Research on the Measurement Method of Optical Path Difference of Long Baseline Stellar Interferometry Based on Channeled Spectrum
The spatial resolution of the long-baseline stellar interferometer can be improved to the milliarcsecond or even sub-milliarcsecond level with the extension of the baseline.The astrometric accuracy of 10 micro-arcseconds can also be achieved by combining differential delay interferometry method.A number of long-baseline stellar interferometers including VLTI,CHARA,NPOI,IOTA have been built all over the world.In China,the research on long-baseline optical interferometry technology is also actively carried out.A long-baseline stellar interferometer for astronomical observations has already been built at the Xuyi Observation Station.The interferometer consists of three 600 mm telescopes and forms a maximum baseline of 100 m.It is used to carry out astronomical high-resolution imaging and high-precision astrometric research.Fast capture and stable tracking of the fringe are the key technologies for long-baseline stellar interferometry.Achieving large dynamic range and high-precision optical path difference detection are considered as the most urgent issue.In this paper,oriented to the 100 m long baseline stellar interferometer under construction in China,an optical path difference detection method based on channel spectrum is proposed.It has low detection frequency requirements and high sensitivity,which is suitable for the application of small-aperture telescopes.In this method,the wideband fringes are expanded into different spectral channels by using dispersive elements,and the corresponding coherence length on each pixel on the detector can be greatly increased.This method effectively improving the dynamic range of optical path difference detection.On the other hand,the intensity of the interference signal on the detector can be expressed as a periodic function of the wavenumber,and the optical path difference between the starlight can be accurately solved by the number of the fringes on the detector.In stellar interferometry observation,the spectrum band is limited and is assigned to different terminal devices according to scientific purpose.Under the condition of narrow spectral band,the detection accuracy of optical path difference can be further approved to the sub-micron level by introducing the periodic diagram and zero-padding algorithm,which effectively improves the utilization efficiency of spectral band.The numerical simulation and experimental results show that under the detection band of 500～600 nm,with the method described in this paper,the accuracy of optical path difference can be improved to 0.75 μm,and the dynamic range can reach±195 μm,which can meet the requirements of fringe tracking and improve the spectral band utilization efficiency.The stellar interferometric optical path difference detection method based on channeled spectrum can effectively solve the problem of fast fringe capture and stable fringe tracking in astronomical observation.It can be expected that by strictly controlling the error of the optical system,optimizing the observation band and subdivision multiple of the resolution,the accuracy of optical path difference detection can be further improved,and this study can provide key technical support for the successful first light of the 100 m long baseline stellar interferometer under construction in China.
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维普
