Femtosecond laser-mediated anchoring of polymer layers on the surface of a biodegradable metal

Mg has received much attention as a next-generation implantable material owing to its biocompatibility,bone-like mechanical properties,and biodegradability in physiological environments.The application of various polymer coatings has been conducted in the past to reduce the rapid formation of hydrogen gas and the local change in pH during the initial phase of the chemical reaction with the body fluids.Here,we propose femtosecond(fs)laser-mediated Mg surface patterning for significant enhancement of the binding strength of the coating material,which eventually reduces the corrosion rate.Analyses of the structural,physical,crystallographic,and chemical properties of the Mg surface have been conducted in order to understand the mechanism by which the surface adhesion increases between Mg and the polymer coating layer.Depending on the fs laser conditions,the surface structure becomes rough owing to the presence of several microscaled pits and grooves of nanoporous MgO,resulting in a tightly bonded poly(lactic-co-glycolic acid)(PLGA)layer.The corrosion rate of the PLGA-coated,fs laser-treated Mg is considerably slow compared with the non-treated Mg;the treated Mg is also more biocompatible compared with the non-treated Mg.The fs laser-based surface modification technique offers a simple and quick method for introducing a rough coating on Mg;further,it does not require any chemical treatment,thereby overcoming a potential obstacle for its clinical use.

Femtosecond laser fabrication of 3D templates for mass production of artificial compound eyes

Compound eyes are unique optical imaging systems that consist of numerous separate light-sensitive units(ommatidia).Attempts have been made to produce artificial compound eyes via advanced 3 D nanotechnologies.Among them,femtosecond laser direct writing(FsLDW)technology has emerged as an effective strategy due to its distinct advantages in 3 D designable and high precision fabrication capability.However,the point-by-point scanning process results in a very low fabrication efficiency,limiting the practical applications of the FsLDW technology.To solve this problem,we propose a high-efficiency method for the mass production of 3 D artificial compound eyes using a photopolymer template fabricated by FsLDW.The resultant 3 D SU-8 compound eye templates could be used to replicate polydimethylsiloxane(PDMS)compound eyes many times(over 50 times)with a highly improved efficiency(nearly 20 times higher than the efficiency of direct fabrication using the point-by-point FsLDW).The PDMS replicas showed good focusing and imaging performances.We anticipate that this method may serve as an enabler for the mass production of 3 D artificial compound eyes and promote their practical applications in the near future.

Femtosecond-laser direct writing 3D micro/nano-lithography using VIS-light oscillator

Here we report a femtosecond laser direct writing(a precise 3D printing also known as two-photon polymerization lithography) of hybrid organic-inorganic SZ2080^(TM)pre-polymer without using any photo-initiator and applying ~100 fs oscillator operating at 517 nm wavelength and 76 MHz repetition rate. The proof of concept was experimentally demonstrated and benchmarking 3D woodpile nanostructures, micro-scaffolds, free-form micro-object “Benchy” and bulk micro-cubes are successfully produced. The essential novelty underlies the fact that non-amplified laser systems delivering just 40-500 p J individual pulses are sufficient for inducing localized cross-linking reactions within hundreds of nanometers in cross sections. And it is opposed to the prejudice that higher pulse energies and lower repetition rates of amplified lasers are necessary for structuring non-photosensitized polymers. The experimental work is of high importance for fundamental understanding of laser enabled nanoscale 3D additive manufacturing and widens technology’ s field of applications where the avoidance of photo-initiator is preferable or is even a necessity, such as micro-optics, nano-photonics, and biomedicine.

Two-photon polymerization of femtosecond high-order Bessel beams with aberration correction

In the femtosecond two-photon polymerization(2PP)experimental system,optical aberrations degrade the fabrication quality.To solve this issue,a multichannel interferometric wavefront sensing technique is adopted in the adaptive laser processing system with a single phase-only spatial light modulator.2PP fabrications using corrected high-order Bessel beams with the above solution have been conducted,and high-quality microstructure arrays of microtubes with 20μm diameter have been rapidly manufactured.The effectiveness of the proposed scheme is demonstrated by comparing the beam intensity distributions and 2PP results before and after aberration corrections.

Femtosecond laser 3D printed micro objective lens for ultrathin fiber endoscope

The most important optical component in an optical fiber endoscope is its objective lens.To achieve a high imaging performance level,the development of an ultra-compact objective lens is thus the key to an ultra-thin optical fiber endoscope.In this work,we use femtosecond laser 3D printing to develop a series of micro objective lenses with different optical designs.The imaging resolution and field-of-view performances of these printed micro objective lenses are investigated via both simulations and experiments.For the first time,multiple micro objective lenses with different fields of view are printed on the end face of a single imaging optical fiber,thus realizing the perfect integration of an optical fiber and objective lenses.This work demonstrates the considerable potential of femtosecond laser 3D printing in the fabrication of micro-optical systems and provides a reliable solution for the development of an ultrathin fiber endoscope.

Isotropic sintering shrinkage of 3D glass-ceramic nanolattices:backbone preforming and mechanical enhancement

There is a perpetual pursuit for free-form glasses and ceramics featuring outstanding mechanical properties as well as chemical and thermal resistance.It is a promising idea to shape inorganic materials in three-dimensional(3D)forms to reduce their weight while maintaining high mechanical properties.A popular strategy for the preparation of 3D inorganic materials is to mold the organic–inorganic hybrid photoresists into 3D micro-and nano-structures and remove the organic components by subsequent sintering.However,due to the discrete arrangement of inorganic components in the organic-inorganic hybrid photoresists,it remains a huge challenge to attain isotropic shrinkage during sintering.Herein,we demonstrate the isotropic sintering shrinkage by forming the consecutive–Si–O–Si–O–Zr–O–inorganic backbone in photoresists and fabricating 3D glass–ceramic nanolattices with enhanced mechanical properties.The femtosecond(fs)laser is used in two-photon polymerization(TPP)to fabricate 3D green body structures.After subsequent sintering at 1000℃,high-quality 3D glass–ceramic microstructures can be obtained with perfectly intact and smooth morphology.In-suit compression experiments and finite-element simulations reveal that octahedral-truss(oct-truss)lattices possess remarkable adeptness in bearing stress concentration and maintain the structural integrity to resist rod bending,indicating that this structure is a candidate for preparing lightweight and high stiffness glass–ceramic nanolattices.3D printing of such glasses and ceramics has significant implications in a number of industrial applications,including metamaterials,microelectromechanical systems,photonic crystals,and damage-tolerant lightweight materials.

A direct frequency comb for two-photon transition spectroscopy in a cesium vapor

A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts, shaped in an original way, and focused into a room-temperature cesium vapor. We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb, and through absolute frequency measurements.

飞秒激光双光子聚合三维微纳结构加工技术

飞秒激光双光子聚合微纳加工技术作为重要的三维微纳结构制备手段,已成为国际前沿研究热点。该技术利用激光与物质相互作用的双光子非线性吸收效应和阈值效应,可以突破经典光学理论衍射极限,实现纳米尺度的激光加工分辨力,在三维功能性微纳器件制备领域正在发挥着十分重要的作用。本文在介绍飞秒激光双光子聚合三维微纳加工技术的光物理和光化学过程基本原理的基础上,重点回顾人们在改善加工线宽及分辨力、提高加工效率等方面的研究进展与发展概况。该技术所制备的各种微光学器件、集成光学器件、微机电系统以及生物医学器件,不仅充分展示了飞秒激光双光子聚合三维微纳加工技术的高空间分辨力和真三维加工特点,也为其在相关前沿领域的应用提供具有启发性的思路。最后,对该技术实现高精度、高效率、低成本、大面积、多功能的三维微纳结构加工所存在的挑战和未来发展方向,进行了讨论和展望。

Simultaneous additive and subtractive three-dimensional nanofabrication using integrated two-photon polymerization and multiphoton ablation

Modern three-dimensional nanofabrication requires both additive and subtractive processes.However,both processes are largely isolated and generally regarded as incompatible with each other.In this study,we developed simultaneous additive and subtractive fabrication processes using two-photon polymerization followed by femtosecond(fs)laser multiphoton ablation.To demonstrate the new capability,submicrometer polymer fibers containing periodic holes of 500-nm diameter and microfluidic channels of 1-mm diameter were successfully fabricated.This method combining both two-photon polymerization and fs laser ablation improves the nanofabrication efficiency and enables the fabrication of complex three-dimensional micro-/nanostructures,promising for a wide range of applications in integrated optics,microfluidics and microelectromechanical systems.

High-aspect 3D two-photon polymerization structuring with widened objective working range (WOW-2PP)

We developed a novel two-photon polymerization(2PP)configuration for fabrication of high-aspect three-dimensional(3D)structures,with an overall height larger than working distance of the microscope objective used for laser beam focusing into a photosensitive material.This method is based on a modified optical 2PP setup,where a microscope objective(1003 high N.A.),immersion oil and cover glass can be moved together into the photosensitive material,resulting in an effective higher and wider objective working range(WOW-2PP).The proposed technique enables the fabrication of high-aspect structures with sub-micrometer process resolution.3D structures with a height of 7 mm are demonstrated,which could hardly be built with the conventional 2PP set-up due to refractive index mismatch and laser beam disturbances.

Remote,selective,and in situ manipulation of liquid droplets on a femtosecond laser-structured superhydrophobic shape-memory polymer by near-infrared light

Droplet manipulation plays a significant role in the fields of biomedical detection,microfluidics,and chemical engineering.However,it still remains a great challenge to simultaneously achieve remote,selective,and in situ droplet manipulation on the same surface.Here,Fe_(3)O_(4)nanoparticles were doped in a shape-memory polymer(SMP)to prepare a photothermal-responsive Fe_(3)O_(4)-SMP composite which showed remarkable near-infrared(NIR)light-triggered shape-memory property.Superhydrophobic micropillar array was constructed on such Fe_(3)O_(4)-SMP composite through femtosecond laser microfabrication and fluoroalkylsilane modification.The surface wettability of the as-prepared surface can transform from a low-adhesive sliding state to a high-adhesive pinning state as the micropillars are deformed by pressing.Interestingly,the deformed micropillars can stand up and restore to their original morphology under remote NIR light irradiation,resulting in the reversible and repeatable recovery of the ultralow-adhesive superhydrophobicity.With such light-triggered wettability switching,the droplets pinning on the sample surface can be remotely,selectively,and in situ released.Furthermore,the superhydrophobic Fe_(3)O_(4)-SMP surface is successfully applied in lossless liquid transfer,selective droplet release,and droplet-based microreactor.The as-fabricated superhydrophobic surfaces with NIR light-controlled reversible wettability will hold great promise in the fields of liquid manipulation,lab-on-a-chip,and microfluidics.

Neural-network・assisted femtosecond laser pulse duration measurement using two-photon absorption

In this work,a neural network(NN)method is developed for pulse duration inferring for an erbium-doped fiber laser at 1550 nm.Experime nt ally,the interferometric autocorrelation trace is observed clearly with the use of the two-photon absorption(TPA)effect in a GaAs photodiode.The intensity autocorrelation function is curvefitted by the NN with an appropriate performance,and the measuring accuracy is consistent with a commercial autocorrelator.Compared with the Levenberg-Marquardt curve-fitting method,the NN can retrieve the intensity autocorrelation function more stably and has a certain noise reduction ability,simplifying the signal processing for a TPA photodiode-based autocorrelator.

Femtosecond fiber laser at 780 nm for two-photon autofluorescence imaging

We present an Er-doped fiber(Er:fiber)-based femtosecond laser at 780 nm with 256 MHz repetition rate, 191 fs pulse duration, and over 1 W average power.Apart from the careful third-order dispersion management, we introduce moderate self-phase modulation to broaden the output spectrum of the Er:fiber amplifier and achieve 193 fs pulse duration and 2.43W average power.Over 40% frequency doubling efficiency is obtained by a periodically poled lithium niobate crystal.Delivering through a hollow-core photonic bandgap fiber, this robust laser becomes an ideal and convenient light source for two-photon autofluorescence imaging.

飞秒激光微加工的研究进展

综述了近年来国内外利用飞秒激光微加工的研究进展。飞秒激光脉冲作为材料微纳加工的一项工具,已经从实验室进入到工业化阶段。介绍了飞秒激光在微纳加工领域的一些研究情况,分别就飞秒激光烧蚀微加工以及双光子聚合加工进行了阐述。最后分析了飞秒激光微加工目前存在的问题及未来发展的主要方向。

飞秒激光双光子聚合方法加工图案化微透镜及其成像测试

为改善以往图案化透镜加工工艺复杂、制造技术昂贵、图案设计方面有限制等缺点,本文将飞秒激光双光子聚合加工技术应用于图案化微透镜的快速、高精度加工。通过球面波因子的变形设计了不同图案的微透镜,利用飞秒激光双光子聚合加工技术在光刻胶样品中加工出图案化的微透镜,然后将光刻胶样品置于显影液中去除未聚合部分,得到图案化微透镜,最后对图案化微透镜进行成像测试和光强均一化分析。将LED光源分别置于不同图案微透镜的下方,光线透过图案化微透镜成功聚焦出光强一致的焦点图案。实验结果表明,使用飞秒激光双光子聚合加工可以实现灵活可控的3D图案化微透镜结构的加工,采用加工功率为7 mW,曝光时间为2 ms,扫描xy步距为0.5μm,z步距为0.8~1.5μm,不仅保证了微透镜结构表面光滑,而且实现了微透镜的快速加工。该技术在加工光学超材料、光学微器件、集成光学器件等方面具有广阔的应用前景。

飞秒激光三维微细加工技术

双光子吸收几率与光强度的平方成正比,因此,双光子吸收引发光致聚合局限在紧密聚焦的焦点区域,通过控制焦点的扫描运动可实现高精度三维加工。基于该原理,提出了一种利用飞秒激光进行微细加工的技术。根据此技术,建立了飞秒激光三维微细加工系统,该系统包括光源系统、显微镜系统、实时监测系统和精密移动系统等。研究发现,该系统加工的直线线宽最小可达500nm;加工线宽与加工速度成反比;激光功率为2mW时,最大和最小临界加工速度分别为80μm/s和1μm/s;制备出线宽1μm,宽度5μm的“CHINA”复杂结构,以及杆间距、层间距均为5μm的三维木堆型光子晶体结构。实验证实,该技术是一种非常灵活的微细加工技术。

双光子光聚合与功能微纳结构制备

随着纳米光电子学及生物医学组织工程领域的发展,器件的小型化、结构多样化及高度集成化,给微纳结构与器件制造领域带来了新的挑战。本文围绕飞秒激光双光子聚合技术,简要综述了双光子光聚合基本原理与双光子引发剂分子的研究进展,并对飞秒激光双光子聚合技术在功能微纳结构与器件制备中的应用及发展前景进行了展望。

双光子聚合加工均匀木堆结构方法的研究

由于双光子聚合所具有的纳米级加工分辨率以及真三维制造能力,被广泛应用于微米纳米制造领域。利用双光子聚合加工的三维木堆结构是实现生物支架、光子晶体、超材料等功能器件的重要途径之一。但是加工结构在经过后处理之后产生的不均匀收缩成为获得高质量木堆结构的重要阻碍,严重时会导致失去其结构的功能性。为了实现木堆结构的均匀性加工,提出一种通过降低加工结构与基底附着力的方法,来实现均匀木堆结构的加工。此外,采用Ormocomp光敏材料以及双光子聚合加工技术,对基底高附着力和低附着力的木堆结构分别进行了加工。通过对加工所得木堆结构的各层尺寸的测量,验证了所提出方法的有效性。

飞秒激光双光子加工的极限分辨力

采用3维压电微移动台高速扫描方式控制曝光时间与高精密转台精确控制圆形渐变衰减片以控制曝光功率两种方法,曝光时间和曝光功率可分别精确控制至0.02 ms和7 pW。通过精确控制聚合阈值附近处的曝光时间和曝光功率,分别在玻璃基板上获得了35 nm和45 nm的聚合物纳米线条,分别为所使用激光波长的1/22和1/17。实验结果表明,当曝光时间或曝光功率在加工阈值附近时,曝光时间和功率的微量减少会使聚合线宽急剧下降。

SU-8胶双光子微加工分辨率与工艺条件研究

为了提高SU-8光刻胶的微加工分辨率,利用飞秒激光双光子聚合技术研究了SU-8光刻胶微加工时的加工工艺条件与分辨率之间的关系。实验在本研究组自主研制的纳米光子学超细微加工系统上进行,以钛蓝宝石飞秒激光器发出的780nm波长激光作为加工光源,考察了不同激光功率与曝光时间等激光加工条件和后烤与无后烤等工艺条件对SU-8聚合点形貌与尺寸的影响。在后烤工艺条件下获得的最小加工点直径为0.22μm,而无后烤过程的加工结果中这一数值为0.47μm。实验结果表明,降低激光功率和缩短曝光时间可以获得尺寸较小的聚合点,后烤工艺有利于降低加工能量并提高加工分辨率,实验结果与基于双光子聚合加工理论的模拟分析具有良好的一致性。