中文摘要：

为CO2激光打标机设计了变焦距f—theta扫描聚焦系统，以使它适用于不同打标面积而不必更换镜头，该系统由三片透镜组成，材料为GaAs，工作波长为10．6μm，系统总长度为41．45mm。利用f—them镜的负畸变效应和机械变焦原理，将三片透镜设计组合为具有三个可变档系统，该系统有效焦距分别为f—theta镜的三个常用焦距：305mm、360mm和410mm，相应扫描范围分别为：210×210mm^2、250×250mm^2和280×280mm^2，扫描角均为±20°。像面上系统在零视场、0．7视场和全视场的光斑都落在相应的爱里斑以内，三种情况下，系统的MTF曲线分别接近相应的衍射极限血线，系统的最大场曲和最大f—theta相对畸变都能满足国内激光打标机的精度要求。

英文摘要：

A varifecal f- theta lens was designed for CO2 laser making scan focusing system, so that it apply to differ making area hut change a lens unnecessarily. The system consists of three lens, made by GaAs. The total length of the system is 41.45mm. Using the minus aberration of f- them lens and machine zoom principle, thc three alterable focus system was designed. The three effective focal lengths of the system are 305mm, 360mm and 410mm, which are usually used in f- them lens. The scanning field is 210 × 210mm^2,250 × 250mm^2 and 280 × 280mm^2, respectively. All of the scanning angles are ± 20°.For the three effective focal lengths, the spots on the image image at zero view field, 0.7 - view field and full view field are all inside the airy disc. The system MTF curve of each effective focal length are accordance with the corresponding diffraction limits curve. The maximun field curvature and maximum f - theta system distortion respectively satisfies the precision demand of the laser marking machine in China.