Forced and spontaneous phase locking of the transverse modes of a He-Ne laser

Forced and spontaneous phase locking of the transverse modes of a He-Ne laser have been observed in the form of a scanning fundamental beam. Scans of about four resolvable spots were obtained by locking approximately seven modes with a tilting mirror modulator. With careful alignment of the laser, spontaneous locking of the scanning beam type was also observed.     

Amplified spontaneous emission and carrier pinning in laser diodes

Theoretical and experimental results for the temperature dependence of amplified spontaneous emission (ASE) in laser diodes (LDs) and light-emitting diodes (LEDs) are presented. The theoretical model takes into account conduction band nonparabolicity and band-gap renormalization. The gain spectrum is calculated from the theoretical spontaneous emission spectrum, and both compare very well with experimental data. From a fit to the observed temperature dependence of ASE for an LED and the gain spectrum for an LD with a structure identical to that of the LED except for mirror reflectivity, it is possible to establish carrier density as a function of injection current for both devices. It is shown that photons fluctuating into cavity modes give rise to substantial subthreshold carrier pinning in laser diodes. These fluctuations extract an extra current from the device and play an increasingly important role with increasing temperature     

Role of spontaneous emission in the dynamics of mode locking by synchronous pumping

Numerical simulations tracing the pulse evolution in the case of mode locking by synchronous pumping are presented. It is argued that strictly steady-state pulses are impossible in principle because the wings of the pulses are embedded in background radiation generated by spontaneous emission. The simulations demonstrate that the perturbations introduced by the stochastic background can be severe, and that these can apparently be minimized only at the expense of the overall quality of the mode-locked pulse envelopes.     

铜蒸气激光器中的放大自发辐射研究

图1是振荡-放大装置的示意图。振荡器和放大器均由平均输出功率为25W的铜蒸气激光器组成。放电管采用φ=35mm,ι=1100mm的陶瓷管。振荡器采用非稳腔输出,以保证放大器的注入光具有良好的方向性。用一台主脉冲信号发生器发出的信号同时控制二台或     

Fractional spontaneous emission coupled into AlGaAs laser mode

Spontaneous-emission power coupled into laser modes in AlGaAs double-heterostructure lasers is evaluated experimentally. The power fraction is proportional to V?1.5.     

Amplified spontaneous emission (ASE) in laser oscillators and amplifiers

Dye-laser oscillators and amplifiers are studied theoretically with inclusion of amplified spontaneous emission (ASE). Assuming pencil-like geometry in both cases, laser signal intensity and ASE intensity are described with appropriate photon-transport equations. In particular, there exist different boundary conditions fox both fluxes in the laser cavity case due to the different feedback behavior of an optical resonator for laser modes and ASE modes. The interaction of laser output and ASE intensity is discussed in detail, including laser output optimization without and with ASE effects. For single- and double-pass amplifiers closed-form solutions for gain saturation due to input signal and ASE flux axe also given. More complicated gain functions, such as inclusion of reabsorption in dye lasers, are also treated in some detail.     

Amplified spontaneous emission in narrow-band pulsed dye laser oscillators--Theory and experiment

We have investigated the effect of amplified spontaneous emission (ASE) on the spectral and temporal characteristics of narrow-band pulsed dye laser oscillators. The space and time dependent rate equations for the molecular populations and photon fluxes have been solved numerically to study the dependence of ASE on various laser parameters and the effects of ASE on the spectral and temporal profile of the dye laser output. To account for the diffraction losses present in a real dye laser oscillator, appropriate feedback factors for the laser and ASE photon fluxes were introduced into the boundary conditions for the oscillator. These theoretical results have been substantiated by experimental measurements of ASE in a narrow-band pulsed dye laser oscillator. We show that a considerable reduction of ASE in a grazing incidence grating dye laser oscillator can be obtained by appropriately shaping the pump pulse. Oscillations observed in the temporal output of pulsed dye lasers are also discussed.     

磷酸盐光波导激光器放大自发辐射的理论研究

系统地研究了Er3 :Yb3 共掺磷酸盐玻璃波导的性质,在稳态情况下建立并求解速率方程.利用数值分析的方法模拟了980nm二极管激光器抽运时激光器的放大自发辐射(ASE)特性.模拟时用到的主要参数为:信号光的散射损耗α(1530)=8.2×10-2dB/cm,980nm时Yb3 的吸收和发射截面积分别为5.4×10-25m2和6.9×10-25m2,980nm时Er3 的吸收和发射截面积分别为1.65×10-25m2和1.21×10-25m2,Yb3 -Er3 间的能量传递系数为1.9×10-23m3/s,共谐上转换系数为8.09×10-25m3/s.     

提高二极管激光阵列外腔锁相效率的实验研究

采用1/4 Talbot外腔实现宽条二极管激光阵列的锁相,在工作电流是35 A时,获得7.56 W的锁相输出功率,输出光束的远场图像是多瓣结构,锁相前后输出光的光谱宽度从2.0 nm压缩到0.2 nm。腔内插入焦距大约为5倍腔长的柱透镜,在相同电流下获得8.75 W的锁相输出功率,输出光的远场图像是多瓣结构,输出超模的数目有所减少,能量向中部集中,输出光的光谱宽度是0.2 nm。     

被动锁相光纤激光相干组束的研究进展

被动锁相光纤激光相干组束是实现大功率、高质量光纤激光输出的有效手段之一。介绍了外腔法、全光纤自组织法、倏逝波耦合以及相位共轭法四种组束方案的原理,综述了被动锁相光纤激光相干组束技术的研究进展,分析了四种组束方案的发展前景。     

静电摇摆器自由电子激光的自发辐射

基于静电摇摆器中电势场的一种典型二维模型 ,在小振幅振动情况下讨论了相对论电子束在其中的运动规律 ,计算得到了该类型自由电子激光的自发辐射谱。上述结果与平面磁摇摆器有类似的形式     

Sideband evolution from spontaneous into amplified emission in a free electron laser

A theoretical study of the evolution of sidebands, originating from large-scale (nonlinear) oscillations in the electron dynamics, is reported for a combined wiggler and guide field system operating near magnetoresonance. These sidebands, already existent in the spectrum of spontaneous emission, are followed up through small signal gain computations, and are finally recovered in the simulations of the nonlinear saturation process. A comparison with a radiation spectrum of an experiment done at the Naval Research Laboratory (NRL) shows good agreement. This indicates that the sidebands, observed in the experiment at saturation power level, are essentially due to the specific structure of the spectrum of spontaneous emission.     

ANGULAR SPECTRUM PROPERTY OF SPONTANEOUS EMISSION IN A TWO-DIMENSIONAL UNDULATOR FREE-ELECTRON LASER

The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l=s, so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively.     

On the "Excess spontaneous emission factor" in gain-guided laser amplifiers

Petennann [1] computed an "excess spontaneous emission factor" for gain-guided laser. In this paper, we investigate further the role of this factor. Such a factor also appears in the treatment of thermodynamic equilibrium in an attenuating medium-a seeming paradox. Further investigation shows that the excess spontaneous emission excitation at thermal equilibrium is cancelled by the excitations in the other modes which are correlated with that in the fundamental mode. In a medium with gain, cancellation also occurs in a short amplifier in which there is no gain discrimination among modes. The "excess spontaneous emission factor" is fully present only in a system in which the different higher order modes have an appreciably smaller gain than the lowest order mode, a high gain amplifier. An analysis of the signal-to-noise ratio of a high gain amplifier reveals that the excess noise factor can be fully compensated by proper input excitation by a lens arrangement. The lens arrangement provides the signal with an "excess gain" factor. An "excess gain" factor is also present when a thermal source is used.     

Equivalent circuit theory of spontaneous emission power insemiconductor laser optical amplifiers

An equivalent circuit model for a semiconductor laser amplifier (SLA) has been developed. This model can be used with a transfer matrix method (TMM) to analyze the performance of a SLA. The validity of the model is explored in this paper by analyzing the spontaneous emission noise power in a Fabry-Perot SLA with a uniform distribution of material gain coefficient. The result is found to be identical with that derived by the Green function approach. The physical reasons for the validity of the equivalent circuit model are also discussed, and possible further applications of the model are suggested     

Analysis of the spontaneous emission of a tunablephase-shift-controlled DFB laser filter

Using a transfer matrix method, the results of analysis of the spontaneous emission spectrum of a three-section phase-controlled distributed feedback (DFB) laser for implementing a continuously tunable optical filter are presented. The influence of various parameters-net field gain, coupling coefficient, phase shift and reflection coefficients-on the spectrum behavior are studied theoretically. The main-to subtransmission peak magnitude ratio can be chosen while varying the frequency, which demonstrates the tunability of the three-section phase-controlled DFB laser filter. Analysis shows that a three-section DFB laser (a passive phase shift control region between two DFB structures) presents a single-mode spontaneous emission spectrum operating over a wide continuous tuning range of less than 1 nm     

Coherent laser radar in Europe

European work in coherent laser radar with 10 μm and shorter wavelength lasers is reviewed. Fundamental aspects include heterodyne studies of signal statistics and fluctuations, and detailed experimental and theoretical work on signal amplification and autodyne arrangements with light reinjected into the laser cavity. Progress with lasers, detectors, and modulators has led to the development of several compact robust field systems both continuous-wave and pulsed. Various ground-based programs are described including local wind field measurement and wake vortex investigation at airfields, and study of range, image, and Doppler shift of hard targets. Airborne systems have investigated avionics problems of true airspeed, pressure error, and wind shear warning. Other airborne studies include ground imaging, obstacle warning, terrain following, and a compendium of atmospheric backscattering over the North and South Atlantic. In recent years, the European Space Energy has supported studies and technology development for a space-borne wind lidar in the Atmospheric Laser Doppler Instrument (ALADIN) program     

Observations of spontaneous phase locking of LiNdP4O12lasers

Spontaneous or self-locking effects of the TEM00mode at 1.05 μm have been observed for an LiNdP4O12(LNP) laser. Pulse repetition frequency was 600 MHz, corresponding toc/2L(c: light velocity,L: cavity length). The effect of low-frequency resonance on self-locking is also discussed experimentally.     

Threshold for spontaneous mode locking in Q-switched lasers

An expression for the threshold output power density for spontaneous mode locking inQ-switched lasers is derived. The resulting expression is readily evaluated in terms of laser emission cross section and linewidth and cavity geometry. The expression is evaluated for several experiments which previously reported spontaneous mode locking.     

On spontaneous emission

The problem of the spontaneous emission from a single excited two-level atom in the presence of N unexcited similar atoms is discussed. A formalism is presented for evaluation of the time-development operator (and thus the density matrix) which has certain desirable features for time-dependent problems in the area, e.g. of atom-field interactions, when the off-diagonal elements are large compared to the diagonal elements of the Hamiltonian. By use of this formalism, it is shown that the spontaneous emission from a single atom is often drastically altered in the presence of unexcited atoms with similar resonances. When the number of atoms present becomes very large relative to the number of modes of the electromagnetic field, the excited atom becomes trapped in its excited state