Study On Holographic Modal Wavefront Sensing Technology

Holographic modal wavefront sensor (HMWFS) is a novel wavefront sensing technology proposed in recent years, which is implemented by recording and sensing several aberration modes with a multiplexed holographic element. Its output signals can be related near linearly to the coefficients of tested aberration modes, and readily transformed into the control signals of wavefront correctors without heavy matrix computation. This may help improve the bandwidth and compactness of adaptive optics (AO) systems, and hence make it possible to transform general software into computer-free, electronics-only and basic circuitry for AO systems. Also, HMWFS is insensitive to the intensity nonuniformity of optical field, and can be adapted to the circumstances such as high turbulence, strong scintillation. HMWFS has valuable potential inapplications in terms of unmanned aerial vehicles'high resolution image, airborne high energy lasers and free-space optical communications. In this dissertation,we carry out extensive investigations on HMWFS in four aspects, respectively, including theoretical analysis, numerical simulation, experimental demonstration and technology extentions. The primary contents are presented as follows: Mode-biased wavefront sensing (MBWFS) technology is theoretically and experimentally analyzed in detail. With the small-phase approximation, we analyze and extend the expressions of correlative factors, i.e., sensitivity factors, of near linear relationships between the output signals of MBWFS and the tested aberration modes'coefficients. We numerically compare and analyze the characteristics of MBWFS's sensitivity response curves corresponding to various types and orders of tested aberration modes, ways of taking information from focal spots, and ways of output signals. We also analyze the impacts upon performance of MBWFS from factors such as bias modes'coefficients, iris size of focal spots. Several approaches of MBWFS with multiple bias modes are summarized. The results indicate that, the normalized intensity difference (NID) or modified NID is suitable to be output signals of MBWFS; for different bias modes, the performance can be optimized by selecting appropriate parameters such as bias modes'coefficients, iris size of focal spots, e.g., absolute sensitivity improvement, dynamic measurement range extensions, intermodal cross-talk restraint, and so on.HMWFS is studied theoretically and numerically by implementing the multiplexed holographic optical element with computer-generated hologram, i.e., multiplexed computer-generated holographic element (MCGHE). It is figured out that the essence of HMWFS belongs to MBWFS with multiple synchronization bias modes. The designed holograms, the diffraction patterns and diffraction efficiencies in focal plane of the phase MCGHEs are comparatively analyzed. HMWFS based on different phase MCGHEs are analyzed in terms of sensitivity response characteristics, calibrated sensitivity matrixs, static aberration modes detection and close-loop correction. The results show that, binary phase MCGHEs can restrain intensity of zero diffraction order, and thus relatively enhance that of first diffraction order; and that, phase MCGHEs coded with linear carrier frequencies have higher diffraction efficiencies and approximate diagonal sensitivity matrixes; the performance of HMWFS is numerically validated through sensing and compensating static phase screens in both open-loop and close-loop AO systems.We establish two experimental systems based on spatial light modulators (SLMs) and micro-lithographic diffractive element respectively, and validate HMWFS through dynamic and static holography experiments accordingly. We demonstrate the sensitivity response characteristics of HMWFS to sense single aberration mode, and verify the properties of optical fields, in focal plane, generated from MCGHEs, which are coded with more multiple modes or quadratic carrier frequencies. The impacts of various carrier frequency distributions on the performance of HMWFS is comparatively demonstrated in experiment.The HMWFS technology is extended by introducing three orthogonal modes of different definitions and characteristics. HMWFS based on MCGHEs coded with deformable mirror (DM) modes could be matched well with particular DM, and the residual error in the close-loop correction systems will be somewhat diminished. Those coded with Karhunen-Loeve modes will be adapted to sensing wavefront aberration distorted by atmospheric turbulence. And those coded with Lukosz-Zernike modes will own effective extended dynamic measurement ranges.