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.

Circularly polarized lasing from chiral metal-organic frameworks

Circularly polarized lasers play a pivotal role in classical optics,nanophotonics,and quantum optical information processing,while their fabrication remains complex.This article begins with examining the interactions between stimulated emission and chiral matter,outlining a simple strategy for producing circularly polarized lasing from chiral metal-organic frameworks(MOFs),such as the zeolitic imidazolate framework(ZIF),embedded with achiral laser dyes(L∕D-ZIF?dyes).It is found that the stimulated emission threshold and intensity are influenced by the interplay between the chiral polarization of the pump light and the inherent chirality of the MOF nanoparticles.We further present the design of a chiral vertical-cavity surface-emitting laser(VCSEL),comprising an L∕D-ZIF?dyes solid-state film sandwiched between a high-reflectivity distributed Bragg reflector(DBR)mirror and a silver film.The cavity-based lasing exhibits higher asymmetry between emitting left-handed and right-handed polarized light compared to chiral spontaneous emission(SE)and amplified spontaneous emission(ASE),with an asymmetry value glum of approximately±0.31.This value is nearly four-fold greater than that of SE and twice that of ASE.Our findings reveal a new approach to amplify chiral signals,promoting the comprehension and application of chiral–matter interactions,and offering a simple yet effective strategy to fabricate chiral lasers.

Wide-field optical sizing of single nanoparticles with 10 nm accuracy

There is an increasing demand for new technologies to rapidly measure individual nanoparticles in situ for applications,including early-stage diagnosis of human diseases and environmental monitoring.Here,we demonstrate a label-free wide-field optical microscopy capable of sizing dispersed non-luminescent dielectric nanoparticles(with diameters down to 22 nm)with 10 nm accuracy.This technique utilizes enhanced nanoparticle-perturbed scattering by surface plasmons created on a gold film.In the meantime,an azimuthal rotation illumination module is installed on this microscope and a differential image processing technique is carried out.The relationship between the scattering intensity and the particle size was experimentally measured with good consistency with the theoretical prediction.The capability of precise measurement of the size of dispersed nanoparticles within a larger field of view in a label-free,non-invasive and quantitative manner may find broad applications involving single nanoparticle chemistry and physics.

Controllable optofluidic assembly of biological cells using an all-dielectric one-dimensional photonic crystal

Opto-thermophoretic manipulation is emerging as an effective way for versatile trapping,guiding,and assembly of biological nanoparticles and cells.Here we report a new opto-thermophoretic tweezer based on an all-dielectric one-dimensional photonic crystal(1 DPC)for reversible assembly of biological cells with a controllable center.To reveal its ability of long-range optofluidic manipulation,we demonstrate the reversible assembly of many yeast cells as well as E.coli cells that are dispersed in water solution.The 1 DPC-based tweezer can also exert short-range optical gradient forces associated with focused Bloch surface waves excited on the 1 DPC,which can optically trap single particles.By combining both the optical and thermophoretic manipulation,the optically trapped single polystyrene particle can work as a controllable origin of the reversible cellular assembly.Numerical simulations are performed to calculate the temperature distribution and convective flow velocity on the 1 DPC,which are consistent with the experimental observations and theoretically confirm the long-range manipulations on the alldielectric 1 DPC platform.The opto-thermophoretic tweezers based on all-dielectric 1 DPC endow the microma-nipulation toolbox for potential applications in biomedical sciences.