, high-intensity shocks are commonly encountered in practical applications involving RMI. Therefore, investigating strong-shock-driven RMI (strong-shock RMI) at a small-amplitude single-mode light-heavy interface is of great significance. The present study aims to investigate this fundamental strong-shock RMI configuration through fine shock-tube experiments, thereby establishing the basis for related research and paving the way toward understanding the underlying physics of hydrodynamic instabilities in real scenarios such as ICF.
RMI is highly sensitive to initial conditions [3]. Therefore, to conduct a reliable RMI experiment, both the shock and interface generation methods are crucial. The experiments are conducted in a newly developed shock-tube facility which is capable of generating planar shocks with Mach number exceeding 3.0 while maintaining a “clean” experimental flow [4]. The polyester film is employed for generating the initial air-SF₆ interface. The excellent mechanical properties of the material and the low height of the test section enable the generation of initial interface without grid support.
Four sets of experiments with varying initial amplitude and wavelength combinations are performed.  Qualitatively, after multiple impacts from transverse shocks, the bubble heads flatten and their connections to the other parts of the shocked interface become sharp, markedly different from the phenomena observed under weak shock conditions [3]. Quantitatively, the impulsive model [1] significantly overestimates the experimental linear growth rate. In contrast, the compressible linear theory [1] provides reasonable predictions for all cases. To the best of our knowledge, this is the first direct experimental confirmation of the validity of the compressible linear theory and the failure of the impulsive model for predicting the linear amplitude evolution in highly compressible flows. For the nonlinear RMI evolution, all considered nonlinear models [5-10] overestimate the bubble evolution since they do not consider the shock-proximity and secondary-compression effects. For the spike, the amplitude growth is promoted by the spike acceleration effect: high-order harmonics concentrate on the spike under high Atwood number conditions, and a model properly describing this effect [10] yields a reasonable prediction.

Richtmyer-Meshkov instability; Single-mode interface; Shock tube experiment