The spectral memory effect in scattering media is crucial for applications that employ broadband illumination,as it dictates the available spectral range from independent scattering responses.Previous studies mainly c...The spectral memory effect in scattering media is crucial for applications that employ broadband illumination,as it dictates the available spectral range from independent scattering responses.Previous studies mainly considered a passive result with the average impact of the scattering medium,whereas it is vital to actively enhance or suppress this effect for applications concerned with large spectral range or fine resolution.We construct an analytical model by integrating the concepts of wave-based interference and photon-based propagation,which manifests a potential physical image for active manipulation by utilizing scattering eigenchannels.Our theoretical predictions indicate that the spectral memory effect is enhanced using high-transmission eigenchannels while it is suppressed using low-transmission eigenchannels.These predictions are supported by finite-difference time-domain simulations and experiments,demonstrating that the spectral memory effect’s range can be actively manipulated.Quantitatively,the experiments achieved variations in enhancement and suppression that exceeded threefold(∼3.27).We clarify the underlying principles of the spectral memory effect in scattering media and demonstrate active manipulation of multispectral scattering processes.展开更多
Feedback-based wavefront shaping focuses light through scattering media by employing phase optimization algorithms.Genetic algorithms(GAs),inspired by the process of natural selection,are well suited for phase optimiz...Feedback-based wavefront shaping focuses light through scattering media by employing phase optimization algorithms.Genetic algorithms(GAs),inspired by the process of natural selection,are well suited for phase optimization in wavelfront shaping problems.In 2012,Conkey et al.first introduced a GA into feedback-based wavefront shaping to find the optimum phase map.Since then,due to its siuperior performance in noisy environment,the GA has been widely adopted by lots of implementations.However,there have been limited studies discussing and optimizing the detailed procedures of the GA.To fill this blank,in this study,we performed a thorough study on the performance of the GA for focusing light through scattering media.Using numerical tools,we evaluated certain procedures that can be potentially improved and provided guidance on how to choose certain parameters appropriately.This study is beneficial in improving the performance of wavefront shaping systems with GAs.展开更多
Single-pixel imaging(SPI)is a promising technology for optical imaging beyond the visible spectrum,where commercial cameras are expensive or unavailable.However,limitations such as slow pattern projection rates and ti...Single-pixel imaging(SPI)is a promising technology for optical imaging beyond the visible spectrum,where commercial cameras are expensive or unavailable.However,limitations such as slow pattern projection rates and time-consuming reconstruction algorithms hinder its throughput for real-time imaging.Consequently,conventional SPI is inadequate for high-speed,high-resolution tasks.To address these challenges,we developed an ultrahigh-throughput single-pixel complex-field microscopy(SPCM)system utilizing frequency-comb acousto-optic coherent encoding(FACE).This system enables real-time complex-field monitoring in the non-visible domain.Operating at 1030 nm,our system achieves a record-high space-bandwidth-time product(SBP-T)of 1.3×10^(7),surpassing previous SPCM(~10^(4)),SPI(~10^(5)),and even certain types of commercial near-infrared cameras(~10^(6)).It supports real-time streaming at 1000 Hz with a frame size of 80×81 pixels and a lateral resolution of 3.76μm across an approximately 300μm field of view.We validated the system by imaging dynamic transparent scenes,including microfluidics,live microorganisms,chemical reactions,as well as imaging through scattering media.This advancement offers a superior solution for high-speed,high-resolution complex-field imaging beyond the visible spectrum,significantly enhancing SPI performance across various applications.展开更多
Framing photography provides a high temporal resolution and minimizes crosstalk between adjacent frames,making it an indispensable tool for recording ultrafast phenomena.To date,various ultrafast framing photography t...Framing photography provides a high temporal resolution and minimizes crosstalk between adjacent frames,making it an indispensable tool for recording ultrafast phenomena.To date,various ultrafast framing photography techniques have been developed.However,simultaneously achieving large sequence depth,high image quality,ultrashort exposure time,and flexible frame interval remains a significant challenge.Herein,we present a spatiotemporal shearing-based ultrafast framing photography,termed STS-UFP,designed to address this challenge.STS-UFP employs an adjustable ultrashort laser pulse train with a spectrum shuttle to illuminate the dynamic scenes for extracting the transient information and records discrete frames using a streak camera via spatiotemporal shearing.Based on its unique design,STS-UFP achieves high-quality ultrafast imaging with a sequence depth of up to 16 frames and frame intervals ranging from hundreds of picoseconds to nanoseconds,while maintaining an extremely short(picosecond)exposure time.The exceptional performance of STS-UFP is demonstrated through experimental observations of femtosecond laser-induced plasma and shockwave in water,femtosecond laser ablation in biological tissue,and femtosecond laser-induced shockwave on a silicon surface.Given its remarkable imaging capabilities,STS-UFP serves as a powerful tool for precisely observing ultrafast dynamics and holds significant potential for advancing studies of ultrafast phenomena.展开更多
Single-pixel imaging(SPI)is a computational imaging technique that is able to reconstruct high-resolution images using a single-pixel detector.However,most SPI demonstrations have been mainly focused on macroscopic sc...Single-pixel imaging(SPI)is a computational imaging technique that is able to reconstruct high-resolution images using a single-pixel detector.However,most SPI demonstrations have been mainly focused on macroscopic scenes,so their applications to biological specimens are generally limited by constraints in space-bandwidth-time product and spatial resolution.In this work,we further enhance SPI's imaging capabilities for biological specimens by developing a high-resolution holographic system based on heterodyne holography.Our SPI system achieves a space-bandwidth-time product of 41,667 pixel/s and a lateral resolution of 4±5μm,which represent state-of-the-art technical indices among reported SPI systems.Importantly,our SPI system enables detailed amplitude imaging with high contrast for stained specimens such as epithelial and esophageal cancer samples,while providing complementary phase imaging for unstained specimens including molecular diagnostic samples and mouse brain tissue slices,revealing subtle refractive index variations.These results highlight SPI's versatility and establish its potential as a powerful tool for advanced biomedical imaging applications.展开更多
The Gerchberg–Saxton(GS)algorithm,which retrieves phase information from the measured intensities on two related planes(the source plane and the target plane),has been widely adopted in a variety of applications when...The Gerchberg–Saxton(GS)algorithm,which retrieves phase information from the measured intensities on two related planes(the source plane and the target plane),has been widely adopted in a variety of applications when holographic methods are challenging to be implemented.In this work,we showed that the GS algorithm can be generalized to retrieve the unknown propagating function that connects these two planes.As a proof-of-concept,we employed the generalized GS(GGS)algorithm to retrieve the optical transmission matrix(TM)of a complex medium through the measured intensity distributions on the target plane.Numerical studies indicate that the GGS algorithm can efficiently retrieve the optical TM while maintaining accuracy.With the same training data set,the computational time cost by the GGS algorithm is orders of magnitude less than that consumed by other non-holographic methods reported in the literature.Besides numerical investigations,we also experimentally demonstrated retrieving the optical TMs of a stack of ground glasses and a 1-m-long multimode fiber using the GGS algorithm.The accuracy of the retrieved TM was evaluated by synthesizing high-quality single foci and multiple foci on the target plane through these complex media.These results indicate that the GGS algorithm can handle a large TM with high efficiency,showing great promise in a variety of applications in optics.展开更多
The multi-dimensional laser is a fascinating platform not only for the discovery and understanding of new higherdimensional coherent lightwaves but also for the frontier study of the complex three-dimensional(3D)nonli...The multi-dimensional laser is a fascinating platform not only for the discovery and understanding of new higherdimensional coherent lightwaves but also for the frontier study of the complex three-dimensional(3D)nonlinear dynamics and solitary waves widely involved in physics,chemistry,biology and materials science.Systemically controlling coherent lightwave oscillation in multi-dimensional lasers,however,is challenging and has largely been unexplored;yet,it is crucial for both designing 3D coherent light fields and unveiling any underlying nonlinear complexities.Here,for the first time,we genetically harness a multi-dimensional fibre laser using intracavity wavefront shaping technology such that versatile lasing characteristics can be manipulated.We demonstrate that the output power,mode profile,optical spectrum and mode-locking operation can be genetically optimized by appropriately designing the objective function of the genetic algorithm.It is anticipated that this genetic and systematic intracavity control technology for multi-dimensional lasers will be an important step for obtaining high-performance 3D lasing and presents many possibilities for exploring multi-dimensional nonlinear dynamics and solitary waves that may enable new applications.展开更多
Optical techniques offer a wide variety of applications as light-matter interactions provide extremely sensitive mechanisms to probe or treat target media.Most of these implementations rely on the usage of ballistic o...Optical techniques offer a wide variety of applications as light-matter interactions provide extremely sensitive mechanisms to probe or treat target media.Most of these implementations rely on the usage of ballistic or quasi-ballistic photons to achieve high spatial resolution.However,the inherent scattering nature of light in biological tissues or tissue-like scattering media constitutes a critical obstacle that has restricted the penetration depth of non-scattered photons and hence limited the implementation of most optical techniques for wider applications.In addition,the components of an optical system are usually designed and manufactured for a fixed function or performance.Recent advances in wavefront shaping have demonstrated that scattering-or component-induced phase distortions can be compensated by optimizing the wavefront of the input light pattern through iteration or by conjugating the transmission matrix of the scattering medium.展开更多
Scattering-induced glares hinder the detection of weak objects in various scenarios.Recent advances in wavefront shaping show one can not only enhance intensities through constructive interference but also suppress gl...Scattering-induced glares hinder the detection of weak objects in various scenarios.Recent advances in wavefront shaping show one can not only enhance intensities through constructive interference but also suppress glares within a targeted region via destructive interference.However,due to the lack of a physical model and mathematical guidance,existing approaches have generally adopted a feedback-based scheme,which requires timeconsuming hardware iteration.Moreover,glare suppression with up to tens of speckles was demonstrated by controlling thousands of independent elements.Here,we reported the development of a method named twostage matrix-assisted glare suppression(TAGS),which is capable of suppressing glares at a large scale without triggering time-consuming hardware iteration.By using the TAGS,we experimentally darkened an area containing 100 speckles by controlling only 100 independent elements,achieving an average intensity of only 0.11 of the original value.It is also noticeable that the TAGS is computationally efficient,which only takes 0.35 s to retrieve the matrix and 0.11 s to synthesize the wavefront.With the same number of independent controls,further demonstrations on suppressing larger scales up to 256 speckles were also reported.We envision that the superior performance of the TAGS at a large scale can be beneficial to a variety of demanding imaging tasks under a scattering environment.展开更多
We introduce non-Hermitian plasmonic waveguide-cavity systems with topological edge states(TESs)at singular points.The compound unit cells of the structures consist of metal-dielectric-metal(MDM)stub resonators side-c...We introduce non-Hermitian plasmonic waveguide-cavity systems with topological edge states(TESs)at singular points.The compound unit cells of the structures consist of metal-dielectric-metal(MDM)stub resonators side-coupled to an MDM waveguide.We show that we can realize both a TES and an exceptional point at the same frequency when a proper amount of loss is introduced into a finite three-unit-cell structure.We also show that the finite structure can exhibit both a TES and a spectral singularity when a proper amount of gain is introduced into the structure.In addition,we show that we can simultaneously realize a unidirectional spectral singularity and a TES when proper amounts of loss and gain are introduced into the structure.We finally show that this singularity leads to extremely high sensitivity of the reflected light intensity to variations of the refractive index of the active materials in the structure.TESs at singular points could potentially contribute to the development of singularity-based plasmonic devices with enhanced performance.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12325408,92150102,62205302,92150301,12274129,12074121,62105101,62175066,12274139,and 12404380)the Fundamental and Applied Basic Research Project of Guangzhou(Grant No.2024A04J2001)the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2024B1515020051 and 2023A1515110742).
文摘The spectral memory effect in scattering media is crucial for applications that employ broadband illumination,as it dictates the available spectral range from independent scattering responses.Previous studies mainly considered a passive result with the average impact of the scattering medium,whereas it is vital to actively enhance or suppress this effect for applications concerned with large spectral range or fine resolution.We construct an analytical model by integrating the concepts of wave-based interference and photon-based propagation,which manifests a potential physical image for active manipulation by utilizing scattering eigenchannels.Our theoretical predictions indicate that the spectral memory effect is enhanced using high-transmission eigenchannels while it is suppressed using low-transmission eigenchannels.These predictions are supported by finite-difference time-domain simulations and experiments,demonstrating that the spectral memory effect’s range can be actively manipulated.Quantitatively,the experiments achieved variations in enhancement and suppression that exceeded threefold(∼3.27).We clarify the underlying principles of the spectral memory effect in scattering media and demonstrate active manipulation of multispectral scattering processes.
文摘Feedback-based wavefront shaping focuses light through scattering media by employing phase optimization algorithms.Genetic algorithms(GAs),inspired by the process of natural selection,are well suited for phase optimization in wavelfront shaping problems.In 2012,Conkey et al.first introduced a GA into feedback-based wavefront shaping to find the optimum phase map.Since then,due to its siuperior performance in noisy environment,the GA has been widely adopted by lots of implementations.However,there have been limited studies discussing and optimizing the detailed procedures of the GA.To fill this blank,in this study,we performed a thorough study on the performance of the GA for focusing light through scattering media.Using numerical tools,we evaluated certain procedures that can be potentially improved and provided guidance on how to choose certain parameters appropriately.This study is beneficial in improving the performance of wavefront shaping systems with GAs.
基金supported in part by the National Natural Science Foundation of China(12404380,12325408,12274129,12374274,12274139,62175069,62175066,62475070,12474404)the Fundamental and Applied Basic Research Project of Guangzhou(2024A04J2001)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(2023A1515110742,2023B1515120044,2024B1515020051)Shanghai Municipal Education Commission(2024AI01007)Science and Technology Commission of Shanghai Municipality(QNKJ2024031).
文摘Single-pixel imaging(SPI)is a promising technology for optical imaging beyond the visible spectrum,where commercial cameras are expensive or unavailable.However,limitations such as slow pattern projection rates and time-consuming reconstruction algorithms hinder its throughput for real-time imaging.Consequently,conventional SPI is inadequate for high-speed,high-resolution tasks.To address these challenges,we developed an ultrahigh-throughput single-pixel complex-field microscopy(SPCM)system utilizing frequency-comb acousto-optic coherent encoding(FACE).This system enables real-time complex-field monitoring in the non-visible domain.Operating at 1030 nm,our system achieves a record-high space-bandwidth-time product(SBP-T)of 1.3×10^(7),surpassing previous SPCM(~10^(4)),SPI(~10^(5)),and even certain types of commercial near-infrared cameras(~10^(6)).It supports real-time streaming at 1000 Hz with a frame size of 80×81 pixels and a lateral resolution of 3.76μm across an approximately 300μm field of view.We validated the system by imaging dynamic transparent scenes,including microfluidics,live microorganisms,chemical reactions,as well as imaging through scattering media.This advancement offers a superior solution for high-speed,high-resolution complex-field imaging beyond the visible spectrum,significantly enhancing SPI performance across various applications.
基金National Natural Science Foundation of China(12325408,12274129,12274139,12374274,62175066,92150102,12474404,12304338,12471368,62475070)Fundamental Research Funds for the Central Universities。
文摘Framing photography provides a high temporal resolution and minimizes crosstalk between adjacent frames,making it an indispensable tool for recording ultrafast phenomena.To date,various ultrafast framing photography techniques have been developed.However,simultaneously achieving large sequence depth,high image quality,ultrashort exposure time,and flexible frame interval remains a significant challenge.Herein,we present a spatiotemporal shearing-based ultrafast framing photography,termed STS-UFP,designed to address this challenge.STS-UFP employs an adjustable ultrashort laser pulse train with a spectrum shuttle to illuminate the dynamic scenes for extracting the transient information and records discrete frames using a streak camera via spatiotemporal shearing.Based on its unique design,STS-UFP achieves high-quality ultrafast imaging with a sequence depth of up to 16 frames and frame intervals ranging from hundreds of picoseconds to nanoseconds,while maintaining an extremely short(picosecond)exposure time.The exceptional performance of STS-UFP is demonstrated through experimental observations of femtosecond laser-induced plasma and shockwave in water,femtosecond laser ablation in biological tissue,and femtosecond laser-induced shockwave on a silicon surface.Given its remarkable imaging capabilities,STS-UFP serves as a powerful tool for precisely observing ultrafast dynamics and holds significant potential for advancing studies of ultrafast phenomena.
基金supported by the National Natural Science Foundation of China(Nos.12471368,12325408,12274129,12274139,and 62475070)the Fundamental and Applied Basic Research Project of Guangzhou(No.2024A04J2001)the Guangdong Basic and Applied Basic Research Foundation(No.2024B1515020051)。
文摘Single-pixel imaging(SPI)is a computational imaging technique that is able to reconstruct high-resolution images using a single-pixel detector.However,most SPI demonstrations have been mainly focused on macroscopic scenes,so their applications to biological specimens are generally limited by constraints in space-bandwidth-time product and spatial resolution.In this work,we further enhance SPI's imaging capabilities for biological specimens by developing a high-resolution holographic system based on heterodyne holography.Our SPI system achieves a space-bandwidth-time product of 41,667 pixel/s and a lateral resolution of 4±5μm,which represent state-of-the-art technical indices among reported SPI systems.Importantly,our SPI system enables detailed amplitude imaging with high contrast for stained specimens such as epithelial and esophageal cancer samples,while providing complementary phase imaging for unstained specimens including molecular diagnostic samples and mouse brain tissue slices,revealing subtle refractive index variations.These results highlight SPI's versatility and establish its potential as a powerful tool for advanced biomedical imaging applications.
文摘压缩超快成像(compressed ultrafast photography,CUP)是目前最快的被动式单次超快光学成像技术,它通过数据获取和图像重构两个步骤实现超快事件的捕捉,已发展为记录不可逆或难以重复超快事件的一种有力工具,且能够探测荧光动力学等自发光瞬态场景.然而,传统的迭代优化型算法在图像重构上的保真度较低,而端到端型深度学习算法则严重依赖训练数据,训练复杂度高、通用性不足,这限制了CUP对超快现象进行高空间分辨率的观测.为此,我们开发了一种新型的免训练自监督式神经网络算法,其通过即插即用框架(plug-and-play,PnP)与深度图像先验(deep image prior,DIP)的结合可实现CUP的低复杂度高保真图像重建,简称为PnP-DIP算法.PnP-DIP基于交替方向乘子法(alternating direction method of multipliers,ADMM),利用DIP和PnP去噪器解决图像恢复子问题,可以在防止数据过拟合和噪声累积的同时,显著提高图像重建的精度与收敛速度.通过数值模拟,我们理论上证明了PnP-DIP算法在重构原始动态信息方面相比传统ADMM算法具有更高的保真度.同时,我们分别利用PnPDIP对自主研制CUP系统观测的皮秒激光脉冲和X射线闪烁体的时空强度演化数据进行重构,实验上验证了其优越的图像重构性能.这一研究有望推动CUP在高时空分辨观测需求中的应用,并为超快动力学的实时探测作出重大贡献.
基金National Key Research and Development Program of China(2018YFB1802300)National Natural Science Foundation of China(61525502)。
文摘The Gerchberg–Saxton(GS)algorithm,which retrieves phase information from the measured intensities on two related planes(the source plane and the target plane),has been widely adopted in a variety of applications when holographic methods are challenging to be implemented.In this work,we showed that the GS algorithm can be generalized to retrieve the unknown propagating function that connects these two planes.As a proof-of-concept,we employed the generalized GS(GGS)algorithm to retrieve the optical transmission matrix(TM)of a complex medium through the measured intensity distributions on the target plane.Numerical studies indicate that the GGS algorithm can efficiently retrieve the optical TM while maintaining accuracy.With the same training data set,the computational time cost by the GGS algorithm is orders of magnitude less than that consumed by other non-holographic methods reported in the literature.Besides numerical investigations,we also experimentally demonstrated retrieving the optical TMs of a stack of ground glasses and a 1-m-long multimode fiber using the GGS algorithm.The accuracy of the retrieved TM was evaluated by synthesizing high-quality single foci and multiple foci on the target plane through these complex media.These results indicate that the GGS algorithm can handle a large TM with high efficiency,showing great promise in a variety of applications in optics.
基金supported in part by US National Institutes of Health(NIH)Grant R01 CA186567(NIH Director’s Transformative Research Award).
文摘The multi-dimensional laser is a fascinating platform not only for the discovery and understanding of new higherdimensional coherent lightwaves but also for the frontier study of the complex three-dimensional(3D)nonlinear dynamics and solitary waves widely involved in physics,chemistry,biology and materials science.Systemically controlling coherent lightwave oscillation in multi-dimensional lasers,however,is challenging and has largely been unexplored;yet,it is crucial for both designing 3D coherent light fields and unveiling any underlying nonlinear complexities.Here,for the first time,we genetically harness a multi-dimensional fibre laser using intracavity wavefront shaping technology such that versatile lasing characteristics can be manipulated.We demonstrate that the output power,mode profile,optical spectrum and mode-locking operation can be genetically optimized by appropriately designing the objective function of the genetic algorithm.It is anticipated that this genetic and systematic intracavity control technology for multi-dimensional lasers will be an important step for obtaining high-performance 3D lasing and presents many possibilities for exploring multi-dimensional nonlinear dynamics and solitary waves that may enable new applications.
基金supported by National Natural Science Foundation of China(NSFC)(81930048,81627805)Hong Kong Research Grant Council(15217721,R5029-19,C7074-21GF)+3 种基金Hong Kong Innovation and Technology Commission(GHP/043/19SZ,GHP/044/19GD)Guangdong Science and Technology Commission(2019A1515011374,2019BT02X105)National Research Foundation of Korea(2015R1A3A2066550,2021R1A2C3012903)Institute of Information&Communications Technology Planning&Evaluation(IITP,2021-0-00745)grant funded by the Korea government(MSIT).
文摘Optical techniques offer a wide variety of applications as light-matter interactions provide extremely sensitive mechanisms to probe or treat target media.Most of these implementations rely on the usage of ballistic or quasi-ballistic photons to achieve high spatial resolution.However,the inherent scattering nature of light in biological tissues or tissue-like scattering media constitutes a critical obstacle that has restricted the penetration depth of non-scattered photons and hence limited the implementation of most optical techniques for wider applications.In addition,the components of an optical system are usually designed and manufactured for a fixed function or performance.Recent advances in wavefront shaping have demonstrated that scattering-or component-induced phase distortions can be compensated by optimizing the wavefront of the input light pattern through iteration or by conjugating the transmission matrix of the scattering medium.
基金National Key Research and Development Program of China(2018YFB1802300)National Natural Science Foundation of China(12004446,92150102,U2001601)+1 种基金Fundamental and Applied Basic Research Project of Guangzhou(202102020603)State Key Laboratory of Advanced Optical Communication Systems and Networks(2021GZKF004)。
文摘Scattering-induced glares hinder the detection of weak objects in various scenarios.Recent advances in wavefront shaping show one can not only enhance intensities through constructive interference but also suppress glares within a targeted region via destructive interference.However,due to the lack of a physical model and mathematical guidance,existing approaches have generally adopted a feedback-based scheme,which requires timeconsuming hardware iteration.Moreover,glare suppression with up to tens of speckles was demonstrated by controlling thousands of independent elements.Here,we reported the development of a method named twostage matrix-assisted glare suppression(TAGS),which is capable of suppressing glares at a large scale without triggering time-consuming hardware iteration.By using the TAGS,we experimentally darkened an area containing 100 speckles by controlling only 100 independent elements,achieving an average intensity of only 0.11 of the original value.It is also noticeable that the TAGS is computationally efficient,which only takes 0.35 s to retrieve the matrix and 0.11 s to synthesize the wavefront.With the same number of independent controls,further demonstrations on suppressing larger scales up to 256 speckles were also reported.We envision that the superior performance of the TAGS at a large scale can be beneficial to a variety of demanding imaging tasks under a scattering environment.
基金National Key Research and Development Program of China(2019YFA0706301)National Natural Science Foundation of China(12004446,61605252).
文摘We introduce non-Hermitian plasmonic waveguide-cavity systems with topological edge states(TESs)at singular points.The compound unit cells of the structures consist of metal-dielectric-metal(MDM)stub resonators side-coupled to an MDM waveguide.We show that we can realize both a TES and an exceptional point at the same frequency when a proper amount of loss is introduced into a finite three-unit-cell structure.We also show that the finite structure can exhibit both a TES and a spectral singularity when a proper amount of gain is introduced into the structure.In addition,we show that we can simultaneously realize a unidirectional spectral singularity and a TES when proper amounts of loss and gain are introduced into the structure.We finally show that this singularity leads to extremely high sensitivity of the reflected light intensity to variations of the refractive index of the active materials in the structure.TESs at singular points could potentially contribute to the development of singularity-based plasmonic devices with enhanced performance.
