Basudeb Sain, Thomas Zentgraf
Metasurface saturable absorbers may result in versatile mode-locking that allows one to obtain stable ultrashort laser pulses with high repetition rates and peak powers, along with broadband operation, within fiber to solid-state laser cavities.
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Spin-momentum locking breakdown on plasmonic metasurfaces
本文提出散射形式理论，揭示结构化多孔等离子体超表面中自旋-动量锁定源于单元胞构型，并证明其破缺在 Kagome 晶格等全局对称系统中同样存在，以表面等离子体激元激发为例加以说明。
The spin-dependent routing of surface plasmons on metal by use of mirror symmetric periodic metasurface is presented and analyzed. We incorporate the intrinsic transverse spin angular momentum of the plasmonic wave in order to efficiently couple the incident light carrying circular polarization to a desired direction. The combination of the oblique incidence of polarized light with the accurately designed momentum matching properties of the grating provides a perfect way to achieve a spin-locking metasurface that routes the plasmonic beams.
Microscopic analysis of spin-momentum locking on a geometric phase metasurface
本文研究等离激元 Berry 超表面中的自旋-轨道耦合，通过散射形式体系揭示晶胞几何导致近似自旋-动量锁定，并结合 Mueller 偏振测量阐明表面波激发时的对称性破缺及新规则。
Laser printing with a spatial light modulator (SLM) has several advantages over conventional raster-writing and dot-matrix display (DMD) writing: multiple pixel exposure, high power endurance and existing software for computer generated holograms (CGH). We present a technique for the design and manufacturing of plasmonic metasurfaces based on ultrafast laser printing with an SLM. As a proof of principle, we have used this technique to laser print a plasmonic metalens as well as high resolution plasmonic color decorations. The high throughput holographic resonant laser printing (HRLP) approach …
We experimentally demonstrate fabrication of tunable high contrast periodic fishnet metasurfaces with 3 um period on 200 nm thick Ge2Sb2Te5 films sputted onto glass and sapphire substrates using direct laser writing technique. We find that the use of sapphire substrate provides better accuracy of metasurface segments due to high thermal conductivity. The advantages of the demonstrated method consist in its simplicity, rapidity, robustness, and the ability of tuning of fabricated structures. This is of crucial importance for the creation of robust and tunable metasurfaces for applications in th…
RF Injection Locking of THz Metasurface Quantum-Cascade VECSEL
本文通过射频注入锁定技术，实现了太赫兹量子级联垂直外腔面发射激光器的往返频率锁定，并将光谱从14 GHz展宽至约100 GHz，为主动锁模和皮秒脉冲产生奠定基础。
Wavelength-tunable vortex fiber lasers that could generate beams carrying orbital angular momentum (OAM) hold great interest in large-capacity optical communications. The wavelength tunability of conventional vortex fiber lasers is however limited by the range of 35 nm due to narrow bandwidth and/or insertion loss of mode conversion components. Optical metasurfaces apart from being compact planar components can flexibly manipulate light with high efficiency in a broad wavelength range. Here, we propose and demonstrate for the first time, to the best of our knowledge, a metasurface-assisted vor…
This article investigates the stability of 'laser sail'-style spacecraft constructed from dielectric metasurfaces with areal densities $<$1g/m$^2$. We show that the microscopic optical forces exerted on a metasurface by a high power laser (100 GW) can be engineered to achieve passive self-stabilization, such that it is optically trapped inside the drive beam, and self-corrects against angular and lateral perturbations. The metasurfaces we study consist of a patchwork of beam-steering elements that reflect light at different angles and efficiencies. These properties are varied for each element …
Self-locking non-volatile coding metasurfaces via origami-based mechanical bits
本文提出基于折纸机械比特的自锁非易失编码元表面，通过离散化机械变形实现稳定二进制状态，具备高鲁棒性和低功耗的电磁信息处理能力。
Amplitude- and frequency-modulated combs from an actively locked metasurface external-cavity laser
研究将频率梳功能引入太赫兹超表面垂直外腔面发射激光器，结合高功率与可重构梳状输出，通过色散工程及射频偏置调制实现模态相位灵活控制，为太赫兹按需梳控及扩展到其他平台和波长范围提供策略。
Optically resonant high-index dielectric metasurfaces featuring Mie-type electric and magnetic resonances are usually fabricated by means of planar technologies, which limit the degrees of freedom in tunability and scalability of the fabricated systems. Therefore, we propose a complimentary post-processing technique based on ultrashort ($\leq$ 10 ps) laser pulses. The process involves thermal effects: crystallization and reshaping, while the heat is localized by a high-precision positioning of the focused laser beam. Moreover, for the first time, the resonant behavior of dielectric metasurface…
Tellurium Metasurface Beam Splitter with Pulse Laser-Controlled Anisotropy
研究利用脉冲激光辐照控制碲晶体c轴取向，开发无光刻的可重构超表面。通过激光写入光轴图案制作分束器，实验验证其光学响应与理论相符。该方法制造简单，能重写和动态配置功能，为非谐振有源超表面等应用提供平台。
Three-dimensional, multi-wavelength beam formation with integrated metasurface optics for Sr laser cooling
本文提出利用集成在熔融石英基板上的六个毫米级超构表面光学器件形成复杂的多波长三维激光束构型，无需庞大的自由空间光学器件即可实现Sr原子的磁光阱，为紧凑型Sr光晶格钟的研发提供了高效集成方案。
Bound states in the continuum (BICs) have attracted much attention in recent years due to the infinite quality factor (Q-factor) resonance and extremely localized field. In this study, BICs have been demonstrated by dielectric metasurfaces with hybrid surface lattice resonance (SLR) in the experiment. By breaking the symmetry of geometry, SLR can be easily switched between BICs and quasi-BICs. Comparing with literature, switching between BICs and quasi-BICs is usually accompanied by wavelength shift. Here, a design rule is proposed to prevent the wavelength shift when the Q-factor is changing.…
High-index dielectric metasurfaces featuring Mie-type electric and magnetic resonances have been of a great interest in a variety of applications such as imaging, sensing, photovoltaics and others, which led to the necessity of an efficient large-scale fabrication technique. To address this, here we demonstrate the use of single-pulse laser interference for direct patterning of an amorphous silicon film into an array of Mie resonators. The proposed technique is based on laser-interference-induced dewetting. A precise control of the laser pulse energy enables the fabrication of ordered dielectr…
Ultracompact, dynamically controllable circularly polarized laser enabled by chiral metasurfaces
提出一种与量子增益介质强耦合的手性超表面激光器设计，通过改变超表面手性响应或线偏振泵浦波偏振方向，实现了动态可调谐的圆偏振相干激光输出。
Plasmonic metasurfaces based on the extraordinary optical transmission effect (EOT) can be designed to efficiently transmit specific spectral bands from the visible to the far-infrared regimes, offering numerous applications in im-portant technological fields such as compact multispectral imaging, biological and chemical sensing, or color displays. However, due to their subwavelength nature, EOT metasurfaces are nowadays fabricated with nano- and micro-lithographic techniques, requiring many processing steps and carried out in expensive cleanroom environments. In this work, we propose and expe…
Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. Here we report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lens…
Vertical cavity surface emitting lasers (VCSELs) have made indispensable contributions to the development of modern optoelectronic technologies. However, arbitrary beam shaping of VCSELs within a compact system still remains inaccessible till now. The emerging ultra-thin flat optical structures, namely metasurfaces, offer a powerful technique to manipulate electromagnetic fields with subwavelength spatial resolution. Here, we show that the monolithic integration of dielectric metasurfaces with VCSELs enables remarkable arbitrary control of the laser beam profiles, including self-collimation, B…
We report soliton rains in a tuneable Tm-doped fiber laser mode locked by carbon nanotubes. We also detect their second- and third-harmonic. We achieve a tuneability of over 56nm, from 1877 to 1933nm, by introducing a polarization-maintaining isolator and two in-line polarization controllers. This makes our system promising as a tuneable filter for ultrafast spectroscopy.
Low Reflectance All-Glass Metasurface Lenses Based on Laser Self-generated Nanoparticles
本文提出利用激光自生成纳米颗粒制备低反射全玻璃超材料透镜，实现高功率激光光学的高孔径、高通量和耐用性需求。
Metasurface lasers programmed by optical pump patterns
通过光学泵浦图案编程超表面激光器，实现对K和M点激光发射的动态控制与对称破缺行为。
Generation of even and odd high harmonics in resonant metasurfaces using single and multiple ultra-intense laser pulses
本文提出利用超薄共振 GaP 超表面在强中红外激光脉冲驱动下实现高效高次谐波产生，借助晶体宽带隙和反演对称性缺失同时产生 1.3–3 eV 的偶次与奇次谐波，并通过共振增强实现低损伤单发测量。
Dual-comb sources with equally spaced and low phase noise frequency lines are of great importance for high resolution spectroscopy and metrology. In the terahertz frequency range, electrically pumped semiconductor quantum cascade lasers (QCLs) are suitable candidates for frequency comb and dual-comb operation. For a single laser frequency comb, the repetition rate can be locked using a microwave injection locking and the carrier frequency can be locked to a highly stable source. However, for the locking of two laser combs, four frequencies (two repetition rates and two carrier offset frequenci…
The ability to generate phase-stabilised trains of ultrafast laser pulses by mode-locking underpins photonics research in fields such as precision metrology and spectroscopy. However, the complexity of conventional mode-locked laser systems, combined with the need for a mechanism to induce active or passive phase locking between resonator modes, has hindered their realisation at the nanoscale. Here, we demonstrate that GaAs-AlGaAs nanowire lasers are capable of emitting pairs of phase-locked picosecond laser pulses when subject to non-resonant pulsed optical excitation with a repetition freque…
High-power laser beam shaping using a metasurface for shock excitation and focusing at the microscale
针对激光诱导强冲击波激发效率与重复性难题，提出多脉冲时空整形形成同心激光环并会聚冲击的光学设计，实验验证高损伤阈值介质超表面可在水样中产生GPa级微尺度冲击。
The nonlinear optical response of materials to exciting light is enhanced by resonances between the incident laser frequencies and the energy levels of the excited material. Traditionally, in molecular nonlinear spectroscopy one tunes the input laser frequencies to the molecular energy levels for highly enhanced doubly or triply resonant interactions. With metasurfaces the situation is different, and by proper design of the nanostructures, one may tune the material energy levels to match the incoming laser frequencies. Here we use multi-parameter genetic algorithm methodologies to optimize the…
Laser-Scrawled Random Plasmonic Metasurface in Nanoseconds for Physical Unclonable Functions
本研究提出一种纳秒脉冲激光刻蚀技术，用于快速制备随机等离子体超材料物理不可克隆函数，通过纳米级结构共振生成独特光学指纹，实现高容量和稳定性。
Mode-locked lasers play a key role in modern science and technology. Not only do they lay the foundation for ultrafast optics and play a central role in nonlinear optics, but also they have important applications in imaging, telecommunications, sensing, and computing. While substantial efforts have focused on mode-locking the spectral modes of lasers, relatively little attention has been paid to mode-locking their temporal modes. However, temporal mode-locking presents ample opportunities to develop new technologies and to study the intersection of nonlinear, non-Hermitian, and topological phe…
Thermally-controlled magnetooptical metasurface for tunable Faraday rotation
本研究提出一种热控可调磁光超表面，可通过加热（含外控激光局部加热）大范围调谐法拉第旋转的符号与数值，还可实现激光偏振自调制，为磁光调控提供新途径。
Dual-wavelength mode-locked fiber laser and wavelength tunable mode-locked fiber laser have emerged as a promising light source. However, there is few reports on generating these two output from just one laser cavity. In this report, we demonstrate a dual-wavelength and wavelength tunable mode-locked fiber laser output from one laser cavity by utilizing short length Lyot filter. The central wavelengths of dual-wavelength mode-locked fiber laser are 1540 nm and 1564 nm and the tunable laser range is about 32 nm. We believe it could provide a simple set-up for generating dual-wavelength and wave…
Yes, it is possible to phase lock 25 fiber lasers but only for a short time. Our experiments on passively phase locking two-dimensional arrays of coupled fiber lasers reveal that the average phase locking level of 25 lasers is low ($20%-30%$) but can exceed 90% on rare instantaneous events. The average phase locking level was found to decrease for larger number of lasers in the array and increase with the connectivity of the array.
Enabling low threshold laser through an asymmetric tetramer metasurface harnessing polarization-independent quasi-BICs
该研究提出在纳米盘四聚体超表面中引入气孔打破面内对称性，实现电信波段双波段准BICs，所构建超紧凑偏振无关器件可通过光泵浦实现超低阈值、窄线宽双模激光，为相关领域应用提供新方案。
Metasurface-controlled high-speed tunable external cavity lasers
本研究提出了一种基于元表面的紧凑型外腔半导体激光器，实现超高速无模式跳变频率调谐与高效率幅度调制，适用于高速光学通信和高精度光谱学。
Comprehensive evidence of lasing from a 2D material enabled by a dual-resonance metasurface
本研究通过双共振介电超表面增强CVD生长的WS₂单层吸收与发射，实现超低阈值（<1 W/cm²）单模激光，并展示超过30 μm的相干长度，为二维材料激光器集成与应用奠定基础。
We present detailed numerical simulations of the laser dynamics that describe optical frequency comb formation by injection-locking a gain-switched laser. The typical rate equations for semiconductor lasers including stochastic carrier recombination and spontaneous emission suffice to show the injection-locking behavior of gain switched lasers, and we show how the optical frequency comb evolves starting from the free-running state, right through the final injection- locked state. Unlike the locking of continuous wave lasers, we show that the locking range for gain switched lasers is considerab…
In-line Dispersion Control of Femtosecond Laser Pulses by Multilayer Huygens' Metasurfaces
本研究实验展示了多层惠更斯超表面实现对飞秒激光脉冲的在线色散控制，无需空间分离光谱成分，累积相位达8π，群延迟色散约3969 fs²，有效补偿啁啾并压缩脉冲，提供紧凑可扩展的集成平台。
We have used injection locking to multiply the repetition rate of a passively mode-locked femtosecond fiber laser from 40 MHz to 1 GHz while preserving optical phase coherence between the master laser and the slave output. The system is implemented almost completely in fiber and incorporates gain and passive saturable absorption. The slave repetition rate is set to a rational harmonic of the master repetition rate, inducing pulse formation at the least common multiple of the master and slave repetition rates.
We demonstrate mode-locking of a thulium-doped fiber laser operating at 1.94μm, using a graphene-based saturable absorber. The laser outputs 3.6ps pulses, with~0.4nJ energy and an amplitude fluctuation~0.5%, at 6.46MHz. This is a simple, low-cost, stable and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics
Injection locking of diode lasers is commonly used to amplify low power laser light, but is extremely sensitive to perturbations in the laser current and temperature. To counter such perturbations, active stabilization is often applied to the current of the injection locked diode. We observe that the diode laser's polarization extinction ratio (PER) greatly increases when injection locked, and therefore the PER provides a measure of injection lock quality. We report robust active stabilization of a diode laser injection lock based on the PER, demonstrating the technique at 399 nm wavelength wh…
We report a 2μm ultrafast solid-state Tm:Lu2O3 laser, mode-locked by single-layer graphene, generating transform-limited~410fs pulses, with a spectral width~11.1nm at 2067nm. The maximum average output power is 270mW, at a pulse repetition frequency of 110MHz. This is a convenient high-power transform-limited laser at 2μm for various applications, such as laser surgery and material processing.
Spatiotemporal mode-locking in a laser with anomalous dispersion is investigated. Mode-locked states with varying modal content can be observed, but we find it difficult to observe highly multimode states. We describe the properties of these mode-locked states and compare them to the results of numerical simulations. Prospects for the generation of highly-multimode states and lasers based on multimode soliton formation are discussed.
Stable ultrashort light pulses and frequency combs generated by mode-locked lasers have many important applications including high-resolution spectroscopy, fast chemical detection and identification, studies of ultrafast processes, and laser metrology. While compact mode-locked lasers emitting in the visible and near infrared range have revolutionized photonic technologies, the systems operating in the mid-infrared range where most gases have their strong absorption lines, are bulky and expensive and rely on nonlinear frequency down-conversion. Quantum cascade lasers are the most powerful and …
Metasurface-Enhanced Mid-Infrared Imaging Spectroscopy with Broadband Quantum Cascade Lasers
提出一种结合宽带梯度超表面与射频调制量子级联激光器的紧凑型中红外成像光谱平台，通过匹配超表面共振与激光发射光谱，实现单帧获取增强吸收条形码图像，将采集时间缩短三个数量级。
Optical injection locking of white light cavity based superluminal lasers
该研究分析白光腔（WLC）激光器的光注入锁定特性，推导其稳态锁定范围与动态阿德勒方程，发现其锁定范围和动态响应速度均显著优于传统激光器，具有潜在应用价值。
Spatio-spectrally tailored multimode metasurface lasers in the visible range
本文提出了一种可见光范围内基于元表面和染料的多模激光器，通过工程化多种共振模式实现多频和角度选择性激光输出，展示了低阈值和高效率的激光性能。
Optical injection locking of integrated ring lasers promises to be a key technology of the future, but it is still lacking experimental verification. In this paper we present two monolithically integrated photonic circuits that experimentally realize Optically injection locking of ring lasers. The presented circuits pave the way for future application in Quantum Key Distribution and coherent communication
Vector soliton operation of erbium-doped fiber lasers mode locked with atomic layer graphene was experimentally investigated. Either the polarization rotation or polarization locked vector dissipative solitons were experimentally obtained in a dispersion-managed cavity fiber laser with large net cavity dispersion, while in the anomalous dispersion cavity fiber laser, the phase locked NLSE solitons and induced NLSE soliton were experimentally observed. The vector soliton operation of the fiber lasers unambiguously confirms the polarization insensitive saturable absorption of the atomic layer gr…
Metasurface-integrated VCSEL designed for polarization control in optical Ising machines
本文设计并制备超表面集成VCSEL以降低其自然各向异性，实现偏振控制，数值证明可增强伊辛系统注入锁定效果，并将3比特光子伊辛机计算精度提升至两倍以上。
Mode-locked lasers exhibit complex nonlinear dynamics. Precise observation of these dynamics will aid in understanding of the underlying physics and provide new insights for laser design and applications. The starting dynamics, from initial noise fluctuations to the mode-locking regime, have previously been observed directly by time-stretched transform-based real-time spectroscopy. However, the regime transition dynamics, which are essential processes in mode-locked lasers, have not yet been resolved because regime transition process tracking is very challenging. Here we demonstrate the first …
Real-time spectroscopy based on an emerging time-stretch technique can map the spectral information of optical waves into the time domain, opening several fascinating explorations of nonlinear dynamics in mode-locked lasers. However, the self-starting process of mode-locked lasers is quite sensitive to the environmental perturbation, which causes the transient behavior of laser to deviate from the true build-up process of solitons. Here, we optimize the laser system to improve its stability that suppresses the Q-switched lasing induced by the environmental perturbation. We therefore demonstrat…
Intelligent mode-locked NPR fiber laser based on laser speckle characteristics
本文提出利用人工智能优化模式锁稳定性的方法，通过分析激光通过散射介质产生的条纹图案特征，实现智能稳定模式锁单脉冲生成。
Saturable absorbers are a key component for mode-locking femtosecond lasers. Polymer films containing graphene flakes have recently been used in transmission as laser mode-lockers, but suffer from high nonsaturable loss, limiting their application in low-gain lasers. Here we present a saturable absorber mirror based on a film of pure graphene flakes. The device is used to mode lock an erbium-doped fiber laser, generating pulses with state-of-the-art, sub-200-fs duration. The laser characteristic indicate that the film exhibits low nonsaturable loss (13% per pass) and large absorption modulatio…
We propose an all-fiber mode-locking device which operates based on nonlinear switching in a novel concentric ring core fiber structure. The design is particularly attractive given the ease of fabrication and coupling to other components in a mode-locked fiber laser cavity. The nonlinear switching in this coupler is studied and the relative power transmission is obtained. The analysis shows that this nonlinear switch is practical for mode-locking fiber lasers and is forgiving to fabrication errors.
Stable 30 fs pulses centered at 1068 nm (less than 10 optical cycles) are demonstrated in a diode pumped Yb:CaYAlO4 laser by using high-quality chemical vapor deposited monolayer graphene as the saturable absorber. The mode locked 8.43 optical-cycle pulses have a spectral bandwidth of ~ 50 nm and a pulse repetition frequency of ~ 113.5 MHz. To our knowledge, this is the shortest pulse ever reported for graphene mode-locked lasers and mode-locked Yb-doped bulk lasers. Our experimental results demonstrate that graphene mode locking is a very promising practical technique to generate few-cycle op…
The influence of nonlinear properties of semiconductor saturable absorbers on ultrashort pulse generation was investigated. It was shown, that linewidth enhancement, quadratic and linear ac Stark effect contribute essentially to the mode locking in cw solid-state lasers, that can increase the pulse stability, decrease pulse duration and reduce the mode locking threshold
We report on an environmentally stable, all-PM-fibre, Er-doped, mode-locked laser with a central wavelength of 1550 nm. Significantly, the laser possesses large net-normal dispersion such that its dynamics are comparable to that of an all-normal dispersion fibre laser at 1 μm with an analogous architecture. The laser is mode-locked with a nonlinear amplifying loop mirror to produce pulses that are externally compressible to 500 fs. Experimental results are in good agreement with numerical simulations.
We demonstrate a technique for locking the frequency of a tunable diode laser to a ring-cavity resonator. The resonator is stabilized to a diode laser which is in turn locked to an atomic transition, thus giving it absolute frequency calibration. The ring-cavity design has the principal advantage that there is no feedback destabilization of the laser. The cavity has a free-spectral range of 1.3 GHz and $Q$ of about 35, which gives robust locking of the laser. The locked laser is able to track large scans of the cavity.
Pulse formation mechanisms switching in hybrid mode-locked fiber laser
本文实验与数值研究了SA与NPE被动混合锁模光纤激光器中SA主导、NPE主导及共同主导三种脉冲形成机制的切换，首次提出定制滤波模拟增益谱方法，为单腔多波长锁模激光器奠定基础。
Continuous-wave mode-locked femtosecond 2 um solid-state laser with a c-cut Tm:CaYAlO4 as gain medium was experimentally demonstrated. The mode locked laser generated stable pulses with average output power as high as 531 mW, pulse duration of 496 fs, and repetition rate of 97 MHz at 1975 nm. The research results show that Tm:CaYAlO4 is an excellent gain medium for femtosecond pulse generation at 2um wavelength.
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