描述了一套二次谐波型频率分辨光学快门(SHG-FROG)装置，用于单次测量红外长波长超快激光脉冲的脉宽和相位信息。针对在该波段宽带的高损伤阈值介质膜镀膜困难，且价格昂贵的问题，采用两个半圆形全反平面银镜来代替传统的半透半反镜进行分光。同时改进后的光路可以减少测量误差，结构更加紧凑且便于调节。采用该装置对基于钛宝石参量放大的红外超快脉冲进行测试，得到当中心波长为1.8 μm时，脉宽为66.9 fs，谱宽54.5 nm，谱相中的二阶群延时色散(GDD)为202.9 fs2。

A frequency-resolved optical gating (FROG) apparatus which can be used to measure the intensity and phase of infrared long wavelength ultra-fast laser pulse in single-shot is described. Because the high damage threshold coating in this waveband is difficult and expensive, we use two half-semicircle mirrors to substitute traditional transmitted beam splitter. Meanwhile, error of measurement in the improved configuration will be diminished, and the whole device becomes more compact and easier to be adjusted. We utilized the apparatus to characterize optical parametric amplifier ultra-fast pulse pumped by Tisapphire laser. With the center-wavelength of 1.8 μm, the pulse has duration of 66.9 fs and spectral width of 54.5 nm. The group delay dispersion (GDD) in spectrum region is 202.9 fs2.