Robust autofocusing propagation in turbulence

Turbulence in complex environments such as the atmosphere and biological media has always been a great challenge to the application of beam propagation in optical communication, optical trapping and manipulation. To overcome this challenge, this study comprehensively investigates the robust propagation of traditional Gaussian and autofocusing beams in turbulent environments. In order to select stable beams that exhibit high intensity and high field gradient at the focal position in complex environments, Kolmogorov turbulence theory is used to simulate the propagation of beams in atmospheric turbulence based on the multi-phase screen method. We systematically analyze the intensity fluctuations, the variation of the coherence factor and the change in the scintillation index with propagation distance. The analysis reveals that the intensity fluctuations of autofocusing beams are significantly smaller than those of Gaussian beams, and the coherence of autofocusing beams is better than that of Gaussian beams under turbulence. Moreover, autofocusing beams exhibit less oscillation than Gaussian beams, indicating that autofocusing beams propagate in complex environments with less distortion and intensity fluctuation. Overall, this work clearly demonstrates that autofocusing beams exhibit higher stability in propagation compared with Gaussian beams, showing great promise for applications such as optical trapping and manipulation in complex environments.

Maskless Microscopic Lithography through Shaping Ultraviolet Laser with Digital Micro-mirror Device

Laser shaping was introduced to maskless projection soft lithography by using digital micro-mirror device (DMD). The predesigned intensity pattern was imprinted onto the DMD and the input laser beam with a Gaussian or quasi-Gaussian distribution will carry the pattern on DMD to etch the resin. It provides a method of precise control of laser beam shapes and?photon-induced curing behavior of resin. This technology provides an accurate micro-fabrication of microstructures used for micro-systems. As a virtual mask generator and a binary-amplitude spatial light modulator, DMD is equivalent to the masks in the conventional exposure system. As the virtual masks and shaped laser beam can be achieved flexibly, it is a good method of precision soft lithography for 2D/3D microstructures.

Parallelized volumetric fluorescence microscopy with a reconfigurable coded incoherent light-sheet array

Parallelized fluorescence imaging has been a long-standing pursuit that can address the unmet need for a comprehensive three-dimensional(3D)visualization of dynamical biological processes with minimal photodamage.However,the available approaches are limited to incomplete parallelization in only two dimensions or sparse sampling in three dimensions.We hereby develop a novel fluorescence imaging approach,called coded light-sheet array microscopy(CLAM),which allows complete parallelized 3D imaging without mechanical scanning.Harnessing the concept of an“infinity mirror”,CLAM generates a light-sheet array with controllable sheet density and degree of coherence.Thus,CLAM circumvents the common complications of multiple coherent light-sheet generation in terms of dedicated wavefront engineering and mechanical dithering/scanning.Moreover,the encoding of multiplexed optical sections in CLAM allows the synchronous capture of all sectioned images within the imaged volume.We demonstrate the utility of CLAM in different imaging scenarios,including a light-scattering medium,an optically cleared tissue,and microparticles in fluidic flow.CLAM can maximize the signal-to-noise ratio and the spatial duty cycle,and also provides a further reduction in photobleaching compared to the major scanning-based 3D imaging systems.The flexible implementation of CLAM regarding both hardware and software ensures compatibility with any light-sheet imaging modality and could thus be instrumental in a multitude of areas in biological research.

Biophotonic rogue waves in red blood cell suspensions

Rogue waves are ubiquitous in nature,appearing in a variety of physical systems ranging from acoustics,microwave cavities,optical fibers,and resonators to plasmas,superfluids,and Bose–Einstein condensates.Unlike nonlinear solitary waves,rogue waves are extreme events that can occur even without nonlinearity by,for example,spontaneous synchronization of waves with different spatial frequencies in a linear system.Here,we report the observation of rogue-wave-like events in human red blood cell(RBC)suspensions under weak light illumination,characterized by an abnormal L-shaped probability distribution.Such biophotonic extreme events arise mostly due to the constructive interference of Mie-scattered waves from the suspended RBCs,whose biconcave shape and mutable orientation give rise to a time-dependent random phase modulation to an incident laser beam.We numerically simulate the beam propagation through the colloidal suspensions with added disorder in both spatial and temporal domains to mimic random scattering due to Brownian motion.In addition,at high power levels,nonlinear beam self-focusing is also observed,leading to a dual-exponential probability distribution associated with the formation of multiple soliton-like spots.Such rogue wave events should also exist in environments with cells of other species such as swimming bacteria,and understanding of their underlying physics may lead to unexpected biophotonic applications.

Optical trapping with structured light: a review

Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer.In the case of 3D trapping with a single beam,this is termed optical tweezers.Optical tweezers are a powerful and noninvasive tool for manipulating small objects,and have become indispensable in many fields,including physics,biology,soft condensed matter,among others.In the early days,optical trapping was typically accomplished with a single Gaussian beam.In recent years,we have witnessed rapid progress in the use of structured light beams with customized phase,amplitude,and polarization in optical trapping.Unusual beam properties,such as phase singularities on-axis and propagation invariant nature,have opened up novel capabilities to the study of micromanipulation in liquid,air,and vacuum.We summarize the recent advances in the field of optical trapping using structured light beams.

Breathing dissipative soliton explosions in a bidirectional ultrafast fiber laser

Soliton explosions,among the most exotic dynamics,have been extensively studied on parameter invariant stationary solitons.However,the explosion dynamics are still largcly unexplored in breathing dissipative solitons as a dynamic solution to many nonlincar systems.Here,we report on the first observation of a breathing dissipative soliton explosion in a nct-normal-dispersion bidirectional ultrafast fiber lascr.The breathing soliton explos ionscould be stimulated by the soliton buildup process or alteration of polarization settings.Transient breathing soliton pairs with intensive repulsion that is sensitive to initial conditions can also be triggered by multiple soliton explosions in the soliton buildup process instead of being triggered by varying polarization settings.The high bchavior similarity also exists in the breathing soliton buildup and explosion process owing to the common gain and loss modulation.In addition,dissipative rogue waves were detected in the breathing soliton explosion,and the collision of breathing soliton significantly enhanced the amplitude of rogue waves,which is characteristic of the breathing solitons in a bidirectional fiber laser.These results shed new insights into complex dissipative soliton dynamics.

Broadband meta-converters for multiple Laguerre-Gaussian modes

Metasurface provides miniaturized devices for integrated optics.Here,we design and realize a meta-converter to transform a plane-wave beam into multiple Laguerre-Gaussian(LG)modes of different orders at various diffraction angles.The metasurface is fabricated with Au nano-antennas,which vary in length and orientation angle for modulation of both the phase and the amplitude of a scattered wave,on a silica substrate.Our error analysis suggests that the metasurface design is robust over a 400 nm wavelength range.This work presents the manipulation of LG beams through controlling both radial and azimuthal orders,which paves the way in expanding the communication channels by one more dimension(i.e.,radial order)and demultiplexing different modes.

Plasmonic resonant nonlinearity and synthetic optical properties in gold nanorod suspensions

We experimentally demonstrate self-trapping of light, as a result of plasmonic resonant optical nonlinearity,in both aqueous and organic(toluene) suspensions of gold nanorods. The threshold power for soliton formation is greatly reduced in toluene as opposed to aqueous suspensions. It is well known that the optical gradient forces are optimized at off-resonance wavelengths at which suspended particles typically exhibit a strong positive(or negative) polarizability. However, surprisingly, as we tune the wavelength of the optical beam from a continuous-wave(CW) laser, we find that the threshold power is reduced by more than threefold at the plasmonic resonance frequency. By analyzing the optical forces and torque acting on the nanorods, we show theoretically that it is possible to align the nanorods inside a soliton waveguide channel into orthogonal orientations by using merely two different laser wavelengths. We perform a series of experiments to examine the transmission of the soliton-forming beam itself, as well as the polarization transmission spectrum of a low-power probe beam guided along the soliton channel. It is found that the expected synthetic anisotropic properties are too subtle to be clearly observed, in large part due to Brownian motion of the solvent molecules and a limited ordering region where the optical field from the self-trapped beam is strong enough to overcome thermodynamic fluctuations. The ability to achieve tunable nonlinearity and nanorod orientations in colloidal nanosuspensions with low-power CW laser beams may lead to interesting applications in all-optical switching and transparent display technologies.