Self-focusing is observed in nonlinear materials owing to the interaction between laser and matter when laser beam propagates. Some of numerical simulation strategies such as the beam propagation method (BPM) based on nonlinear Schrödinger equation and ray tracing method based on Fermat’s principle have applied to simulate the self-focusing process. In this paper we present an iteration nonlinear ray tracing method in that the nonlinear material is also cut into massive slices just like the existing approaches, but instead of paraxial approximation and split-step Fourier transform, a large quantity of sampled real rays are traced step by step through the system with changing refractive index and laser intensity by iteration. In this process a smooth treatment is employed to generate a laser density distribution at each slice to decrease the error caused by the under-sampling. The characteristics of this method is that the nonlinear refractive indices of the points on current slice are calculated by iteration so as to solve the problem of unknown parameters in the material caused by the causal relationship between laser intensity and nonlinear refractive index. Compared with the beam propagation method, this algorithm is more suitable for engineering application with lower time complexity, and has the calculation capacity for numerical simulation of self-focusing process in the systems including both of linear and nonlinear optical media. If the sampled rays are traced with their complex amplitudes and light paths or phases, it will be possible to simulate the superposition effects of different beam. At the end of the paper, the advantages and disadvantages of this algorithm are discussed.
In high power laser systems, nonlinear effect, one of the key factors of beam wavefront aberration and even
irreversible damage to system, has always been one of the top considerations of researchers for decades. A hybrid
ray-tracing method for both linear media and nonlinear media based on geometric optics is presented in this paper and
realized by programming. In a simple optic system with KDP crystal, an obvious decline of beam quality is observed in
high laser power density conditions and a method taking component intervals as compensation of beam quality is proved
feasible. Considering the complexity of traditional modeling method based on surfaces, a modeling method based on
components is established. Hopefully, the conclusions and flaws of this paper can shed light on relevant work and further
Zernike polynomials have been widely used to fit lens surface figure error and the wavefront aberration of optical systems, for its orthogonality in the unit circle and its corresponding relationships with optical aberrations1. Because the current extensively used Zernike polynomials are just functions of the aperture, without consideration of the field factor, it can only represent single field wavefront aberration. This is incomplete for the description of the wavefront aberration, especially for lithographic lens with a large field and high imaging quality2. Thus, considering the field factor in the description of wavefront aberration becomes very necessary. This paper presents a convenient and practical method to describe the full field wavefront aberration. A rotationally symmetric optical system has been taken as an example, in the scope of normalized full field, taking the Chebyshev zero points as nodes, and applying the Chebyshev polynomials to the fitting of Zernike coefficients of different fields. Meanwhile, the influence of the degree of Chebyshev polynomials and the number of fitting nodes on the fitting accuracy is taken into account. The results show that the fitting method used in this paper is of high accuracy, and this fitting method is very significant for the analysis of full field wavefront aberration.