The design method of a double freeform surface lens is being widely applied in non-imaging optical systems. In this paper, a diffuse reflection freeform surface is introduced into the design of a double freeform surface lens. Different from the universal double freeform surface lens, this double freeform surface lens is divided into a small-angle freeform surface and a large-angle diffuse reflection freeform surface. The small-angle freeform surface firstly limits and forms the lighting area. Then, the large-angle freeform surface is designed to improve the efficiency of lighting the area. And this front light diffuse reflection effectively avoids the influence of light source projection onto the lighting effects. Based on this design method, the double freeform surface lens is obtained. The results show that the efficiency of a circular lighting area reaches 81% and the uniformity of the irradiance distribution reaches 91%. And this design is also suitable for forming different shapes of lighting areas while maintaining a better lighting effect.

中文翻译：

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漫反射双自由曲面透镜的设计方法

双自由曲面透镜的设计方法在非成像光学系统中得到广泛应用。在本文中，漫反射自由曲面被引入到双自由曲面透镜的设计中。与通用双自由曲面透镜不同，这种双自由曲面透镜分为小角度自由曲面和大角度漫反射自由曲面。小角度自由曲面首先限制并形成照明区域。然后，设计大角度自由曲面以提高该区域的照明效率。并且这种前光漫反射有效地避免了光源投射对灯光效果的影响。基于这种设计方法，得到了双自由曲面透镜。结果表明，圆形照明区域效率达到81%，辐照度分布均匀度达到91%。而且这种设计也适合形成不同形状的照明区域，同时保持更好的照明效果。