摘要
法布里-珀罗(F-P)滤光器是太阳二维成像光谱观测系统的重要组成部分,为了实现高精度太阳二维成像光谱观测,要求F-P滤光器必须具有准确的中心波长。由于滤光器只能提供控制器数值,无法直接获取波长信息,提出一种基于双波长强度调制的定标方法,利用F-P滤光器强度调制的周期性和双波长强度调制的差异性,建立控制器数值和滤光器腔长及波长的对应关系,实现波长精确定标。在实验室开展F-P滤光器定标测试,测试结果表明,对于Hα谱线,滤光器的波长定标精度达到0.0093A,满足1 m新真空太阳望远镜(NVST)下一代二维成像光谱观测系统的指标要求。
Objective The Fabry‒Perot(F-P)filter,with the advantages of narrow bandwidth,high transmittance,and large aperture,is an essential component in solar twodimensional imaging spectrometers.It is also a crucial optical element in the nextgeneration twodimensional imaging spectrometer for the New Vacuum Solar Telescope(NVST).To achieve highprecision solar spectrum observation,the F-P filter must have an accurate center wavelength.However,in practical applications,the filter can only provide controller values and cannot obtain wavelength information directly.Additionally,the accuracy and stability of cavity length are affected by material defects,component fatigue,and environmental changes,resulting in center wavelength drift.Therefore,the center wavelength of the filter must be calibrated.Traditional calibration methods require a stable continuous spectrum light source and a spectrometer or interferometer with a resolution higher than that of the filter,which are large and expensive.Currently,the common calibration method uses the sun as a standard light source,but this is limited by variations in the solar spectrum.We propose a novel method for calibrating the center wavelength of the F-P filter.This method is simple in structure and does not require additional spectrometers or interferometers,avoiding the problem of singlewavelength 2πentanglement and overcoming the limitations of solar spectral calibration.The calibration accuracy is better than 0.01Å,fully meeting the requirements of the NVST twodimensional imaging spectrometer.Methods Our method for calibrating the center wavelength of the F-P filter is based on the periodicity of the intensity modulation curve of the F-P filter.First,we measure the unit step of the controller using the adjacent peaks of the singlewavelength intensity modulation curve.The 2πentanglement problem is then solved using the dualwavelength intensity modulation curve,and the corresponding relationship between cavity length and the controller value is established according to the positions between adjacent peaks of the dualwavelength intensity modulation curve.Using this relationship,we adjust the cavity length of the F-P filter to the position of the center wavelength and calibrate the wavelength accurately.Finally,we conduct a calibration test on the F-P filter and verify the feasibility of this calibration method.Results and Discussions We carry out the calibration test of the ET100-FS100 F-P filter produced by IC Optical Systems Ltd.The test results show that when observing the Hαsolar spectral line,adjusting the controller to the-101st step,and with a corresponding cavity length is 1001.81121μm,we obtain a center wavelength of 6562.8Åwith an accuracy of 0.0093Å.Analysis reveals that the errors mainly arise from two sources:random errors,including laser intensity stability,detector photon noise,electronic noise of F-P filter,digitaltoanalog conversion quantization error,and nonlinear error,resulting in a wavelength drift of 0.0079Å;and the numerical quantization error of the controller,resulting in a wavelength drift of 0.0014Å.The average unit step of the controller measured by the calibration test is 429.8 pm,compared to the theoretical value of 488.4 pm provided by the manufacturer,with a difference of 58.6 pm.The discrepancy may be due to differences between the laboratory calibration environment and the manufacturer’s test environment.The changes of environmental factors(such as temperature,humidity,and pressure)cause the filter material to expand and contract,electronic components to become unstable,and the refractive index of air in the cavity to change,resulting in differences between measured and theoretical values.This indicates that the measured unit step of the controller is only valid for the environment at the time of calibration.Once the environment changes,recalibration is necessary,or temperature control of the F-P filter is required to ensure its stability.Conclusions We propose a novel method for calibrating the center wavelength of the F-P filter based on the periodicity of the intensity modulation curve.By using the dualwavelength intensity modulation curve of the filter,we measure the unit step of the controller,establish the corresponding relationship between cavity length and the controller value,and accurately calibrate the wavelength of the filter.A calibration system is built in the laboratory for testing the ET100-FS100 F-P filter produced by IC Optical Systems Ltd.The results show that the unit step of controller is 429.8 pm.When observing the Hαsolar spectral line,adjusting the controller to the−101st step,and with a corresponding cavity length of 1001.81121μm,the center wavelength of the F-P filter is 6562.8Å,with a calibration accuracy of 0.0093Å,fully meeting the requirements of the NVST twodimensional imaging spectrometer.
作者
朱瑾
马琳
金振宇
穆恒宇
Zhu Jin;Ma Lin;Jin Zhengyu;Mu Hengyu(Yunnan Observatories,Chinese Academy of Sciences,Kunming 650216,Yunnan,China;University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《光学学报》
CSCD
北大核心
2024年第24期177-184,共8页
Acta Optica Sinica
基金
国家自然科学基金(12073074,11833010)
国家重点研发计划(202103AD50013)
云南省科技计划项目(202105AB160001)
云南省科技人才与平台计划(202305AH340002)
云南省兴滇英才人才培养计划(202305AS350029)。
