三能级Λ-系统探测光的频率调制效应研究

研究了三能级Λ系统探测光的频率调制效应. 从经典电子运动方程着手得到介质的极化率；从量子角度出发，应用Bessel函数将频率调制项展开，研究探测光频率调制对系统的影响. 适当调节探测光频率和调制系数，得到系统粒子数随时间周期变化的结论. 还得到系统处于稳态时探测光对应的极化率.     

三能级∧-系统探测光的频率调制效应研究

研究了三能级∧-系统探测光的频率调制效应．从经典电子运动方程着手得到介质的极化率；从量子角度出发，应用Bessel函数将频率调制项展开，研究探测光频率调制对系统的影响．适当调节探测光频率和调制系数，得到系统粒子数随时间周期变化的结论．还得到系统处于稳态时探测光对应的极化率．     

调制转移光谱光频率标准系统中电光参数的优化研究

根据窄带相位调制光在非线性吸收介质中的近简并四波混频的物理机理,分析了采用电光调制器实现调制转移光谱(MTS)技术的电磁场激励及其动态演化过程,建立了MTS中频率色散谱和吸收谱的理论模型. 研究结果表明:以分子吸收谱线色散谱信号作为频率误差鉴别信号时,系统调制频率取0.72倍谱线线宽附近可以得到最佳的色散信号强度;解调相位的变化对吸收谱的影响很大,但对色散谱而言,解调相位在90°附近的小范围波动对频率误差信号解调效果影响不大;调制度在0.5–1区域可以得到较好的综合稳频效果. 关键词： 光频率标准 调制转移光谱 频率稳定 电光参数优化     

级联三能级系统中高阶非线性效应的研究

本文采用二阶相干函数理论研究了级联三能级系统中三阶及五阶极化拍频(TPBCTS及FPBCTS)的非线性效应.通过对泵浦光为宽带及窄带情形的分析,我们发现三阶及五阶极化拍频信号的强度在时域内的变化取决于激光的统计特性和跃迁的横向驰豫率,从而在测量原子能级分裂时可以得到消除多普勒极限增宽的精度.另外,我们对信号的空间调制也进行了分析.     

V型三能级系统中高阶非线性效应的研究

本文采用二阶相干函数理论研究了V型三能级系统中三阶及五阶极化拍频（TPBVTS及FPBVTS）的非线性效应。通过对泵浦光为宽带及窄带情形的分析，我们发现三阶及五阶极化拍频信号的强度在时域内的变化取决于激光的统计特性和跃迁的横向弛豫率，从而在测量原子能级分裂时可以得到消除多普勒极限增宽的精度，另外，我们对信号的空间调制也进行了分析。     

CCD相机在系统奈奎斯频率处的调制传递函数

调制传递函数是成像系统性能的重要参数，在进行CCD相机调制传递函数测试时，通常采用矩形靶标而非正弦靶标，使调制传递函数的测试值与相机系统实际调制传递函数值存在差异，本文对CCD相机在系统奈奎斯特频率处的调制传递函数测试结果进行了理论分析。     

二次偏振调制测距系统中调制频率与测距精度的关系

本文在基于二次偏振调制激光测距系统的基础上, 对调制频率与激光测距系统精度的关系做了深入的理论推导和实验验证. 最终得出结论: 相位法激光测距系统的测量精度会随着调制频率的增大而提高, 且精度的提高程度正比于调制频率的不确定度Δf与测程范围内半波长数N值的比值. 并通过选取合适的调制频率来提高系统的测距精度, 提高后的测距精度可达10^-7.     

光纤频率调制光谱技术中残余幅度调制特性的研究

频率调制光谱(FMS)技术不仅可以用来同时测量原子和分子的吸收和色散,还是噪声免疫腔增强光外差分子光谱(NICE-OHMS)的关键技术,由于光纤器件的引入或光源输出光的偏振态不稳定等因素会诱发残余幅度调制(RAM),RAM的产生使得FMS技术在痕量气体检测中的应用受到极大的限制,因此研究光纤FMS中RAM的特性具有非常重要的意义。研究首先通过理论分析了无吸收时的FMS信号的线型及RAM的影响因素,实验测量无吸收时输入偏振方向和输出偏振方向及电光调制器(EOM)温度对光纤FMS中RAM的影响,均与RAM存在线型关系,验证了理论分析结果,并为RAM的抑制工作以及基于RAM的其他应用提供了依据。     

V型三能级系统中高阶非线性效应的研究

本文采用二阶相干函数理论研究了V型三能级系统中三阶及五阶极化拍频(TPBVTS及FPBVTS)的非线性效应.通过对泵浦光为宽带及窄带情形的分析,我们发现三阶及五阶极化拍频信号的强度在时域内的变化取决于激光的统计特性和跃迁的横向弛豫率,从而在测量原子能级分裂时可以得到消除多普勒极限增宽的精度.另外,我们对信号的空间调制也进行了分析.     

频率调制强吸收光谱中残余幅度调制的理论分析

由电光调制器(EOM)中双折射效应及线偏光不完全沿EOM调制方向诱发的残余幅度调制(RAM)使频率调制(FM)光谱技术在微量气体检测中的应用受到极大的限制。基于光场与晶体相互作用及光学干涉原理推导出存在RAM时FM光谱的线型表达式,确定出输入线偏光角度、EOM中双折射效应、FM系数等是影响线型的主要因素,且当入射EOM光的偏振角度偏离调制方向越大,双折射效应引起的特征偏振方向相位差越大,线型扭曲越严重;同时在FM色散光谱中存在一个受两者影响的直流偏置;最后给出通过伺服控制这两过程可以达到抑制RAM的目的。这些现象及线型的分析将为基于光纤器件的FM光谱提供必要的理论支持。     

The effects of frequency region and level on the temporal modulation transfer function

Temporal modulation transfer functions (TMTFs) were measured using narrow-band AM and QFM noises with upper spectral edges from 0.6 to 4.8 kHz, and spectrum levels of 10 and 40 dB SPL. The cutoff frequency of the TMTF increases as the upper spectral edge is increased up to 4.8 kHz at low levels, and is constant at higher levels. Sensitivity increases with bandwidth if frequency region is constant. In a second experiment, these results were compared to predictions of a model incorporating peripheral and central limitations to modulation detection. To obtain an estimate of peripheral filtering, frequency selectivity was measured using the notched-noise method, with probe frequencies and levels chosen to parallel those in the first experiment. The TMTF data were then predicted using the model. Predicted cutoff frequencies as a function of the upper spectral edge of the test stimulus were lower than but parallel to those of the subjects at the lower stimulus level. The model predicted only a slight increase in cutoff frequency with level, and thus predicted an increase in cutoff frequency with frequency region at the higher level as well, in contrast to the measured data. These results suggest that there are peripheral and central limitations to temporal resolution, but the psychoacoustically derived auditory filter may be only an indirect measure of peripheral filtering, and/or a more complex model may be needed.     

频率变化的光场对双光子过程中量子纠缠的调控

运用量子信息熵理论研究了二能级原子与频率随时间变化的相干态光场作用的双光子过程中纠缠度演化,主要讨论了光场频率随时间作正弦调制和脉冲调制两种情况下,纠缠随时间的演化特性. 当光场频率随时间作正弦调制时,原子与光场的纠缠度明显增大,并保持高纠缠度. 通过改变光场频率调制的频率β和振幅α,发现原子与光场纠缠度的演化过程对调制的振幅更加敏感. 当光场频率随时间作脉冲调制时,在纠缠度最大值处开始加脉冲比在最小值处加脉冲能够更快、更容易实现原子与光场纠缠度的提高和稳定. 脉冲调制的突变使 关键词： 纠缠 场熵 相干态 双光子Jaynes-Cummings模型     

Nonequivalent spectra of unpaired electrons in field and frequency modulation

We report a difference in the spectral lineshapes of continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy between field and frequency modulation. This finding addresses the long-standing question of the effect of modulation in EPR absorption. We compared the first-derivative EPR spectra at 1.1 GHz for lithium phthalocyanine crystals, which have a single narrow linewidth in the EPR absorption spectrum, using field and frequency modulation. The experimental findings suggest that unpaired electrons have different behaviors under perturbation due to field and frequency modulation.     

Propagation effects in three level systems

Certain features of the problem of resonant stimulated Raman scattering using ultrashort pulses are discussed. In particular, for the special case of exact resonance, and when the two pulses have identical initial profiles, the appropriate equation is shown to be the sine-Gordon equation; multisolition solutions are therefore possible for this model system. Effects of pulse propagation on coherent population trapping are discussed.     

Modulation frequency and modulation level owing to vocal microtremor

Vocal microtremor designates a normal slow modulation of the vocal cycle lengths of speakers who do not suffer from pathological tremor of the limbs and whose voices are not perceived as tremulous. Vocal microtremor is therefore distinct from pathological vocal tremor. The objective is to report data about the modulation frequency and modulation level owing to vocal microtremor. The modulation data have been obtained for vowels [a], [i], and [u] sustained by normophonic and mildly dysphonic male and female speakers. The results are the following. First, modulation frequencies and relative modulation levels do not differ significantly for male and female speakers, normophonic and mildly dysphonic speakers, as well as for vowel timbres [a], [i], and [u]. Second, the typical interquartile intervals of the modulation frequency and modulation level are equal to 2.0-4.7 Hz and 0.4%-1.3%, respectively. Third, dissimilarities between data reported by different studies are due to different cutoff frequencies below which spectral peaks are considered not to contribute to vocal microtremor.     

双模场与V型三能级原子玻色-爱因斯坦凝聚体相互作用系统的光场压缩效应

研究了V型三能级原子玻色-爱因斯坦凝聚体与双模压缩相干态光场相互作用系统中的光场压缩的特性。数值计算结果表明：光场的正交分量呈现周期性压缩,其周期与原子间相互作用密切相关,而最大压缩量与持续时间与初始光场的压缩因子有关。     

The influence of carrier level and frequency on modulation and beat-detection thresholds for sinusoidal carriers

This paper is concerned with modulation and beat detection for sinusoidal carriers. In the first experiment, temporal modulation transfer functions (TMTFs) were measured for carrier frequencies between 1 and 10 kHz. Modulation rates covered the range from 10 Hz to about the rate equaling the critical bandwidth at the carrier frequency. In experiment 2, TMTFs for three carrier frequencies were obtained as a function of the carrier level. In the final experiment, thresholds for the detection of either the lower or the upper modulation sideband (beat detection) were measured for "carrier" frequencies of 5 and 10 kHz, using the same range of modulation rates as in experiment 1. The TMTFs for carrier frequencies of 2 kHz and higher remained flat up to a modulation rate of about 100-130 Hz and had similar values across carrier frequencies. For higher rates, modulation thresholds initially increased and then decreased rapidly, reflecting the subjects' ability to resolve the sidebands spectrally. Detection thresholds generally improved with increasing carrier level, but large variations in the exact level dependence were observed, across subjects as well as across carrier frequencies. For beat rates up to about 70 Hz (at 5 kHz) and 100 Hz (at 10 kHz), beat detection thresholds were the same for the upper and the lower sidebands and were about 6 dB higher than the level per sideband at the modulation-detection threshold. At higher rates the threshold for both sidebands increased, but the increase was larger for the lower sideband. This reflects an asymmetry in masking with more masking towards lower frequencies. Only at rates well beyond the maximum of the TMTF did detection for the lower sideband start to be better than that for the upper sideband. The asymmetry at intermediate frequency separations can be explained by assuming that detection always takes place in filters centered above the stimulus spectrum. The shape of the TMTF and the beat-detection data reflects a limitation in resolving fast amplitude variations, which must occur central to the inner-ear filtering. Its characteristic resembles that of a first-order low-pass filter with a cutoff frequency of about 150 Hz.