纳秒激光刻蚀玻璃基质铬薄膜直写微光栅结构

利用波长为351 nm的半导体泵浦全固态脉冲激光器,采用双光束干涉方法,对蒸镀在石英玻璃衬底上的铬薄膜直接刻蚀形成微光栅结构的方法进行了实验研究.通过实验,分析了激光能量和脉冲数与微光栅结构槽形和一级衍射效率之间的关系.利用光学显微镜和原子力显微镜检测分析光栅槽形,测得槽深为253 nm的最佳微光栅结构,并测得其在波长为532 nm的激光的一级衍射效率为6.5%.结果表明：在激光能量为1 150 μJ时,适当增加曝光脉冲数有利于提高制备光栅的槽深和一级衍射效率.     

纳秒激光刻蚀玻璃基质铬薄膜直写微光栅结构

利用波长为351 nm的半导体泵浦全固态脉冲激光器,采用双光束干涉方法,对蒸镀在石英玻璃衬底上的铬薄膜直接刻蚀形成微光栅结构的方法进行了实验研究.通过实验,分析了激光能量和脉冲数与微光栅结构槽形和一级衍射效率之间的关系.利用光学显微镜和原子力显微镜检测分析光栅槽形,测得槽深为253 nm的最佳微光栅结构,并测得其在波长为532 nm的激光的一级衍射效率为6.5%.结果表明:在激光能量为1 150 μJ时,适当增加曝光脉冲数有利于提高制备光栅的槽深和一级衍射效率.     

多光束纳秒紫外激光制作硅表面微结构

使用波长351 nm的半导体泵浦全固态脉冲激光器作为光源,经过位相光栅分束,形成干涉光场,在硅表面直接刻蚀微结构,制作了周期为0.55 μm,槽深可达55 nm的一维微光栅和周期为1.25 μm,刻蚀深度45 nm的正交微光栅结构.给出了微光栅形貌结构的扫描电子显微镜和原子力显微镜的测量结果.正交微光栅的一级衍射效率在1.8%～6.3%之间.该研究是改变硅表面微结构,优化硅材料特性的一种新方法,并扩展了大功率激光刻蚀在表面微加工领域的应用.     

多光束纳秒紫外激光制作硅表面微结构

使用波长351 nm的半导体泵浦全固态脉冲激光器（DPSSL）作为光源,经过位相光栅分束,形成干涉光场,在硅表面直接刻蚀微结构,制作了周期为0.55 µm,槽深可达55 nm的一维微光栅和周期为1.25 µm,刻蚀深度45nm的正交微光栅结构。给出了微光栅形貌结构的扫描电子显微镜(SEM)和原子力显微镜(AFM)的测量结果。正交微光栅的一级衍射效率在1.8%到6.3%之间。该研究是改变硅表面微结构,优化硅材料特性的一种新方法,并扩展了大功率激光刻蚀在表面微加工领域的应用。     

宽带镀金正弦光栅

为了满足强激光系统中大尺寸镀金光栅对糟深均匀性的要求,采用梯形光栅-涂胶-离子束溅射镀膜和全息光刻-离子束溅射镀膜两种方法,分别制作了线密度为1 740线/mm,槽深为210 nm的宽带镀金正弦光栅.测得其TM波、-1级自准值平均衍射效率在750～850 nm范围内大于87％,最高可达90％.这两种方法易控制光栅槽深,去掉光刻胶后基底可继续使用,且制作的光栅的衍射效率和带宽能满足国内一般宽带镀金脉冲压缩光栅的使用要求.     

宽带镀金正弦光栅（英文）

为了满足强激光系统中大尺寸镀金光栅对糟深均匀性的要求,采用梯形光栅-涂胶-离子束溅射镀膜和全息光刻-离子束溅射镀膜两种方法,分别制作了线密度为1 740线/mm,槽深为210nm的宽带镀金正弦光栅.测得其TM波、-1级自准值平均衍射效率在750~850nm范围内大于87%,最高可达90%.这两种方法易控制光栅槽深,去掉光刻胶后基底可继续使用,且制作的光栅的衍射效率和带宽能满足国内一般宽带镀金脉冲压缩光栅的使用要求.     

梯形介质膜光栅衍射特性分析

基于严格耦合波理论建立了梯形介质膜光栅的衍射机理模型,利用该模型讨论了底角为70°的梯形介质膜光栅-1级的衍射行为.通过对梯形介质膜光栅的占空比、槽深和剩余厚度的优化,设计了应用于1053 nm和51.2°角度入射的梯形介质膜光栅.对于顶层为HfO2的介质膜光栅,当槽深为200 nm,剩余厚度为100 nm,占空比为0.35时.其衍射效率优于99.5%,而对于顶层为SiO2的梯形光栅,为获得99.5%的衍射效率.其槽深为800 nm,剩余厚度为320 nm.而且,获得同样的衍射效率,顶层为HfO2的梯形光栅具有更宽的光谱特性.数值计算表明,严格耦合波理论模型对梯形介质膜光栅衍射效率的计算具有很好的收敛性和稳定性.     

飞秒激光烧蚀LiNbO3晶体的形貌特征与机理研究

采用了不同能量的单脉冲和多脉冲飞秒激光对LiNbO₃晶体进行烧蚀，并刻蚀了表面衍射型光栅.通过扫描电镜和原子力显微镜观察了烧蚀点的形貌特征，首次发现利用单束飞秒激光脉冲对LiNbO₃晶体烧蚀，可以得到超衍射极限的烧蚀点，当聚焦光斑直径约为2μm、能量为170nJ的单脉冲飞秒激光作用时，烧蚀点的直径约为400nm，100nJ，17个脉冲作用时烧蚀点的直径约为800nm.同时可以观察到在能量较低的多脉冲飞秒激光作用下， LiNbO₃晶体呈现出大约200nm周期性分布的波纹状结构.实验结果表明，选择合适参数的飞秒激光脉冲可以对LiNbO₃晶体进行超衍射极限加工，这对于利用飞秒激光制作LiNbO₃基质的微纳光电子器件有十分重要的意义.     

超短激光脉冲对宽带光学物质的微加工

通过讨论超快飞秒激光脉冲和长脉冲宽度的激光脉冲紧导致宽能隙透明电介质的损伤机理和比较超短激光脉冲与长激光脉冲对宽能隙透明电介质的损伤程度，得出超短激光脉冲是一种可对透明宽带电介质进行加工的有效工具的结论。当波长为800nm，脉冲宽度为150fs的激光脉冲紧聚焦到不同的宽能隙透明电介质（K9玻璃和ZK6玻璃）体内时，可制作不同光栅常数的光栅，并在波长为635nm的He-Ne连续激光的垂直照射下，对光栅的远场相对衍射效率和光栅的衍射效率进行了测量。     

不同干涉激光偏振态对偶氮分子玻璃表面起伏光栅形成的影响

研究了在不同偏振态干涉Ar+激光作用下,一种偶氮无定形分子玻璃膜表面形成起伏光栅的特性.实验采用p+P,p+s,RCP+LCP三种干涉激光偏振态,利用实时光栅衍射效率测定和原子力显微镜观察等方法,考察了偶氮无定形分子玻璃(IAC-4)膜表面起伏光栅的形成速率和起伏深度.实验发现,当IAc-4形成表面起伏光栅时,其衍射效率增加速度和表面起伏光栅的深度为RCP+LCP>p+s>p+P.在RCP+LCP干涉激光照射下,IAC-4能够极快地形成表面起伏光栅;而用p+P干涉激光照射,则效率最低.在单束激光强度为58 mW/cm2的RCP+LCP偏振态干涉激光照射下,经过80 s～2 min,一级衍射效率即可达62 oA并接近饱和,光栅起伏深度达到734 nm.而在同样强度的P+P,p+S偏振态干涉激光照射下,一级衍射效率和光栅起伏深度分别为3.1%,23 nm和9.3%,120 nm.采用p+s偏振干涉激光时,得到的光栅周期为干涉光场周期的一半.上述实验结果表明,偶氮无定形分子玻璃(IAC-4)材料可很好地用于表面起伏光栅制备,但刻写效果则取决于干涉激光的偏振态.     

Investigation of thermo-mechanical behaviour of diffractive optical elements for CO2 lasers

Phase diffractive optical elements are at present proposed for use with infrared high power lasers, for material surface treatment applications. However, the heating of the component exposed to several kilowatts per square centimetre can be a problem for practical implementation. The deformations due to thermal expansion of a gold binary diffraction grating under high power CO₂ laser exposure at 10.6 μm are estimated by a Finite Element Method. They are compared to the geometrical tolerances obtained by a rigorous electromagnetic Fourier modal method which is used to calculate the optical performances. Several exposure parameters (duration, average laser power) and grating parameters (period, line space ratio) are investigated. The laser exposure should be limited to a few milliseconds with a power density on the grating of 10⁴ W/cm², so that the amplitude of the deformations does not exceed the 75 nm tolerance on the grating depth. One is thus assured that the diffraction efficiency in the first order remains superior to 38.5%.     

变栅距光栅实现啁啾脉冲光谱整形

为了充分利用放大介质的增益带宽,获得脉宽更短,功率更高的输出脉冲,需要将输入到主放大链的种子脉冲进行光谱整形来补偿放大过程中的增益窄化效应。提出了利用变栅距反射光栅实现中心波长1053nm,谱宽6nm啁啾脉冲的光谱整形。运用严格的光栅衍射耦合波理论分析光栅的衍射特性,发现该方案不会引入相位畸变。分别计算和分析了刻槽深度、入射角大小、光栅周期以及入射光波长的变化对衍射效率的影响,通过选取适当的光栅参量可获得0.5%~84%的光谱调制深度。     

Optimizing the efficiency of femtosecond-laser-written holograms

Computer-generated binary holograms are written on a polished copper surface using single 800-nm, 120-fs pulses from a 1-kHz-repetition-rate laser system. The hologram efficiency (i.e. the power in the holographic reconstructed image relative to the incoming laser power) is investigated for different laser-structuring parameters. Theoretical diffraction grating efficiencies for a binary amplitude grating show good agreement with the experimental measurements for diameters of the laser-formed holes below the pitch. Modelling based on straightforward geometrical arguments is used to find the optimal hole size. For a coverage (i.e. relative laser-structured area) of ～43 %, the efficiency reaches ～10 %, which corresponds to a relative power transferred to one reconstructed image of ～20 %. The efficiency as a function of pitch (for fixed coverage) is fairly constant from 2 to 6 μm.     

Compact diode-pumped passively Q-switched tunable Er-Yb double-clad fiber laser

Efficient repetitive passive Q switching of a cladding-pumped Er-Yb fiber laser has been demonstrated by use of an external-cavity configuration containing a Co(2+): ZnS crystal as a saturable absorber. Energies of as much as 60muJ in pulses of durations as short as 3.5 ns (FWHM), corresponding to a peak power of >10kW, have been generated, and the maximum slope efficiency with respect to the absorbed pump power was 13%. Using a bulk diffraction grating in the Littrow configuration to provide wavelength-selective feedback, we tuned the passively Q -switched fiber laser over 31 nm from 1532 to 1563 nm. The prospects for further improvement in performance are discussed.     

基于光谱合束技术的透射光栅模拟设计

半导体激光器光谱合束技术能够实现近衍射极限的高功率激光输出,已成为当前研究热点。衍射光栅的性能直接决定光谱合束的激光输出效果。模拟设计了一种针对940 nm波长、熔融石英材料的亚波长透射光栅。基于严格耦合波理论对光栅结构进行初步设计,运用Rsoft软件依次对光栅占空比、脊高和周期等参数进行优化确定,同时分析了各个参数对光栅衍射效率的影响。所设计的透射式光栅实现第-1级衍射级次的波分复用功能,衍射效率达到91.2%(TE模式),同时压缩其他衍射级次,使其衍射效率降到1.2%以下。同时在光栅入射角度59°±3°范围内保持90%以上的衍射效率,实现高功率激光输出的同时具有较高的误差容错率,易于调节,满足光谱合束技术的要求。     

Broadband and high efficiency metal multi-layer dielectric grating based on non-quarter wave coatings as reflective mirror

This article deals with designing broadband and high efficiency metal multi-layer dielectric grating (MMDG) used to compress and stretch ultra-short laser pulse. The diffraction characteristics of MMDG are analysed with the method of rigorous coupled-wave method. The multi-layer dielectric used as reflective mirror is made up of non-quarter wave coatings. Taking the diffraction efficiency of the -1 order as the value of merit function, the parameters such as groove depth, residual thickness, duty cycle, and reflective mirror are optimized to obtain broadband and high diffraction efficiency. The optimized MMDG shows an ultra-broadband working spectrum with the average efficiency exceeding 97% over 160 nm wavelength centred at 1053 nm and TE polarization. The optimized MMDG should be useful for chirped pulse amplification.     

UV beam-assisted efficient formation of surface relief grating on azobenzene polymers

An efficient method is demonstrated to improve the formation of a surface relief grating (SRG) with a high amplitude. The SRG is realized by a two-beam interference technique (λ=532 nm) in an azobenzene side-chain copolymer. An UV laser beam (λ=355 nm), called assisting beam, was used to accelerate the photoisomerization process from cis-form to trans-form, resulting in a rapid cis-form ? trans-form cycle. This UV beam-assisted method allowed to increase the diffraction efficiency of the formed SRG as well as its depth. Stable gratings with modulation depth as high as 410 nm were obtained at room temperature with moderate laser power.