1064nm固体激光器和光纤激光器在制备压缩真空态光场实验中的对比研究

实验和理论研究了单频固体激光器和单频光纤激光器的相对强度噪声对压缩真空态光场测量精度的影响.在实验中分别采用单频固体激光器和单频光纤激光器作为实验系统的光源,直接探测到的压缩真空态光场的压缩度分别为(13.2±0.2) dB和(10±0.2) dB.通过理论计算得知本实验中影响可测压缩度的主要因素是光源的相对强度噪声,为实用化的高压缩度压缩真空态光场发生器的研制提供了理论和实验指导.     

利用周期性极化KTP外腔谐振倍频过程实现明亮振幅压缩光

利用自制的单频连续Nd:YVO4激光器输出的1064 nm激光作为抽运源,通过周期性极化KTP晶体外腔倍频过程实现了倍频绿光的正交振幅压缩,并研究了绿光压缩度对抽运光功率的依赖关系,当抽运光功率为59 mW时,实验中观察到压缩度为0.6 dB(考虑到探测效率,实际压缩度为1.1 dB)的明亮绿光振幅压缩光,实验结果与理论预测基本一致。     

不完善探测对强度差压缩度及光学测量精度的影响

文章讨论了探测系统的传输损耗与非理想探测器对量子相关一光束强度差压缩度和低于散离噪声极限光学测量精度的影响，特别推导出两臂不平衡下探测效率的数学表达式，并结合实验参量了数值计算，理论分析五实验结果基本一致。     

自锁定半导体激光器中强度压缩及位相噪声的减小

采用外部F-P腔自锁定单模量子阱半导体激光器，观察到强度噪声的压缩现象，并同时大幅度降低了位相起伏.在35MHz附近观察到19.3%的强度压缩，对应激光输出的压缩度为37.8%，在9kHz-100MHz范围内观察到约3个数量级的位相噪声降低.获得了近最小测不准态. 关键词：     

二极管泵浦内腔倍频抑制绿光噪声的实验研究

 报道了在Nd:YAG棒和腔镜间插入四分之一波片，或在KTP倍频晶体和腔镜间插入四分之一波片，以及使用交叉双倍频晶体用以抑制二极管泵浦内腔倍频Nd:YAG激光器绿光噪声的实验结果。实验研究表明，使用上述三种方法之一能有效地减小折叠腔内的绿光噪声。用交叉倍频晶体可使噪声减小18％～25%。实验结果与理论一致，对实验中一些问题和值得进一步改进的地方也进行了讨论。     

激光二极管泵浦腔内倍频Nd：YVO4／KTP绿光噪声研究

从实验上测量了Ｎｄ：ＹＶＯ４／ＫＴＰ腔内激光器绿光噪声和腔长、泵浦功率的变化关系，并从理论上进行了分析计算、，找出多纵模情况下影响绿光噪声大小的关键因素。理论计算与实验结果相一致。     

1064 nm高功率明亮压缩态光场制备实验中绿光诱导红外吸收效应

通过实验和理论研究连续变量高功率明亮压缩态光场制备实验中高功率种子光注入光学参量放大器引起的绿光诱导红外吸收效应。首先,通过优化实验系统工作参数,提升反馈控制回路的锁定稳定性,当种子光功率为500 mW、泵浦光功率为145 mW时,在分析频率为3 MHz处,获得光功率为200μW、压缩度为(-10.7±0.2) dB的明亮压缩态光场。然后,根据实验数据,定量分析高功率明亮压缩态光场与压缩真空态光场产生过程中周期极化磷酸氧钛钾晶体的吸收损耗,发现高功率明亮压缩态光场实验系统的总光学损耗为(9±0.05)%,其中由周期极化磷酸氧钛钾晶体吸收导致的内腔损耗为(5.8±0.05)%,占总光学损耗的(64.4±0.05)%。该条件下周期极化磷酸氧钛钾晶体对高功率明亮压缩态光场的吸收系数为(6.0±0.05)×10^-2 cm^-1。当泵浦光单独注入光学参量放大器时,周期极化磷酸氧钛钾晶体对压缩真空态光场的吸收系数约为2.1×10^-4 cm^-1。由此可知,当高功率种子光注入光学参量放大器时,绿光诱导红外吸收效应使周...     

级联四波混频系统中纠缠增强的量子操控

各类系统中的纠缠操控是量子信息科学的重要问题之一.本文研究了热原子蒸气的级联四波混频过程中产生的纠缠增强及纠缠增强的相位敏感特性.研究表明,该级联四波混频过程第二级输出的探针光和共轭光的量子纠缠较第一级明显增强,最大可达5 dB以上,且随着强度因子的增大可实现完美纠缠.文中还详细讨论了量子关联类型及纠缠大小与抽运光相位、非线性强度因子之间的变化关系,结果显示,由于纠缠增强及纠缠类型对抽运光相位的敏感性,通过控制相位和强度因子可改变光场噪声特性从而实现对探针光和耦合光之间纠缠增强、纠缠度大小、纠缠类型的量子操控.该理论研究对实验实现纠缠增强及双模压缩态压缩角、压缩度的光学参量操控具有重要的指导意义.     

非旋波近似下压缩真空场与三能级原子依赖强度耦合系统的光场压缩

利用全量子理论,研究了非旋波近似下压缩真空场与V型三能级原子依赖强度耦合相互作用系统中光场的压缩效应.数值计算结果表明:光场呈现出周期性压缩现象,而虚光子过程则对光场的压缩具有抑制作用并产生量子噪声,量子噪声大小依赖于光场的初始压缩因子r和光场频率ω,且与原子-光场耦合强度g有关.随着r的增大,虚光子过程对光场压缩抑制作用程度由弱到强再由强到弱;随着ω和g的增大,量子噪声分别减小和增大.     

利用外腔谐振倍频产生780nm原子吸收线明亮振幅压缩光

采用连续单频1.56μm激光光源作为泵浦光,通过周期极化铌酸锂晶体外腔倍频过程实验制备出位于原子吸收波线的780nm明亮振幅压缩态光场。在利用2个模清洁器过滤基频光的强度噪声、使之在分析频率4MHz处达到散粒噪声的基础上,利用谐振倍频获得输出功率为10mW、转换效率达40%的倍频光,实测的780nm明亮振幅压缩光的压缩度为0.6dB。     

Amplitude squeezing by means of quasi-phase-matched second-harmonic generation in a lithium niobate waveguide

We demonstrate that traveling-wave second-harmonic generation produces amplitude-squeezed light at both the fundamental and the harmonic frequencies. Quasi-phase-matched second-harmonic conversion efficiencies approaching 60% were obtained in a 26-mm-long single-mode LiNbO(3) waveguide with pulses from a mode-locked laser at 1.53 microm. The amplitude noise of the transmitted fundamental field was measured to be 0.8 dB below the shot-noise level, and the generated 0.765-microm harmonic light was measured to be amplitude squeezed by 0.35 dB. The conversion-efficiency dependence of the observed squeezing at both wavelengths agrees with theoretical predictions. Waveguide losses appear to degrade the squeezing, but the maximum observed squeezing is currently limited only by the available input power.     

受驱动V型三能级激光的光子噪声压缩及其物理机制

应用Scully-Lamb理论研究受驱动V型三能级激光的光子噪声压缩及其物理机制.结果表明该系统可达到10%的腔内压缩和近20%的腔外压缩.尽管V型系统的噪声压缩程度远比Λ型系统(近50%的腔内和腔外压缩)低，V型系统具有与Λ型系统相同的噪声压缩机制. 关键词：     

低分析频率压缩光的实验制备

基于PPKTP晶体的阈值以下光学参量振荡(OPO)过程,制备了共振于铷原子D1线795 nm的压缩真空态光场,研究了分析频率处于千赫兹范围的主要噪声来源,特别是795 nm激光及其二次谐波397.5 nm激光在晶体内吸收引起的非线性损耗增加和系统热不稳定的问题(397.5 nm激光处于PPKTP晶体透光范围边缘,具有高于其他波长数倍的吸收系数).以795 nm和1064 nm为例,分析了非线性损耗及晶体内热效应对压缩度的影响.受限于以上因素,795 nm压缩光很难得到1064 nm波段同样的压缩度.探测系统中的噪声耦合则限制了压缩频带.实验上对分析频率为千赫兹的经典噪声进行了有效控制,通过使用真空注入的OPO、垂直偏振及反向传输的腔长锁定光、低噪声的平衡零拍探测器、高稳定度的实验系统及量子噪声锁定等方法,最终在2.6—100 kHz的分析频段得到了约2.8 dB的795 nm压缩真空.该压缩光可用作磁场测量系统的探测光以提高测量灵敏度.     

Generation of amplitude squeezed green light from a high efficiency PPKTP frequency doubler

We report on a high-efficiency 532 nm green light conversion from an external cavity-enhanced second harmonic generation of a home-made 1064 nm single-frequency Nd:YVO₄ laser with a periodically poled KTP crystal. A stable green power of 60 mW with a conversion efficiency of 75% was measured. Meantime, we investigate the quadrature amplitude noise of the green light at the same experimental setup and 0.6 dB green light squeezing was experimentally observed (taking into account the total detection efficiency of 58%, the squeezing should be 1.1 dB). The squeezing as a function of input power was also studied and we found qualitative agreement with theoretical prediction.     

Squeezing in the audio gravitational-wave detection band

We demonstrate the generation of broadband continuous-wave optical squeezing from 280 Hz-100 kHz using a below-threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational-wave detectors.     

热噪声的相干态和压缩态中的高阶涨落

利用热场动力学的方法研究了具有热噪声的相干态和压缩态中场正交分量的高阶涨落和高阶压缩.利用测量相位算符讨论了这些热化态中相位的高阶涨落.从而得到在有限温度下这些态的低阶及高阶涨落与温度的关系和压缩特性与温度的关系.由于实际的场态总是在一有限的温度下，所以讨论温度对涨落和压缩的影响是很有意义的. 关键词：     

Quantum-noise measurements in high-efficiency single-pass second-harmonic generation with femtosecond pulses

The quantum-noise properties of single-pass second-harmonic blue-light generation with femtosecond pulses have been measured. A conversion efficiency of as much as 63.5% of second-harmonic generation at 428.8 nm was observed in a KNbO(3) crystal with femtosecond (130-fs) pulses with wavelengths centered at 857.6 nm. The quantum noise on the generated blue light was measured to be 1.0 dB (1.4 dB of squeezing inferred) below the shot-noise limit. The noise reduction was found to be sensitive to the average power and the center wavelength of the input fundamental pulses under the condition of strong pump depletion.     

Quantum interference of spontaneous decays: noise reduction in V lasers without inversion

For a four-level double-V laser without inversion we show that the interference of spontaneous decays leads to intensity noise squeezing. The optimum amount of noise reduction is 50%, which is the maximum squeezing in a resonant three-level inversionless Λ-laser with coherent driving and a resonant three-level Raman laser. By transforming into a combination state basis, the Mandel parameter and the output fluctuation spectrum are calculated and the mechanism is interpreted.     

The atom-cavity system as a generator of quadrature squeezed states

This paper describes experiments with a coupled atom-cavity system generating quadrature squeezed states of light. A wide range of parameters was explored and a regime was found where a beam of laser light with significant power (0.17 mW) and good noise suppression (measured 18±3%, inferred 50±10%) was observed. An analysis of the exact phase of the noise suppression shows it to be a minimum uncertainty state with reduced noise in a combined amplitude/phase quadrature. The observations are in good qualitative agreement with a full quantum theory of squeezing in optical bistability.