石英光纤中二次非线性级联波长转换的理论分析

提出了利用周期性热及电场诱导D型光纤光栅的二次非线性级联(χ⁽²⁾∶χ⁽²⁾),实现在波分复用网中波长转换的方法,并进行了理论分析.推导出χ⁽²⁾ ∶χ⁽²⁾的耦合模方程,得出了小信号条件下转换产生光波的场强振幅和 功率,以及转换效率η的解析式,该式与数值计算相吻合.解析式和数值结果都表明,在近 似满足相位匹配条件下,η与抽运光功率平方、光栅总长度L和二次非线性系数d的四次方分 别成对数关系.计算结果表明,这种光纤光 关键词： 石英光纤 二次非线性 级联 波长转换 光纤光栅 诱导     

Theory of the effects of nuclear structure on internal conversion in Tl203

The Fermi-liquid method is applied to consider the effects of the strong interaction on the penetration matrix element for the conversion transition in Tl²⁰³. The theoretical value agrees well with experiment.We are indebted to M. A. Listengarten for discussions.     

Wavelength conversion based on high nonlinear microstructured fiber

A wavelength conversion based on high nonlinear microstructured fiber is demonstrated. Core diameter and pitch of the microstructured fiber used in this wavelength conversion method are 2.05 μm and 5.0 μm, respectively. Diameter of the air-holes in the fiber cladding is 4.50 μm, the nonlinear coefficient of the microstructured fiber is 112.2 W^?1 km^?1 and it is 60 times higher than that of a conventional dispersion-shift fiber, the length of the fiber is 100 m. Four-wave-mixing effect is improved in the high nonlinear microstructure fiber and then the efficiency of the wavelength conversion is improved also. 10 Gbps Not-Return-to-Zero (NRZ) modulation format and 10 Gbps Return-to-Zero (RZ) modulation format are converted effectively by our method. This study can provide a new alternative solution for high effective all-light wavelength conversion in high speed optical communication systems with multi-wavelengths and all-light optical networks.     

Precise measurement of hyperfine coupling in CH F based on nuclear spin conversion

A new method is proposed for the experimental determination of the hyperfine coupling in molecules. The method is based on the level-crossing effect in the spin isomer conversion in alternating electric fields. An experiment performed with the ¹³CH₃F molecules has revealed the strength of the off-diagonal in K () nuclear spin-spin coupling kHz, which is only by kHz larger than the theoretical value calculated on the basis of the molecular structure. Received 25 January 2000 and Received in final form 11 May 2000     

Measurement of compound-nucleus lifetime by X-ray spectroscopy in the 106Cd(p,p')106Cd reaction

A new method for measuring compound-nucleus lifetimes in the range of 10^?18–10^?16 s is presented. The method is based on the comparison between the known lifetime of an atomic excited state used as a reference and the nuclear delay time to be measured. On-line coincidences performed between the nuclear reaction products and the emitted X-rays enable the selection of the atomic vacancies decaying during the compound stage of the nuclear interaction. The main characteristics of this technique are illustrated by measurements of lifetimes of the ¹⁰⁷In compound nucleus excited at 13.6 and 15.6 MeV in the ¹⁰⁶Cd(p, p')¹⁰⁶Cd reaction. They are found in agreement with statistical model calculations. The spurious effect associated with decay by internal conversion of final states populated by the competitive (p, n) reaction is emphasized.     

Monte Carlo modelling of human body for dose conversion coefficients of 137Cs in soil of the Eastern Black Sea region of Turkey

Absorbed dose conversion coefficients for a human body standing on the soil surface were calculated for ¹³⁷Cs in the soil of Eastern Black Sea region of Turkey using the Monte Carlo simulation method. The results were given in nGy h^?1 per Bq cm^?2 as a function of depth. Simple numerical integration of this function multiplied with the known specific activity as a function of depth gives the absorbed dose conversion coefficients for any distribution of ¹³⁷Cs in soil. Gaussian distribution of ¹³⁷Cs in the soil was considered for calculations.     

Detailed spectroscopy in the superdeformed second minimum of 240Pu

Spectroscopic studies in the superdeformed shape isomer of ²⁴⁰Pu using γ-spectroscopy, conversion electron spectroscopy and transmission resonance spectroscopy have been performed. In a high-resolution and high-efficiency γ-spectroscopy experiment the out-of-band decays of several excited superdeformed rotational sequences with K=2^? and 1^? could be identified together with evidence for a weakly populated 0^? octupole band. Surprisingly, no low-lying collective quadrupole excitations could be observed. Complementary information could be obtained in conversion electron measurements in coincidence with isomeric fission, resulting in the first identification of the lowest ß-vibrational K=0⁺ band. For all rotational bands the variation of the moment of inertia with spin could be studied. A predominant population of negative parity states in the second well could be observed, which can be explained by the selective population and depopulation of the second minimum. Complementary transmission resonance measurements have been performed, yielding new information on the fine structure of high-lying (ß-)vibrational multi-phonon states. A new method could be established to determine the excitation energy of the fission isomer ground state from measured level densities.     

Nonlinear frequency conversion in 2D χ (2) photonic crystals and novel nonlinear double-circle construction

The analytic solution to the wave equation for small-signal sum-frequency process is derived in 2D χ ⁽²⁾ photonic crystals with use of the Green function method. It is predicted that the sum-frequency electrical field at quasi-phase matching (QPM) resonance is proportional to the angle-dependent effective crystal length. This implies that multiple wavelength QPM frequency conversion with controllable intensity output can be realized in a single 2D χ ⁽²⁾ photonic crystal. It is revealed that efficient frequency conversion requires both the QPM and the proper structure matching. A novel double-circle construction, different from the conventional Ewald construction, is presented to reflect important QPM processes. It is also shown that the QPM resonance tuning of second-harmonic generation can operate over the whole transparent wavelength range of crystals. Received 19 April 2001     

Raman microspectroscopic mapping or thermal system used to investigate milling‐induced solid‐state conversion of famotidine polymorphs

Confocal Raman microspectroscopy was used to nondestructively determine the polymorphic conversion of famotidine in the course of the milling process. A mapping system was applied to assess the blending uniformity of each polymorphic component in the milled mixture. Raman microspectroscopy combined with a thermal analyzer was also used to investigate the synergistic co‐effects of milling and heating on the polymorphic conversion of famotidine polymorphs. Famotidine has two polymorphs, forms A and B, the raw material of famotidine used was proved to be of form B. The Raman peak intensity ratio of the 2920 cm⁻¹ band for form A and 2897 cm⁻¹ band for form B was used to act as an indicator to evaluate the polymorphic conversion of famotidine form B to form A after different milling courses. The results indicate that the peak intensity at 2897 cm⁻¹ gradually decreased with the milling time, whereas the peak intensity at 2920 cm⁻¹ slowly enlarged, suggesting the polymorphic conversion of famotidine from form B to form A. The longer milling process might strongly induce and promote this polymorphic conversion of famotidine. Both polymorphic forms of famotidine were found to be well uniformly distributed within the milled samples due to their smaller varieties by using the Raman microscopic mapping system. The temperature effect could synergistically accelerate the polymorphic conversion of famotidine from form B to form A in the milled sample. The thermal‐dependent critical temperature for sharply enhancing the content of famotidine form A in each milled sample was also identified. Copyright © 2007 John Wiley & Sons, Ltd.     

Discrete conversion of gamma rays in 229Th and in highly ionized 125TeQ ions

The complex of problems associated with the discrete conversion of gamma rays is considered. The analogue of the internal conversion coefficient is determined for the case of discrete conversion, and specific computations are made. The calculated values of the half-life of the nuclear level E _γ = 35.492 keV in ¹²⁵Te^Q ions (Q = 45–48) are in good agreement with the measured quantities. Computations for the spectrum of optical photons accompanying the de-excitation of the nuclear level E _γ = 3.5 ± 1 eV in ²²⁹Th, carried out using the Dirac-Fock multiple configuration method, show that the highest-intensity spectral lines are situated in the region of 2.3–2.4 eV, which is in accord with the experimental data.     

钍俘获反应率离线伽马测量方法

为了测定聚变-裂变反应堆模型钍包层中的钍俘获率以及钍-铀转化率, 探索了一种新的钍活化离线γ测量法. 利用测量²³²Th俘获反应产物²³³Th衰变链中²³³Pa衰变放出的311.98 keV 特征γ射线, 来反推计算并最终确定²³²Th(n,γ)²³³Th的反应率, 测试实验中不确定度约6% (²³³Th/²³²Th量级为10^-17情况下). 详细介绍了此方法的背景和原理方法, 并进行简单的校验实验, 证明其能够较好地得到模拟装置中的俘获率. 与瞬发γ测量法以及质谱分析法进行对比, 本方法更适合用于聚变-裂变反应堆模型钍包层中的钍俘获率以及钍-铀转化率测量, 并有望进一步测量其他相关参数.     

Nuclear spin conversion in diatomic molecules

A mechanism of the internal interaction in dimers that mixes different nuclear spin modifications has been proposed. It has been shown that the intramolecular current associated with transitions between electronic terms of different parities can generate different magnetic fields on nuclei, leading to transitions between spin modifications and to the corresponding changes in rotational states. In the framework of the known quantum relaxation process, this interaction initiates irreversible conversion of nuclear spin modifications. The estimated conversion rate for nitrogen at atmospheric pressure is quite high (10^?3–10^?5 s^?1).     

Internal conversion studies of transitions in96Mo

The internal conversion spectrum from the decay of⁹⁶Tc has been investigated using a 50 cm radius double-focussing beta-ray spectrometer. Relevant features of the internal conversion spectrum from the decay of⁹⁶Nb have also been reexamined in the same way. Special interest has been focussed on investigating a proposed doublet level structure at about 2.44 MeV and higher lying levels in⁹⁶Mo. Internal conversion coefficients have been obtained for most transitions by combining the measured conversion electron intensities obtained in this work with recently reported gamma-ray intensities from Ge(Li) detector measurements. A level scheme has been compiled and deduced transition multipolarities have been used for a discussion of spins and parities for the levels.     

Very converted transitions and particle-core coupling in neutron-deficient odd-mass au isotopes

Levels in^{185, 187}Au have been studied by radioactive decay of isotopically separated^{185, 187}Hg. A number of low-energy very-converted transitions are observed in the decay. It is shown that the enhanced conversion in these cases comes from an E0 component rather than from an anomaly in theM1 conversion process. A systematic pattern of bands interconnected with these very converted transitions is presented as evidence for a new type of particle-core coupling in^{185, 187}Au.     

Triggering the <Superscript>178<Emphasis Type="Italic">m</Emphasis>2</Superscript>Hf isomer via resonance conversion

Experiments on photoinduced deexcitation of ^178m2Hf are reanalyzed. A mechanismof triggering the 12.7-keV E3 transition, based on resonance conversion, is considered. That rises the efficiency by an order of magnitude. The main obstacle for enhancing the efficiency is a high internal conversion rate. For this reason, isomers with low multipole order (E1, M1) with high enough energy of the triggering transition are more suitable for triggering. Another way is offered by partial ionization of the outer electrons for decreasing the conversion rate. The results are applied to experiments in laser-produced plasma. The text was submitted by the authors in English.     

The beta branching ratio and conversion coefficients in the137Cs decay

The decay of¹³⁷Cs has been reinvestigated using several precision counting methods. The emission rate ofβ-particles plus internal conversion electrons was measured by the 4π-proportional counter method using vacuum evaporated sources free of self-absorption and checked by the liquid scintillation method. TheK-conversion coefficient was determined by the electron X-ray coincidence method using a magnetic spectrometer and a high resolution Si(Li) detector. TheK/(L+M+...) conversion ratio and a second less accurate value for the β-branching ratio were obtained from the recorded electron spectra. Theγ-ray emission rate of all sources was determined to within ±0.14%, on the average, with a calibrated NaI(Tl) crystal detector. As results the intensity of theβ-decay to the ground state of¹³⁷Ba could be determined to (5.4±0.3)% of the¹³⁷Cs decays, theK-conversion coefficient to 0.0916±0.0004, and theK/(L+M+...) conversion ratio to 4.41±0.04. From these values the γ-ray emission intensity is (85.1±0.4)% of the¹³⁷Cs decays and theK X-ray emission intensity is (8.13±0.10)% of the emittedγ-rays. All errors are discussed in detail.     

Open-channel fluorescence imaging of atoms in high-gradient magnetic fields

A method of imaging distributions of cold atoms under the presence of large trapping-field-induced level shifts is investigated. By utilizing a probe laser tuned to an open transition, the fluorescence yield per atom is largely fixed throughout the trap volume, independent of the trapping field. This enables a reliable conversion of fluorescence images into atomic-density profiles. The method is applied to measure distributions of ⁸⁷Rb atoms in a high-gradient (2.7 kG/cm) magnetic atom guide. We characterize the parameters for which the open-channel imaging method performs best. Results of quantum Monte Carlo simulations verify the underlying assumptions of the method.     

Excited states of 154Tm

A high-spin level structure of the nucleus ¹⁵⁴Tm has been established for the first time up to 6.14 MeV. The ¹¹⁸Sn + ⁴⁰Ca reaction at 205 MeV associated with the recoil shadow method was used to identify the I ^π = (19)⁺ isomeric state at 2.74 MeV. In-beam γ-ray and conversion electron spectroscopy have been applied on the ¹⁴⁴Sm(¹⁴N, 4n)¹⁵⁴Tm reaction at 95 MeV to build the level scheme. The level structure of ¹⁵⁴Tm is compared to other structures observed in N = 85 neighbouring nuclei. Received: 4 January 2002 / Accepted: 15 March 2002     

Mössbauer spectroscopy in determining the gas molecular state

A possibility of conversion electron Mössbauer spectroscopy for determining the gas molecular state is shown. For acceleration of gas interaction with active surface the thin iron layer enriched with ⁵⁷Fe was applied on aluminum foil and gas discharge is used.     

Generation of thermonuclear energy by fusing hydrogen and lithium atoms

A method of designing a thermonuclear reactor based on the modified Cockroft-Walton accelerator, where the lithium-proton fusion was first observed, is considered. It is proposed that the reactor have the form of a spherical capacitor with a point lithium cathode used as the inner electrode and a spherical anode, as the outer electrode. The interelectrode space is filled with hydrogen. A high-voltage electric pulse applied to the electrodes is used as a driver. The reactor parameters providing an ion temperature of 100 keV and a proton flux of 8.6×10¹⁵ W/cm² to the cathode are determined. The basic elements of a system generating thermonuclear fusion energy, including those of the energy conversion chamber with a fusion chamber inside, are listed, and possible applications of the system are indicated.