Kerr lens effects in a folded-cavity four-mirror linear resonator

The Kerr-lens model locking of a folded-cavity four-mirror linear Ti: sapphire laser is simulated by applying the ABCD ray-tracing technique for a Gaussian beam. The intensity dependent Kerr-lens ABCD matrix of the Brewster-plate shaped active medium is derived. A split-step parabolic refractive index model is used. the astigmatism compensation condition is derived from the ABCD ray-tracing. Simulations are carried out for a symmetric resonator and an asymmetric resonator design. Hard-aperture loss mode locking and soft-aperture gain mode locking are discussed. The optimum design parameters (slit position for hard-aperture loss mode locking, pump beam focusing for soft-aperture gain mode locking, gain cavity spacing, gain medium position) for Kerr-lens mode locking are determined.     

10 GHz可调谐主动锁模光纤环形激光器研究

采用主动锁模技术 ,在光纤环形激光器中实现了脉冲重复率为 10GHz、脉冲宽度为 10ps、线宽为 0 171nm的激光输出 ,波长调谐范围达 37 8nm。实验结果表明 ,主动锁模光纤激光器由于其输出脉冲窄、脉冲啁啾小、波长调谐方便及与光纤系统兼容等优点 ,有望成为未来超高速光通信系统中的理想光源。     

Ytterbium doped all-fiber-path all-normal dispersion mode-locked laser based on semiconductor saturable mirror

In this paper, we describe a compact all-fiber-path picosecond pulse based on Ytterbium doped fiber oscillator. A home-made novel SESAM mounted on fiber is reported, by which stable mode locking is obtained. The SESAM possesses the low saturation flux 20 μJ/cm² (versus prior low saturation flux 32 μJ/cm²), which effectively reduces the pump power threshold of mode locking. The fiber laser generates 15 ps pulse trains without a dispersive delay line or anomalous dispersion in the cavity. Mode locking pulse with 30 MHz basic repetition-rate was produced, with 10–30 mW scale average output power at 1064 nm. Through 60 h of uninterrupted laser operating, mode locking is steady as ever.     

用于激光冷却的半导体激光器大频差边模注入锁定的理论及实验研究

利用注入锁定技术实现了与自由运转频率相差1300?GHz的大功率半导体激光器的边模注入 锁定.实验上利用饱和吸收谱和光学外差拍方法详细研究了锁定后主从激光器之间的相干转 移特性,并测量了注入光功率与锁频范围的关系和注入锁定模式建立过程,与利用带注入项 的多模速率方程得到的边模注入锁定的范围相吻合.理论上计算了实现边模注入锁定所满足 的注入光阈值条件,并作了实验验证. 关键词：     

The general approach to mode-locking mechanism analysis for CW solid-state lasers with a nonlinear Fabry-Pérot interferometer

The effective mode locking of a CW solid-state laser with a nonlinear Fabry-Pérot interferometer with a period matched to that of the main cavity period (mode locking by additional cavity, or coupled-cavity mode locking) is considered. The main features of the ultra-short pulse generation obtained on the basis of numerical simulations in the framework of the fluctuation model are interpreted using an analysis of nonlinear reflectivity of the interferometer. A correlation between parameter ranges for effective mode locking and self-consistent solutions of the system describing the CW ultra-short pulse generation allows one to explain a discrete range character. A new mode-locking regime has been described and the influence of interferometer bistability on the mode-locking efficiency has been evaluated.     

Mode locking of argon ion laser by use of cylindrical ultrasonic waves

The phenomenon of light diffraction by a cylindrical ultrasonic wave has been investigated. The diffraction was applied in a new type of acousto-optic modulator used for laser mode locking. The paper describes the modulator and presents results on mode locking of argon ion laser. The mode locking was obtained by means of a cylindrical acoustic wave launched in water at the frequencies of ultrasound 33-34 MHz. A standing wave regime of operation of the modulator resulted in a reliable generation of laser pulses with the duration 720 ps.     

Frequency locking a laser to an optical cavity by use of spatial mode interference

We present a novel technique to frequency lock a laser to an optical cavity. This technique, tilt locking, utilizes a misalignment of the laser with respect to the cavity to produce a nonresonant spatial mode. By observing the interference between the carrier and the spatial mode one can obtain a quantum-noise-limited frequency discriminator. Tilt locking offers a number of potential benefits over existing locking schemes, including low cost, high sensitivity, and simple implementation.     

用腔内半导体可饱和吸收镜钛宝石激光器中自锁模状态的实验研究

用可饱和吸收体镜(SESAM)的掺钛蓝宝石激光器能够稳定运转在三种不同的锁模状态,即可饱和吸收体被动锁模、孤子锁模加被动锁模和KLM锁模.分析了三种自锁模的机理和SESAM的作用.对SESAM实现KLM锁模的自启动机制进行了实验观察和讨论.从该激光器的KLM锁模状态,获得了小于18飞秒的锁模脉冲序列. 关键词： 半导体可饱和吸收镜 自锁模 钛宝石激光器     

Fast, low-noise, mode-by-mode, cavity-enhanced absorption spectroscopy by diode-laser self-locking

A new technique of cavity enhanced absorption spectroscopy is described. Molecular absorption spectra are obtained by recording the transmission maxima of the successive TEM_oo resonances of a high-finesse optical cavity when a Distributed Feedback Diode Laser is tuned across them. A noisy cavity output is usually observed in such a measurement since the resonances are spectrally narrower than the laser. We show that a folded (V-shaped) cavity can be used to obtain selective optical feedback from the intracavity field which builds up at resonance. This induces laser linewidth reduction and frequency locking. The linewidth narrowing eliminates the noisy cavity output, and allows measuring the maximum mode transmissions accurately. The frequency locking permits the laser to scan stepwise through the successive cavity modes. Frequency tuning is thus tightly optimized for cavity mode injection. Our setup for this technique of Optical-Feedback Cavity-Enhanced Absorption Spectroscopy (OF-CEAS) includes a 50 cm folded cavity with finesse ∼20 000 (ringdown time ∼20 μs) and allows recording spectra of up to 200 cavity modes (2 cm⁻¹) using 100 ms laser scans. We obtain a noise equivalent absorption coefficient of ∼5×10⁻¹⁰ cm⁻¹ for 1 s averaging over scans, with a dynamic range of four orders of magnitude.     

Critical behavior of a passively mode-locked laser: rational harmonic mode locking

The critical behavior of passive mode locking has been demonstrated in a figure-eight fiber laser that performs rational harmonic mode locking (RHML). On both the repetition rate and the pulse amplitude distribution, the observed pulse trains near the threshold exhibit the same regulations as the rational harmonic mode-locked ones. The theory also shows that there should be a middle status of RHML before achieving normal mode locking. It is important to note that the results provide what we believe to be the first confirmed attempt to address a fundamental question: how does a laser become mode locking with an increase of pump power?     

一种连续Nd：YAG激光锁模的新技术

本文首次报道了在连续运转的Ｎｄ：ＹＡＧ激光器上通过移动腔镜实现锁模的实验研究。获得平均宽度为６０ｐｓ的锁模脉冲序列。文中提出了实验结果的初步解释，表明这种锁模现象是一种增强的自锁模。     

Nonlinear refractive indices of disordered NaT(XO4)2 T=Y, La, Gd, Lu and Bi, X=Mo, W femtosecond laser crystals

The nonlinear refractive index (n₂) of several NaT(WO₄)₂ (T?=?Y, La, Gd, Lu and Bi) and NaY(MoO₄)₂ femtosecond laser crystals has been measured using the z-scan technique. These tetragonal crystals with structural local disorder present significant n₂ values, which should allow their efficient laser pulsed operation by Kerr-lens mode locking, especially NaBi(WO₄)₂, 68×10^-16 cm²/W (for σ light), which is about twice than for the others. This difference is attributed to the high polarizability associated with the lone electron pair of Bi³⁺.     

Black phosphorus saturable absorber for ultrafast mode‐locked pulse laser via evanescent field interaction

Black phosphorus, or BP, has found a lot of applications in recent years including photonics. The most recent studies have shown that the material has an excellent optical nonlinearity useful in many areas, one of which is in saturable absorption for passive mode‐locking. A direct interaction scheme for mode‐locking, however, has a potential to optically cause permanent damage to the already delicate material. Evanescent field interaction scheme has already been proven to be a useful method to prevent such danger for other 2‐dimensional nanomaterials. In this report, we have utilized the evanescent field interaction to demonstrate that the optical nonlinear characteristics of BP is sufficiently strong to use in such an indirect interaction method. The successful demonstration of the passive mode‐locking operation has generated pulses with the pulse duration, repetition rate, and time bandwidth product of 2.18 ps, 15.59 MHz, and 0.336, respectively.     

Theoretical study of harmonic injection locking of millimeter wave harmonic gunn oscillators

Harmonic injection locking behavior of millimeter wave second harmonic Gunn oscillators is studied based on an equivalent circuit model. A large signal model of Gunn device in harmonic mode operation is employed. Injection locking curves of voltage amplitude and phase difference between injected current and harmonic voltage are calculated by means of describing function technique. Stability of the locked harmonic oscillators is also investigated. It is revealed that the harmonic locking bandwidth is much smaller than that of fundamental wave oscillators and is closely related to the susceptance slope parameter of fundamental wave circuit. It is also found that the stable region is smaller than that of fundamental wave oscillators. Some conclusions have been made for the application of harmonic injection locking technique.     

腔内含有多量子阱饱和吸收体的自启动锁模钛宝石激光器研究

本文报道了腔内含有多量子阱饱和吸收体的自启动锁模钛宝石激光器。该激光器输出最短光脉冲为180fs.     

注入锁定改善大口径稳定腔CuBr激光器的输出特性

报道了在稳定腔中采用注入锁定技术，钭自锁模ＣｕＢｒ激光脉冲成功地进行了注入锁定放大，得到了高平均功率的锁模铜激光脉冲，并且通过这种注入锁定，首次在稳定腔中得到了在２０ｍｍ光斑内空间高度相干的高功率铜激光辐射。     

Direct generation of a 10 GHz 816 fs pulse train from an erbium-fiber soliton laser with asynchronous phase modulation

By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.     

Diode-pumped passively mode-locked and passively stabilized Nd3+:BaY2F8 laser

Continuous-wave mode locking (CW-ML) of a diode-pumped Nd3+:BaY2F8 laser is reported for the first time to our knowledge. Pulses as short as 4.8 ps were measured with a total output power of approximately 1 W at 1049 nm, corresponding to 3.4 W of absorbed power from the pump diode at 806 nm. A novel technique for passive stabilization of CW-ML has been demonstrated.     

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.