Picosecond gain-switched polymer fiber random lasers

Random lasers are a type of lasers that lack typical resonator structures,offering benefits such as easy integration,low cost,and low spatial coherence.These features make them popular for speckle-free imaging and random number generation.However,due to their high threshold and phase instability,the production of picosecond random lasers has still been a challenge.In this work,we have developed three dyes incorporating polymer optical fibers doped with various scattering nanoparticles to produce short-pulsed random fiber lasers.Notably,stable picosecond random laser emission lasting600 ps is observed at a low pump energy of 50μJ,indicating the gain-switching mechanism.Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level.When the intensity of the continuously pumped light reaches a specific value,the number of inversion populations in the“scattering cavity”surpasses the threshold rapidly.Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon.This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.

Mutual aid instead of mutual restraint:interactive probing for topological charge and phase of a vortex beam of large aberrations

An imperfect propagation environment or optical system would introduce wavefront aberrations to vortex beams.The phase aberrations and orbital angular momentum in a vortex beam are proved to be mutually restrictive in parameter measurement.Aberrations make traditional topological charge(TC)probing methods ineffective while the phase singularity makes phase retrieval difficult due to the aliasing between the wrapped phase jump and the vortex phase jump.An interactive probing method is proposed to make measurements of the aberrated phase and orbital angular momentum in a vortex beam assist rather than hinder each other.The phase unwrapping is liberated from the phase singularity by an annular shearing interference technique while the TC value is determined by a Moirétechnique immune to aberrations.Simulation and experimental results proving the method effective are presented.It is of great significance to judge the characteristics of vortex beams passing through nonideal environments and optical systems.

Novel Anti-fouling Strategies of Live and Dead Soft Corals(Sarcophyton trocheliophorum):Combined Physical and Chemical Mechanisms

At present,biomimetic antifouling research objects are mostly concentrated on the fast-moving marine organism,but the anti-fouling effect of the low-speed or static marine equipment is not obvious.This paper describes the anti-fouling mechanism of soft coral(Sarcophyton trocheliophorum),including the physical defense mechanism and the bactericidal ability of mucus and coral powder.As a sessile organisms,soft coral lacks escape mechanism.Therefore,the study on its antibacterial strategy is significant because it can provide theoretical guidance for static antifouling.Results showed that the live soft coral would molt in unfriendly environment,and the secreted mucus could defend themselves against fouling microorganism.Then,Liquid Chromatography-Mass Spectrometry(LC-MS)analysis was conducted to identify the bioactive compounds of the coral powder and mucus.Results revealed that both powder and mucus contained a wide variety of toxic components,which had bactericidal effects.Moreover,at the same concentration,the inhibitory effect of the main components on Gram-negative bacteria was stronger than that on positive bacteria.These findings enhance the understanding about the antifouling mechanism of soft coral and provide new ideas for design and prepare novel antifouling strategy to combat biofouling under static condition.