中心波长121.6nm的真空紫外窄带滤光片设计和制备

采用双半波法布里-珀罗(F-P)干涉滤光片结构设计了中心波长在121.6 am的窄带滤光片,其峰值透射率为6.78%,通带半宽度为10.7 nm.通过设计、制备和测量峰值波长在217 nm的滤光片验证了设计用到的光学常数和膜厚定标都比较精确.在此基础上制备了121.6 nm的窄带滤光片,到合肥同步辐射实验室测量的结果是中心波长在120.74 nm,峰值透射率为5.94%,通带半宽度为12 nm.可以看出实际制备的滤光片和预先设计的基本吻合但还是有一定的偏差,最后对实际测量的和理论设计的偏差进行了分析.     

Nonlinear coupling and relaxation of fluctuations and the central peak

A simple model Hamiltonian for a structural phase transition is discussed. It is shown that using the modecular field approximation one obtains a nonlinear coupling of the order parameter and entropy fluctuations. This results in a central peak in the order parameter fluctuation spectrum. The width of the central peak is proportional to the entropy relaxation rate.     

考虑自作用后二能级原子的共振荧光谱

本文考虑了在驱动场及原子辐射场作用下,二能级原子的共振荧光谱,这样计算得的荧光谱与只考虑驱动场作用的荧光谱比较有许多新的特点,其中很重要的是由自作用引起的中峰的真空场Rabi分裂,以及由边峰作用出现的中峰。 关键词：     

EPR in SrTiO3: Dynamical or dirt effect?

The inhomogeneous broadening of the EPR line due to imperfections is shown to have a critical anomaly in the vicinity of structural phase transitions. On the basis of the result, conclusions about the nature and the width of the central peak are drawn and a new experimental test is proposed to decide between the different explanations of the central peak.     

Low-frequency Raman scattering study of the ferroelectric phase transition in the DKDP crystal

The low-frequency Raman scattering spectra of the DKDP ferroelectric crystal are studied in the temperature range 30–393 K. At temperatures above 150 K, the Raman spectra exhibit a central peak which reflects the lattice relaxation susceptibility. The width and integrated intensity of the central peak are derived from the experimental spectra. The critical slowing down of the relaxation response predicted by the Ginzburg-Landau-Devonshire theory is observed throughout the temperature range in which the central peak persists. Its integrated intensity does not, however, follow the predictions of the theory and reveals a strong temperature dependence in the ferroelectric phase and a weaker dependence in the paraphase. It is shown that the thermal activation law describes well the temperature dependence of the intensity of the central peak. An interpretation is proposed according to which the intensity of order parameter fluctuations is related to the activation barrier whose height is proportional to the deviation from the phase transition temperature.     

On the hydrodynamic theory of central peak in displacive structural phase transitions

A model involving nonlinear coupling between the overdamped phonon mode and temperature fluctuations is studied using the dynamic renormalization group method. It is shown that the behavior of the central peak in the dynamic form factor depends on the specific heat exponent α. For α < 0 and as T → T_c the central peak is found to merge with the over-damped phonon mode and the coupling goes to zero at T_c as (T ? T_c)^?α. An argument on the intensity of the central peak in the critical region in presented and it is concluded that the hydrodynamic coupling may not be the dominant mechanism of the central peak in SrTiO₃.     

Impurities and the static central peak in lead germanate

The static central peak in the Raman spectrum of lead germanate (Pb₅Ge₃O₁₁) has been studied as a function of barium-doping and oxygen concentration. It is found that the substitution of barium for lead dramatically increases the intensity and temperature spread of the central peak while also shifting it and the Curie point to much lower temperatures. On the other hand, variations in the observed central peak intensity in nominally pure samples cannot be correlated with variation in oxygen content and must be attributed to some as yet unidentified impurities or defects.     

Properties of tight-binding electrons in a two-dimensional quasi-lattice

A numerical evidence is given that indicates the existence of a central peak with side gaps in the tight-binding electronic spectra in a Penrose tiling with one type of interaction. The central peak and the side gaps disappear as another type of interaction with sufficient strength is introduced. By examining the spatial extent of eigenfunctions, it is predicted that most of eigenstates are not extended nor localized in the conventional sense.     

On the universal regularities of the lattice dynamics in ferroelectrics

The main regularities revealed for the dynamic response in recent Raman spectroscopic investigations of ferroelectric crystals of the displacive type (LiNbO₃, LiTaO₃) and the order-disorder type (KDP, DKDP) are discussed. The characteristic feature of the dynamic response for all the crystals (KDP, DKDP, LiNbO₃, LiTaO₃) under investigation in the vicinity of the phase transition temperature is an intense central peak that follows from the theoretical predictions for the order-disorder phase transition. The possible factors responsible for the central peak, the character of the behavior of this peak outside the aforementioned temperature range, and the specific features of the behavior of the width and intensity of the central peak over a wide range of temperatures for order-disorder crystals are analyzed.     

Dynamic structural form-factor of quasi-one-dimensional ferroelectrics with random impurities

We consider a one-dimensional model of displacive structural phase transitions with random temperature-type impurities. The modification to the central peak is calculated. It is shown that random-temperature impurities lead to a divergence in the central peak intensity. We find good agreement between our results and the experimental temperature dependence of the central peak.Translated from Izvestiya Vysshikh Uchebnikh Zavedenii, Fizika, No. 4, pp. 57–62, April, 1988.     

Study of the central peak in Raman spectra of <Emphasis Type="Italic">SBN</Emphasis> crystals

The Raman spectra of SBN crystals were recorded over wide spectral and temperature ranges. It is shown that a central peak representative of relaxation processes is observable in different spectral configurations of Raman measurements and cannot be described in the single relaxation time approximation. In the vicinity of the temperature corresponding to the onset of nucleation of polar regions (the Burns temperature), no specific features in the behavior of the central peak were observed.     

Critical dynamics in the presence of relaxing defects

The influence of defects coupling linearly to the order parameter on the critical behaviour of structural phase transitions is studied. A continuum model for the statics and dynamics is introduced and is investigated by the renormalization group theory. If the defects are slow a central peak is found, the characteristic width of which is determined by the defects. Concerning the critical behaviour the dynamical model belongs to the same universality class as the one studied previously by Grinstein, MA, and Mazenko. The concentration dependence of the central peak response is discussed inside and outside the critical region.     

Frequency and intensity readouts of micro-wave electric field using Rydberg atoms with Doppler effects

A scheme of electric-field measurement of micro-waves is proposed in Rydberg atoms with Doppler effects. A cascade-type electromagnetically-induced-transparency (EIT) system is disturbed by a perturbative field coupling a metastable transition. The original dark state splits and two EIT window appear with a central absorption peak. When a micro-wave (MW) field couples the Rydberg transition, the central absorption peak is divided into two. The frequency splitting of two central peaks is proportional to the MW field intensity, which can be used to probe MW electric field strength. This frequency-readout method based on a double-dark state system increases the probe sensitivity nearly by a factor of 7, compared with that of the single-dark state case. At room temperature, Doppler effects can enhance the absorption spectrum, moreover, its peak value varies linearly with the MW field strength. This can also serve to measure MW electric field strength. Numerical results show that the latter intensity-readout method after Doppler averaging improves the probe sensitivity by a factor of 10 with respect to the case without Doppler effects.     

Observation of a central peak in lead germanite by light scattering

Brillouin-Raman scattering measurements on single domain lead germanate over the temperature interval 300–455 K reveal an unresolved (less than 80 MHz) central peak. At about T_c?20 K this peak begins to increase in intensity, reaching a maximum at T_c, and then falls away rapidly with increasing temperature above the transition. The central peak anomalous intensity, which is visible to the naked eye, is much larger than the intensity contributions due to phonons, including the ferroelectric soft mode, and appears to be a static effect.     

一维扭折声子气的动力性质

本文采用投影算子方法统一处理了一维扭析声子耦合气体的动力结构因数。得到了反映扭声作用的中心峰和软化阻尼声子峰,其中的中心峰大为不同于用重整化扭折平均密度直接求得的。 关键词：     

Sideband structure spontaneous spectrum without the rotating wave approximation

The effects of the non-rotating wave approximation (non-RWA) on the spontaneous emission of a V-type three-level atom are studied, where the excited states are coupled to a common ground state by a weak laser field and the upper-level doublet is driven by a strong microwave field. When the non-RWA is applied to the interaction of the atom with the microwave field, for some values of the parameters involved, the spontaneous emission spectrum is comprised of a central peak and a series of sidebands with a constant spacing of the microwave frequency, and the central peak and/or sidebands can be split into two components. The physical interpretation of the spectral characteristics is given in light of the dressed states.     

基于血清紫外-可见吸收光谱的胆固醇含量研究

将血清紫外-可见吸收光谱与神经网络理论结合用于血液中胆固醇含量的分析。研究表明,在350～600 nm波段范围内, 吸收光谱具有以下几个特征：(1)不论胆固醇含量如何,在416 nm处均有一个较强的吸收峰;(2)在波段450～500 nm之间有一肩峰, 其中心波长位于460 nm处; (3)在578 nm处还有一个较弱的峰;(4)不同胆固醇含量的吸收光谱的形状是明显不同的。血清吸收光谱是胆固醇等多种组分光谱叠加的结果, 416 nm处的吸光度与胆固醇含量之间无明显相关性,呈现出一种随机的关系, 因此不能由416 nm处的吸光度来确定胆固醇的含量是否异常。基于波段455～475 nm范围内血清的吸光度与胆固醇含量有明显的相关性,文章构建了血清吸收光谱与胆固醇含量之间关系的神经网络模型。     

Measurement of thicknesses of thin films by the Fourier spectrometry method

A Fourier spectrometry method for measuring the thickness of thin and ultrathin films with the help of an additional peak that depends on the optical thickness of the deposited film and is situated outside the region of the central peak of the interferogram is proposed. The experiment demonstrates the necessity of considering the change in optical path in the substrate that is induced by the deposited film.     

Non-linear spin fluctuations and phase transitions in itinerant electron magnets: CMR manganites

We present a review analyzing the effects of coupling of transverse magnons with longitudinal spin fluctuations in isotropic itinerant ferro- and antiferromagnets. It is shown that this coupling essentially changes the spectrum of longitudinal fluctuations. At low-temperatures their spectrum is dominated by the linear Landau relaxation, is purely quasielastic and described by a broad central peak of a paramagnon type. On approaching the critical temperature non-linear magnetic relaxation due to mode–mode couplings can dominate and lead to a rapid increase of the central peak and to a new mechanism of magnetic phase transitions governed by non-linear spin fluctuations. The formalism is applied to the CMR manganites where the observed quasielastic fluctuations can be viewed as non-linear spin-lattice fluctuations strongly affected by magnons.     

Elastic and anelastic properties of ferroelectric SrTi(18)O3 in the kHz-MHz regime

Resonant ultrasound spectroscopy has been used to follow elastic softening in SrTi(18)O3 in the frequency range ～0.2-1 MHz. A dramatic softening of C44 occurs as the Curie temperature T(c) = 24 K is approached from above or below, which correlates with the development of a central peak in Raman and Brillouin spectra. This is attributed to strong coupling between the acoustic mode and the central peak mode. A weaker anomaly is seen in a resonance mode which is believed to be controlled by 1/2(C11-C12). Significant attenuation accompanies this softening and an additional dissipation peak has also been observed at ～80-90 K. This extends earlier work by a factor of 150,000× from the 30 GHz regime and helps address the question as to whether the ferroelectricity is stimulated primarily by a soft mode into a homogeneous ground state or by clustering of rhombohedral nanoregions into an inhomogeneous ground state.