3-D Analysis Of Deposition Nanostructures For Cr Atoms Based On Straight Edge Diffraction Effect

The converging technology that neutral atoms are manipulated by laser standing waveis one of the important branches in atom lithography field. The stable structure ofchromium grating can be successfully treated as a nanoscale length benchmark using thedeposition technique of laser focusing. In the practical deposition experiment, straight edgediffraction effect leads directly to the redistribution of laser standing wave, consequently,the deposited nanostructures will change accordingly. Therefore, it is very significant tostudy the deposition process of neutral atoms with straight edge diffraction effect.Fresnel straight edge diffraction is confirmed by the basic diffraction characteristic ofdeposition substrate. Cr atom is taken as the object to build an ideal model of fundamentalmode Gaussian laser standing wave. Furthermore, the disturbance of substrate is added to astraight edge diffraction model, and the3-D characteristics of standing wave are comparedbetween the ideal field and diffraction field. The results show that the ideal standing wavequality is better than the diffraction one. Owing to the impact of diffraction effect, theshaded area of transverse standing wave generates a little optical potential, whileintensified fluctuations in the light propagation area, at the same time, longitudinalstructure takes on the shape of standing wave, the period of which is half of laserwavelength. Finally, the optimal capture location will deviate from substrate surface.Based on the semi-classical theory, the computation model of atomic trajectories isestablished in straight edge diffraction field. The fourth-order Runge-Kutta algorithmwhich is set to appropriate step length, was adopted to simulate3-D trajectory anddeposition stripe structure under different influence factors, such as the position relationsamong substrate, mirror and laser beam, atomic divergence, laser beam waist radius and soon. After data analysis, it can be found that the actual atomic convergence is affected bythe diffraction of substrate edge. When the waist radius of highly collimated fundamentalmode Gaussian laser equals62.5um, diffraction edge is close to laser beam waist center,namely the position of mirror, and substrate surface is moved to10below laser medialaxis, high quality nano-grating will be obtained.The3-D simulation results of deposition nanostructures get closer to the actualsituation, and intuitively reflect3-D panorama information. It provides a useful theoreticalfoundation and data information for the experimental research on atom lithography.