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1.
研究了利用反向泵浦-探测双光子吸收材料的方法来测量脉冲激光的相干时间,并测量量了23ps,532nm Nd:YAG激光脉冲的相干时间。实验和理论分析表明,光束相干作用增加了双光子吸收,利用此方法可测量其它脉宽激光的相干时间。 相似文献
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相干合成技术是实现高功率、高亮度光纤激光系统的重要技术途径.然而, 脉冲激光阵列中常常存在时域误差,这将影响脉冲激光的相干合成效果. 建立了脉冲激光存在时域误差时的相干合成理论模型,并在不同波形(方波、三角波、正弦波) 的脉冲激光存在时域误差时,对相干合成光束在远场的脉冲波形、峰值功率、 光强分布和桶中功率(PIB)等特性进行了数值计算和对比分析.计算结果表明: 方波脉冲激光相干合成光束的脉冲波形受时域误差影响严重,光强分布和PIB随着时域误差 的增大发生线性变化;三角波脉冲激光相干合成光束的脉冲波形和峰值功率受时域误差 影响严重,光强分布和PIB在时域误差较大时随着时域误差的增大发生较为剧烈的变化; 正弦波脉冲激光相干合成光束具有较好的输出特性,在两路正弦波脉冲激光相干合成中, 将两脉冲之间的时延控制在脉冲持续时间的10%以内,就能取得良好的合成效果. 相似文献
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CARS技术中泵浦激光光场相干特性的研究 总被引:1,自引:1,他引:0
本文从理论上指出,在分子振动能级的横向弛豫时间远小于激光相干时间的条件下,相干反斯托克斯喇曼散射(CARS)信号能够反映出激光光场的相干特性,据此可直接了解其相干时间并推算出激光的线宽。实验记录了苯、甲苯的CARS光信号与激光延时时间的关系,得出了激光的相干时间和线宽。 相似文献
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利用激光感应瞬态光栅技术测量超短激光脉冲宽度 总被引:1,自引:0,他引:1
描述了利用激光感应瞬态光栅技术测量超短脉冲激光的脉冲宽度和相干时间的方法,来自同一光源的两束激光在非线性介质中相干形成积分光栅,测量光栅自衍射强度与两束光脉冲之间的延迟时间关系,利用相干光束的四阶相干函数关系,可以求出光源的脉冲宽度和相干时间。 相似文献
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稳态无粒子数反转亚泊松激光的量子理论 总被引:2,自引:2,他引:0
在理论上研究了相干、非相干泵浦的常规三能级激光器的稳态和噪声行为,指出:在相干、非相干泵浦率与激光下能级自发辐射率可以比拟的激光非优化区,相干、非相干泵浦常规三能级激光器的输出光场都呈现亚泊松统计,但只有相干泵浦情况由于量子相干效应能产生无粒子数反转亚泊松激光,且噪声压缩水平高于非相干泵浦情况。 相似文献
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用密度矩阵的方法从理论上分析了不同频率的两个激光场混合泵浦的光纤放大器中,由光场诱导的原子相干效应。并由此引入相干修正因子,通过修正的速率方程讨论了两光场与原子的相干作用对放大器增益的影响。 相似文献
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由于受到受激布里渊散射(SBS)等非线性效应的限制,单频激光放大器的功率在百瓦量级,以非单频激光多波长激光作为种子源能够有效地抑制SBS并提高放大器功率.与单频激光相干合成相比,非单频率、多波长激光的相干合成有望将输出激光功率成量级地提高.基于随机并行梯度下降(stochastic parallel gradient descent,SPGD)算法,实现了四波长激光的相干合成.在系统闭环时,四路多波长激光合成后的主瓣能量能够提高3倍,达到理想值的75%.验证了多波长、非单频激光相干合成的可行性,为高功率相干合成的发展提供了新的途径. 相似文献
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The effect of spontaneously generated coherence on the probe response in an open ladder atomic system with equispaced levels is studied. The result shows that by adjusting the strength of spontaneously generated coherence (SGC), electromagnetically induced transparency (EIT) and high dispersion (index of refraction) with zero absorption can be realized, a much larger gain without inversion (GWI) than that without SGC can be obtained. Moreover, in the open system and for some strength of SGC, GWI without the incoherent pumping is much larger than that with the incoherent pumping; however, in the corresponding closed system, when the incoherent pumping is absent, we cannot obtain any gain (with or without inversion) for any strength of SGC. In addition, the manipulation role of the atomic exit and injection rates on SGC-dependent absorption property is analyzed for the case when the incoherence pumping does not exist. 相似文献
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Comparison between effects of Doppler broadening on pure and non-pure inversionless gains with frequency up-conversion 下载免费PDF全文
A study is made of the effects of Doppler broadening on
pure gain without inversion, which means that neither one-photon
nor two-photon inversions are allowed, and non-pure gain without
inversion, which means that one-photon inversion does not occur
but two-photon inversion is present, in a closed Λ-type
three-level system with incoherent pumping. It is shown that when
the driving field is resonant but the probe field is not, in a
certain range of Doppler width, for the case of the lower degree of
frequency up-conversion, generally, pure gain without inversion
increases monotonically and non-pure gain without inversion does
not monotonically increase or decrease with increasing Doppler width;
for the case of the higher degree of frequency
up-conversion, pure gain without inversion decreases
monotonically but non-pure gain without inversion cannot be
produced. In the case of two-photon resonance, in some range of
Doppler width, pure gain without inversion does not
monotonically increase or decrease while non-pure gain without
inversion decreases monotonically with Doppler width increasing.
Finally, an experimental scheme for examining our theoretical result
is given. 相似文献
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在旋波、慢变振幅近似下,求解考虑了驱动场相位扩散后的系统密度矩阵运动方程,并给出了这个三能级梯型系统稳态线性解析解.利用得到的稳态线性解析解分析驱动场相位扩散是如何影响该系统输出无反转激光的.对稳态线性解析解数值计算的结果显示:由于驱动场相位扩散会导致无反转激光增益减小;即使由于驱动场相位扩散引起的线宽足够大,在该系统中仍能够获得无反转激光;线宽往往是破坏无反转激光产生和折射率的提高;因驱动场相位扩散导致无反转激光增益的减小,并不是总能够通过增大驱动场的Rabi频率得到补偿. 相似文献
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N. G. van Kampen 《Journal of statistical physics》1974,11(6):475-480
The Lotka-Volterra equations for the population growth of a system of interacting species are linearized around equilibrium. The linear equations are solved for a special choice of the coefficients. It is shown that, in the limit of a large number of species, each one of them obeys a Langevin equation without memory. Subsequently, following Zwanzig, one species is added that is treated without linearization. The character of the equation governing its population is materially dependent on the special choice of the interaction coefficients. It is concluded that no general statement can be made concerning the stochastic behavior of the solutions of the Lotka-Volterra equations without being more specific about the coefficients than has been customary so far. 相似文献
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The Pauli principle is included in a multisubband deterministic solver for two-dimensional devices without approximations.The nonlinear Boltzmann equations are treated properly without compromising on accuracy,convergence,or CPU time.The simulation results indicate the significant impact of the Pauli principle on the transport properties of the quasi-2D electron gas,especially for the on state. 相似文献
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SNAPSHOT-FLASH is a recently developed, ultrafast imaging technique, based on conventional FLASH imaging. The application of this new variant to 3D imaging allows the acquisition of a 128 x 128 x 32 data set in 12.5 seconds without triggering, or for cardiac imaging with gating within 32 heartbeats. Compared to standard 3D-FLASH this is 128 times faster, because triggering is only required when the 3D phase-encoding gradient is incremented. The method depicts for the first time fast three-dimensional views of the human heart without motional artifacts. The images are spin-density weighted. Using suitable prepulses any desired T1- or T2-contrast may be achieved. The generation of 3D movies is possible without an increase of the total scan time. 相似文献
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A scheme for ultrashort X-ray lasing without inversion 总被引:1,自引:0,他引:1
A scheme for obtaining a laser without inversion in the deep X-ray regime is proposed based on the principle of gain without inversion. A ladder scheme is proposed in the Ar8+ system. In this system, conventional lasing with population inversion in a neonlike scheme is used. This lasing field is proposed for the drive field on the higher transition of the ladder. A coherent field obtained in the high harmonics ultrashort laser provides the probe field to be amplified. The ground level is incoherently pumped into the highest level, while the latter is incoherently depumped into the ground level, at a different adjustable rate. A detailed density matrix calculation of the ladder configuration is performed [3], and the conditions under which the system exhibits inversionless gain, as well as regular gain, are derived. Numerical calculations in the bare state picture exhibits gain without inversion both at resonance and at the generalized Rabi side bands. The probe lineshape is shown to be constructed of two symmetrical dispersionlike features each centered at the generalized Rabi side bands. This is evidence of the quantum interference occurring at these locations and the basis for the gain without inversion. 相似文献
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We study (inverse) photoemission from systems
with strong coupling of doped carriers to phonons.
Using an adiabatic approximation, we develop a method for
calculating spectra. This method is particularly simple for
systems where the electron-phonon coupling can be neglected in
the initial state, e.g., the undoped t-J model. The theory
then naturally explains why the electron-phonon coupling just
leads to a broadening of spectra calculated without electron-phonon
coupling, without changing the dispersion. This is in agreement
with recent angle-resolved photoemission spectroscopy (ARPES)
on undoped cuprates, and it supports the interpretation in terms
of strong electron-phonon interaction. The theory also shows that
for systems with strong electron-phonon coupling in the initial
state, the result cannot in general be related to the spectrum
obtained without electron-phonon coupling. 相似文献
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