飞秒激光成丝过程中的太赫兹波超光速传输现象研究

通过使用太赫兹(Terahertz,THz)时域光谱系统,探测从不同长度飞秒激光光丝辐射出的THz脉冲,观察到THz波在飞秒激光成丝过程中超光速传输的实验现象。进一步的分析表明:THz波在等离子体光丝区域的折射率小于其在空气中的折射率,这是使得THz波能够在成丝过程中超光速传输的主要原因。由此可以推测:THz脉冲极有可能是在等离子体光丝中进行导引传输的。最后,通过数值模拟获得了光丝区域内的THz本征模式,从而验证了上述推测。

中红外飞秒激光场中氮分子高次谐波的多轨道干涉特性研究

通过系统研究氮分子高次谐波产生过程中的电子超快动力学过程,实验上发现在中红外飞秒强激光场驱动下高次谐波谱的截止区附近存在清晰的谐波谱极小值.进一步研究表明谐波谱极小值对应的光子能量强烈依赖于驱动激光脉冲的光强和波长,而与分子取向角无关,由此推断该极小值来源于氮分子最高占据分子轨道和次最高占据分子轨道产生的高次谐波之间的相消干涉.本研究结果将对极端强场条件下多轨道电子超快动力学研究起到积极推动作用.

外窗对建筑能耗综合影响分析——以黄山地区某办公建筑为例

基于黄山建设大厦项目,在多因素条件下,如窗墙比、传热系数、形式与深度外遮阳板等,模拟研究南北向窗户对建筑采暖能耗、空调能耗与总能耗的影响,同时开展了经济性分析。研究发现,随着北向窗墙比的增大,建筑全年空调能耗均随之增大,且在相同条件下,外窗的传热系数减小,建筑的全年空调能耗并不一定都降低。南向外窗窗墙比从0.2增至0.6,传热系数为5.7 W/m^ 2·K、4.7 W/m^ 2·K、3.0 W/m^ 2·K、2.2 W/m^ 2·K、1.7 W/m^ 2·K时的采暖能耗分别下降了-2.66%、4.84%、9.84%、10.80%、12.96%,传热系数越小,采暖能耗下降幅度越大。窗墙比对空调能耗影响程度南向大于北向,总能耗与窗墙比成正相关。另外,水平遮阳板较垂直遮阳的节能效果好,且在0.8 m深度窗户传热系数为2.2 W/m^ 2·K时生命周期费用最低。以上5种传热系数下建筑南窗设置0.8m深度的水平遮阳板较未设置遮阳的总能耗分别减少了3.33%、4.37%、6.91%、8.94%、7.58%,建筑节能改造后全年单位面积采暖能耗、空调能耗、总能耗分别降低了34.08%、26.38%、30.65%。

Electro-Optically Switchable Optical True Delay Lines of Meter-Scale Lengths Fabricated on Lithium Niobate on Insulator Using Photolithography Assisted Chemo-Mechanical Etching

Optical true delay lines(OTDLs)of low propagation losses,small footprints and high tuning speeds and efficiencies are of critical importance for various photonic applications.Here,we report fabrication of electro-optically switchable OTDLs on lithium niobate on insulator using photolithography assisted chemo-mechanical etching.Our device consists of several low-loss optical waveguides of different lengths which are consecutively connected by electro-optical switches to generate different amounts of time delay.The fabricated OTLDs show an ultra-low propagation loss of^0.03dB/cm for waveguide lengths well above 100 cm.

基于虚拟仿真实验的热力发电厂教学改革探索

为了提升教学质量文章首先阐述了热力发电厂教学存在的问题,并提出了基于虚拟仿真实验的热力发电厂教学改革思路,最后重点论述了基于虚拟仿真实验的热力发电厂教学改革路径。

Dramatic Spectral Broadening of Ultrafast Laser Pulses in Molecular Nitrogen Ions

We investigate nonlinear interaction of nitrogen molecules with a two-color laser field composed by an intense 800 nm laser pulse and a weak 400 nm laser pulse.It is demonstrated that the spectrum of 400 nm pulses is dramatically broadened when the two beams temporally overlap.In comparison,the spectral broadening in argon is less pronounced,although argon atoms and nitrogen molecules have comparable ionization potentials.We reveal that the dramatic spectral broadening originates from the greatly enhanced nonlinear optical effects in the near-resonant condition of interaction between the 400 nm pulses and the nitrogen molecular ions.

基于整形飞秒激光脉冲的三维微纳制备

飞秒激光脉冲加工具有热效应小、加工精度突破衍射极限、三维内部加工能力等特性,在微纳制备领域独具优势。综述了利用飞秒激光脉冲整形技术结合飞秒激光三维直写进行透明介质中微纳制备的最新进展,这些技术有望在新型集成光学和微纳光学中发挥重要的作用。

Two-dimensional materials in photonic integrated circuits:recent developments and future perspectives[Invited]

The heterogeneous integration of photonic integrated circuits(PICs)with a diverse range of optoelectronic materials has emerged as a transformative approach,propelling photonic chips toward larger scales,superior performance,and advanced integration levels.Notably,two-dimensional(2D)materials,such as graphene,transition metal dichalcogenides(TMDCs),black phosphorus(BP),and hexagonal boron nitride(hBN),exhibit remarkable device performance and integration capabilities,offering promising potential for large-scale implementation in PICs.In this paper,we first present a comprehensive review of recent progress,systematically categorizing the integration of photonic circuits with 2D materials based on their types while also emphasizing their unique advantages.Then,we discuss the integration approaches of 2D materials with PICs.We also summarize the technical challenges in the heterogeneous integration of 2D materials in photonics and envision their immense potential for future applications in PICs.

超低损耗铌酸锂光子学

铌酸锂光子集成是推动未来高速光通信和光信息处理领域变革性发展的重要前沿技术。介绍了利用铌酸锂光子芯片制造技术制备集成光路中关键光子结构与器件的最新研究进展。得益于单晶铌酸锂晶体的高非线性系数和强电光效应,利用制备的高性能铌酸锂光子器件演示了多种高效的非线性光学过程。

PAC-3导弹拦截巡航导弹目标试验获得成功

2012年4月25日,洛马公司的爱国者先进能力-3（PAC-3）导弹利用联合对陆攻击巡航导弹防御增强网络传感器（JLENS）和爱国者系统进行了一次前所未有的互操作验证试验,成功拦截并摧毁一枚巡航导弹目标。

Ultrafast gain dynamics in N_2^+ lasing from highly excited vibrational states pumped by circularly polarized femtosecond laser pulses

We experimentally demonstrate N2^＋ lasing actions at the wavelengths of 353.3, 353.8, and 354.9 nm using a circularly polarized femtosecond laser. The three laser lines correspond to the B2∑u^＋（v＇ = 5, 4, 3） → X2∑g^＋（v = 4, 3, 2） transitions, respectively. Particularly, we reveal the pressure-dependent gain dynamics of these lasing actions from highly excited vibrational states with a pump-probe scheme. Our experimental results confirm that electron eollisional excitation plays an important role in the establishment of a population inversion of N2^＋ lasing at these wavelengths.

Intensity-independent molecular rotational decoherence lifetimes measured with mean wavelength shifts of femtosecond pulses

We report on an experimental investigation on the dynamic decoherence process of molecular rotational wavepackets during femtosecond laser filamentation based on time-dependent mean wavelength shifts of a weak probe pulse. Details of periodic revival structures of transient alignment can be readily obtained from the measured shifted spectra due to the periodic modulation of the molecular refractive index. Using the method, we measured decoherence lifetimes of molecular rotational wavepackets in N2and O2under different experimental conditions. Our results indicate that decoherence lifetimes of molecular rotational wavepackets are primarily determined by the relative population of rotational states in the wave packet and intermolecular collisions,rather than the focusing intensity.

High-quality-factor optical microresonators fabricated on lithium niobate thin film with an electro-optical tuning range spanning over one free spectral range [Invited]

We demonstrate high-quality(intrinsic Q factor∼2.8×106)racetrack microresonators fabricated on lithium niobate thin film with a free spectral range(FSR)of∼86 pm.By integrating microelectrodes alongside the two straight arms of the racetrack resonator,the resonance wavelength around 1550 nm can be red shifted by 92 pm when the electric voltage is raised from−100 V to 100 V.The microresonators with the tuning range spanning over a full FSR are fabricated using photolithography assisted chemo-mechanical etching.

Effect of spatio-temporal coupling on ultrafast laser direct writing in glass

Spatio-temporal coupling characteristics of ultrafast laser pulses are quantitatively tailored. An asymmetric microstructure is induced in the focal volume when the laser scans perpendicularly to the direction of the spatial chirp in fused silica. The tilted direction reverses when adding a Dove prism into the light path. The sign of the pulse front tilt can be turned from positive to negative by changing the group delay dispersion by steps. We reveal that the tilted direction of a microstructure depends on spatial chirp, and the interplay between spatiotemporal chirp leads to the change of tilted angles.