Wavefront Shaping Technique And Its Study In Focusing Through Scattering Medium

With the further development of laser technology,wavefront shaping technique is playing a more and more important role in optical micromanipulation,biomedical imaging and micro-nano device fabrication,etc.From the perspective of multi-dimensional wavefront modulation,we have systematically studied the optical modulation in the manners of amplitude,phase,polarization and spectrum,the research development and application of novel structured beams and emphasized the generating method of special light fields and their propagation dynamics.Besides,based on a digital spatial light modulator with high speed,we have exploited various hologram methods to create a variety of peculiar beams exhibiting different structures and behaviors,and investigated beam property during their propagation.Meanwhile,due to scattering effect,the beam wavefront will be randomly changed and seriously distorted,as it propagates in the complex medium,such as in the biological tissue,etc.Thus,the scattering will prevent the beam's further application in some related areas.Especially in the biomedical field,that effect influences the depth and quality in the micromanipulation and microscopy,so that effective manipulating and imaging deep animal tissue in-vivo becomes basically impossible.Therefore,tailoring the light propagation in the scattering medium becomes a significant topic in the biomedical areas.In order to solve this problem,we control light propagation through wavefront shaping technique in this thesis,and have focused light through the strong scattering medium.The research progresses and developments are presented as follows:1.We have systematically introduced the propagation dynamics and applications of some complex structured beams,such as self-accelerating Airy beams,vortex beams with spiral wavefront structure and diffracting-free Bessel beams.2.In order to satisfy various applications,we take advantage of a variety of algorithm to generate the holograms for beams with special modes,and study their propagation dynamics,as they propagate in free space.3.We have investigated two ways of optical phase conjugation to modulate light's propagation in scattering medium.Specifically,the first one is traditional phase conjugation method that uses photorefractive crystal and four-mixing principle;another one is digital optical phase conjugation that exploits high-performance camera and digital spatial light modulator.4.We have studied focusing light into scattering medium based on time-reversal ultrasonic encoding technique,holding promises for micro-manipulation and microscopy deep inside the animal tissue in vivo.The innovations of this thesis are also shown as follows:1.We have generated a special type of optical vortex,called perfect vortex beam,whose spatial profile is independent of topological charges,then compare the fidelity and efficiency for two digital hologram approaches.Besides,we initially proposed a new kind of accelerating polygon beams with peculiar features,which has two different modes of lobes travelling along parabolic trajectories and never been reported before.At same time,we adopt the catastrophe theory to analyze and explain its origin,and study its propagation property through experimental approach.2.Based on those aforementioned beams,we encode vortex component into some of the Airy-like beams,thus creating multiple modes of hybrid beams,including vortex symmetric Airy beams,vortex circular Airy beams(VCAB)and superimposed VCABs.The spatial profiles and propagation dynamics of these beams can be dynamically tailored through the position of the projected vortex.3.We focused light through turbid medium based on both traditional and digital optical phase conjugation system,thus promoting the focusing quality and depth.These breakthroughs show their potentials in the biomedical areas.Especially in biomedical field,exploiting wavefront shaping in focusing light inside or through scattering medium will provide a feasible method for imaging and manipulation in animal's deep tissue.We anticipate that the research works will not only attract intensive attention from academia,but also play a significant role in clinical area.