The difficulty of tracing rays through the random index medium, like atmosphere, or flowing liquid, lies on how to fast
obtain the refractive index and gradient values of each location along the ray trajectory in space. Recently, the method of
"self-adapting grid" has been developed to efficiently describe such a medium. There are several available numerical
techniques for tracing rays through inhomogeneous medium, such as Taylor method and 3rd order Runge-Kutta method,
the combinations of the self-adapting grid with different ray tracing techniques result in different accuracy and require
different computational effort. In this paper, according to the fundamentals of numerical computation, the derivation of
4th order Runge-Kutta method is presented. For the convenience of comparison, the ray trace through a regular gradient
medium (GRIN) has also been made by these methods, and the results are compared with that from other commercial
lens design codes. The results show that the 4th order Runge-Kutta method has the highest accuracy for the same step
size, but it consumes the longest time. When the ray trace step is relatively large, i. e., one fifth of the GRIN rod size, the
4th Runge-Kutta method is much more accurate than the 3rd method, however, there's few difference of the accuracy
when ray trace with a small step size. Therefore, the 3rd order Runge-Kutta method is the optimum choice for ray tracing
in self-adapting grid when comprehensively considering the accuracy and computational efforts.
The refractive index distribution in atmosphere or fluid medium is irregular and inhomogeneous, and cannot be
described by a usual gradient index formula due to the influence of flowage and change of temperature. In this paper a
novel method, namely, self-adaptive grid is used for describing the refractive index in irregular inhomogeneous medium,
the refractive index data are stored in RAM as a dynamic octree, the criterion of grid division for refractive index and its
gradient are given and the interpolation method is used for calculating the refractive index and its gradient at positions
along the ray trace trajectory. A gradient index (GRIN) rod in which the refractive index can be described by a formula is
also analysis as an example, the self-adaptive grid is created and the refractive indexes and its gradient at some positions
with high accuracy are output. The RMS error is under 7e-5 and can be used for ray tracing.
Headlamps are installed at the head of automobiles for road lighting. About the illumination and anti-dazzle, some standards such as the standard of ECE are established. Now more and more free face reflective headlamps (FFR headlamps) are applied, and the light distribution design of FFR mirror becomes an important subject in the field of automobile assembling part. In this paper the surface shape of FFR headlamps is analyzed and described as a multi-partition aspherical surface with some simple parameters. According to the fundamental principles of geometrical optics and using the theory of ray transmission with energy, millions of real rays emitted from lower beam filament and high beam filament are traced and the relative intensity of illumination at the test screen with distance of 25m from the automobiles is obtained. In this paper the description of FFR mirrors is discussed, the algorithm of FFR headlamp design is presented, the flow chart is given and the light distribution simulation software with friendly interfaces is developed. In the light distribution graphic interface of the software, the illumination area could be dragged to a certain position while the parameters of current partition at the FFR mirror will be automatically changed. Using this software the FFR headlamps satisfying criteria will be designed very quickly and the 3D coordinates of any points at the mirror will be obtained. This makes CAM of FFR headlamps easy.
Diffraction components are applied in high power laser systems for beam shaping and harmonic separation. Because of the multi-order diffraction and multi-reflection to high power laser, the distributions of stray light energy and ghosts are much more completed in the systems than in conventional optical systems. In this paper a data structure of tree is presented for describing the stray light caused by multi-order diffraction and multi-reflection. All the nodes of the tree can be dynamically saved and be deleted, and the intermediate results those are useful for the next calculation step can be reserved in RAM. Using this method the multiple repeated calculations in conventional stray light analysis methods such as Monte Carlo technique are avoided and the analysis time is reduced. According to the paraxial tracing, the software which can be used for analyzing the stray light caused by multi-order diffraction and multi-reflection in high power laser systems is developed and the stray light tree of a laser system based on paraxial tracing is built. As shown by the example that this algorithm is available for quickly analyzing stray light in the systems including diffraction components, and the ghost positions with energy descriptions can be given by the software. The ghosts those are harmful to the important components will be picked.
The technical integration line (TIL), which is the full scale prototype for Shengguang-III laser facility (SG-III), now under construction at CAEP, will contain a neodymium glass laser system with more than 70 large (40-100 cm) optical components. Reflections from these surfaces (so-called ghost reflections) are numerous and extensive computation has been required to track them in the TIL optical system. The tremendous number of ghost paths requires a visualization method that allows overlapping ghosts on optics, and then sums them up to illustrate its potential damage on critical surfaces. Therefore, how to make an effective identification and visualization of multi-order "ghost" has been a major part of the optical design effort. This paper addresses the following aspects of TIL ghost analysis: 1, comparison of several methods for ghost energy simulation. 2, some techniques for visualization of complex optical systems in 3D space including mirrors and pinholes. 3, attempts at visualizing “ghost energy” distribution near some critical surfaces so as to provide detailed references for mitigation of ghost caused damage.