被动调Q固体激光器非线性动力学研究

被动调Q固体激光器具有结构紧凑、效率高和光束质量优异等特点,因此在基础科学研究、军事、工业加工、医疗卫生等众多领域具有广阔的应用前景.目前,相关研究主要集中在处于单周期动力学态下激光器的特性,而对于处于其他非线性动力学态下激光器特性的研究十分缺乏,尤其是进入混沌的分岔路径还未见报道.该研究基于四能级系统速率方程,数值研究了被动调Q Nd:YAG固体激光器的非线性动力学特性,并分析了一些关键系统参量的影响.结果表明：在不同的参数下,被动调Q固体激光器可呈现单周期、倍周期、多周期以及脉冲混沌等多种动力学态;连续变化参量数值,动力学态呈现多种演化路径;数值模拟结果再现了工作在脉冲混沌态的被动调Q固体激光器中出现的极端事件.     

基于SESAM的被动调Q环形腔掺饵光纤激光器

研究了一种环形结构的基于SESAM（半导体可饱和吸收镜）的被动调Q掺饵光纤激光器,并对该激光器的输出光谱特性进行了研究。该激光器的中心波长为1560nm,重复频率在10kHz以内,斜率效率为1．2％,阈值泵浦功率约为48mW,最大输出功率约为0．95mW。     

脉冲掺铒波导激光器研究进展

目前发展的用于脉冲掺铒光波导激光器的技术主要有：调Q技术、半导体饱和吸收镜被动锁模技术以及带尾纤的碳纳米管（CNTs）饱和吸收被动锁模技术。对基于调Q技术的波导嫩光器、基于半导体饱和吸收镜被动锁模技术的波导激光器、带尾纤的碳纳米管（CNTs）饱和吸收被动锁模技术的波导激光器的发展现状以及存在的问题进行了分析研究,并针对目前存在的问题,指出了其发展方向。     

连续激励斩光盘式调Q CO2脉冲激光器的研制

针对激光加工的特殊要求,研制出连续激励斩光盘式调Ｑ ＣＯ２脉冲激光器,获得了高重复频率、高峰值功率、短脉宽并具有较高的平均功率和较好模式的ＣＯ２调Ｑ脉冲输出。     

一种全自动调节的锁模光纤激光器

通过在非线性偏振旋转环形腔中引入一种全光纤化的角度可调的起偏器,简化了被动锁模光纤激光器的结构,通过调节环形腔内的光纤起偏器和1/4波片的角度就能够实现锁模脉冲的输出。基于此简化结构,引入基于单片机的触发反馈电路,控制偏振片和波片的旋转状态,实现了腔内锁模脉冲的自动调节输出,得到平均功率为8mW的、重复频率为5.6 MHz的全自动锁模脉冲稳态输出。     

声光调Q YAG脉冲激光修锐和整形超硬磨料砂轮

超硬磨料砂轮的修整是制约其优良磨削性能发挥的瓶颈。本文采用声光调Q YAG脉冲激光径向辐照砂轮表面，利用自己开发的一套在线检测闭环控制系统，控制激光脉冲的输出，对砂轮表面进行修整，达到了理想的整形精度，并发现可同时实现修锐，使超硬磨料砂轮的激光修锐和整形可合二为一，通过单脉冲试验研究总结出激光参数和工艺参数对砂轮修整效果的影响特点，选择优化的参数进行修整，获得了较好的修整效果。     

非相干双光反馈半导体激光器的混沌动态特性的实验研究

实验研究了非相干双光反馈半导体激光器(SL)系统的非线性动力学行为,并考察了在一系列不同外腔长度 比例下的混沌演化特性.结果表明:与非相干单光反馈SL系统相比,在合适的双腔长度比例下,非相干双光反馈 SL系统所产生的混沌序列的外腔延时特征得到显著消减,功率谱分布更加平坦,且自相关特性更加理想.进一步 的实验证实,这种消减现象不仅在双外腔长度为近似相等时发生,对于外腔长度为分数倍时同样存在.另外通过微 调外腔长度比例,非相干双光反馈SL系统的混沌特性可被显著改变,外腔延时特征也可被显著增强.     

偏振改变光反馈垂直腔面发射激光混沌系统时延特征的隐藏

利用相关函数和峰值平均比率,数值研究了偏振改变光反馈垂直腔面发射激光器输出混沌的时延特征.结 果表明,在合适的条件下,该偏振改变光反馈垂直腔面发射激光混沌系统能够在较大的参数范围内实现时延特征 的隐藏;当光反馈系数相对较小、偏置电流相对较大时,时延特征更容易被隐藏.     

激光辐射对水稻表型变异的影响

本试验利用3种不同的激光器(He-Ne激光器、半导体泵浦全固体激光器、Nd3+YAG固体脉冲激光器)、不同的处理时间(5、10、15、20 min),对两个不同的水稻品种吉粳88和吉农大18催芽种子进行了处理。结果表明:在水稻品种吉粳88的11个激光处理材料中,利用半导体泵浦全固体激光器处理20 min的处理组其表型变异最明显,抽穗期比未经激光处理的对照晚了6 d,株高也比对照矮7.5 cm左右。利用Nd3+YAG固体脉冲激光器处理20次的处理组的抽穗期也比未经处理的对照晚了6 d;同样在水稻品种农大18的11个激光处理材料中,利用Nd3+YAG固体脉冲激光器处理20次的处理组其抽穗期发生了明显的变异,比对照晚了5d。利用He-Ne激光器处理了20 min的处理组抽穗期比对照晚了4 d,处理5 min和10 min的处理组虽然有变化,但不明显。利用半导体泵浦全固体激光器处理的3组处理组都没有产生明显的变化。     

长苞铁杉种群空间格局的分形特征

种群格局关联维数是种群个体空间关联尺度变化规律的反映,表明了种群个体的空间相关程度。采用关联维数对福建省天宝岩国家级自然保护区珍稀濒危植物长苞铁杉种群格局的分形特征进行了研究。结果表明,不同样地长苞铁杉种群个体空间关联的无标度区介于1-32 m,种群格局关联维数值1.032 4-1.580 1,不同样地种群关联维数的大小为Q5>Q1>Q2>Q4>Q6>Q3,从而揭示出长苞铁杉在不同样地中个体空间关联尺度变化的差异。     

光生微波／毫米波系统中信号控制研究

提出了一种基于单模光纤FP腔的光生微波／毫米波技术中的输出信号控制方法,得到了输出信号数目与外加应力之间的解析表达式。利用波长为1550.337nm的连续激光,经过100MHz的RF信号调制后入射单模光纤FP腔,得到了频率为1．25GHz微波信号序列的波形图。通过适当调节所施加的外力,可得到从微波到毫米波的光生信号。     

A photomicrodynamic system with a mechanical resonator monolithically integrated with laser diodes on gallium arsenide

A cantilever resonant microbeam, laser diodes, and a photodiode have been fabricated on the surface of a gallium arsenide substrate. The microbeam is excited photothermally by light from a laser diode. The vibration is detected with a photodiode as the variation in light output caused by the difference in optical length between the microbeam and another laser diode. A high carrier-to-noise ratio (45 decibels) is achieved with a short (3 micrometers) external cavity length. Such a small distance allows a lensless system, which increases the ease of fabrication. This work could lead to applications in which photomicrodynamic systems are monolithically integrated on a gallium arsenide substrate with surface micromachining technology.     

Ultrafast X-ray Pulses from Laser-Produced Plasmas

A high-temperature plasma is created when an intense laser pulse is focused onto the surface of a solid. An ultrafast pulse of x-ray radiation is emitted from such a plasma when the laser pulse length is less than a picosecond. A high-speed streak camera detector was used to determine the duration of these x-ray pulses, and computer simulations of the plasmas agree with the experimental results. Scaling laws predict that brighter and more efficient x-ray sources will be obtained by the use of more intense laser pulses. These sources can be used for time-resolved x-ray scattering studies and for the development of x-ray lasers.     

Electrically driven single-cell photonic crystal laser

We report the experimental demonstration of an electrically driven, single-mode, low threshold current (approximately 260 microA) photonic band gap laser operating at room temperature. The electrical current pulse is injected through a sub-micrometer-sized semiconductor wire at the center of the mode with minimal degradation of the quality factor. The actual mode of interest operates in a nondegenerate monopole mode, as evidenced through the comparison of the measurement with the computation based on the actual fabricated structural parameters. As a small step toward a thresholdless laser or a single photon source, this wavelength-size photonic crystal laser may be of interest to photonic crystals, cavity quantum electrodynamics, and quantum information communities.     

Electron acceleration by a wake field forced by an intense ultrashort laser pulse

Plasmas are an attractive medium for the next generation of particle accelerators because they can support electric fields greater than several hundred gigavolts per meter. These accelerating fields are generated by relativistic plasma waves-space-charge oscillations-that can be excited when a high-intensity laser propagates through a plasma. Large currents of background electrons can then be trapped and subsequently accelerated by these relativistic waves. In the forced laser wake field regime, where the laser pulse length is of the order of the plasma wavelength, we show that a gain in maximum electron energy of up to 200 megaelectronvolts can be achieved, along with an improvement in the quality of the ultrashort electron beam.     

Effects of pulse shaping in laser spectroscopy and nuclear magnetic resonance

Pulsed excitation fields are routinely used in most laser and nuclear magnetic resonance (NMR) experiments. In the NMR case, constant amplitude (rectangular) pulses have traditionally been used; in laser spectroscopy the exact pulse shape is often unknown or changes from shot to shot. This article is an overview of the effects of radio-frequency and laser pulse shapes and the instrumental requirements for pulse shaping. NMR applications to selective excitation, solvent suppression, elimination of phase roll, and reduced power dissipation are discussed, as are optical applications to soliton generation, velocity selective excitation, and quantitative population transfer.     

蓖麻秆显微构造和纤维形态的研究

蓖麻Ricinus communis秆是一种优质的纤维原料。为了更好地研究和利用蓖麻秆,采用扫描电子显微镜和光学显微镜研究了蓖麻秆皮部、木质部和髓部的显微结构：并利用Motic Images Plus2．0图像处理系统测量了蓖麻秆皮部和木质部的纤维尺寸。结果表明,蓖麻秆皮部含有纤维细胞、轴向薄壁细胞和射线细胞;木质部的结构类似于散孔材,靠近髓的部位管孔较发达,具有单列或双列的异型木射线,纤维细胞壁上可见具缘纹孔,节部纤维弯曲;髓部多为多面体的薄壁细胞,可观察到螺纹导管。皮部纤维长度最大可达26．50mm,长宽比高达540．00,壁腔比0．56～0．83;枝丫部分的纤维最长．长宽比最大：穗部的纤维最短,长宽比和壁腔比最小。木质部纤维的平均长度为0．75～0．90mm,宽度4。38～5．40μm,长宽比31．78～37．54,壁腔比0．56～0．83。蓖麻秆纵向上枝丫部分的平均长度、腔宽和长宽比小于秆部,壁腔比大于或等于秆部;穗部纤维的长度、宽度和腔宽均最小,长宽比和壁腔比最大。径向上靠近木质部中部的细胞长度、细胞腔宽度和长宽比较大：最外侧细胞的宽度、壁厚和壁腔比最大。蓖麻秆是一种优质的纤维原料,可用来造纸和制造人造板等工业化利用：其不同部位的纤维形态不同,呈一定的规律变化。图9表3参10     

Stimulated Raman scattering in hydrogen-filled hollow-core photonic crystal fiber

We report on stimulated Raman scattering in an approximately 1-meter-long hollow-core photonic crystal fiber filled with hydrogen gas under pressure. Light was guided and confined in the 15-micrometer-diameter hollow core by a two-dimensional photonic bandgap. Using a pulsed laser source (pulse duration, 6 nanoseconds; wavelength, 532 nanometers), the threshold for Stokes (longer wavelength) generation was observed at pulse energies as low as 800 +/- 200 nanojoules, followed by a coherent anti-Stokes (shorter wavelength) generation threshold at 3.4 +/- 0.7 microjoules. The pump-to-Stokes conversion efficiency was 30 +/- 3% at a pulse energy of only 4.5 microjoules. These energies are almost two orders of magnitude lower than any other reported energy, moving gas-based nonlinear optics to previously inaccessible parameter regimes of high intensity and long interaction length.     

非线性光子晶体中腔场的平均光子数分布研究

考虑腔模与Mollow峰的中心峰共振的情况,通过解析稳态方程,讨论了处于非线性光子晶体微腔中的二能级原子在外加相干场的驱动下腔场平均光子数的分布情况。研究结果表明,当光子晶体的态密度很大时,腔场的平均光子数随着驱动场拉比频率的增加而增加,最终达到饱和。