Femtosecond Cr:forsterite laser with mode locking initiated by aquantum-well saturable absorber

We studied a mode-locked Cr:forsterite laser pumped by a diode pumped Nd:YVO₄ laser. Both the Kerr lens mode locking and the semiconductor saturable absorber initiated mode locking have been demonstrated. Using our measured dispersion data of the forsterite crystal, together with our dispersion compensation technique, we obtained 20-fs pulses for the pure Kerr lens mode locking and 36-fs pulses for semiconductor saturable absorber initiated mode locking, respectively     

Active mode locking of broadband quantum cascade lasers

Active mode locking in broadband quantum cascade (QC) lasers with a repetition rate of about 14.3 GHz has been achieved through the modulation of the laser bias current. At low driving currents, the active mode locking in broadband QC lasers resembles the active mode locking in single-wavelength QC lasers, while at high driving currents, the mode locking properties are governed by the broad spectral gain of these lasers. At high bias currents, the active modulation excites Fabry-Perot modes across the entire gain spectrum from 6.7 to 7.4 /spl mu/m, with clear evidence of mode locking. The spectral width of the optical gain in the broadband QC lasers exceeds 2 THz and indicates the potential for generating subpicosecond pulses.     

Active mode locking of lasers using an electrooptic deflector

The deflector shows excellent loss modulation characteristics in a laser cavity under large signal operation. The mode locker is capable of generating very short optical pulses comparable to those obtained by passive mode locking. In experiments, an LiTaO₃ double-prism deflector is used as the mode locker for an Nd:glass laser. As a result, stable 6-ps pulses are obtained     

A highly stable 30 W average power mode-locked Nd:YAG laser

Mode locking of a CW pumped Nd:YAG laser operating in the TEM01or donut mode using an intracavity acoustooptic AM modulator is described. Mode-locking investigations to date have concentrated on obtaining as short pulses as possible at the expense of average and peak laser output power. We describe a mode-locked system for field use having an average output of 30 W, with pulses recurring at a 100 MHz rate and having a peak power in excess of 0.5 kW. Detector limited pulses of 0.6 ns duration were recorded and the mode locking was stable for several hours requiring no feedback loop or fine adjustment.     

Optical generation of amplitude-equalized pulses from a rational harmonic mode-locked fiber laser incorporating an SOA loop modulator

Rational harmonic active and passive mode locking has been demonstrated in an erbium-doped fiber laser using an all-optical approach. Based on the modulation and the self-switching effects of a semiconductor optical amplifier nonlinear loop mirror, hybrid mode locking and pulse-amplitude equalization are simultaneously achieved in the laser. In our setup, amplitude-equalized pulse trains up to about 12 GHz are obtained at 1.55 /spl mu/m using 3-GHz optical driving pulses.     

Femtosecond pulse generation in the red/deep red spectral region

Optical pulses as short as 55 fs in duration have been generated near 675 nm in a synchronously pumped, hybridly mode-locked, sulforhodamine 101 dye laser. Hybrid mode locking of rhodamineBin the same cavity arrangement yielded 187 fs pulses at 650 nm.     

非线性放大复合环形镜及被动锁模掺铒光纤激光器的研究

提出采用两个光纤耦合器构成具有复合环的非线性放大环形镜。分析表明，改变构成非线性放大复合环形镜的光纤耦合器的耦合系数可以改变非线性复合光纤环形镜的非线性传输特性，调节非线性光反射和透射率。采用非线性放大复合环形镜与半导体饱和吸收体组成复合腔掺铒光纤激光器，获得了十分稳定的被动锁模脉冲输出，得到了重复频率为２４８ＭＨｚ的谐频锁模脉冲序列。实验表明，采用非线性放大复合环形镜构成复合腔光纤激光器，有可能获得高重复频率的锁模脉冲。     

Experimental study of additive-pulse mode locking in an Nd:glasslaser

Self-starting additive-pulse mode locking (APM) has been investigated experimentally in a continuous-wave Nd:glass laser. Stress has been put on the study of the self-starting process and relaxation oscillation instabilities. An intensity threshold for self-starting APM is observed and related to the linewidth of the first beat note of the power spectrum of the free-running laser output. Under steady-state conditions, two distinct operating regimes are obtained: mode locking with repetitive self-Q switching and pure mode locking. Increasing the intracavity power gives rise to a strong chirp developing on the mode-locked pulses and to a simultaneous disappearance of self- Q switching     

基于非线性偏振旋转锁模孤子光脉冲的产生及模拟

非线性偏振旋转(NPR)技术是被动锁模光纤激光器中实现超短脉冲的一种有效方式,因其结构紧凑,可靠性高而备受关注。本文利用基于NPR锁模的掺铒光纤激光器,在1557.7 nm波段,获得了脉冲宽度为1.35 ps,基频重复率为9.49 MHz的脉冲序列输出。利用耦合的金兹堡-朗道方程,数值模拟了激光器中锁模孤子光脉冲的产生,并对锁模建立过程中孤子时域和频域演化进行了分析,模拟分析和实验观察相吻合。该结果有助于加深人们对NPR锁模光纤激光器中孤子锁模动力学特性的理解。     

Short pulse injection seeding of Q-switched Nd:glass laseroscillators-theory and experiment

A 0.5-GW-peak-power solid-state laser source that is based on injection seeding a Q-switched Nd:Glass laser is discussed. In the first experimental demonstration, a Q-switched oscillator producing 101 mJ was seeded by a train of 11-ps pulses from a CW (continuous-wave) mode-locked laser to produce injection-mode-locked pulses under a 91-ns envelope. A theoretical analysis of injection seeding of a high-gain Q-switched oscillator by the output of a mode-locked oscillator is presented. The numerical analysis predicts the minimum signal power required for injection mode locking and the temporal shape of the output pulse. The experimental results agree well with the theoretical predictions. The amplification demonstrated by this technique is 104.4 dB, which is much greater than that demonstrated by a multipass or regenerative amplifier. The experimental advantages of injection mode locking include greater than 100 dB of effective amplification and noncritical cavity length adjustment of the seed resonator     

Picosecond and femtosecond pulse generation in a regenerativelymode-locked Ti:sapphire laser

The authors have produced transform-limited pulses ranging from 100 ps to 40 fs duration from a Ti:sapphire laser. Output powers in excess of 1 W and peak powers of 0.5 MW have been observed. They describe the technique of regenerative mode locking and present evidence that a transient with a peak power of more than 10 kW is required to initiate mode locking. The role of group velocity dispersion is highlighted and a value of -750 fs² is measured for the group delay dispersion in an operating laser. The authors describe the limits on both the power and pulsewidth obtainable from this laser and present pulse compression experiments which produce 17 fs pulses with 70 mW of average power     

High-repetition-rate optical pulse generation using a rationalharmonic mode-locked fiber laser

Rational harmonic mode locking takes place in an actively mode-locked fiber laser when the modulation frequency f_m=(n+1/p)f_c, where n and p are both integers and f_c is the inverse of the cavity round-trip time, the 22nd order of rational harmonic mode locking has been observed when f_m ≈1 GHz. An optical pulse train with a repetition rate of 40 GHz has been obtained using a modulation frequency f_m=10 GHz. The theory of rational harmonic mode locking has also been developed. The stability of the mode-locked pulses is improved considerably when a semiconductor optical amplifier is incorporated into the fiber laser cavity. The supermode noise in the RF spectrum of a mode-locked laser is removed for a certain range of current in the semiconductor optical amplifier     

采用Cr~(4+):YAG为可饱和吸收体的Nd:YAG调Q锁模

在实验上,以Ｃｒ４＋ ：ＹＡＧ为可饱和吸收体,对Ｎｄ：ＹＡＧ激光实现调Ｑ锁模,得到平均脉宽为１９０ｐｓ的脉冲序列。利用被动锁模的涨落理论,分析了Ｃｒ４＋ ：ＹＡＧ对Ｎｄ：ＹＡＧ激光调Ｑ锁模的动力学过程及各种影响因素,同时讨论了Ｎｄ：ＹＡＧ的克尔透镜效应在调Ｑ锁模过程中的作用,得到了与实验较为一致的结果。     

Active mode locking of a high-pressure pulsed N2O laser

Experimental results on the active mode locking of a transversely excited N2O laser at subatmospheric pressures are presented. Nanosecond pulses of 10.8-μ radiation were produced with typical peak-power outputs in the 100-kW range.     

Influence of saturable-absorber transmission and optical pumping on the reproducibility of passive mode locking

Following the Letokhov model for passive mode locking, which describes the buildup of ultrashort light pulses from noise, the statistical behavior of passive mode locking and the discrimination characteristics of the nonlinear absorber are examined. The probabilityWof having a second ultrashort pulse of a certain intensity within the resonator round-trip time2t_{L}is described. This probability is essentially a function of the initial dye absorption coefficient x0and a pumping parameter tpthat is a measure for the excitation rate of the optical pump. Experimental results are reported that confirm these theoretical considerations.     

Observations of spontaneous phase locking of TEM00qmodes at 0.063µ

Two types of spontaneous phase locking of the TEM00qmodes at 0.63μ have been observed for a mixed isotope tube (Ne²⁰, Ne²⁰). In both cases the mode locked laser output consisted of pulses which were less than 1 ns in duration. The pulse repetition frequencies werec/2Landc/Lfor the two types. Adjacent mode competition appears to play a role in determining which type occurs. The persistence of the self-locking was adversely affected by simultaneous 3.39μ oscillation. The mode power spectra for the self-locked configuration revealed a dip close to the center of the gain curve. The mode power spectra for the self-locked and the free-running situations were shifted to the high-frequency side of the gain profile, and for a mixed isotope tube this can be accounted for by an asymmetric gain curve. For a pure isotope tube (Ne²⁰) only one type of self-locking was observed, and the power spectra for the self-locked and free-running configurations were shifted to the low-frequency side of the gain curve. On the basis of the experiments performed, it proved possible to calculate the magnitude of the third-order nonlinear susceptibility of the active medium at 0.63μ which, it is believed, was responsible for the spontaneous mode locking. The possibility of employing nonlinear crystals as passive mode locking devices was examined and it was found that the effect required for locking for a piece of deuterated KDP 3 cm in length and placed within the optical cavity was ∼ six orders of magnitude too small.     

Parametric mode locking

The conditions under which a synchronously pumped intracavity parameter generation causes mode locking in a homogeneously broadened laser are investigated experimentally and theoretically. An expression for the steady-state duration of parametric mode-locked pulses is derived and compared with experimental results. Contributions from both parametric AM and FM mode locking are included, and the conditions to optimize pulse narrowing, frequency upconversion, and active dispersion compensation are determined and discussed