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 ran...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.展开更多
Parametric interaction allows both forward and backward energy transfers among the three interacting waves.The back-conversion effect is usually detrimental when unidirectional energy transfer is desired.In this theor...Parametric interaction allows both forward and backward energy transfers among the three interacting waves.The back-conversion effect is usually detrimental when unidirectional energy transfer is desired.In this theoretical work,we manifest that the back-conversion effect underpins the direct generation of the picosecond pulse train without the need for a laser resonator.The research scenario is an optical parametric amplification(OPA)that consists of a second-order nonlinear medium,a quasi-continuous pump laser and a sinusoidal amplitude-modulated seed signal.The back-conversion of OPA can transfer the modulation peaks(valleys)of the incident signal into output valleys(peaks),which inherently induces spectral sidebands.The generation of each sideband is naturally accompanied with a phase shift of±π.In the regime of full-back-conversion,the amount and amplitude of the sidebands reach the maximum simultaneously,and their phase constitutes an arithmetic sequence,leading to the production of a picosecond pulse train.The generated picosecond pulse train can have an ultrahigh repetition rate of 40 GHz or higher,which may facilitate ultrafast applications with ultrahigh speed.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12174002,11874012,11874126,and 51771186)the Excellent Scientific Research and Innovation Team of Anhui Province(No.2022AH010003)+3 种基金the Key Research and Development Plan of Anhui Province(No.202104a05020059)the Innovation Project for the ReturnedOverseasScholarsofAnhuiProvince(No.2021LCX011)the University Synergy Innovation Program of Anhui Province(No.GXXT-2020-052)the Anhui Young Wanjiang Scholars Talent Project(No.Z010118167)。
文摘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.
基金This work was supported by the National Natural Science Foundation of China(Nos.61727820,61905142,61975120,and 91850203).
文摘Parametric interaction allows both forward and backward energy transfers among the three interacting waves.The back-conversion effect is usually detrimental when unidirectional energy transfer is desired.In this theoretical work,we manifest that the back-conversion effect underpins the direct generation of the picosecond pulse train without the need for a laser resonator.The research scenario is an optical parametric amplification(OPA)that consists of a second-order nonlinear medium,a quasi-continuous pump laser and a sinusoidal amplitude-modulated seed signal.The back-conversion of OPA can transfer the modulation peaks(valleys)of the incident signal into output valleys(peaks),which inherently induces spectral sidebands.The generation of each sideband is naturally accompanied with a phase shift of±π.In the regime of full-back-conversion,the amount and amplitude of the sidebands reach the maximum simultaneously,and their phase constitutes an arithmetic sequence,leading to the production of a picosecond pulse train.The generated picosecond pulse train can have an ultrahigh repetition rate of 40 GHz or higher,which may facilitate ultrafast applications with ultrahigh speed.
