Executive Summary : | The purpose of the proposed project is to investigate the optical nonlinear phenomenon of harmonic generation in anharmonic clusters via the interaction of the laser beam. These structures convert into tenuous plasma when irradiated by an intense laser pulse. The phenomenon of harmonic generation emerged in these interactions, occupies a very important place in the fabrication of efficient radiation source, and have several applications from scientific and technological point of view. Due to the efficient absorption of laser energy by clusters, their optical nonlinearities are significantly enhanced. Hence, the use of clusters for the generation of reliably detectable harmonic signals is of great importance in harmonic-generation experiments than in any other nonlinear media like plasma and semiconductors. The laser source, required for the generation of harmonics in clusters, is of smaller power and hence, comparatively cheaper and is easily attainable. Clusters are nanoscale van der waal bonded assemblies, specially created in subsonic and supersonic gas jets under appropriate conditions with optimized nozzle dimensions and gas jet backing pressure. Cluster assemblies contain 10² - 10⁷ atoms and the size of clusters varies from a few angstroms to 1000 angstroms. The physical mechanisms involved in the dynamics of laser-cluster interaction can be described using the nanoplasma model. The obstacle to the applicability of this unique radiation source is the low conversion efficiency of incident laser energy into the energy of generated radiation. A variety of techniques have been put forward by various analysts/ experimentalists to enhance phase matching. The present proposal aims to exploit the increased understanding of the mechanisms to optimize the qualities of the second and third harmonic radiation in laser-cluster interaction for potential applications. The study includes an in-depth understanding of the process and development of different models of enhancement of harmonic conversion efficiency by fulfilling phase-matching conditions in the interaction of laser with clustered nanoplasma. In different techniques, one can apply the wiggler magnetic field, density ripple on clusters, can use step density profile of clusters, or can use different laser profiles to enhance the power of generated harmonic or radiation. The expansion of clusters will be taken into consideration in the proposed research work because it affects the conversion efficiency of the generated harmonics. During the expansion of the cluster when the cluster electron plasma frequency becomes equal to laser frequency, plasma resonance occurs. This is responsible for the sharp enhancement in the laser-cluster-induced nonlinear optical phenomenon. The second and third harmonic radiation can act as a diagnostic tool to study the important information about the structure and dynamics of the material (cluster) through which radiations are emitted. |