集成光子芯片是将激光光源、低损耗波导、调制器、探测器等多类光电器件结合在一起，实现功能化集成，在高速光通讯、量子信息处理、光学传感等领域有具有重要的应用。然而由于不同的光电器件基于不同材料体系，实现多材料体系的光电器件集成极其困难。传统的异质集成和单片集成方法难以同时解决定位精度不足、低拓展性、高损耗、低带宽等一系列问题。基于飞秒激光的双光子聚合技术具有高精度和高穿透的优势，可以实现多材料体系的片上微纳光学元件增材制造，具有极高的加工自由度。本文对片上光学元件的激光增材制造这一领域进行综述，探讨了光子引线键合和微空间光路元件两种技术路径，总结了现有技术的发展现状，并对未来的发展前景进行了展望。

土壤有机质是土壤的重要成分, 也是农作物生长的重要营养指标。 快速、 准确检测土壤有机质含量对施肥管理具有重要意义。 近年来, 近红外光谱被广泛应用于土壤有机质的快速检测, 然而土壤有机质敏感波段易受土壤水分干扰, 从而会影响到土壤有机质的预测结果。 在山西省境内采集了140个土壤样本, 采用ASD光谱仪分别获取了不同含水率(0%, 5%, 10%, 15%, 17%)土壤样本谱图曲线(350~2 500 nm)。 为了提高土壤有机质预测模型精度, 提出特征波长积分算法, 即通过特征波长处吸光度的积分值作为自变量进行建模的方法, 建立了土壤有机质预测模型及抗水分干扰修正系数模型。 结果表明: (1)使用特征波长处吸光度的积分值作为自变量建立的土壤有机质预测模型统计参数优于传统的使用特征波长处的吸光度值作为自变量的建模方法; (2)校正后的湿土光谱更加接近干土土样, 在一定程度上解决了传统水分修正系数在水分含量较高时修正效果较差的问题; (3)提高了湿土样本的预测精度, 预测相关系数(R_P)提升了约0.09, 预测均方根误差(RMSEP)降低了约1.72 。 说明该方法可以有效降低水分对土壤有机质光谱的影响, 提高不同含水率土壤有机质的预测精度, 可为后续仪器开发提供理论支持。

Stimulated Raman scattering (SRS) in plasma in a non-eigenmode regime is studied theoretically and numerically. Different from normal SRS with the eigen electrostatic mode excited, the non-eigenmode SRS is developed at plasma density $n_{e}>0.25n_{c}$ when the laser amplitude is larger than a certain threshold. To satisfy the phase-matching conditions of frequency and wavenumber, the excited electrostatic mode has a constant frequency around half of the incident light frequency $\unicode[STIX]{x1D714}_{0}/2$, which is no longer the eigenmode of electron plasma wave $\unicode[STIX]{x1D714}_{pe}$. Both the scattered light and the electrostatic wave are trapped in plasma with their group velocities being zero. Super-hot electrons are produced by the non-eigen electrostatic wave. Our theoretical model is validated by particle-in-cell simulations. The SRS driven in this non-eigenmode regime is an important laser energy loss mechanism in the laser plasma interactions as long as the laser intensity is higher than $10^{15}~\text{W}/\text{cm}^{2}$.

Absolute instability modes due to secondary scattering of stimulated Raman scattering (SRS) in a large nonuniform plasma are studied theoretically and numerically. The backscattered light of convective SRS can be considered as a pump light with a finite bandwidth. The different frequency components of the backscattered light can be coupled to develop absolute SRS instability near their quarter-critical densities via rescattering process. The absolute SRS mode develops a Langmuir wave with a high phase velocity of about $c/\sqrt{3}$ with $c$ the light speed in vacuum. Given that most electrons are at low velocities in the linear stage, the absolute SRS mode grows with very weak Landau damping. When the interaction evolves into the nonlinear regime, the Langmuir wave can heat abundant electrons up to a few hundred keV via the SRS rescattering. Our theoretical model is validated by particle-in-cell simulations. The absolute instabilities may play a considerable role in the experiments of inertial confinement fusion.