Laser beam induced nanoscale spot through nonlinear “thick” samples: A multi-layer thin lens self-focusing model

Abstract

Self-focusing is a well-researched phenomenon. Nanoscale spots can be achieved through selffocusing, which is an alternative method for achieving high-density data storage, high-resolution light imaging, and maskless nanolithography. Several research groups have observed that self-focusing spots can be reduced to nanoscale levels via incident laser power manipulation. Self-focusing spots can be analyzed by solving the nonlinear Schr€ odinger equation and the finite difference time domain method. However, both procedures are complex and time-consuming. In the present work, a multilayer thin-lens self-focusing model that considers diffraction effects and changes of refractive index along the radial and film thickness directions is proposed to analyze the self-focusing behavior and traveling process of light beams intuitively. The self-focusing behaviors of As 2 S 3 are simulated, and results show that a nanoscale self-focusing spot with a radius of about 0:12 lm can be formed at the bottom of nonlinear sample when the incident laser power exceeds 4:25 mW. Our findings are basically consistent with experimental reports and provide a good method for analyzing and understanding the self-focusing process. An appropriate application schematic design is also provided.

Saturable absorption optimization of silica protected thin Sb2Te3 layers towards super-resolution applications

“…Another way to surpass the diffraction limit is to use the nonlinear absorption and/or the nonlinear refraction [3,4]. Both processes can result to a decrease of the size of a focused Gaussian beam by the material itself.…”

Impact of Nonlinear Kerr Effect on the Focusing Performance of Optical Lens with High-Intensity Laser Incidence

“…They divided the propagation media into multiple thin layers and traced the evenly spaced light rays in the transverse plane to simulate the Kerr effect. In 2014, based on the work of Kasparain and Wolf [6], Wei and Yan proposed a multilayer thin-lens self-focusing model to understand the formation and propagation characteristics of self-focusing beam spot inside nonlinear samples based on Fermat principle, which was utilized to calculate the light field distributions of nanoscale spots on the focal plane [7]. However, the ray-tracing approaches based on geometric optics have inherent shortcomings since the light field distributions are obtained indirectly according to the relationship between the number density of light rays and light intensity, which is with limited simulation accuracy.…”

Numerical Approach to Modeling and Characterization of Refractive Index Changes for a Long-Period Fiber Grating Fabricated by Femtosecond Laser

“…The refractive index profile induced by CO 2 laser was calculated using an empirical formula based on numerically obtained thermal stresses [32]. A multi-layer thin lens self-focusing model that considers the refractive index and diffraction effects was proposed to analyze the self-focusing behavior of light beams [33]. The reported methods rely on mathematical functions to describe the refractive index profile independently of the laser intensity distribution within the focal volume [23,24,25,26,27,34].…”