共查询到20条相似文献,搜索用时 15 毫秒
1.
Xin Zhou Xiaoping Zheng He Wen Hanyi Zhang Yili Guo Bingkun Zhou 《Optics Communications》2011,284(15):3706-3710
We propose and experimentally demonstrate an all optical arbitrary waveform generation by optical frequency comb (OFC) based on cascading intensity modulation. By selecting spectral lines of interest from OFC through optical filters, 10 GHz, 20 GHz, and 60 GHz sinusoidal signals with low phase noise and more complex waveforms, including ultra-short pulse, half-wave cosine, and single frequency modulated MMW signals, are generated easily. 相似文献
2.
Investigation of three-pulse photon echo in thick crystal using finite-difference time-domain method 下载免费PDF全文
This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works.The influence of thickness on the three-pulse photon echo's amplitude and efficiency is analyzed with the Maxwell-Bloch equations solved by finite-difference timedomain method.We demonstrate that the amplitude of three-pulse echo will increase with the increasing of thickness and the optimum thickness to generate three-pulse photon echo is 0.3 cm for Tm~(3+):YAG when the attenuation of the input pulse is taken into account.Meanwhile,we find the expression 0.09 exp(α'L),which is previously employed to describe the relationship between echo's efficiency and thickness,should be modified as 1.3 · 0.09 exp(2.4 ·α'L) with the propagation of echo considered. 相似文献
3.
G. G. Fedoruk 《Journal of Applied Spectroscopy》1998,65(3):420-426
Attenuation of the signals of the nutation echo of E’-centers in crystalline and glass quartz was experimentally investigated
at room temperature. The nutation echo in EPR was excited in the single-photon regime and formed by two Zeeman-field pulses
with duration t1 and t2 (t1<t2) and time interval between them τ. The echo signal was recorded during the second pulse at t≈2t1+τ. It was established that this signal attenuation, measured as t1 increased, follows an, exponential law, its rate Γ is much less than 1/T2 (T2 is the transverse relaxation time), and it linearly increases with an increase in the amplitude of the exciting SHF field
B1. The parameters of the dependence of Γ on B1 correlate with the parameters of the analogous dependence revealed previously for attenuation of nutation of E’-centers in
quartz in the two-photon regime at T=4.2 K. At the same time, the value of Γ measured with different values of τ is independent
of B1 and is equal to 1/T1, where T1 is the longitudinal relaxation time.
A. N. Sevchenko Scientific Research Institute of Applied Physical Problems, 7, Kurchatov St., Minsk, 220064, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 405–411, May–June, 1998. 相似文献
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V. A. Tolkachev 《Journal of Applied Spectroscopy》1999,66(6):874-881
The sensitivity of the delay time of the molecular rotational quantum echo to change in the rotational constants of molecules
was investigated with a model of the rotational quantum echo considered as an optically induced quantum synchronization of
the Fourier rotational modes of an asymmetric molecular top. The J-echo and the K-echo were investigated for the A- and C-configurations
of rotation of a top molecule. The contour maps of the dependence of the sensitivity of the delay time of these types of echo
to changes in the rotational constants on the parameters of the molecular tops have been obtained for all the rotational constants.
They show that the delay time of the rotational quantum echo is greatly dependent on the configuration of rotation of the
top molecule and on the rotational constants. It is shown that the optical probing of the rotational quantum echo can also
be performed by the optical rotation of the investigated molecule, and in this case the rotational force is dependent on the
intramolecular orientation of the magnetic dipole moment. It was determined that a high sensitivity of the delay time of the
echo to changes in the rotational constants can be responsible for the broadening of the echo pulse and even for its disappearance.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus;
e-mail: lssm@imaph.bas-net.by. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 758–764, November–December,
1999. 相似文献
6.
Numerical simulation of four-wave mixing efficiency and its induced relative intensity noise 下载免费PDF全文
Four-wave mixing,as well as its induced intensity noise,is harmful to wavelength division multiplexing systems.The efficiency and the relative intensity noise of four-wave mixing are numerically simulated for the two-wave and the three-wave fiber transmissions.It is found that the efficiency decreases with the increase of both the frequency spacing and the fiber length,which can be explained using the quasi-phase-matching condition.Furthermore,the relative intensity noise decreases with the increase of frequency spacing,while it increases with the increase of fiber length,which is due to the considerable power loss of the pump light.This investigation presents a good reference for the practical application of wavelength division multiplexing systems. 相似文献
7.
A. Mendoza-García J.L. Paz A. Romero-Depablos E. Castro P. Martín 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(1):155-159
In this work, the absorptive and dispersive profiles of a molecular system have been calculated through a methodology based on the averaging of the coherence obtained by the resolution of the optical stochastic Bloch equations. To this aim, a generalized Lorentzian approximation to the Voigt function has been used as a probability distribution, which allows a more generalized analysis of the interactions between the solvent and the molecule. This has been modeled with the parameters of the standard organic dye Green Malaquite, which exhibits a nonlinear behavior under the interaction with a high intensity electric field. 相似文献
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在建模和理论分析的基础上, 对三脉冲飞秒激光作用下核壳结构CdSe/ZnS量子点量子阱中1se1sh激子光跃迁引起的受激光子回波效应进行了深入研究.运用有效质量近似方法求解了载流子的静态薛定谔方程,得到能量本征值和对应波函数.基于光学Bloch方程,分析了受激光子回波的参量相关性.结果显示受激光子回波信号可以通过量子点量子阱结构和尺寸的改变进行有效调节.同时,在量子尺寸限制理论的基础上讨论了结构和尺寸的变化对受激光子回波信号的具体影响. 相似文献
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J.L. Paz A. Mendoza-García A. Mastrodoménico 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(1):100-108
In this study, we determined the absorptive and dispersive optical profiles of a molecular system coupled with a thermal bath. Solvent effects were explicitly considered by modelling the non-radiative interaction with the solute as a random variable. The optical stochastical Bloch equations (OSBE) were solved using a time-ordered cumulant expansion with white noise as a correlation function. We found a solution for the Fourier component of coherence at the third order of perturbation for the nonlinear Four-wave mixing signal and produced analytical expressions for the optical responses of the system. Finally, we examined the behaviour of these properties with respect to the noise parameter, frequency detuning of the dynamic perturbation, and relaxation times. 相似文献
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The general expressions of the average dissipative and dipole forces acting on a A-configuration three-level atom in an arbitrary light field are derived by means of the optical Bloch equations based on the atomic density matrix elements, and the general properties of the average dissipative and dipole forces on a three-level atom in the linearly-polarized high-order Bessel beams (HBBs) are analysed. We find a resonant property (with two resonant peaks) of the dissipative force and a non-resonant property (with two pairs of non-resonant peaks) of the dipole force on the three-level atom, which are completely different from those on the two-level atom. Meanwhile we find a saturation effect of the average dissipative force in the HBB, which comes from the saturation of the upper-level population. Our study shows that the general expressions of the average dissipative and dipole forces on the three-level atom will be simplified to those of the two-level atom under the approximation of large detuning. Finally, we study the axial and azimuthal Doppler cooling of atoms in ID optical molasses composed of two counter-propagating HBBs and discuss the azimuthal influence of the HBB on the Doppler cooling limit. We also find that the Doppler limit of atoms in the molasses HBB is slightly below the conventional Doppler limit of hГ/(2kB) due to the orbital angular momentum lh of the HBB. 相似文献
15.
It is shown that for certain optically excited symmetric top molecules which lase in the far-infrared that it is possible to increase their lasing efficiency through resonant pumping of the higher k quantum number transitions which have increased statistical weights due to increased molecular symmetry. 相似文献
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二倍频晶体温升分布对输出光场分布的影响 总被引:1,自引:1,他引:0
利用分步快速傅里叶变换和四阶龙格-库塔法,对具有一定温升分布的倍频晶体的二次谐波转换过程进行了研究。综合考虑了谐波转换过程中的离散、衍射、二阶、三阶非线性等效应,着重讨论了倍频晶体吸收光能后,晶体内温升分布对晶体内o光和e光的折射率分布的影响,定量分析了温度分布引起的相位失配量、输出光场分布、二次谐波转换效率随倍频晶体温度分布变化的规律。结果表明:在高功率倍频系统中,倍频晶体温升分布引起基频光、倍频光的相位失配,相位失配导致输出光场光强分布的变化以及谐波转换效率的降低。 相似文献
18.
Using low intensity ultrasound to improve the efficiency of biological phosphorus removal 总被引:2,自引:0,他引:2
Low intensity ultrasound can produce various effects on biological materials, such as stimulating enzyme activity, cell growth, biosynthesis, etc., which may improve the efficiency of enhanced biological phosphorus removal (EBPR). We adopt total phosphorus (TP) and dehydrogenase activity (DHA) as indicators to confirm the feasibility of applying low intensity ultrasound in EBPR. Single-factor experiments and orthogonal test were conducted in batch anaerobic/oxic (A/O) process simulation to study the influence of ultrasonic intensity and exposure time in the EBPR process. The results showed that the optimal ultrasonic parameters were 0.2 W/cm2 and 10 min under which condition the TP concentration in the effluent was 35–50% lower than that of the control (without ultrasonic irradiation). Changes of sludge activities after ultrasonic irradiation were examined. The improvement of sludge activity by ultrasound took 4 h after irradiation to reach the peak level, when an increase above 50% of DHA has been achieved by ultrasonic irradiation, and the enhancing effects induced by ultrasound disappeared in 16 h after irradiation. A tentative mechanism of biological phosphorus removal enhancement stimulated by ultrasound was discussed based on these phenomena. 相似文献
19.
缩短射频脉冲宽度, 有助于解决脉冲电力消耗大、样品吸收率高、信噪比低等极端条件核磁共振探测的关键问题. 本文首先分析射频脉冲角度对核磁共振自旋回波信号强度的影响机理, 基于Bloch方程推导了回波信号幅度与扳转角、重聚角的关系. 在特制核磁共振分析仪上采用变脉冲角度技术, 分别在均匀磁场和梯度磁场条件下实现对扳转角和重聚角与回波信号强度关系的数值模拟和实验测量. 结果表明, 梯度场中, 扳转角为90°、重聚角为140°的射频脉冲组合获得最大首波信号强度, 比180°脉冲对应的回波幅值提高13%, 能耗降低至78%. 选用该重聚角(140°) 优化设计饱和恢复脉冲序列探测流体的纵向弛豫时间T1特性, 准确获得 T1分布.该结果对于低电力供应、且对信噪比有较高要求的核磁共振测量, 如随钻核磁共振测井和在线核磁共振快速检测等, 具有重要意义.
关键词:
核磁共振
信号强度
重聚脉冲角度
Bloch方程 相似文献
20.
Hiroki MONJO Yoshihiro FUKUMOTO Tsuyoshi ASAI Hiroki KUBO Kensuke OHSHIMA Hirotsugu TAJITSU Shota KOYAMA 《Physical Therapy Research》2020,23(2):188
Objective: The stroke survivors exhibit change in muscle quantity and quality compared to healthy older adults. This study aimed to compare the muscle thickness (MT) and echo intensity (EI) values of individual muscles between stroke survivors and age- and sex-matched healthy older adults. Methods : In total, 27 stroke survivors and 34 healthy older adults participated in this study. The MT and EI values of the following muscles were assessed from transverse ultrasound images: rectus abdominis (RA), external oblique, internal oblique, transversus abdominis, rectus femoris, vastus intermedius (VI), vastus lateralis (VL), vastus medialis (VM), tibialis anterior (TA), gastrocnemius (Gas), and soleus (Sol). The MT and EI values of these muscles were compared between stroke survivors and healthy older adults. Results : The MT values of the VL, VM, and RA on the non-paretic sides were significantly higher and those of the TA, Gas, and Sol on the paretic sides were significantly lower in the stroke survivors than in the healthy older adults (P < 0.05). The EI values of the VI, VL, VM, TA on the paretic sides and those of the Gas on both the paretic and non-paretic sides were significantly higher in the stroke survivors than in the healthy older adults (P < 0.05). Conclusion : Stroke survivors seem to develop muscle hypertrophy of the non-paretic thigh muscles owing to a compensatory strategy. In addition, the lower-leg muscles on the paretic side of stroke survivors tend to show both quantitative and qualitative muscle changes. 相似文献