Transfer of intensity quantum correlation with twin beams

We demonstrate experimentally a protocol of transferring nonclassical quantum properties using two pairs of quantum-correlated twin beams in the continuous variable regime. The intensity quantum correlation from one twin beam is transferred to two initially independent idler beams with the help of a displacement transformation. It makes two originally independent beams exhibit an intensity quantum correlation of 0.8 dB below shot-noise level.     

Experimental characterization of quantum-correlated twin beams and a quantum channel with twin beams

We report the generation and characterization of quantum-correlated twin beams and their application to a quantum channel. Compared with our previous results, the characterization of twin beams and the quantum channel have been studied with 7.0-dB intensity difference squeezing. The measured inference variance of twin beams is decreased to 0.40 ± 0.02. For the quantum channel, the bit error rate will be 0.035 by using 7.0-dB intensity difference squeezing compared with our previous result of 0.067 by using 4.9-dB intensity difference squeezing.     

Phase singularity annihilation of focused partially coherent beams

Expressions for focused Gaussian Schell-model (GSM) beams are derived and used to study the annihilation and subwavelength structures of phase singularities in the focal region, and to compare with the case of fully coherent Gaussian beams. It is found that the truncation parameter δ and normalized coherence length ε both affect the presence and spatial distribution of phase singularities in the focal plane. Additionally, during the creation and annihilation process the saddle point near the phase singularity does not disappear in the focal plane for GSM beams.     

相干合成子光束一致性检测研究

分析了激光相干合成装置及其光路调整要求,提出利用剪切干涉检测合成光路中子光束一致性的方法。分析剪切干涉原理,建立了剪切板干涉物理模型,以相干合成中两路矩形光束拼接组束为例,数值模拟并研究了子光束的整体倾斜、离焦所对应的剪切干涉条纹,得到了条纹图像与子光束光轴误差、离焦误差之间的对应关系,用于相干合成光路中子光束光轴和发散角误差的判断。光轴倾斜大于5μrad时,可以直接观察互干涉和自干涉条纹变化,发散角在大于10μrad时,干涉条纹变化明显。此外,剪切干涉的自干涉条纹平移可用来检测子光束间的活塞误差,可作为光束拼接相干合成中闭环相位检测和控制的手段。     

相干合成子光束一致性检测研究

分析了激光相干合成装置及其光路调整要求,提出利用剪切干涉检测合成光路中子光束一致性的方法。分析剪切干涉原理,建立了剪切板干涉物理模型,以相干合成中两路矩形光束拼接组束为例,数值模拟并研究了子光束的整体倾斜、离焦所对应的剪切干涉条纹,得到了条纹图像与子光束光轴误差、离焦误差之间的对应关系,用于相干合成光路中子光束光轴和发散角误差的判断。光轴倾斜大于5 rad时,可以直接观察互干涉和自干涉条纹变化,发散角在大于10 rad时,干涉条纹变化明显。此外,剪切干涉的自干涉条纹平移可用来检测子光束间的活塞误差,可作为光束拼接相干合成中闭环相位检测和控制的手段。     

部分相干余弦高斯光束在左手材料中的光强分布

基于积分衍射理论和相干偏振理论,研究了部分相干余弦高斯光束在左手材料中的光强的分布。研究结果表明:中心光强随工作频率增大,先增大后逐渐趋于稳定,但是随相干参量增大而减小;横向光强随相干参量增大而减小,随偏心参量增大光强的最大峰值不变,但是光强的峰值数目在不断增加。     

Gyrator transform of Gaussian beams with phase difference and generation of hollow beam

The optical expression of Gaussian beams with phase difference, which is caused by gyrator transform (GT), has been obtained. The intensity and phase distribution of transform Gaussian beams are analyzed. It is found that the circular hollow vortex beam can be obtained by overlapping two GT Gaussian beams with π phase difference. The effect of parameters on the intensity and phase distributions of the hollow vortex beam are discussed. The results show that the shape of intensity distribution is significantly influenced by GT angle α and propagation distance z. The size of the hollow vortex beam can be adjusted by waist width ω₀. Compared with previously reported results, the work shows that the hollow vortex beam can be obtained without any model conversion of the light source.     

Partially coherent vortex beams with a separable phase

We propose and experimentally implement a method for the generation of a wide class of partially spatially coherent vortex beams whose cross-spectral density has a separable functional form in polar coordinates. We study phase singularities of the spectral degree of coherence of the new beams.     

Phase sensitivity of two nonlinear interferometers with inputting entangled coherent states

We investigate the phase sensitivity of the SU(1,1) interfereometer [SU(1,1)I] and the modified Mach–Zehnder interferometer(MMZI) with the entangled coherent states(ECS) as inputs. We consider the ideal case and the situations in which the photon losses are taken into account. We find that, under ideal conditions, the phase sensitivity of both the MMZI and the SU(1,1)I can beat the shot-noise limit(SNL) and approach the Heisenberg limit(HL). In the presence of photon losses, the ECS can beat the coherent and squeezed states as inputs in the SU(1,1)I, and the MMZI is more robust against internal photon losses than the SU(1,1)I.     

Generation of azimuthally and radially polarized beams by coherent polarization beam combination

A new architecture for generating pure azimuthally and radially polarized beams is presented. It involves coherent polarization beam combination of two orthogonally polarized LP(11) fiber modes. Experimental results reveal that high purely polarized (polarization purity of 95% or better) azimuthal and radial beams can be generated.     

Generalized beam propagation factors of truncated partially coherent cosine-Gaussian and cosh-Gaussian beams

Based on the method of truncated second-order moments, the analytical expressions of the generalized beam propagation factor for truncated partially coherent cosine-Gaussian and cosh-Gaussian beams are derived. The beam propagation factors of the truncated partially coherent cosine-Gaussian and cosh-Gaussian beams depend on the acentric parameter, the truncation parameter, and the coherent parameter. According to the derived expressions, the beam propagation factors are illustrated and analyzed with numerical examples, and the influences of the different parameters on the beam propagation factors are also discussed in detail.     

On the possible production and detection of coherent low-energy neutrino beams

Seminal experiments are discussed to prove or disprove the possibility of producing and detecting collimated coherent beams of low-energy neutrinos with the assistance of lasers. Expressions are given for the relative probability that a laser-beam-aligned co- or counter-propagating neutrino-antineutrino pair is emitted instead of a laser photon, during stimulated de-excitations of lasable excited states inside a lasing medium. For a neodymium laser this probability is approximately 10^?7. To detect coherent beams of epithermal neutrinos and antineutrinos emitted from a pulsed high-power laser, it is anticipated that resonant non-absorptive stimulated de-excitations of lasing levels by neutrinos can be exploited to register their fly-through in a second near-threshold laser.     

Experimental demonstration of sub-shot-noise intensity correlations in an intense twin beam

Twin-beam states of light produced by spontaneous parametric downconversion are endowed with sub-shot-noise photon-number correlations at any intensity regime. We have demonstrated sub-shot-noise photon-number correlations in a ps-pulsed intense (more than 1000 photons) twin beam by measuring the variance of the difference in the number of photons detected in the two outputs of the crystal. The variance is 3.25 dB below the shot-noise level. Measurements show that detection of sub-shot-noise correlation requires a careful selection of twin coherence areas and that these areas depend on the pump intensity.     

All-fiber coherent beam combining with phase stabilization via differential pump power control

Coherent beam combining enables power scaling beyond the limits of single amplifiers. Therefore, improving the performance and simplicity of coherent combination techniques is of great interest for many high power applications. Here, we show all-fiber coherent beam combining of two ytterbium doped amplifiers with and without a dedicated phase actuator and a total output power up to 25 W. Instead of a dedicated phase actuator, we directly controlled the two ytterbium amplifiers to also stabilize their relative phase. We compared the performance of this method with phase stabilization using two piezo driven fiber stretchers. In both cases, power noise was dominated by the single amplifier.     

Color coherent phenomena with hadron beams

We outline major ideas involved in discussion of color coherence phenomena (CCP) at intermediate energies. We point out that the recent advances in calculating cross sections of hard exclusive processes off light nuclei allow to use the lightest nuclei for sensitive tests of CCP. Consistency of the results of the measurements of color transparency in quasielastic A(p,2p) and A(e,e′p) processes is emphasized. Evidence for presence of significant color fluctuations in nucleons and pions emerging from the study of diffractive processes is summarized. A new class of hard processes leading to three particle final state is suggested for electron and hadron projectiles.     

Coincidence Imaging and interference with coherent Gaussian beams

we present a theoretical study of coincidence imaging and interference with coherent Gaussian beams. The equations for the coincidence image formation and interference fringes are derived, from which it is clear that the imaging is due to the corresponding focusing in the two paths. The quality and visibility of the images and fringes can be high simultaneously. The nature of the coincidence imaging and interference between quantum entangled photon pairs and coherent Gaussian beams are different. The coincidence image with coherent Gaussian beams is due to intensity-intensity correspondence, a classical nature, while that with entangled photon pairs is due to the amplitude correlation a quantum nature. Selected from Acta Sinica Quantum Optica, 2005, 11(4)(in Chinese)     

光束相干合成中填充因子对远场光强分布的影响

理论推导了相干光束阵列远场光强分布的解析表达式.介绍了填充因子及五种相干合成效果评价参数的定义.分析了填充因子对远场光强分布的影响,发现填充因子通过影响空间调制因子来改变远场光强分布.求得了相干合成效果评价参数与填充因子的关系式,并绘制了关系曲线.计算结果表明,斯特列尔比与填充因子无关,恒为1;中央主瓣半径与填充因子成正比关系;中央主瓣能量密度受填充因子的影响较小;中央主瓣能量比与填充因子的平方成近似正比关系;桶中功率与填充因子的关系很复杂,但总体上随着填充因子的√减小而减小.分析显示,若要保证中央主瓣能量比和PIB值均大于最佳值的一半,则填充因子应大于2/2.     

Investigation of the photon-number statistics of twin beams by direct detection

We present the results of an experiment in which we observed photon-number statistics of twin beams emerging from a nondegenerate optical parametric oscillator. We generated the photocurrent for recording by detecting the light and mixing it with a standard electrical oscillator. The measured photocurrent variances exhibited a quantum correlation of as much as -4.9 dB between signal and idler, whereas their photon number distributions were super-Poissonian. We also obtained the difference photon-number distribution.     

Axial intensity distribution and focal shifts of focused partially coherent conical Bessel–Gauss beams

Based on the generalized Huygens–Fresnel diffraction integral and the theory of partially coherent light, the axial intensity distribution and the focal shifts of focused partially coherent conical Bessel–Gauss beams are investigated. The dependence of the maximum on-axis intensity and the associated focal shift on the Fresnel number and the coherence parameter are examined and illustrated numerically. The results related to the J ₀-correlated beams and the fully coherent Bessel–Gauss beams are obtained as particular cases of this study.