Two-photon absorption and stimulated emission in poly-crystalline Zinc Selenide with femtosecond laser excitation

The optical nonlinearity in polycrystalline zinc selenide(ZnSe),excited with 775 nm,1 kHz femtosecond laser pulses was investigated via the nonlinear transmission with material thickness and the Z scan technique.The measured two photon absorption coefficientβwas intensity dependent,inferring that reverse saturated absorption(RSA)is also relevant dur-ing high intensity excitation in ZnSe.At low peak intensity I<5 GW cm^(-2),we findβ=3.5 cm GW^(-1) at 775 nm.The spec-tral properties of the broad blueish two-photon induced fluorescence(460 nm-500 nm)was studied,displaying self-ab-sorption near the band edge while the upper state lifetime was measured to be τ_(e)~3.3 ns.Stimulated emission was ob-served when pumping a 0.5 mm thick polycrystalline ZnSe sample within an optical cavity,confirmed by significant line narrowing fromΔλ=11 nm(cavity blocked)toΔλ=2.8 nm at peak wavelength λ_(p)=475 nm while the upper state life-time also decreased.These results suggest that with more optimum pumping conditions and crystal cooling,polycrystal-line ZnSe might reach lasing threshold via two-photon pumping atλ=775 nm.

Functional nonlinear optical nanoparticles synthesized by laser ablation

Nonlinear optics is an important research direction with various applications in laser manufacturing,fabrication of nano-structure,sensor design,optoelectronics,biophotonics,quantum optics,etc.Nonlinear optical materials are the funda-mental building blocks,which are critical for broad fields ranging from scientific research,industrial production,to military.Nanoparticles demonstrate great potential due to their flexibility to be engineered and their enhanced nonlinear optical properties superior to their bulk counterparts.Synthesis of nanoparticles by laser ablation proves to be a green,efficient,and universal physical approach,versatile for fast one-step synthesis and potential mass production.In this review,the development and latest progress of nonlinear optical nanoparticles synthesized by laser ablation are summarized,which demonstrates its capability for enhanced performance and multiple functions.The theory of optical nonlinear absorption,experimental process of laser ablation,applications,and outlooks are covered.Potential for nanoparticle systems is yet to be fully discovered,which offers opportunities to make various types of next-generation functional devices.

Thermal response and optical absorptance of metals under femtosecond laser irradiation

A detailed study on correlation between residual thermal response of a sample and its optical absorptance change due to laser-induced sur-face structural modifications in multi-shot fem-tosecond laser irradiation is performed. Ex-periments reveal an overall enhancement for residual thermal coupling and absorptance in air. Surprisingly, residual thermal coupling in air shows a non-monotonic dependence on pulse number and reaches a minimum value after a certain number of pulses, while these behaviors are not seen in absorptance. In vacuum, how-ever, both suppression and enhancement are seen in residual energy coupling although ab-sorptance is always enhanced. From these ob-servations, it appears that air plasma plays a dominant role in thermal coupling at a relatively low number of applied pulses, while the forma-tion of craters plays a dominant role at a high number of pulses.

Nonlinear Ionization of Molecules by Intense Transform-Limited Gaussian Laser Pulses

We present in this paper an investigation of the nonlinear process of above-threshold ionization. The process arises when an atomic or molecular system, exposed to an intense laser pulse, continues to absorb more photons than that needed for the ionization to occur. We trigger this nonlinear process in a simple molecular system by exposing it to an intense transform-limited Gaussian laser pulse of 267-nm wavelength which is the third harmonic of an 800-nm wavelength Tisapphire laser. We explore the characteristics of the process by analyzing the kinetic-energy spectra of the electrons ejected from the molecular system under different laser peak intensities.

A theoretical model of the femtosecond laser ablation of semiconductors considering inverse bremsstrahlung absorption

The mechanism of the femtosecond laser ablation of semiconductors is investigated. The collision pro cess of free electrons in a conduction band is depicted by the test particle method, and a theoretical model of nonequilibrium electron transport on the femtosecond timescale is proposed based on the FokkerPlanck equa tion. This model considers the impact of inverse bremsstrahlung on the laser absorption coefficient, and gives the expressions of electron drift and diffusion coefficients in the presence of screened Coulomb potential. Numerical simulations are conducted to obtain the nonequilibrium distribution function of the electrons. The femtosecond laser ablation thresholds are then calculated accordingly, and the results are in good agreement with the experimental results. This is followed by a discussion on the impact of laser parameters on the ablation of semiconductors.

飞秒激光脉冲诱导透明介质的非线性吸收和折射率改变轮廓研究

实验研究了飞秒激光脉冲诱导熔融石英的非线性吸收特性 ,利用激光诱导自由电子等离子体浓度取决于多光子吸收系数和入射光强的关系 ;数值模拟了激光诱导折射率变化区域的大小 ,结合非线性吸收机理和飞秒激光脉冲与介质的相互作用 ,解释了飞秒激光脉冲超精细加工不受衍射极限的约束 ,可实现纳米级加工的机理 结果表明 ,电介质的电离能越大 ,飞秒脉冲诱导的折射率变化区域就越小 ,但要求的激光脉冲能量也越大 ;

飞秒激光加工最新研究进展

飞秒激光作为一种先进的加工技术,以其"冷加工"、多光子非线性效应、突破衍射极限等特质可实现对任意材料由微纳到宏观尺度复杂三维零件的精密加工,在微纳和精密机械、微纳电子、微纳光学、表面工程、生物医学等领域展露了巨大的市场应用前景。文章重点针对近三年来飞秒激光刻蚀、切割、制孔、功能表面制备、体内加工和聚合加工的研究进展进行综述,并探讨了飞秒激光在与材料相互作用机制、加工精度、加工方式、加工对象等方面面临的机遇和挑战。

超短脉冲激光对透明介质的烧蚀特性研究

用波长800 nm,脉宽分别为20 fs,100 fs,1 000 fs高斯型激光脉冲研究熔石英的烧蚀机制,采用一种新的模型来计算烧蚀过程中电子数密度随时间的演化,同时确定了不同情况下材料的烧蚀阈值,并分析了在这个过程中多光子电离,隧道电离及雪崩电离的作用,本文结果与以前研究结果符合得较好.

基于复耦合模型的面齿轮飞秒激光加工参数影响研究

分析了飞秒激光精微加工面齿轮材料18Cr2Ni4WA的机理,在光子与电子,电子与晶格之间温度传递的双温模型的基础上建立了耦合动态热力学参数的复耦合模型,通过模型仿真分析,得出了电子与晶格的温度变化过程,预测了去除高于蒸发温度的材料烧蚀形貌。对面齿轮材料进行飞秒激光扫描加工实验,得出随着能量密度的增大,凹坑半径和深度都会有一定程度的增大,当能量密度为1.98 J/cm^(2)时,烧蚀形貌较好,当能量密度继续增大达到2.18 J/cm^(2)时,凹坑内部开始产生少量的熔融物堆积;随着脉宽的增大,形貌变化不大,但产生的熔融物逐渐减少,凹坑趋于平整;随着扫描速度的增大,沟槽的深度逐渐减小,宽度逐渐增大。采用三维超景深仪观测烧蚀形貌,实验结果与仿真结果基本一致,为飞秒激光精微加工面齿轮提供了依据。

飞秒激光共振吸收对掺Pr-Nd硅玻璃烧蚀阈值的影响

为了进一步研究共振吸收在飞秒激光烧蚀加工中对靶材烧蚀阈值的影响,针对具有特定吸收光谱的掺Pr-Nd硅玻璃(Pr-Nd玻璃)和无特定吸收的石英玻璃,分别采用共振吸收波长585,807 nm和非共振吸收波长720,775 nm对2种靶材进行烧蚀加工,并基于烧蚀轮廓,提出一种靶材烧蚀阈值的计算方法。研究结果表明:在烧蚀阈值附近,靶材的初始种子电子产生方式主要为多光子电离;Pr-Nd玻璃在共振波长585 nm和807 nm的作用下,多光子电离较为剧烈,烧蚀轮廓长度较石英玻璃分别增长19.8%和6.8%,且对于加工波长807 nm,烧蚀阈值较石英玻璃降低12.3%;而对于非共振波长720 nm和775 nm的烧蚀加工,共振烧蚀效应消失,2种靶材的烧蚀轮廓长度和烧蚀阈值基本一致。

飞秒脉冲激光单粒子效应评估技术的研究现状及发展趋势

总结分析国内外关于飞秒脉冲激光双光子吸收诱发单粒子效应研究的现状和技术发展趋势,分析了双光子吸收、自由载流子吸收和折射等非线性光学现象对双光子吸收诱发产生的载流子密度分布的影响;基于载流子密度分布模型,探讨基于Z扫描确定器件敏感深度的方法。通过总结飞秒脉冲激光在单粒子效应机理深度研究、空间任务器件筛选、电子设备抗辐射评估等方面的应用需求及前景,为进一步拓展飞秒脉冲激光单粒子效应实验技术在航天装备及卫星电子设备抗辐射性能评估方面提供建议和意见。

化学钢化玻璃的激光焊接及其机械强度

超短脉冲激光因具有加工精度高、热影响区小、效率高等优点,在玻璃焊接领域有着广阔的发展前景。在实际场景中玻璃往往通过强化提升自身强度,以满足其应用的可靠性。本文利用红外超短脉冲激光成功实现化学钢化玻璃之间的焊接,通过显微镜观察焊点形状,总结出了焊接功率、频率、速度与焊点尺寸的回归方程,并验证了回归方程的准确性。结果表明:在焊接频率为500 kHz、焊接速度为10 mm/s条件下,随着焊接功率升高,焊接化学钢化玻璃的机械强度先增大后减小,化学钢化玻璃焊接剪切应力最大可达11.09 MPa,拉伸应力最大可达7.10 MPa;激光焊接时化学钢化玻璃不仅受到本身热膨胀的压力还叠加了张应力,更容易造成周围区域的破坏。

飞秒激光加工最新进展

综述了飞秒激光进行材料加工的多种机理和理论;主要介绍了飞秒激光对玻璃、石英、金属、聚合物等各种材料加工的最新研究进展状况及各方面的应用;飞秒激光加工是门新兴的学科,具有重要的应用前景。

飞秒激光烧蚀面齿轮材料的形貌特征研究

飞秒激光加工面齿轮材料18Cr2Ni4WA是一种面齿轮精微修正的新型加工技术。首先,根据烧蚀凹坑的直径和激光功率的定量关系得到激光的烧蚀阈值,根据烧蚀凹坑的深度和激光功率的定量关系得到材料的吸收系数。然后,考虑到能量累积效应,从高斯激光的聚焦方式考虑变离焦量效应,建立材料内部的能量吸收模型。最后,通过改变脉冲数和激光功率,研究飞秒激光烧蚀凹坑直径和深度的变化规律。实验结果表明,脉冲频率为200 kHz的飞秒激光脉冲数大于20时,烧蚀凹坑的直径和深度趋于稳定,这与理论结果相吻合。随着激光功率的增大,飞秒激光的加工质量有明显下降,当激光功率为1 W时,飞秒激光的加工质量良好且烧蚀深度足够深。

飞秒激光诱导纳米材料的图案化生长研究进展及其应用

纳米材料具备小尺寸和大比表面积的特点,在能源器件、集成电路和生物医学等领域中具有众多独特的优势。目前,研究人员通过固相、液相或者气相沉积等方法实现了各类纳米材料的高质量制备,但这些方法主要聚焦于纳米材料的生长过程,通常需要后续多步工艺配合才能实现微纳器件的制备。因此,对纳米材料的直接图案化制备将有效提高器件的集成度,并将充分发挥纳米材料的尺寸优势。尽管已有部分方法能够实现原位免转移的纳米材料图案化制备,如紫外光刻、电子束光刻、溶液直接成型以及连续/长脉冲激光选择性诱导生长等,但仍难以满足纳米材料的图案定制化、精密化以及在热敏、柔性和曲面衬底上原位异质集成的需求。飞秒激光作为一种具有高峰值功率的“冷加工”手段,在实现纳米材料的原位图案化生长方面具有独特的优势。回顾了现有的纳米材料的原位图案化制备方法,总结了这些方法存在的问题,并重点介绍了飞秒激光诱导纳米材料的图案化生长方面的研究进展,包括金属、金属氧化物、金属硫化物以及碳基纳米材料的图案化生长及其应用。最后探讨了飞秒激光诱导纳米材料图案化生长需要解决的问题以及其在未来微纳功能器件制造中的应用前景和发展潜力。

超连续白光光谱特性研究

利用中心波长为800 nm、脉冲宽度为35 fs的飞秒激光脉冲开展了以蓝宝石晶体为介质的超连续白光光谱特性研究,通过对比不同入射脉冲能量下焦距为40 mm的球面透镜产生的白光光谱发现:随着入射脉冲能量的增强,白光光谱向蓝边方向展宽,当能量增加到210 nJ时,光谱范围不再变化。对比焦距为40 mm的球面透镜和消色差透镜产生的白光光谱发现:消色差透镜产生的光谱的整体强度小于球面透镜,且光谱有一定蓝移,蓝移波长可达450 nm。采用Zemax软件对两种透镜产生的焦斑进行仿真,比较了两种透镜产生的焦斑的大小和能量,并分析了蓝移现象产生的原因。同时,本研究对比了焦距为40 mm和100 mm球面透镜、消色差透镜产生的白光光谱的范围和稳定性,结果表明,焦距为40 mm的透镜产生的白光光谱的稳定性较好,光谱范围较宽,约为450~700 nm。罗丹明B的瞬态吸收实验结果表明,使用焦距为40 mm的消色差透镜时,罗丹明B的瞬态吸收信号最为明显,信噪比最高。本实验表明,针对不同的样品特性,可以通过选择不同的透镜来优化瞬态吸收实验结果。