大口径长焦距光学检测系统强制对流方法

Forced convection method for optical testing system with large aperture and long focal length

大口径、长焦距的水平光学检测系统极易受到气流扰动的影响,气流扰动会引起光路中温度、速度、压强等多个物理量在时间和空间上随机动态变化。尤其是温度在空间上呈现梯度分布,以及在时间上存在缓慢漂移,均将会直接导致空气折射率的动态变化,从而导致点扩散函数退化、引起波前倾斜、出现波前时变。为了抑制气流扰动对检测光路的影响以及提高检测精度,基于计算流体动力学(Computational Fluid Dynamics,CFD)方法,提出了风扇强制对流的室内温度场控制方法,确定风扇放置方式与风扇数量。采用温度最大峰值(Peak to Valley,PV)并引入了最大光程差概念,综合评价光路温度场的均匀性。经过多次实验验证,采用强制对流方案,将0°像散标准差从0.0263λ(λ=632.8nm),显著提高了光路温度场的均匀性与稳定性,大幅降低了光学检测误差,提高了检测精度。为今后保障狭长通道内长光路、大口径光学检测系统的测量精度提供了借鉴。

The horizontal optical testing system with large aperture and long focal length is extremely susceptible to the airflow disturbance,which will cause random dynamic changes in time and space of multiple physical quantities in the optical path,such as temperature,velocity and pressure.In particular,the spatial heterogeneity and temporal stability of temperature will directly affect the dynamic change of air refractive index,resulting in the degradation of the point spread function,the tilt of the wavefront and the change of the wavefront over time.In order to suppress the influence of airflow disturbance on the testing optical path and improve the testing accuracy,based on the Computational Fluid Dynamics(CFD),a forced convection method was proposed to improve the uniformity of the indoor temperature field,which can be used to determine the array mode and number of fans.The Peak to Valley(PV)of the temperature was adopted and the concept of maximum optical path differences was introduced to comprehensively evaluate the uniformity of the indoor temperature field.Verified by several groups of experiments,the forced convection scheme reduces the standard deviation of the astigmatism coefficient from 0.146λ to 0.0263λ(λ=632.8nm),which significantly improves the uniformity and stability of the indoor temperature field,greatly reduces the optical testing error,and improves the testing accuracy.It provides a reference for ensuring the optical testing accuracy of the optical testing system with long optical path and large aperture in the future.