Generation of Intense THz Pulsed Lasers Pumped Strongly by CO2 Pulsed Lasers

A theoretical method dealing with two intense laser fields interacting with a three-level molecular system is proposed. A discussion is presented on the properties of the solutions for time-independent and time-dependent absorption coefficients and gain coefficient on resonance for strong laser fields, based on analytic evaluation of the rate equations for a homogeneously broadened, three-level molecular system. The pump intensity range can be estimated according to the analytic expression of pump saturation intensity. The effects of pulse width, gas pressure and path length on the energy absorbed from pump light are studied theoretically. The results can be applied to the analysis of pulsed, optically pumped terahertz lasers.     

Analysis of time domain characteristics of high energy nano-second optical parametric oscillator

The time domain characteristics of high energy nano-second optical parametric oscillator are analysed with discrete-approximation method, and the procedure of signal wave is modeled. Different pulse widths result in varied build-up times and optimum crystal lengths, which dominate the efficiency of pulse pump. When the pump energy remains fixed, there is an optimum pulse width for the pump wave, with which the highest efficiency could be expected. In addition, for the first time, the analytic solutions for both small and large signal gain conditions are supplied with the discrete-approximation method. We also give the equations for the build-up time, the optimum crystal length and the efficiency, both in accurate form and simple form for estimation, and finally apply the results to the experiments.     

Threshold analysis for a THz-wave parametric oscillator with a quasi-phase-matching scheme in lithium niobate

The analytical expressions of the parametric gain for the terahertz wave (THz-wave) and the Stokes wave of THz-wave parametric oscillator (TPO) with a quasi-phase-matching scheme in periodically poled LiNbO₃ (PPLN) are deduced. The pump threshold expression of the TPO with a quasi-phase-matching scheme in PPLN is derived based on the gain expression of the Stokes wave. The expression is theoretically analyzed to find the relationship between the pump threshold and the parameters of the resonant cavity.     

非简并光学参量振荡腔的经典增益

采用双晶体串接,温度调谐及光楔补偿方法,实现了参量振荡腔内泵浦场与非简并亚谐波场之间的三模同时共振,测定了系统的经典增益,实验结果与半径典理论计算符合.     

Laser-diode side-pumped actively Q-switched eye-safe intracavity optical parametric oscillator

Eye-safe laser of 1573 nm wavelength from a laser-diode (LD) side-pumped actively Q-switched Nd:YAG/KTP intracavity optical parametric oscillator (IOPO) with acousto-optic (AO) modulator is presented. The dependences of the average output power, the pulse width, pulse energy, and the peak power on incident pump current for the generated-signal-light pulses are obtained. By considering the Gaussian spatial distributions of the pump light in laser medium, the photon densities of the fundamental, the signal, and the idle waves as well as the initial population-inversion density and the coupled rate equations of this IOPO are described, in which the influence of the pump rate, the thermal effect in the gain medium and the change of the photon density along the cavity axis have been also taken into account. These coupled equations are solved numerically, and the theoretical calculations are consistent with the experimental results.     

Quantization of plasma density irregularities under the action of a powerful electromagnetic wave: The spectrum of upper hybrid oscillations self-consistently trapped in density cavities

We present a theoretical model of the self-localization of the upper hybrid (UH) oscillations in plasma density depletions due to thermal nonlinearities driven by a homogeneous and monochromatic pump electric field. The Bohr-Sommerfeld condition for the trapped UH oscillations demands that the parameters of the density cavity be quantized. The depth and square of the depletion width across the magnetic field is proportional to an integer. The depth of the parabolically shaped cavity is proportional to the square of its width. The characteristic relative value of the density minimum is a few percent and the width is of the order of one meter for the pump wave amplitudes used in the ionospheric F-region experiments. We consider also the parametric decay of primary, localized UH oscillations trapped in the quantized plasma density depletions into secondary UH oscillations and lower-hybrid waves. We calculated the spectrum of the non-linear stabilized secondary UH oscillations which are also self-consistently trapped in the same density cavity. The spectrum of the UH oscillations is consistent with the observed spectrum of the downshifted (DM) and upshifted (UM) maximum in the stimulated electromagnetic emissions (SEE). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 7, pp. 641–650, July 1999.     

Dual picosecond dye lasers synchronously pumped by a mode locked cw yag laser

The performance of a novel dual dye laser system synchronously pumped by the frequency doubled output of a mode-locked CW-YAG laser is evaluated in relation to pulsewidth, pulse substructure, pulse spectral width and timing jitter. The behavior of the system is adequately described by a theoretical model which includes the time dependent gain and losses due to frequency bandwidth, cavity length mismatch and output coupler. The jitter is significantly reduced from that obtained with CW gas laser pumping as a result of the shorter pump pulse (50 ns instead of ≈100 ps). A routine operating condition uses 2-plate birefringen filters, 0.8 W pump power at 532 nm, to yield two 2.0 ps pulses having a cross correlation width of 3.8 ps, and 30 mW average power from each laser.     

高阶色散对高双折射光纤增益谱的影响

根据参量放大和拉曼效应共同作用下的耦合波方程,在考虑高阶色散情况下,当输入泵浦波偏振方向同双折射轴成45时,通过引入拉曼增益的洛伦兹模型,研究了高双折射光纤中,参量放大和拉曼效应共同作用下的增益谱随相关参量的变化关系。结果表明:高双折射光纤中,在不同色散区,不同的输入参量（输入功率、群速度失配等）条件下,参量放大和拉曼效应共同作用下的增益谱受到高阶色散的影响,增益谱的结构、强度和谱宽产生了变化, 高阶色散对增益谱的影响不可忽略;可以利用增益谱在大群速度失配区域远离中心频率偏移的性质,提取T频率脉冲。     

A degenerate three-level laser with a parametric amplifier

The aim of this paper is to study the squeezing and statistical properties of the light produced by a degenerate three-level laser whose cavity contains a degenerate parametric amplifier. In this quantum optical system the top and bottom levels of the three-level atoms injected into the laser cavity are coupled by the pump mode emerging from the parametric amplifier. For a linear gain coefficient of 100 and for a cavity damping constant of 0.8, the maximum intracavity squeezing is found at steady state and at threshold to be 93%.     

The effect of phase mismatch on two-pump fiber optical parametrical amplifier

In the paper, the effect of phase mismatch on two-pump fiber optical parametric amplifier is investigate based on analytic solutions of parametric gain. The phase mismatch is mainly induced by the fiber losses, the fourth-order dispersion and zero-dispersion wavelength fluctuations. The fiber losses reduce the pump powers resulting in a fall of the parametric gain, and make the phase mismatch vary with propagation distance leading to an obvious gain ripple. When the fiber losses are taken into account, the fourth-order dispersion produces a deeper ripple on the parametric gain and deteriorates the gain flatness. Zero-dispersion wavelength fluctuations result in variations of gain spectrum, and the long-scale fluctuations are more devastating than the short-scale ones.     

4.5-ns Pulse generation at a 500-kHz repetition rate from a short-cavity acoustooptically Q-switched Nd:YVO<Subscript>4</Subscript> laser

In an end-pumped 20-mm-cavity-length acoustooptically Q-switched Nd:YVO₄ laser, 4.5-ns pulses at a 500-kHz repetition rate with a 5-kW peak power are produced. The pulse width is <10 ns at repetition rates lower than 1.1 MHz. The short cavity results in a short roundtrip time of light within the cavity and a high gain with a modest pump power, and both are essential for short-pulse and high-repetition rate operation. The output pulse width versus the pump power and repetition rate is experimentally studied. The output transmission also has a considerable influence on the pulse width and shape, and there exists an optimum transmission for the shortest pulse width and symmetrical pulse shape.     

Intracavity power addition with a close-ended composite four-mirror cavity

We present a novel four-mirror cavity with two active gains to combine power intracavity and also give a detailed theoretical analysis of the combined gain. By using the effective field method, the four-mirror cavity with two gain media can be regarded as a linear resonator with one effective combined gain (ECG), and we procure a theoretical model of the ECG and deduce its exact analytical expression. When the two branch gains are close to each other, the combined gain can be reduced to their product, and the simplified presentation of ECG has been demonstrated. The combined output power which directly reflects the small signal ECG of the four-mirror cavity is studied experimentally, and the results are in good agreement with the theoretical ones.     

高质量高效率高稳定性参量放大光产生的研究

针对光参量放大实验中存在的参量转换效率低、输出光脉冲形状畸变和输出稳定性差等问题进行了详细研究，对注入信号光强、抽运光耗尽、增益饱和、和频过程等因素对参量过程的影响进行了详细分析讨论，并进行了光学参量放大的实验研究.理论和实验研究结果表明通过优化选择合适的注入信号光强、抽运光强和晶体长度等参数，使参量放大运行在深度增益饱和状态的稳定区，完全可以获得高质量高效率高稳定性的参量放大输出光. 关键词： 光参量放大 抽运光耗尽 增益饱和 稳定性     

Time delay limits of stimulated-Brillouin-scattering-based slow light systems

We discuss the maximum achievable time delay of stimulated-Brillouin-scattering-based systems that rely on the superposition of gain and loss spectra. As we will show, the time delay can be enhanced up to 8.5 times if the gain is superimposed with a broad loss and 9.5 times if two narrow losses are superimposed at the wings of the gain. Furthermore, we show that the parametric interaction between the different pump waves is negligibly small. Our theoretical analysis does not include pulse distortions that are accompanied by the delay.     

Efficient two-photon light amplification by a coherent biexciton wave

A reversible coupling between photon pair states and a long-lived, highly coherent biexciton wave in CuCl allows efficient phase-sensitive two-photon amplification or attenuation of ultrashort light pulses. We demonstrate a gain of 350 cm(-1) for a pump intensity of 1 MW/cm(2), nearly 2 orders of magnitude higher than that achievable with conventional parametric crystal amplifiers. We develop a theoretical model that describes this new type of parametric converter where the light pump is replaced by a coherent biexciton wave and show that it is well suited for the generation of entangled photons and the squeezing of an optical beam with ultrafast time gating.     

Investigation of pump-wavelength dependence of terahertz-wave parametric oscillator based on LiNbO3

This paper investigates the performances of terahertz-wave parametric oscillators(TPOs) based on the LiNbO 3 crystal at different pump wavelengths.The calculated results show that TPO characteristics,including the frequency tuning range,the THz-wave gain and the stability of THz-wave output direction based on the Si-prism coupler,can be significantly improved by using a short-wavelength pump.It also demonstrates that a long-wavelength-pump allows the employment of a short TPO cavity due to an enlarged phase-matching angle,that is,an increased angular separation between the pump and oscillated Stokes beams under the THz-wave generation at a specific frequency.The study provides an useful guide and a theoretical basis for the further improvement of TPO systems.     

注入功率比可调控的双泵浦复合腔501 nm青光激光器

为了探究提高500?nm附近激光高准确度应用的理论和技术依据,本文采用双泵浦源复合腔结合非线性和频变换,实现腔内两种波长基频光无增益竞争,可提高基频光输出功率,同时在复合腔内进行多次非线性频率变换,通过调控基频光注入功率比,使腔内光子数配比达到1:1,从而有效提高了光-光转换效率及和频输出功率.对首次建立的理论模型进行...     

基于光纤光参量放大的光脉冲压窄技术的研究

在高重复频率的光窄脉冲源中,为了获得更窄的脉冲,需要增加泵浦功率|但泵浦功率的提高会使光放大器的增益趋于饱和,放大的自发辐射噪音增强,脉冲光信噪比下降.为此,提出了利用啁啾管理和光纤光参量放大相结合的脉冲压窄方案.将强度调制后的泵浦光通过相位调制引入线性负啁啾,由于经参量过程后在新的闲频光上啁啾会加倍,从而进一步增大了信号的谱宽,并通过色散补偿介质实现了光脉冲压缩.实验给出了10 GHz速率下的结果,通过泵浦光的相位调制在0.5 W平均泵浦光功率条件下得到了脉宽19 ps的光脉冲,结果与理论分析基本吻合.     

二极管泵浦折叠式电光调Q激光器

针对机载激光测距及激光指示应用需求,设计了一种紧凑可靠的电光调Q脉冲激光器。从调Q速率方程出发,分析了激光器输出能量随优化参数z增大而增大、脉宽随z增大而减小的关系。采用?6 mm×56 mm的Nd:YAG激光晶体,LD侧面泵浦,角锥棱镜作为折光器的u形折叠式非稳腔,在增益满足的前提下,提高谐振腔抗失调能力。在注入电脉冲1.2 J条件下,激光器单脉冲能量输出为108 mJ,脉冲宽度为11.8 ns,能量不稳定度 < 0.8%;光-光效率18%,可长时间稳定运行。     

拉曼效应和参量放大共同作用下增益谱特性

根据激光脉冲在双折射光纤中传输时, 拉曼效应和参量放大共同作用下所所遵循的耦合模方程, 基于平行拉曼增益的洛伦兹模型, 给出了输入抽运波偏振方向沿相互正交的双折射轴时, 拉曼效应和参量放大共同作用所导致的增益. 讨论并分析了在不同色散区相关参量对增益谱特性的影响. 结果表明, 拉曼效应改变了非线性和色散的相互平衡, 使得参量放大斯托克斯波与反斯托克斯波增益谱彼此不对称; 当输入功率一定时, 其增益谱结构确定, 非线性系数和色散系数两者之间相对变化时, 增益谱的强度和展宽有所改变.