Forward four-wave interactions in bismuth silicon oxide-theory and experiment

The interaction between two strong pump beams and two signal beams is investigated both theoretically and experimentally. It is shown that the frequencies of the beams need to satisfy the relation that the sum of the pump beam frequencies should be equal to the sum of the signal beam frequencies. The gain is shown to depend on the detuning of the pump beams relative to the incident signal beam and on the direction of the signal beam. Maximum gain is obtained when the signal beams bisect the pump beams.     

Competition between subharmonic and signal beams for photorefractive gain in BSO with two pump beams

It is shown that two pump beams incident upon a bismuth silicon oxide crystal give rise to a subharmonic beam bisecting the pump beam. Simultaneously a signal beam injected between the pump beams may be strongly amplified at the expense of the pump beams. It is shown that the amplified signal beam grows with a faster time constant than the subharmonic beam and that there is competition for gain in the steady state regime.     

Two-color continuous-variable entanglement generated in nondegenerate optical parametric oscillator

A scheme is proposed to produce two-color continuous-variable (CV) entanglement in nondegenerate optical parametric oscillator with an injected signal (INOPO). The quantum correlations between signal and idler beams are calculated by applying sufficient inseparability criteria for bipartite CV entanglement. The results indicate that two-color CV entangled beams can be produced when the INOPO is operating both below and above the threshold. The injected signal does not markedly diminish the quantum correlations between the signal and idler beams. The degree of entanglement dependence on damping rates is also investigated.     

自散焦介质中光束聚焦的最佳参数选择

对自散焦介质中由交叉相位调制效应引发的光束聚焦过程进行了细致的系统研究,讨论了抽运光初始振幅、抽运光信号光初始间距和抽运光信号光波长比三个参量对信号光聚焦过程的影响.数值模拟结果表明:抽运光越强,信号光聚焦程度越大;抽运光信号光初始间距和抽运光信号光波长比均存在一个最佳值,使得光束聚焦达到最佳效果.通过参数最佳值的选择,可提高光束聚焦的效率 关键词： 非线性折射率系数 交叉相位调制效应 自散焦介质 光束聚焦     

Speckle interferometry of phase-modulated beams

It is shown experimentally that a scatterer placed in the interference field of the signal and the reference beams can be used for detecting phase-modulated optical signals. The signal observed in this case is formed by the space-time modulation of the speckle structure of the beams. The influence of the geometry of the interferometer and the amplitude of phase modulation on the parameters of the output signal is considered.     

Modulational instability of incoherently coupled beams in azobenzene-containing polymer with photoisomerization nonlinearity

The modulational instability of two incoherently coupled beams in azobenzene-containing polymer with photoisomerization nonlinearity is investigated analytically and numerically. Our results show that as a precursor to spatial optical soliton formation, modulational instability can be adjusted and controlled by the wavelength combinations of the signal and background beams. We also discuss the dependences of strength of modulational instability on intensities of two signal beams and background beam. These findings make it possible to predict the formation of incoherently coupled soliton pairs in azobenzene-containing polymer.     

Sub-shot-noise high-sensitivity spectroscopy with optical parametric oscillator twin beams

Nondegenerate optical parametric oscillators generate above-threshold signal and idler beams that have intensity fluctuations correlated at the quantum level (twin beams). We describe what is to our knowledge the first high-sensitivity spectroscopy experiment using twin beams emitted by a cw optical parametric oscillator: a very weak two-photon absorption signal, in the 10(-7) range, is recorded on the 4S(1/2)-5S(1/2) transition of atomic potassium with a noise background that is reduced by 1.9 dB with respect to the shot-noise limit of the light used in the experiment.     

EPR纠缠光束时域量子关联的实验验证

我们利用平衡零拍探测系统和数据采集系统直接测量了EPR纠缠光束信号光场与闲置光场正交分量之间的时域量子起伏,验证了其量子关联.通过对EPR纠缠光束中的一束光场进行延迟,验证了信号光与闲置光不同步时将导致量子关联减弱乃至消失.我们的实验结果为开展连续变量量子密钥分发、非高斯态的实验制备和纠缠纯化奠定了实验基础.     

复色光伏孤子的稳定性

给出求解复色孤子半高宽的近似方法，该方法对分析复色光束的演化提供一个定性的基础 .进一步的数值模拟结果表明，当入射双曲正割光束满足复色光伏孤子半高宽与中心光强的 关系时，双曲正割光束在晶体中的传播就非常接近孤子，表明复色光伏孤子对于小的微扰是 稳定的.此外，复色光伏孤子对于小的轴偏离具有较好的稳定性；复色光伏孤子对因温度微 扰引起折射率变化的情况也具有较好的稳定性.一般情况下，初始光强分布接近复色光伏孤 子光强分布的两束光的光强在传播过程中不断地起伏，形成呼吸状结构，但如果入射面处的 光强明显偏离孤子的光 关键词： 复色光伏空间孤子 稳定性     

Phase modulation of the signal beam in three-wave forward mixing in photorefractive bismuth silicon oxide

The interaction of three forward beams in a BSO crystal is investigated under conditions when the two pump beams are anti-symmetrically detuned and the signal beam is phase modulated. For sinusoidal phase modulation the signal gain is shown to be dependent on the instantaneous frequency detuning. Single and double maxima in gain are obtained depending on the voltage amplitude applied to the piezoelectric mirror. For triangular phase modulation a slight asymmetry is found in the gain versus detuning curve.     

Analysis of directly produce pump,signal, and idler three-color continuous-variable entanglement

Analysis is presented in this paper to directly produce three-color continuous-variable (CV) entanglement by nondegenerate optical parametric oscillator (NOPO) with an injected signal. The quantum entanglement among the pump, signal, and idler beams are calculated by applying sufficient inseparability criteria for CV entanglement which proposed by van Loock and Furusawa [Phys. Rev. A 67, 052315 (2003)]. The results indicates that strong three-color CV entangled beams, i.e. pump, signal, and idler beams, can be generated when the NOPO operating above the threshold. The degree of entanglement dependence on damping rates is also investigated.     

Self-focusing in photorefractive two-wave mixing

Self-focusing and self-defocusing of light in two-wave mixing are investigated experimentally. Amplification and self-focusing are measured as functions of the frequency shift between signal and pump beams. A frequency dependence is found in Kramers-Kronig form, as is plausible by the analogy of photorefractive amplification and laser amplification. Reversal of the external dc field on the material or a change in the frequency shift between the signal and pump beams is found to change self-focusing to self-defocusing.     

Non-linear and quantum optics of a type II OPO containing a birefringent element

We describe theoretically the quantum properties of a type-II Optical Parametric Oscillator containing a birefringent plate which induces a linear coupling between the orthogonally polarized signal and idler beams and results in phase locking between these two beams. As in a standard OPO, the signal and idler waves show large quantum correlations which can be measured experimentally due to the phase locking between the two beams. We study the influence of the waveplate on the various criteria characterizing quantum correlations. We show in particular that the quantum correlations can be maximized by using optimized quadratures.     

全光准稳态空间孤子对波长的依赖性

在进行全光准稳态空间孤子的实验中,发现在相同光强条件下,利用不同波长的光作为信号光束,准稳态孤子存在的时间不相同.一般来说,波长较长的光束形成准稳态孤子的时间区间较长.特殊的,当波长大至一定程度时,将形成稳态的空间孤子,这完全不同于以往所观察到的准稳态孤子 关键词： 屏蔽效应 光伏效应 空间孤子     

洛仑兹脉冲光束的复振幅包络解和复解析信号解的比较研究

使用复振幅包络表示式和复解析信号表示式推导了洛仑兹脉冲光束的传输公式. 通过具体数 值计算对脉冲光束的复振幅包络解和复解析信号解在不同带宽时的传输进行了对比研究. 数 值结果表明脉冲光束为窄带时，在传输方向轴中心的一定范围内两种解是一致的，而对于宽 带脉冲光束，复振幅包络解在轴中心较近的距离即表现出奇异性，复解析信号解才是符合物 理意义的表示式. 由数值计算得出了选择脉冲光束研究方法的条件，并从所得公式对复振幅 包络解出现奇异性的现象进行了解释. 关键词： 复振幅包络 复解析信号 窄带脉冲 宽带脉冲     

Simultaneous and sequential power transfer between coherent beams by photorefractive coupling

The power of several coherent laser beams can be transferred into a single diffraction-limited signal beam by photorefractive coupling. The efficiency of the power transfer is investigated experimentally in the case of two pump beams. Two different geometrical arrangements, one with overlapping (simultaneous) and the other with separate (sequential) pump beams are compared in a BaTiO₃:Ce crystal, with diffusion-driven photorefraction. We measured about the same power transfer efficiency in both arrangements for strong signal beams, but the efficiency was higher in the sequential arrangement for weak signals. A simple theoretical model of the power transfer process based on the standard linear two-wave-mixing theory is presented and the observed stationary beam-coupling behavior for different pump-to-signal intensity ratios is found to be in qualitative agreement with the theoretical predictions. Received: 10 November 1998 / Revised version: 22 December 1998 / Published online: 24 March 1999     

Prospects for increasing average power of optical parametric chirped pulse amplifiers via multi-beam pumping

We demonstrate optical parametric amplification of broadband chirped pulses in BBO crystal pumped by several intersecting beams extracted from independent laser amplifiers. The energy of amplified signal ranged from 0.23 to 0.72 mJ depending on a number of pump beams used as well as pumping configuration employed. The conversion efficiency dependence on intersection angles of pump beams is revealed and modeling of interplay of interacting waves is presented.     

Diamagnetic and Paramagnetic Effects in Free-Electron Lasers

The effect of high-current relativistic electron beams (REB's) on the undulator field amplitude in free-electron lasers (FEL's) is investigated. Two mechanisms of excitation of periodic magnetostatic self-fields by REB are considered: 1) a static mechanism that is realized at stationary motion of REB in the undulator field; and 2) a dynamic mechanism that is realized at signal wave amplification. The static mechanism in the absence of an axial magnetic field leads to a decrease of the total undulator field amplitude (a diamagnetic effect). The dynamic mechanism for low-density beams leads to an increase of the total undulator field amplitude (a paramagnetic effect), with a subsequent increase of electron efficiency. For high-density beams, the effect of the phase shift of the total undulator field is most essential, due to which the growth of the signal wave amplitude is limited by nonlinear mismatch of synchronism.     

Light modulation by acoustic signals for high diffraction efficiency

A theoretical discussion is presented on strong Bragg acoustooptic interaction AOI of light beams in the dynamic field of an acoustic signal. A system of integrodifferential equations is formulated to describe the evolution of the angular and frequency spectra of the beams in the AOI region for a high level of acoustooptic coupling. The third-order approximation in the perturbation method is used to obtain an analytic solution. Calculations are presented on the modulation of monochromatic beams by acoustic pulses having rectangular envelopes and propagating in a lithium niobate crystal, and the same for a signal having linear frequency modulation LFM in a paratellurite crystal, which demonstrate the broadening of the beam spectrum as the depth of the acoustooptic coupling increases, together with the occurrence of an asymmetry specific to strong AOI in the response of the light field to the symmetrical acoustic signal. Tomsk State University for Control Systems and Electronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 1, pp. 99–106, January, 1999.     

Improving the efficiency of an acoustooptic modulator with a two-lobe directivity pattern by correcting the two-frequency electric signal

The feasibility of forming an efficient two-lobe directivity pattern at Bragg acoustooptic diffraction is theoretically substantiated for the first time. It is shown that the efficiency of diffraction into main beams can be increased by mixing the two-frequency signal with additional spectral components that correspond to the closest combination frequencies. Mixing is accomplished using an original electronic circuit designed for polynomial nonlinear correction of the control signal. Bragg diffraction by the corrected signal is studied experimentally in a high-efficiency paratellurite (TeO₂) modulator. Satisfactory agreement with the theory is obtained, and results of applied interest are obtained. In particular, the maximal overall efficiency of diffraction into two main beams is increased from 68 to 79%.