瞬态同步泵浦锁模腔长负失谐现象的观察

用主被动锁模Nd:YAG倍频脉冲序列作泵浦源,研究了仅有十二次调制的瞬态同步泵浦锁模若丹明激光脉冲的时间特征,着重观察了瞬态同步泵浦锁模染料激光器的腔长负失谐情况,发现腔长负失谐下激光脉冲呈双峰结构,双峰间距和次峰大小均与失谐量成正比。当腔长     

泵浦抽空状态下的同步泵浦光学参量振荡器

用计算机数字模拟了Nd:YAG锁模激光器倍频光同步泵浦下LiNbO_3光学参量振荡器的脉冲形成过程。泵浦抽空状态下,输出信号脉冲序列中各脉冲的波形与宽度各不相同,起始脉冲窄(～7微微秒),后面脉冲宽(～20微微秒)而且有亚结构。腔长失谐主要降低输出能量,对脉冲加宽作用不大。器件增益对脉冲波形、宽度和腔长失谐量均有影响。     

泵浦功率对同步泵浦激光器输出脉冲的影响

在理论和实验上研究了腔长固定情形下泵浦功率对同步泵浦激光器输出脉冲的影响。证明最佳锁模腔长与泵浦功率有关。     

同步泵浦锁模染料激光器

所用泵浦方式是纵向激励,泵浦源是被动锁模磷酸盐钕玻璃激光(1.054微米)的二次谐波(0.527微米),脉宽5～7微微秒,0.527微米的脉冲序列,能量为7.5毫焦耳,KDP二次谐波转换效率为40%.染料激光器是准共心腔,腔长1.4米,若丹明     

基于内腔的调Q锁模光参量振荡器的研究

为了实现内腔型光参量振荡器（OPO）的调Q锁模脉冲输出,通过设计并匹配OPO谐振腔和基频激光腔的腔长,满足了同步泵浦条件,最终在实验上得到了信号光的调Q锁模输出;在实验中,采用氙灯泵浦Nd:YAG作为基频激光,以KTP晶体为非线性转换介质,采用电光开关作为调Q手段,测量了OPO的近红外信号光的输出波形、输出能量、光谱构成等输出特性。在泵浦能量12.8 J、调制频率20 kHz时,得到了锁模深度为100%的信号光输出,并发现信号光锁模脉冲重复率依赖于基频激光;得到了调Q锁模信号光输出能量随泵浦能量、电光调制频率的变化关系。     

用非线性附加耦合腔来产生超短脉冲的实验研究

本文对在非线性附加耦合腔中加KTP倍频晶体来锁定脉冲Nd:YAG激光器模式进行了系统的实验研究,给出了主腔与附加腔之间的腔长失谐度,KTP晶体所放位置,激光器工作电压以及腔镜的反射率等参量与锁模激光输出特性之间的关系曲线。在     

易于开启和维持自锁模的适度失谐腔克尔介质自锁模激光器

提出工作于谐振腔适度失谐时的克尔介质自锁模激光器易于开启和维持自锁模的理论。根据克尔镜锁模原理和动态可饱和高斯增益特性，利用激光传输矩阵理论，对系统进行了数值模拟计算，确证了最佳腔镜失谐角的存在．结论与已有的实验结果相符，并对它们赋予了新的合理解释。     

国内外简讯

2808～3150(?)连续可调谐微微秒激光器安徽光机所利用该所研制的SJ-2型主被动锁模重复率YAG激光器的基波(1.06μm)经一级放大后,通过铌酸锂晶体倍频获0.53μm锁模脉冲序列,再由此同步泵浦染料激光器获得稳定的5547～6543(?)连续可调微微秒光脉冲。染料Rh6G、RhB、RM01均分别溶于无水乙醇,浓度的配比通过自制透过率测试仪确定。激光器腔长为泵浦光源腔长的一半,较等腔长结构者具有腔内损耗小、输出强度高等优点。调谐元件为ZF_6棱镜和光栅。调谐输出的脉冲序列间隔     

钛宝石激光器的多模式运转

在一台双光束泵浦的钛宝石激光器中实现了可调谐连续输出、独立自锁模、交叉锁模和多脉冲模运转式。分析了可调谐连续输出模式下两个激光腔的增益竞争,研究了飞秒和皮秒激光腔内的群速弥散、自相位调制、交叉相位调制以及自振幅调制。结果表明,可调谐连续输出模式下两个激光腔的输出主要取决于泵浦激光的功率,独立自锁模工作模式下,群速弥散和自相位调制决定了自锁模的稳定性;交叉锁模工作模式下,交叉相位调制是影响飞秒和皮秒脉冲之间同步性的主要因素。多脉冲工作模式下,脉冲自相关曲线的测量结果表明,飞秒脉冲仍然是单脉冲,而皮秒脉冲分裂为3个次脉冲。     

基于宽带高反镜色散补偿的高功率克尔透镜锁模飞秒激光器

半导体激光器泵浦的高功率飞秒激光器在工业加工和生物医学等领域中均发挥着重要的作用。一般而言，无论是被动锁模飞秒激光器还是克尔透镜锁模飞秒激光器，都需要在腔内引入一定的负色散平衡自相位调制，产生稳定的飞秒孤子。特别是随着平均功率的增加，腔内自相位调制增强，需要更多的负色散量进行平衡。常用的色散补偿器件有棱镜对、啁啾镜以及GTI(Gires-Tournois interferometer)镜等，棱镜对导致振荡器结构复杂，而啁啾镜和GTI镜的价格较为昂贵。实现了基于宽带高反镜色散补偿的高功率克尔透镜锁模运转，在泵浦功率为18 W时，利用Yb∶CYA晶体获得了平均输出功率为3.6 W、脉冲宽度为92 fs、100 min功率稳定性均方根值（RMS）为0.46%的稳定锁模脉冲，有利于进一步降低高功率飞秒激光器的成本。     

Active harmonic modelocking of an erbium fiber laser withintracavity Fabry-Perot filters

We present both experimental and theoretical investigations of the operation of a harmonically modelocked erbium fiber ring laser stabilized by an intracavity bit-rate etalon. Our model analyzes the effects of cavity components and operating parameters on laser stability and output pulse characteristics. The model predicts the output pulsewidth variation with laser cavity parameters such as cavity length, dispersion, and finesse of intracavity Fabry-Perot etalons. If the laser cavity length is not optimized, a maximum 50% increase in pulsewidth can occur at 5 Gb/s pulse rate. A repetition rate etalon with a finesse of 50 is sufficient to provide a side-mode suppression ratio of over 50 dB in the laser output. We also discuss how detuning from the optimal modulation frequency increases the excess noise that affects the laser stability. The theory predicts a maximum detuning range of ±100 kHz, which agrees with the experimental observations. These theoretical results can guide the design of similar lasers over a wide range of operating parameters     

Theory of active mode locking of a semiconductor laser in an external cavity

An analytical treatment is given for the active mode locking of a semiconductor laser in an external resonator. The width of the mode-locked pulses is obtained as a function of the laser and cavity parameters and the amount of frequency detuning. The effects of self-modulation and saturation are included in the treatment. The pulse output is compared with that obtained by a strong modulation of the laser diode with no external cavity.     

Theory of timing jitter in actively mode-locked lasers

An analysis of the pulse-to-pulse timing jitter in an actively mode-locked laser is presented. The model includes spontaneous emission noise, mode-locker driver phase noise, and cavity length detuning. Analytical expressions for the laser pulse train phase noise spectrum, the intensity power spectrum, and the RMS timing jitter are given. The timing fluctuations are characterized by a time constant proportional to the cavity round-trip time times the number of locked modes squared divided by the modulation depth. The contribution from the mode-locker driver phase noise will dominate unless high-stability RF sources are used. The residual timing jitter due to spontaneous emission noise is very sensitive to cavity detuning     

The Michelson resonator free-electron laser. II. Supermodestructure and mirror detuning effects

For pt.I, see ibid., vol.29, no.2, p.452-64 (1993). Conventional mode-locked laser theory is applied to the longitudinal mode structure in an RF linac-driven Michelson resonator free-electron laser (FEL). A greatly simplified derivation of the small-signal small-gain FEL coupled mode equations is obtained. These equations are solved numerically in the frequency domain to study the supermode evolution in the presence of mode dependent cavity losses. The results are compared with simulations of the detuned Michelson resonator FEL using a pulse propagation code based on the Maxwell-Lorentz equations of motion. Increasing the interferometer detuning broadens and shifts the cavity detuning curve, narrows the supermode spectrum, and decreases the hypermode decay rates. The practical consequences of each of these effects are discussed. A simple theory describing the dependence of the hypermode decay rates on interferometer detuning, in which the decay rates are abruptly decreased beyond a critical detuning that depends primarily on the slippage length, is outlined     

Pulse-train stability in high bit rate intracavityfrequency-modulated Er-Yb laser transmitters

The stability of pulse trains at 2.5 Gbit/s generated by Er-Yb:glass laser transmitters operated in frequency modulation and frequency modelocking regimes is comparatively analysed. Bit error rate measurements show a stability enhancement against cavity length detuning by a factor of ~7 when the laser is operated under asynchronous frequency modulation     

Picosecond optical pulse generation from mode-locked phased laser diode array

Actively mode-locked 26 ps optical pulses are generated from a gain-guided, 10-stripe, phased laser GaAs diode array with an external cavity consisting of two cylindrical lenses and a corner reflector. To our knowledge, this is the shortest pulse width yet demonstrated from a mode-locked phased laser diode array. The detuning bandwidth of the mode-locking is measured as 2.5 MHz.<>     

Cavity length detuning characteristics of the synchronously mode-locked CW dye laser

We present both theoretical and experimental details on the effects of cavity length deturning of the synchronously mode-locked CW dye laser. The theory predicts an increase in cavity length sensitivity with intracavity bandwidth, and an asymmetric variation in the pulsewidth and pulse power with length detuning from the "matched" position. The predictions are shown to be in close agreement with the results of our experiments on the Rhodamine 6G dye laser.     

Theory of dynamical relaxation oscillations and frequency lockingin a synchronously-pumped laser diode

It is shown that the rate equations for the plasma density and the light intensity, together with a delayed feedback of the light in the external resonator, can be used to describe the nonlinear dynamics of actively mode-locked laser diodes. In particular, the relaxation oscillations of the laser intensity and the plasma density around the stationary pulse solutions are calculated for a laser diode in a long resonator with a periodically pulsed pump current. For small negative detuning between the round-trip period and the pump period, slow dynamical relaxation oscillations that give rise to megahertz-sidemodes in the intensity correlation spectrum occur. For larger negative detuning the delayed feedback gives rise to a frequency locking between the light pulse frequency and the modulation frequency     

Self Q switching of a CW mode-locked Nd:YLF laser bycavity length detuning

The cavity length of a CW mode-locked Nd:YLF laser is detuned to investigate the effect of detuning on the output of the laser. Negative detunings of 0.4 to 2.4 μm result in periodic modulations of the pulse envelope. Further negative detunings of 2.4 to 3.4 μm produce undamped regular spikings, that is, stable self-Q-switching behavior with mode-locked pulses of 30~47 ps pulsewidths, which are as short as those of plain mode locking without Q switching. Similar self-Q-switching behavior is also produced by positive detunings, but the stability is very poor     

Superradiant short-pulse propagation in the free-electron laseroscillator

A numerical study has been made of free-electron laser oscillators in which the electron pulse length is comparable to the slippage. It is shown that the saturated optical pulse exhibits superradiant spiking behavior in which the peak power is proportional to the square of the current and the efficiency grows in proportion to the square root of the current. The authors investigate the optimum cavity detuning length necessary to beat the lethargy in the small-signal regime and to obtain maximum overlap between the optical and the electron pulses during every bounce of the radiation within the optical cavity