The miniaturized femtosecond laser in near infrared-II region is the core equipment of three-photon microscopy. In this paper, we design a compact and robust illumination source that emits dual-color linearly polarized light for three-photon microscopy. Based on an all-polarization-maintaining passive mode-locked fiber laser, we shift the center wavelength of the pulses to the 1.7μm band utilizing cascade Raman effect, thereby generate dual-wavelength pulses. To enhance clarity, the two wavelengths are separated through the graded-index multimode fiber. Then we obtain the dual-pulse sequences with 1639.4nm and 1683.7nm wavelengths, 920fs pulse duration, and 23.75MHz pulse repetition rate. The average power of the signal is 53.64mW, corresponding to a single pulse energy of 2.25nJ. This illumination source can be further amplified and compressed for three-photon fluorescence imaging, especially dual-color three-photon fluorescence imaging, making it an ideal option for biomedical applications.

高功率可见光至近红外波段的超连续谱光源在光电对抗、光学相干层析成像和高光谱激光雷达等方面具有广泛的应用前景。最近几年，涌现了一些用于产生高功率超连续谱光源的新方法，推动了高功率超连续谱光源的进一步发展。本文从主振荡功率放大结构、随机光纤激光器结构以及多路非相干合成这三种用于高功率超连续谱产生的主流方案出发，着重介绍了近年来有代表性的高功率可见光至近红外波段超连续谱光源的研究进展，并综合分析了这三种方案的优缺点以及未来的发展潜力。

本文综述了基于渐变折射率多模光纤可饱和吸收体的全光纤锁模激光超短脉冲与束缚态孤子产生机理与技术研究现状.采用这种新型全光纤结构的锁模调制器件，光纤激光器可输出传统孤子的单脉冲能量达nJ量级，同时可实现时空锁模运转.渐变折射率多模光纤作为全光纤非线性可饱和吸收体在激光器中具有重要的研究意义和广泛的应用，为更高能量超短脉冲的产生提供了一条重要技术途径.

提出了一种新型的基于渐变折射率波导自聚焦效应的模斑变换器,分析了均匀折射率波导和渐变折射率波导的模式场分布及传输特性,研究了自聚焦效应的原理。利用时域有限差分法,计算得到了该变换器的插入损耗和回波损耗,所提模斑变换器与现有的最好模斑变换器的性能相当,但长度缩短至其1/6。该新型模斑变换器可用于集成光学系统中。

为实现对微小位移的精确测量,提高位移精度,提出了基于表面等离子体共振的微位移光纤传感器。利用渐变折射率多模光纤中光束的传播角度随入射光位置的变化而变化的特性,结合表面等离子体共振传感器的共振波长对共振角度变化具有很高灵敏度的特性,实现对微小位移的精确测量。为满足共振条件,将渐变折射率多模光纤研磨成具有合适角度的楔形,精确控制渐变折射率多模光纤的长度,并将光纤探针浸入到一定折射率的液体中。通过630 nm单模光纤将白光光源从渐变折射率多模光纤的端面耦合到光纤探针中,搭建位移平台,精确控制单模光纤和渐变折射率多模光纤的径向相对位置,通过光谱仪检测共振波长随相对位置的变化规律。实验结果表明:当光纤研磨角度为12°,且液体折射率为1.350时,该传感器具有高达10.32 nm·μm ^-1的灵敏度,位移分辨率高达1.9 nm。

SiO2薄膜是光学薄膜领域内常用的重要低折射率材料之一。在文中研究中, 通过测量薄膜的椭偏参数, 使用非线性最小二乘法反演计算获得薄膜的光学常数。采用离子束溅射和电子束蒸发两种方法制备了SiO2薄膜, 在拟合过程中, 基于L8(22)正交表设计了8组反演计算实验, 以评价函数MSE为考核指标。实验结果表明: 对IBS SiO2薄膜拟合MSE函数影响最大的为界面层模型, 对EB SiO2薄膜拟合MSE函数影响最大的为Pore模型。同时确定了不同物理模型对拟合MSE函数的影响大小和反演计算过程模型选择的次序, 按照确定的模型选择次序拟合, 两种薄膜反演计算的MSE函数相对初始MSE可下降35%和38%, 表明拟合过程模型选择合理物理意义明确。文中提供了一种判断薄膜物理模型中各因素对于薄膜光学常数分析作用大小的途径, 对于薄膜光学常数分析具有指导意义。

针对半导体激光二极管(LD)与单模尾纤(SMF)的耦合问题, 提出了一种基于渐变折射率光纤(GIF)的耦合机制。GIF被设计为SMF的前端耦合部分, 采用大芯径以匹配LD输出远场分布, 椭圆形的纤芯形状可有效匹配LD椭圆输出光束, 并实现有效聚焦与控制。基于有限差分束传播法对耦合过程进行的理论分析表明, 采用该方法功率耦合效率可达到88%, 1 dB插入损耗对应的GIF长度容差为75 μm,长轴与短轴方向的横向偏移容差分别为28 μm和10 μm。该方案对高功率LD耦合单模光纤设计有一定的参考价值。

With the rapid development of life sciences, there is an increasing demand for intravital fluorescence imaging of small animals. However, large dimensions and limited working distances of objective lenses in traditional fluorescence microscopes have limited their imaging applications mostly to superficial tissues. To overcome these disadvantages, researchers have developed the graded-index (GRIN) probes with small diameters for imaging internal organs of small animals in a minimally invasive fashion. However, dynamic imaging based on GRIN lens has not been studied extensively. Here, this paper presented a fluorescence endoscopic imaging system based on GRIN lenses using one-photon and two-photon excitation. GRIN lenses with 1.15 mm diameter and 7.65 mm length were used in the system. The images were acquired by a compact laser scanning imaging system with a resonant galvo-mirror system to scan the laser beam and a photomultiplier tube (PMT) to detect fluorescence signals. Experimental results showed that this system using two-photon excitation could implement dynamic fluorescence microendoscopic imaging and monitor the movement of blood flow beneath the skin in anesthetized mice while producing images with higher contrast and signal to noise ratio (SNR) than those using one photon excitation. It would be a useful tool for studying biological processes of small animals or plants in vivo.