Importance sampling is a Monte Carlo technique in which rays are generated and propagated in specific directions in the optical system, which are “important” in determining the results you need. This improves sampling by increasing the number of rays reaching the surface or surfaces of interest to the user. Importance sampling is essential in a stray light analysis, where the attenuation of incident light can be very great, and can be helpful in other types of analyses. In a stray light analysis, there should be an importance sampling target for each optical surface in the optical system. It is important to remember that importance sampling is used only to enhance the sampling of scattered and diffracted light or surface sources. Designs that include only specular reflection and transmission cannot take advantage of importance sampling — the direction of the rays is determined by the Law of Reflection and Snell’s Law. ZP<<cyY  
Figure 7.1 on page 7.3 illustrates importance sampling for the simple case of a lens that scatters from its second surface. A second object is shown that corresponds to a detector. In this case rays from an off-axis field position are imaged such that all of the specular rays miss the detector. Generally, scattering is stronger close to the specular direction of the un-scattered ray so the probability of a randomly scattered ray hitting the detector is very small. When an importance target is applied, it guarantees that the one or more importance rays will hit the detector for each incident ray.

重點(diǎn)采樣是一種Monte Carlo技術(shù)，光線在光學(xué)系統(tǒng)里是按照特定的方向產(chǎn)生及傳播的，這些方向在決定你需要的分析結(jié)果上面是非常重要的。重點(diǎn)采樣通過增加到達(dá)用戶感興趣的表面的光線數(shù)來提高采樣。重點(diǎn)采樣在雜散光分析里是必要的，因?yàn)槿肷涔獾乃�減可能很大，當(dāng)然在其他的分析力也是很有用的。在雜散光分析里應(yīng)該為光學(xué)系統(tǒng)里的每一個光學(xué)表面設(shè)定重點(diǎn)采樣目標(biāo)(improtant sampling target)。