FROG方法诊断飞秒脉冲的振幅与相位

详细讨论了一种基于二次谐波一频谱分辨光闸法 (简称SHG_FROG方法 )的矩阵迭代算法 ,实现了对飞秒脉冲的振幅和相位的诊断 ,得出其脉冲形状为双曲正割型、相位是时间的三次幂形式。     

Sub-10-fs pulse generation directly from a KLM Ti: sapphire laser

By reducing the effects of frequency dependent mode size and intracavity gain saturation of a KLM Ti: sapphire laser, the pulse bandwidth broadening is enhanced significantly. 8.5 fs pulses with the bandwidth of 92 nm at wavelength of 710 nm have been generated directly from this laser and measured with an extracavity group velocity dispersion compensation system.     

Control of the carrier-envelope phases of a synchronously pumped femtosecond optical parametric oscillator and its applications

The intrinsic synchronization, multi-color outputs and related carrier-envelope phases （CEP） among pulses bring advantages to synchronously pumped femtosecond optical parametric oscillators and the pumping sources for broadband frequency comb generation and ultrashort waveform coherent syn-thesis. In this paper, we discuss our latest research results in this field, which cover the following as-pects： the phase relationship and energy conservation law in an OPO and related experimental verifi-cation; control of the pumping Ti-sapphire femtosecond laser＇s CEP by self-referencing technology, and its repetition-rate locking by piezoelectric transducer （PZT）; CEP locking of the pulses from the OPO by beating the non-phase-matched visible outputs against pump supercontinuum to obtain a driving signal for a fast PZT on the OPO end mirror; the generation of a broadband frequency comb spanning from 400 nm to 2.4 μm with 1.2 kHz bandwidth; and the realization of coherent interference between phase controlled pump pulses and signal second harmonic pulses.     

Carrier-envelope phase passively stabilized near-infrared laserpulses from a dual-frequency pumped noncollinear opticalparametric amplifier

By inversing the signal and idler in a two-stagenoncollinear optical parametric amplifier which is, respec-tively, pumped by the second harmonic and fundamentalwave of femtosecond Ti：sapphire laser at repetition rate of1 kHz, the carrier-envelope phase （CEP） passively stabilizedpulses with a tunable wavelength from 1.1 to 1.6 μm areobtained with maximum energy of95 μJat 1.3 μm underthepump energy ofS00 μJ. The CEP jitter of pulses is 108 mradmeasured by anf-2finterferometer. This work demonstratesa new way to efficiently generate tunable near-infraredfemtosecond laser pulses with self-stabilized CEP.     

飞秒激光在蓝宝石晶体表面加工微细结构的实验研究

由于蓝宝石晶体具有很高的硬度和耐磨蚀性,很难进行机械和化学腐蚀加工。笔者利用波长780 nm、频率1 kHz和脉冲宽度164 fs的飞秒脉冲激光在蓝宝石晶体表面进行了微细结构加工的实验研究。采用飞秒激光静态照射蓝宝石晶体表面,通过飞秒激光烧蚀孔的直径和脉冲能量的关系,计算了飞秒激光烧蚀蓝宝石晶体的两种烧蚀状态下的烧蚀阈值和有效烧蚀半径。通过直线扫描实验,在不同实验条件下在蓝宝石晶体表面加工微槽,获得微槽的宽度和深度与飞秒激光主要参数之间的关系。研究结果表明,微槽的加工表面可通过增加扫描次数而得到明显的提高,且扫描次数的增加对微槽的宽度和深度基本无影响。利用聚焦的飞秒激光束沿着轨迹扫描,在蓝宝石晶体表面加工出比较清洁的微小结构,可以为实现微结构的精密加工提供指导。     

Editor’s note

The past two decades have witnessed great progress in development of ultrashort laser pulse in laser science, often at an unexpected speed. It has found various applications, both theoretical and practical, in the frontiers of science.     

High energy femtosecond mid-infrared generation pumped by a two-color Ti:sapphire multipass amplifier

Intense mid-infrared was generated by direct frequency mixing two pulses from a dual-wavelength Ti：sapphire system. From a multipass amplifier we generated two tunable wavelength femtosecond pulses with a total energy of 15 mJ. Pulse energy of 1.6 μJ and 7.4 μJ of mid-infrared light is achieved with and without its multipass amplifier at 9-11μm, with pulse duration of 500 fs.     

自锁模钛宝石激光器突破10飞秒

自锁模钛宝石飞秒激光器以其优越的性能和广泛用途备受人们青睐和广泛研究,特别是在脉冲压缩方面,人们采用了多种措施,以获得亚１０ ｆｓ脉冲．美国 ＭＩＴ的研究小组于 １９９９年采用双啁啾镜技术,由该类激光器获得短于５．４ｆｓ的脉冲［１］,这是至今为止直接由此类激光器产生的最短脉冲．国内的报道为 １２ ｆｓ［２］．我们在自行研制的自锁模钛宝石激光器于１９９８年获得 １５ ｆｓ脉冲［３］的基础上,进一步优化激光器腔结构,实现了在７３０～８５０ｎｍ范围内连续可调谐自启动锁模运转,并在７５０ｎｍ附近得到最短为 ８．…     

测量飞秒光参量产生器输出光脉冲脉宽的自相关仪的设计

设计出一台只用一块非线性晶体就能够测量宽波长范围的飞秒激光脉冲脉宽的单次脉冲自相关仪,适用于测量由光参量产生获得的可调谐飞秒激光脉冲的脉宽.     

高阶孤子飞秒激光脉冲的成形机制

根据实验上普遍观察到的10fs左右激光脉冲的脉冲分裂现象，以高阶孤子特征分析了飞秒激光器中克尔透镜锁模脉冲的类孤子成形机制，以至进一步了解克尔透镜锁模脉冲成形机制。     

Sub-10 fs laser pulses with repetition rate of 1.1 GHz by a Ti: sapphire oscillator

We demonstrate a compact Ti： sapphire oscillator with ring cavity configuration. By optimizing the intra-cavity dispersion with chirped mirrors, pulses with repetition rate of 1.1 GHz are coupled out by the uncoated wedges in the cavity. Under 7W CW pump laser centered at 532 nm, the average power of the output pulses is about 30 mW, the duration is less than lOfs and the spectrum spans from 670 nm to 920 nm.     

Ultrahigh resolution optical coherence tomography with femtosecond Ti:sapphire laser and photonic crystal fiber

Optical coherence tomography （OCT） with ultrahigh axial resolution was achieved by the super-continuum generated by coupling femtosecond pulses from a commercial Ti：sapphire laser into an air-silica microstructure fiber. The visible spectrum of the super-continuum from 450 to 700 nm centered at 540 nm can be generated. A free-space axial OCT resolution of 0.64 pm was achieved. The sensitivity of OCT system was 108 dB with incident light power 3 mW at sample, only 7dB below the theoretical limit. Subcellular OCT imaging was also demonstrated, showing great potential for biomedical application.     

基于纳飞秒双脉冲激光的蓝宝石蚀除研究

蓝宝石作为一种典型的宽带隙半导体材料具有良好的理化特性,在机械电子、航空航天、微电子等领域具有广阔的应用前景.本文提出采用纳飞秒双束激光进行蓝宝石加工的方法,利用飞秒脉冲峰值功率高的特性,通过多光子电离与碰撞电离,激发蓝宝石表面自由电子从而提高了蓝宝石对纳秒激光的吸收率,同时利用纳秒激光能量相对较大,技术成熟的优势,实现对蓝宝石材料的高质高效加工.为了揭示纳飞秒双束激光与蓝宝石材料的能量耦合机制,采用Fokker-Plank方程、Drude模型、双温模型对飞秒激光诱发的自由电子的演化过程及自由电子与入射激光之间的相互作用进行研究,并通过有限元仿真模拟了纳飞秒双激光与蓝宝石材料相互作用的能量耦合过程与蚀除过程,分析了纳飞秒双脉冲激光作用下,不同脉冲延时下等离子浓度的时空演化规律及其对入射激光吸收系数及反射率等表面光学特性的影响规律,揭示了纳飞秒双激光高效高质加工蓝宝石材料的机理.该研究对实现蓝宝石等宽带隙半导体等脆硬材料的高质高效加工具有重要意义.     

Multi-peak spectrum of KML Ti: Sapphire pulse

The multi-peak spectrum of Ti:sapphire pulses observed experimentally under ultra-broad bandwidth conditions (< 15 fs pulse length) has been explained theoretically. It is shown that the self-phase-modulation effect is equivalent to the process of degenerate four-wave frequency-mixing. Based on this theoretical underpinning, the presence or absence of a multipeak spectrum provides a practical measure of whether the intracavity group-velocity-dispersion is ideally compensated for or not.     

飞秒脉冲激光产生及捕获微气泡的实验研究

采用高速光学摄像及高频超声成像技术对飞秒脉冲激光在介质水中发生光学诱导击穿的过程进行实验研究.结果表明,光学诱导击穿产生后,在高能激光自聚焦的焦点处产生一系列微气泡,最后只有一个微气泡可以被激光束稳定地捕获,并且这个微气泡可以在超声作用下进行非接触式三维操控.进一步分析了沿激光束产生和捕获的微气泡的时空特性以及激光束捕获微气泡的力学特性.实验结果为应用微气泡进行分子水平的靶向性治疗提供了全新的技术手段.     

全反射相干自相关法测量飞秒脉冲的特性分析

 全反射相干自相关法在测量紫外-X光波段的超短脉冲和宽频带脉冲方面具有优势。借助数值模拟,比较了全反射相干自相关和传统相干自相关方法测量不同相位结构脉冲时信号特征的异同。利用自建的组合式自相关装置测量了钛宝石激光器输出的飞秒脉冲及经由40 mm厚BK7玻璃块展宽而成的啁啾脉冲。理论分析和实验结果表明,同一脉冲的两种自相关曲线是基本相似的,因而在传统自相关方法不适用或操作不便的情况下,可以用全反射相干自相关法来替代。     

掺钛蓝宝石激光器自锁模机制分析

掺钛蓝宝石自锁模激光器中产生自锁模的主要因素是自振幅调制（ＳＡＭ）、自相位调制（ＳＰＭ）和群速度色散（ＧＶＤ）。本文详细地分析了三要素在锁模脉冲形式的不同阶段所起的作用,指出在整个过程中自振幅调制对脉宽压缩起主要作用,而引入的适量负群速度色散在后期对ＳＰＭ效应与正ＧＶＤ起补偿作用,可获得最窄脉冲。最后,讨论了形成不稳定锁模脉冲的可能性。     

Ways to produce and measure atto- and femtosecond soft X-ray pulses

The ways to produce and measure atto-and femtosecond soft X-ray pulses are reported. The laser phase relation of high-order harmonic generation(HHG) shows two different radiation energy distribu-tions in time(or laser phase) domain. These energy-phase relations are helpful for realizing the dy-namic processes of HHG. Two presented parameterized formulas can be used to calculate the durations of the energy distributions with a bandwidth of the pulse. These formulas are useful in calculating and simulating pulses transports and interactions with mediums. The time structures of atto-and femto-second soft X-ray pulses can be directly measured with photoelectron spectrum transfer equations and the related laser phase determination methods without any previous pulse shape and the instantane-ous frequency assumptions. These equations and methods can be used to evaluate and improve the technical parameters of the ultra-short X-ray sources. They have wide measurement ranges and high time resolutions,which may enable ultra-fast measurements to reach metrological precisions,and lead to a new tide of scientific researches in physics,chemistry,biochemistry,etc. The application of atto-and femtosecond X-rays as well as the theoretical and technical problems in measurements are briefly discussed.     

非共线相位匹配飞秒脉冲光参量过程的研究

对非共线相位匹配飞秒脉冲光参量产生过程作了理论研究,计算了非共线相位匹配结构的光参量产生过程中非共线角与相位匹配角的关系,参量带宽和群速度失配参数随非共线角变化的情况.说明采用非共线相位匹配结构可以补偿泵浦光、信号光和闲频光之间的群速度失配,大大地提高飞秒脉冲光参量产生过程的转换效率.     

Ge基硫卤玻璃的形成与非线性光学性能

采用传统的熔融淬冷法制备Ge基硫卤玻璃。通过采用DSC、热膨胀、吸收光谱和Z-扫描等测试手段和技术,对该系统玻璃的物理化学性能进行了研究。结果表明该系列玻璃具有良好的玻璃稳定性(ΔT110℃)。根据Z-扫描测试原理用钛宝石飞秒激光器测试Ge基硫卤玻璃样品在开孔条件下的透过率曲线,由实验结果拟合得出样品具有较强的非线性吸收特性。该系列玻璃有可能成为全光学器件的新型非线性光学材料。