Atmospheric Turbulence And Double-layer Conjugate System Laser Imaging Study

An atmospheric imaging is unavoidable for the optical systems,such as satellite remote sensing,navigation mapping and radar imaging,working under the environment of atmospheric turbulence.Commonly,the angular resolution of the optical system is decided by the diffraction limitation of the pupil(λ/D).However,the angular resolution of the atmospheric imaging systems is mostly limited by the coherence length (λ/r₀) which is ordinarily smaller than the pupil aperture.As a rule,the angular resolution of the long-time exposal imaging of the big-aperture systems is only equal to which of a 0.1m aperture telescope.To resolve the problem,an adaptive optics system (AOI) is adopted.The AO technology can be subtle to the wavefront aberrance caused by atmospheric distortion,the fluctuation of the environment temperature etc.and allows to perform a real-time correction through adjusting the optical system,which makes the large telescope equipped with AO offer high resolution to the diffraction limitation.It is great,however,that a wavefront dislocation influences more accurate reconstruction of the aberrant wavefront with AO,when a beam is propagating in atmospheric turbulence.The same time,there is atmospheric anisoplanatic effects.The very small field of view(FOV),ordinarily it is about several arcseconds,characterized by the isoplanatic angle remains a serious limitation,if keeping high resolution imaging with AO.And when the observed target slightly deviates the light axis,the resolution begins to degrade rapidly.Those will deteriorate the AO performance severely,limit application extension of AO systems consumedly.To attain more large FOV of high resolution imaging,a new correcting way, named dual-conjugate adaptive optics(DCAO),is adopted,which is a simple system of multi-conjugate adaptive optics(MCAO) belonging to the category of AO.The base theory of the MCAO system is that the atmospheric turbulence is divided into lots of layers,and a deformable mirror(DM) is displayed the conjugate height of every layer so that the wavefront aberrance caused by that turbulent layer is corrected. Through the simulation of atmospheric imaging with optical transfer function (OTF) of optical systems(ideal,turbulence,classical AO and DCAO),the results show the imaging of DCAO system is more legible than classical AO,whose resolution is up to the diffraction limitation.And with the analysis of the performance parameters such as isoplanatic angle,coherence length,scintillation index and strehl ratio,a conclusion is that the DCAO system has a great advantage in atmospheric turbulence correctionThe DCAO,presently,is a trend of AO technology,which is one of hot spots of optical correction.And in the future,there is a stream to multi-conjugate AO(3,4 layers, and so on).