Researchers were able to prove a theoretical phenomenon and measure periodic wave packets. In the experiment carried out, the team of researchers stimulated periodic wave packets of surface gravity waves
A new study by Tel Aviv University was able to measure for the first time the absence of the Talbot effect at distances fractions of the Talbot distance, a phenomenon that until now had only been predicted theoretically. This is a phenomenon according to which when a light wave of a single color passes through a periodic structure, a periodic light pattern is obtained after it repeatedly, at fixed distances called Talbot distances xT. This wave phenomenon is not limited to light waves and has been studied for many different types of waves, including matter waves and sound waves. The researchers showed that the symmetry breaking can be explained by a more accurate wave equation called the Dysthe equation.
excite periodic wave packets
The scientific discovery was made possible as part of a study that examined the propagation dynamics of periodic wave packets in surface gravity waves over water, by measuring their development along a 5-meter-long pool of water waves. The team of researchers included Georgi Gerry Rosenman, from the Raymond and Beverly Sackler School of Physics and Astronomy, Prof. Wolfgang Schleich from Ulm University, Prof. Adi Aryeh from the School of Electrical Engineering and the head of the Marco and Lucy Shaul Nano-Photonics Chair, and Prof. Lev Shemer from the School of Mechanical Engineering. The research was published in the prestigious journal Physics Review Letters.
The propagation dynamics of periodic wave packets has also been studied theoretically in the non-linear domain. The scientist Neil Akhmediev found an analytical solution called "Akhmediev breather" which means "breathing wave", since its shape repeats itself cyclically. However, there is an important difference compared to the linear case, which is that only the original structure is received in a cyclical form, while the structures in the shorter cycle do not appear.
In the experiment carried out, the team of researchers stimulated periodic wave packets of surface gravity waves. For this purpose, the breathing wave of Achmediev was chosen (Achmediev breather). When the exciting waves have a large amplitude, the non-linear dynamics of the surface gravity waves becomes significant and causes the periodic patterns with short cycles to disappear, for example at half the Talbot distance.
The wave pool at Tel Aviv University where the experiment was carried out
In addition, the researchers discovered in the course of the study that when the nonlinearity is higher, the measurements deviate from Ahmedayev's analytical solution, and an asymmetric breaking of the wave function can be seen. This breaking causes the wave envelope to accelerate slightly and then decelerate back to the speed of the group. This breaking of symmetry is caused by a high-order nonlinearity, which is not taken into account in the simple wave equation - the nonlinear Schrödinger equation.
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