Broadband spectral shaping in a Ti:sapphire regenerative amplifier

A birefringent crystal quartz plate of known thickness has been used as a spectral filter for spectral shaping in a Ti:sapphire regenerative amplifier. The spectral profile of the amplified pulse ejected from the regenerative amplifier was observed while adjusting the birefringent crystal plate in the cavity. By altering the gain spectrum, the bandwidth of the regeneratively amplified pulse was increased from 18 to 35 nm by using a 0.34-mm thick birefringent plate. The output pulse spectrum from the regenerative amplifier neared the bandwidth of the seed pulse. As a comparison, we used a coated filter outside the regenerative amplifier cavity, and the bandwidth of the regeneratively amplified pulse was stretched to 28 nm. When the bandwidth was stretched to 35 nm, the pulse was compressed to 35 fs.     

大色散稳定腔长的光纤锁模激光器的锁模特性研究

报道了一种新型的采用大色散腔结构的光纤锁模激光器,它可以有效地克服激光器腔长抖动对锁模的不良影响,同时,实验中发现,该结构对超模噪声也有很好的抑制作用。完成了大色散控制,电光调制器调制的,稳定的光纤锁模激光器实验,得到形状为sech^2的光脉冲输出,脉冲宽度为7.6ps,脉冲带宽积为0．335。     

High-resolution cavity-tuned ringdown spectrometer using a narrow-bandwidth pulsed laser source

A novel method of cavity ringdown spectroscopy is proposed to achieve high spectral resolution with tunable narrow bandwidth pulsed lasers. We demonstrate a cavity-tuned ringdown configuration in which only a single cavity mode is kept excited near the carrier frequency of a narrow bandwidth pulse laser. This is done simply by making a cavity resonance actively track the frequency reference served by the cw injection seed of the pulsed laser source. We present the servo mechanism used in the cavity resonance tracking, reliable procedures for transverse mode matching, and the evidence of single longitudinal mode excitation. The spectrometer performance is tested to record weak molecular overtone features of acetylene around the wavelength of 570 nm, showing cavity tracking stability within 5-MHz uncertainty which overcomes the bandwidth limit of pulsed laser sources itself. PACS 42.62.Fi; 42.60.Da; 33.20.Kf     

Generation, measurement and optimization of a variable duration, short pulse, mode-locked cavity-dumped Nd:YAG laser

Spectral and temporal measurements undertaken on a single picosecond laser pulse from a flash lamp pumped, cavity dumped, active/passive mode-locked Nd:YAG laser are presented in this paper. Optimization of several parameters of the resonator cavity produced a single pulse with 0.7 mJ energy and 10² contrast. The pulse duration was variable from 24 to 120 ps by using intra-cavity etalons of different thicknesses. The pulse width and spectrum of the pulse were simultaneously measured using a second harmonic autocorrelator and a spectrometer. The time bandwidth product was 0.445, which is close to theoretical limit for a bandwidth limited pulse.     

Pulse Evolution Characteristics in Self-Similar Mode-locked Fibre Laser

A self-similar mode locked fibre laser is studied based on a numerical model. By introducing a dimensionless factor k to characterize the pulse shape, the self-similar pulse evolution, formation and the temporal and spectral shape changes due to the elements in the cavity are investigated throughout the laser cavity. The results show that in the self-similar mode locked fibre laser, self-similar pulse is first formed in the single-mode fibre, which is then amplified in the gain fibre. Gain bandwidth has a small influence on pulse shape, so high energy self-similar pulse can be obtained after amplification. Because net cavity dispersion directly influences the pulse width as well as peak power after compression by a pair of gratings, which can determine the pulse self-similar evolution, it is very important to control the net cavity dispersion to a certain range to obtain self-similar pulses.     

滤波位置相关的全正色散掺Yb3+锁模光纤激光器的实验研究

采用非线性偏振旋转锁模,构建了一种全正色散掺Yb³⁺光纤环形激光器.在该激光腔内采用了10 nm带宽的光纤滤波器提供附加的自振幅调制.通过改变滤波器在腔内的位置,实验证明了滤波器位置对高啁啾脉冲的整形过程起到重要的作用.在320 mW的抽运功率下,最终获得平均功率为922 mW,脉冲重复频率为266 MHz,脉冲宽度为62 ps的稳定脉冲输出,单脉冲能量达35 nJ的优化结果.通过数值模拟与实验结果的验证表明,两者相符很好. 关键词： 锁模光纤激光器 全正色散 滤波效应 高啁啾脉冲     

Passive compression of microwave pulses with a bounded spectrum by a nonreflective cavity

The effect of the bandwidth of a microwave pulse on the efficiency of its compression by a nonreflective cavity is considered as applied to linear accelerators. In the case of a Gaussian pulse, it is shown that the optimal time dependence of the phase approaches the quadratic dependence upon a decrease in the bandwidth.     

Spectral filtering for mode locking in the normal dispersive regime

A theoretical model that characterizes the physical process responsible for generating ultrashort, high-energy, mode-locked pulses in a normal-dispersion laser cavity with strong spectral filtering is developed. According to this model, two of the critical physical parameters used to achieve optimal performance are the ratio of the filter bandwidth to the gain bandwidth and the placement of the output coupler in the laser cavity. The spectral filtering plays a crucial role in maintaining a short pulse duration with high energy. This phenomenon is generic to mode locking with normal dispersion.     

非线性偏振旋转锁模自相似脉冲光纤激光器的研究

利用耦合非线性薛定谔方程（CNLSE）为非线性偏振旋转（NPE）锁模自相似光纤激光器建立了一种新的数值模型.模型中,用CNLSE描述脉冲在单模光纤中的传播,在增益光纤中同时考虑了增益带宽和增益饱和作用,用传输矩阵描述构成NPE锁模的光学元件.优化了腔内净色散和光纤长度等参数,模拟了脉冲在激光腔内的演化特性,得到了典型的自相似脉冲运行区域及特点.在最佳自相似脉冲运行区域内,得到了能量约为7 nJ、脉宽约11 ps、线性啁啾的抛物脉冲.比较了不同腔内净色散条件下输出脉冲的特点,给出了三阶色散对输出脉冲的影响. 关键词： 自相似脉冲 非线性偏振旋转锁模 耦合非线性薛定谔方程 数值模拟     

A self-quenching picosecond distributed feedback dye laser pumped by a picosecond laser pulse

A tunable single short pulse laser system with a transform–limited bandwidth pumped by a picosecond Nd:YAG laser (ca. 120 ps pulse width) is demonstrated. With this configuration, the relaxation oscillations coming from a distributed feedback dye laser cavity are completely removed. Because the pumping pulsewidth is shorter than the lifetime of dye molecule on the upper laser state, the gain of the laser medium is depleted by the first pulse. The laser wavelength could be precisely tuned with the transform-limited bandwidth (for example, a linewidth of 0.02 nm). After amplification, we obtain a single short laser pulse energy up to 500 μJ at the pulsewidth of 8.2 ps.     

Ti:sapphire Regenerative Amplifier at 1.056 μm

The design and performance of a Ti:sapphire regenerative amplifier operating at 1. 056 μm are described. A laser pulse with an initial pulsewidth of 100 fs is amplified to ≥1.5 mJ in the amplifier after firstly stretched to 850 ps. The amplified pulse can be re-compressed to ～300 fs with energy of ～1 mJ. Loss of the spectrum happens in the regenerative cavity since bandwidth of the coat of optics in the cavity is not enough adequate.     

宽谱窄脉冲高功率微波产生的初步研究

为了探索短电脉冲产生高功率微波技术,采用理论和粒子模拟方法分析了短电脉冲(脉宽不大于30ns)驱动S波段相对论扩展互作用腔振荡器(REICO)产生高功率宽谱的技术可行性,开展了原理性的实验验证。采用Marx发生器产生的前沿15ns、后沿30ns、电压560kV、束流2.8kA的类三角形电子束脉冲激励REICO,模拟产生了410MW、脉宽8ns、相对瞬时带宽2.7%的微波,实验输出了160MW、脉宽10ns、中心频率2.75GHz、瞬时相对带宽2.8%的高功率微波。     

980-nm all-fiber mode-locked Yb-doped phosphate fiber oscillator based on semiconductor saturable absorber mirror and its amplifier

A 980-nm semiconductor saturable absorber mirror(SESAM) mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 m W and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-m W maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission(ASE) nor harmful oscillation around 1030 nm is observed. Moreover,through a two-stage all-fiber-integrated amplifier, an output power of 740 m W is generated with a pulse width of 200 ps.     

Environmentally stable picosecond Yb fiber laser with low repetition rate

A SESAM-mode-locked, all-polarization-maintaining Ytterbium fiber laser producing picosecond pulses with narrow spectral bandwidth is presented. A simple linear all-fiber cavity without dispersion compensation is realized using a uniform fiber Bragg grating (FBG). Different cavity lengths are investigated and repetition rates down to 0.7 MHz are obtained. Bandwidth and pulse duration of the output pulses are mainly determined by the choice of FBG. Pulses between 30 and 200 ps are generated employing different FBGs with bandwidths between 17 and 96 pm. The experimental results are in good agreement with numerical simulations. The laser holds great potential for simple amplification setups without pulse picking.     

147 fs碳纳米管倏逝场锁模全光纤掺铒光纤激光器

利用化学腐蚀法在光纤包层表面成功制备了调制深度为3.9%的单壁碳纳米管饱和吸收体.组建了环形腔结构的全光纤掺铒光纤激光器,以制备的单壁碳纳米管薄膜为锁模元件,利用倏逝场锁模实现了锁模输出.锁模脉冲的中心波长为1556 nm,3 dB光谱带宽为24 nm,脉冲宽度为147 fs,重复频率为150 MHz.在520mW抽运功率下,平均输出功率为21 mW,相应的单脉冲能量为0.14 nJ.     

远红外自由电子激光器脉冲结构

 采用整体数值模拟方法，研究了中物院远红外自由电子激光装置的起振和脉冲结构。给出了为克服激光呆滞效应起振所需的腔长失谐值，腔长调节精度和调节范围。预计了装置的增益、功率、脉冲宽度和谱线宽度等重要参量。研究了不同腔长失谐值下光脉冲结构的变化。     

滤波对8字腔掺铒光纤激光器锁模运转的影响

构建了基于损耗非对称非线性光学环镜的8字腔掺铒光纤锁模激光器,并讨论了腔内滤波带宽对腔内脉冲演化和激光器输出特性的影响.在非线性光学环镜中引入双向输出耦合器,耦合器和传输光纤位置的不对称产生非互易性,实现锁模运转.利用自制的可调谐滤波器实验研究了滤波带宽对激光器的影响.当滤波带宽为2.1 nm时,腔内脉冲的演化过程受滤波和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲半高全宽分别为583.7fs和2.94 ps.随着滤波带宽增大,滤波的作用逐渐减弱,激光器两路输出脉冲参数逐渐接近,并接近傅里叶变换极限脉冲.当滤波带宽较大时,腔内脉冲的演化过程受增益谱和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲均为变换极限脉冲,半高全宽约为440 fs.通过调节滤波器中心波长实现了对激光器输出脉冲光谱的连续调谐,调节范围大于30 nm.     

Continuous-wave mode-locked solid-state lasers with enhanced spatial hole burning

We systematically investigate the difference between both actively and passively mode-locked lasers with Gain-at-the-End (GE) and Gain-in-the-Middle (GM) at the example of Nd:YLF lasers. The GE laser generates pulse widths approximately three times shorter than a comparable GM cavity. This is due to enhanced Spatial Hole Burning (SHB) which effectively flattens the saturated gain and allows for a larger lasing bandwidth compared to a GM cavity. We first investigate enhanced SHB by measuring the cw mode spectrum, where we have observed that the mode spacing in GE cavities depends primarily on the crystal length. This was also confirmed for a Nd:LSB crystal, where the pump absorption length was significantly shorter than the crystal length. In mode-locked operation, pulse widths of 4 ps for passive mode locking and 5 ps for active mode locking are demonstrated with GE cavities, compared to 11 ps for passive and 17 ps for active mode locking with GM cavities. Additionally, the time-bandwidth product for the GE cavity is approximately twice the ideal product for a sech² pulse shape and cannot be improved by dispersion compensation alone, while the GM cavity has nearly ideal time-bandwidth-limited performance. The results for the GM cavity compare well to existing theories taking into account the added effect of pump-power-dependent gain bandwidth which increases the bandwidth of Nd: YLF from 360 to > 500 GHz. In a following paper [1] (called Part II) a rigorous theoretical treatment of the effects due to SHB will be presented.     

Theory of synchronously pumped dye lasers

An analysis of cw synchronously pumped dye lasers is presented. Under the assumption that the cavity (tuning element) bandwidth is much wider than the bandwidth of the transform limited pulses generated, the pulse forming dynamics is rigorously treated. It is shown that for a finite mismatch between the lengths of the dye and the pump lasers, a steady-state pulse develops in the dye laser cavity with a conserved pulseshape. The characteristics (energy, shape, peak power, duration) of these pulses of ultimate width are quantitatively determined as a function of cavity mismatch. An analytical solution for the pulse envelope is determined, which yieldsI(t)∝Sech²(t/t _p ) to a good approximation.     

On the pulse width of synchronously pumped lasers

The pulse width of a synchronously pumped laser chiefly depends on the available cavity bandwidth and the pump-pulse duration. A functional form of this dependence was suggested in the literature. We present an alternate relation which is supported by analytical and numerical results, as well as by experimental results, obtained by us and by others.