Experimental study of waves and solitons in complex plasmas

This is a first grant proposal for a collaboration project between the University of Liverpool (UL) and Max-Planck-Institute for Extraterrestrial Physics (MPE), the collaboration agreement is attached. The project aim is to use a new form of matter (complex plasma) to model phonons and solitons in solids and liquids in a unique and novel way. Complex plasmas is a highly interdisciplinary topic, which links many physics disciplines: plasma physics, solid state physics, acoustics, optics, nonlinear science, physics of electronic devices, gas and fluid dynamics, thermodynamics, and nanoscience. Complex plasmas is a new field of plasma physics, it allows to observe solid and liquid systems at the kinetic level (with motion of every ``molecule'' or grain resolved). This makes it possible to study linear and nonlinear wave phenomena (which we propose here) on the intermolecular length scales. Such a study in real solids and liquids would require following individual molecules in real time, which is almost impossible at the current level of technology. Waves and solitons with short wavelengths and their interactions are important for practical applications such as optical telecommunications and acoustic imaging. Their understanding in a model system - complex plasma can also lead to novel applications. The fundamental questions that can be answered using waves in complex plasmas include scattering of phonons on defects, nonlinear phonon-phonon interaction, mean free path of short-wavelength phonons (which affect thermal properties of solids and liquids), acoustic and thermal properties of nanostructures, nanoclusters, alloys, and semiconductors. Short-wavelength phonons also yield information about inter-grain forces and potentials. They are equivalent to terahertz phonons in solids which are being actively studied due to possible applications in sasers (Sound Amplification by Stimulated Emission of Radiation), generation of coherent phonon beams, and scanning acoustic microscopy (SAM). SAM has resolution comparable to soft X-ray imaging, but it is significantly less destructive to the material. Solitons are nonlinear localized waves which have a remarkable property of propagating without changing their shape and without destructive interaction with other solitons. This makes them very useful in optical telecommunications. Short-wavelength solitons are used in holey fibers to increase the baud rate of the transmission line. Due to energy dissipation the amplitude of the soliton decreases, while the width increases. Fine tuning the dispersion and nonlinearity of the medium, it is possibble to minimize the spreading of the soliton. As the soliton width decreases and becomes comparable with the intermolecular distances, it becomes more important to know how the medium anisotropy, scattering on defects, and interactions with other solitons affect propagation.We are planning to answer the long standing questions about the phase relation between the components in waves with mixed (longitudinal and transverse) polarisation and about the reduction of the phonon mean free path compare to the damping length of a monochromatic wave, possibly due to phonon interaction with other phonons and/or with defects.The proposed research gives us an opportunity to study waves and solitons at intermolecular scales. This is an extremely timely subject because of the growing interest for short wavelength wave phenomena and their direct applications in optical telecommunications, scanning acoustic microscopy, coherent phonon beams, etc.