Mesoscopic nanomaterials generated by interfering femtosecond laser processing

Mesoscopic nanomaterials with a size ranging from a few nanometers to hundreds of nanometers were generated on a metallic thin film by interfering femtosecond (fs) laser processing. Because the nanomaterials seemed to demonstrate liquid behavior, we named their structure nano water drop. The structure is considerably similar to that of a real water drop observed with a high-speed camera. Using the phase shift between interfering beams, a duplicate structure was generated. This is a new surface modification technique, using a top-down approach.     

Sub-micron ablation of metallic thin film by femtosecond pulse laser

The ability to machine very small features in a material has a wide range of applications in industry. We ablated holes into thin film of 100 nm thickness made from various metals by femtosecond pulsed laser ablation. Using a Ti:Sapphire laser which supplies a laser pulse of 150 fs duration at central spectrum wavelength of 400 nm, we have produced a series sub-micron holes, whose diameters are less than 200 nm with a focused laser spot of 1.7 μm. We found that the material damage threshold has a great influence on the quality of the produced features. Experimental results shows that the heat-affected zone and the degree of being affected reduce with the increase of threshold value.     

Sub-micron patterning of solid materials with ultraviolet femtosecond pulses

The treatment of solid materials using subpicosecond laser pulses at 248 nm is studied. The potential of the combination of femtosecond pulse durations with ultraviolet wavelengths for precise material processing is demonstrated. Imaging techniques combined with diffractive optical elements are exploited for the fabrication of nanometer-scale features on practically all classes of materials including metals, semiconductors, and dielectrics. Two-dimensional periodic surface structures with excellent quality and reproducibility over large areas with feature sizes down to the 100 nm range are reached .An extension of this technique to transparent solids to reach defect sizes of a few hundreds of nanometers inside various materials is also possible. As a technical highlight, efficient drilling of a great number of holes with diameters below 500 nm through metal foils is demonstrated.Irradiation is performed using a UV laser system based on a Ti:Sapphire-Excimer hybrid device generating 300 fs pulses at 248 nm. Operation at 300 Hz (resulting in 10 W average output power) allows high speed machining, opening up new possibilities in industrial applications. PACS 42.15.Eq; 41.85.Ct; 52.38.Mf; 81.16.Rf; 81.65.Cf     

利用多束飞秒激光干涉在金属箔和金属薄膜上形成阵列孔

报道了利用五束飞秒激光干涉，在镍箔和镀在玻璃上的铝膜上制备阵列孔的方法。光学显微镜和扫描电镜观察发现飞秒激光照射后在金属箔和薄膜上形成了微米量级的阵列孔。这一技术允许一步、大尺寸、微米量级的加工金属材料，具有潜在的工业应用价值。     

Laser-active colour centres with functional periodic structures in LiF fabricated by two interfering femtosecond laser pulses

We report a new technique to fabricate both laser-active F₂ and F₃⁺ colour centres in lithium fluoride and permanent periodic gratings with fringe spacings as fine as sub-micron size simultaneously by two interfering infrared femtosecond (fs) laser pulses. In particular, the optical properties of such colour centres produced by a single fs laser pulse are compared with those created by damage from radiation such as X-rays. Moreover, the present technique is applied to the first production of three-dimensional active channel waveguide and a pulsed distributed-feedback (DFB) laser at around 700 nm in LiF containing F₂ colour centres with fine-pitched micro-grating structures.     

飞秒激光诱导图案独立显示研究

介绍了采用中心波长为800nm的飞秒激光在不锈钢(316L)表面诱导产生独立显示图案的研究。结果表明,当扫描速率为15mm/s,扫描行距为20μm,能量密度为1.1J/cm2时,飞秒激光能够在不锈钢表面形成均匀的周期为540nm的亚波长条纹结构。利用条纹结构的方向与激光光波偏振方向严格垂直的特性,通过改变激光偏振,可以在金属表面形成不同方向的条纹图案。在照明白光的辐照下,改变样品的方位角,形成的图案能够以彩色方式显示出来。此外,对使图案彩色显示的坐标区域与图案色彩能够覆盖的可见光谱范围进行了研究,并对其可能的应用进行分析。     

Er:Yb-doped waveguide laser fabricated by femtosecond laser pulses

Laser action is demonstrated in a 20-mm-long waveguide fabricated on an Er:Yb-doped phosphate glass by femtosecond laser pulses. An output power of 1.7 mW with approximately 300 mW of pump power coupled into the waveguide is obtained at 1533.5 nm. Waveguides are manufactured with the 520-nm radiation from a frequency-doubled, diode-pumped, cavity-dumped Yb:glass laser operating at a 166-KHz repetition rate, with a 300-fs pulse duration.     

Computer-generated volume holograms fabricated by femtosecond laser micromachining

We define computer-generated volume holograms (CGVHs) as arbitrary 3D refractive index modulations designed to perform optical functions based on diffraction, scattering, and interference phenomena. CGVHs can differ dramatically from classical volume holograms in terms of coding possibilities, and from thin computer-generated holograms in terms of efficiency and selectivity. We propose an encoding technique for designing such holograms and demonstrate the concept by scanning focused femtosecond laser pulses to produce localized refractive index modifications in glass. These CGVHs show a significant increase in efficiency with thickness. Consequently, they are attractive for photonic integration with free-space and guided-wave devices, as well as for encoding spatial and temporal information.     

飞秒激光诱导图案独立显示研究

介绍了采用中心波长为800 nm的飞秒激光在不锈钢(316L)表面诱导产生独立显示图案的研究。结果表明,当扫描速率为15 mm/s,扫描行距为20 m,能量密度为1.1 J/cm2时,飞秒激光能够在不锈钢表面形成均匀的周期为540 nm的亚波长条纹结构。利用条纹结构的方向与激光光波偏振方向严格垂直的特性,通过改变激光偏振,可以在金属表面形成不同方向的条纹图案。在照明白光的辐照下,改变样品的方位角,形成的图案能够以彩色方式显示出来。此外,对使图案彩色显示的坐标区域与图案色彩能够覆盖的可见光谱范围进行了研究,并对其可能的应用进行分析。     

Embedded birefringent computer-generated holograms fabricated by femtosecond laser pulses

Birefringent computer-generated holograms are fabricated in bulk fused silica by tight focusing of infrared femtosecond laser pulses. The polarization properties of the elliptically polarized diffracted light are in excellent agreement with the theoretical model. We experimentally demonstrate that for such birefringent structures the signal-to-noise ratio increases by approximately 9 dB when polarization filtering is used to suppress the undiffracted beam.     

Sub-micron scale patterning using femtosecond laser and self-assembled monolayers interaction

Standard positive photoresist techniques were adapted to generate sub-micron scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. Self-assembled monolayers formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well-known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200 nm is necessary for oxidation to occur. In this study, solid state femtosecond laser of wavelength 800 nm is applied for photolithography. The results show that ultrafast laser of near infrared (NIR) range wavelength can replace deep UV laser source for photopatterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with monolayer coverage on a solid surface. Femtosecond laser photolithography could be applied to fabricate the patterning of surface chemical structure and the creation of three-dimensional nanostructures by combination with suitable etching methods.     

飞秒激光制备彩色镍

采用飞秒脉冲激光在空气条件下扫描处理镍片表面,制备了彩色镍。用扫描电子显微镜、紫外-可见-近红外分光光度计、拉曼光谱仪等对其进行了表征。扫描电子显微镜测量显示,彩色镍表面出现了纳米激光诱导周期表面结构,结构周期为480～510 nm;紫外-可见-近红外分光光度计测量表明,彩色镍对波长为200～2 200 nm的光的反射率大大降低;拉曼谱表明样品表面形成了一定含量的氧化镍。     

飞秒激光制备彩色镍

 采用飞秒脉冲激光在空气条件下扫描处理镍片表面,制备了彩色镍。用扫描电子显微镜、紫外-可见-近红外分光光度计、拉曼光谱仪等对其进行了表征。扫描电子显微镜测量显示,彩色镍表面出现了纳米激光诱导周期表面结构,结构周期为480～510 nm;紫外-可见-近红外分光光度计测量表明,彩色镍对波长为200～2 200 nm的光的反射率大大降低;拉曼谱表明样品表面形成了一定含量的氧化镍。     

飞秒脉冲激光辐照下硅表面光致荧光特性

采用钛宝石飞秒脉冲激光对单晶硅在空气中进行辐照,研究了硅表面在不同扫描速度和能量密度下的光致荧光特性。光致荧光谱（PL）测量表明,在样品没有退火处理的情况下,激光扫描区域观察到橙色荧光峰（603 nm）和红色荧光带（680 nm附近）。扫描电子显微镜（SEM）测量显示,在飞秒脉冲激光辐照硅样品的过程中硅表面沉积了大量的纳米颗粒。利用傅里叶变换红外光谱仪（FT-IR）检测到了低值氧化物SiOx（x＜2）的存在,并且结合能谱仪（EDS）检测结果发现氧元素在光致发光中起着重要作用。研究表明：603 nm处橙色荧光峰来自微构造硅表面低值氧化物SiOx,680 nm附近红色荧光带来自量子限制效应。同时样品表面硅纳米颗粒的尺寸和氧元素的浓度分别决定了红色荧光带和橙色荧光的强度,通过调节飞秒激光脉冲的扫描速度和能量密度,可以有效地控制样品的荧光强度。     

Large-area surface-enhanced Raman scattering-active substrates fabricated by femtosecond laser ablation

A rapid and simple approach to fabricate large-area surface-enhanced Raman scattering-active(SERS-active) substrates is reported.The substrates are fabricated by using femtosecond laser(fs-laser) direct writing on Silicon wafers,followed by thin-film coating of metal such as gold.The substrates are demonstrated to exhibit signal homogeneity and good enhancement ability for SERS.The maximum enhancement factor(EF) up to 3×10 7 of such SERS substrates for rhodamine 6G(R6G) at 785 nm excitation wavelength was measured.This technique could demonstrate a functional microchip with SERS capability of signal homogeneity,high sensitivity and chemical stability.     

高厚度薄膜-泡沫平面调制靶的飞秒激光微加工

利用数值孔径为0.14的显微物镜聚焦中心波长800 nm、脉宽120 fs、重复频率1 kHz的飞秒激光,采用焦点逐线扫描等距下移方式,选取的入射平均功率为30 mW,加工速度为300 μm/s,对瑞利-泰勒(R-T)不稳定性实验靶用的厚度1.5 mm聚苯乙烯（PS）薄膜-聚4-甲基-1-戊烯（PMP）泡沫双层复合长条块体样品进行精确切割成型,并与纳秒激光切割情形对比。结果表明：利用飞秒激光微加工有效控制了切割区变形和材料分层,获得了整齐的切割边缘和平坦的切割面,样品最大切割深度超过800 μm。     

Microlens arrays of high-refractive-index glass fabricated by femtosecond laser lithography

Microlens arrays of high-refractive-index glass GeO₂-SiO₂ were fabricated by femtosecond laser lithography assisted micromachining. GeO₂-SiO₂ thin glass films, which were deposited by plasma-enhanced chemical vapor deposition, have a refractive index of 1.4902 and exhibit high transparency at wavelengths longer than 320 nm. Using a femtosecond laser, three-dimensional patterns were written inside resists on GeO₂-SiO₂ films, and then the patterns were transferred to the underlying films by CHF₃ and O₂ plasma treatments. This combined process enabled us to obtain uniform microlens structures with a diameter of 38 μm. The heights of the transferred lenses were approximately one-quarter the height of the resist patterns, due to differences in the plasma etching rates between GeO₂-SiO₂ and the resist. The lens surfaces were smooth. When 632.8-nm-wavelength He-Ne laser light was normally coupled to the lenses, focal spots with a diameter of 3.0 μm were uniformly observed. The combined process was effective in fabricating three-dimensional surfaces of inorganic optical materials.     

高厚度薄膜-泡沫平面调制靶的飞秒激光微加工

 利用数值孔径为0.14的显微物镜聚焦中心波长800 nm、脉宽120 fs、重复频率1 kHz的飞秒激光,采用焦点逐线扫描等距下移方式,选取的入射平均功率为30 mW,加工速度为300 μm/s,对瑞利-泰勒(R-T)不稳定性实验靶用的厚度1.5 mm聚苯乙烯（PS）薄膜-聚4-甲基-1-戊烯（PMP）泡沫双层复合长条块体样品进行精确切割成型,并与纳秒激光切割情形对比。结果表明：利用飞秒激光微加工有效控制了切割区变形和材料分层,获得了整齐的切割边缘和平坦的切割面,样品最大切割深度超过800 μm。     

飞秒激光作用下的硅表面微结构及发光特性

采用近红外飞秒激光辐照浸泡在硫酸溶液中的N型单晶硅片,激光波长800 nm,脉宽200 fs,重频1 kHz,平均功率为100 mW,而硫酸溶液的质量分数分别选择为0.1%和1%。辐照后硅表面呈直径为5~8 mm,高度15 mm的柱型结构。分析其荧光特性,并通过比较硅材料表面微结构与激光光源、扫描参数、硅片背景环境的关系,确定最佳辐照条件为激光扫描速度750 mm/s,扫描间距5 mm/s。最终在厚度0.5 mm、直径26 mm的硅片上获得10 mm×10 mm的方形扫描区域,荧光光谱显示激光扫描后的区域在700 nm附近有很强的荧光发射。分析结果表明飞秒激光扫描改变了样品的表面微结构尺寸,增大了吸收面积,扩展了荧光激发波长,有效提高了样品的吸收效率和荧光发光相对强度(超过扫描前发光相对强度的2倍),荧光发射谱的变化是由量子限制效应和表面态模型共同作用的结果。