摘要
为满足红外探测系统对大视场、轻量化、低成本的需求,设计并研制了一款用于制冷型红外探测器的自由曲面离轴四反全铝光机系统。光学设计采用具有实出瞳的离轴无遮拦全反射式光路形式,并利用7次XY多项式表征各反射镜面型。在紧凑包络约束下,实现了6.25°×5°的视场角,全视场RMS几何弥散斑半径<6.0μm。各反射镜和支撑结构材料均选用6061-T651铝合金,各反射镜进行了柔性支撑设计,以降低装调时的刚性连接应力。采用激光干涉仪对光机系统波像差进行了测试,典型视场波像差<RMS0.7λ@632.8nm。相比传统的离轴反射系统,文中系统采用“全自由曲面+全铝光机"新构型,能够用更紧凑的包络实现更大视场,且整机具有轻量化、低成本以及无热化的特点,在红外探测领域具有重要应用前景。
Objective Infrared detection technology has the advantage of passive thermal radiation detection and continuous work day and night.It can greatly reduce the restriction of environmental factors such as the light conditions.It is widely used in ecological environment monitoring,night vision detection,precision guidance and other fields.In recent years,with the development of infrared detection technology,especially in the field of aviation and aerospace remote sensing,in order to improve the timeliness of infrared remote sensing detection and realize the large-scale deployment of infrared detection system,the demand for large-field-of-view,high-compact,lightweight and low-cost infrared detection system is becoming more and more urgent.For this purpose,a freeform off-axis four-mirror all-aluminum infrared optical detection system with a large field of view and a compact package is designed in this paper.Methods A freeform off-axis four-mirror all-aluminum infrared optical detection system is designed and built in this paper.The optical system has a real exit pupil to connect the cold aperture of a cooled infrared detector(Fig.2).The 7th order XY polynomials is used to represent the surface of the four freeform mirrors.The full-field geometric spot radius,wave aberration,modulation transfer function,and distortion grid are analyzed(Fig.5-9).The Monte Carlo algorithm is used for tolerance analysis to determine the influence of the alignment errors of the four mirrors(Tab.3).The optical system adopts an all-aluminum optomechanical design(Fig.12),in which the aluminum freeform mirror employs a three-ear flexible support mode to reduce the rigid connection stress(Fig.13).The optical,mechanical and thermal integration analysis is carried out,and the athermal effect of the optical system is verified(Fig.14-16).The optical system is assembled,and the full-field wave aberration is measured(Fig.17-18).Results and Discussions The optimized freeform off-axis four-mirror optical system has a large field of view of 6.25°×5°. The maximal geometric spot radius over the whole field of view is 5.36 μm, which is far less than theradius of the airy spot (Fig.5-6). The full-field wavefront error is less than 0.037λ@8.85 μm, which approachesthe diffraction limit (Fig.7). The minimal MTF at 20 lp/mm is 0.48 (Fig.8). Considering the conventionalalignment errors of the four mirrors (Tab.3), the geometric spot radius of the optical system is expect to be lessthan 19.8 μm. According to the optical, mechanical and thermal integration analysis, the maximal full-fieldgeometric spot radius is slightly changed from 5.36 μm to 5.49 μm when the working temperature is changedfrom 20 ℃ to 30 ℃ (Fig.16). The result proves that the all-aluminum optomechanical system potentially has theoptically athermal characteristics. The prototype has a focal length of 146.2 mm and a NETD of 26.8 mK. Themeasured wavefront error of the prototype is less than RMS 0.7λ@632.8 nm, which meets the technicalrequirements (Fig.18).Conclusions A freeform off-axis four-mirror all-aluminum infrared optical system with a real exit pupil, a largefield of view and a compact package is built in this paper. The optical system has a field of view of 6.25°×5°. Thedesigned full-field geometric spot radius, wavefront error and modulation transfer function all approach thediffraction limit. The tolerance analysis of the alignment errors of the four mirrors is carried out based on theMonte Carlo algorithm, which leads to a full-field geometric spot radius of less than 19.8 μm. The optical systemadopts an all-aluminum optomechanical design, which naturally possesses an optically athermal potentiality. Theoptical, mechanical and thermal integration analysis for a temperature rise of 10 ℃ of the optical system verifiesthe optical athermality of the optical system. The measured full-field wavefront error of the prototype is less thanRMS 0.7λ@632.8 nm. The captured far field infrared image shows the high performance of the prototype.Compared with the traditional off-axis reflective optical system, the demonstrated optical system adopts a newconfiguration of "all-freeform optical surfaces + all-aluminum optomechanics". It can achieve a larger field ofview with a more compact envelope. And, the system has the characteristics of lightweight, low cost and opticalathermality, which has important application prospects in the field of infrared detection.
作者
高荣
毛祥龙
李锦鹏
徐志晨
谢永军
Gao Rong;Mao Xianglong;Li Jinpeng;Xu Zhichen;Xie Yongjun(Xi'an Institute of Optics and Precision Mechanics,Chinese Academy of Sciences,Xi'an 710119,China)
出处
《红外与激光工程》
EI
CSCD
北大核心
2023年第7期52-62,共11页
Infrared and Laser Engineering
基金
国家自然科学基金项目(62105357)
中国科学院青年创新促进会项目(2019394)。
关键词
红外探测系统
自由曲面
离轴四反
全铝光机
infrared detection system
freeform surface
off-axis four mirror
all-aluminum optomechanics
作者简介
高荣,女,工程师,硕士,主要从事自由曲面结构设计方面的研究;通讯作者:毛祥龙,男,研究员,博士,主要从事自由曲面光学设计、加工与检测方面的研究。
