In the case of water waves in intermediate depth (kh<1.363) the defocusing nonlinear Schrödinger equation (NLS) admits a family of stationary solutions, referred to "dark solitons". The amplitude profiles of these solutions exhibit a dip in the uniform carrier wave, which remains unchanged during propagation of the wave field. These solitons have been observed and investigated for water waves by Chabchoub et al. (2013) and Chabchoub et al. (2014). Gagnon (1993) derived by a direct integration method an exact solution of the NLS, that describes a collision and therefore the nonlinear interaction of two dark solitons in intermediate depth. We present first observations of dark soliton collision and dark soliton fission in water waves within the framework of an exact NLS solution, analytically derived by Gagnon (1993). Experiments, which have been conducted in a large wave facility of the Tainan Hydraulics Laboratory (THL) in Taïwan are in good agreement with the theoretical prediction.

Bibliography:

A.Chabchoub, O.Kimmoun, H.Branger, N.Hoffmann, D.Proment, 2013, "experimental observation of dark solitons on the surface of water". Physical Review Letters 110 (12).

A.Chabchoub, O.Kimmoun, H.Branger, C.Kharif, N.Hoffmann, M.Onorato, 2014, "Gray solitons on the surface of water". Physical Review E 89 (1).

L.Gagnon, 1993, "Solitons on a continuous-wave background and collision between two dark pulses: some analytical results". Journal of the Optical Society of America B; 10(3).