Phase and amplitude control of the inversionless gain in a microwave-driven <Emphasis Type="Bold">Λ</Emphasis>-type atomic system

In order to achieve the phase-sensitive probe gain without population inversion, we investigate a three-level Λ-type atomic system driven by a coherent field and a microwave field. It is shown that, by modulating the relative phase of applied fields, we can obtain quite high inversionless gain at different probe detunings and change the gain behavior of the probe correspondingly. We find that amplitudes of the coherent field and the microwave field are also important factors that can result in different gain behavior of the probe. Here, we use the microwave field to induce the quantum coherence between the two ground levels, which is necessary for phase-sensitive effects, since it can result in the interference between two different transition channels. Received 20 June 2002 / Received in final form 5 December 2002 Published online 4 March 2003     

Anisotropic diffraction of stratified volume holographic grating in photorefractive media

We have studied the anisotropic diffraction properties of the stratified volume holographic gratings recorded in photorefractive media using the anisotropic coupled wave theory. It is shown that the diffraction efficiency of such system exhibit the uniform periodic Bragg selectivity properties. In addition the dependence of the stratified volume holographic optical elements (SVHOEs) diffraction properties on the buffer-layer thickness, grating-layer thickness, number of modulation layers, and total thickness of system are discussed in detail.     

Ce:KNSBN光折变类光纤简并四波混频特性研究

研究了Ce:KNSBN光折变类光纤在泵浦光和信号光夹角分别为小角度和大角度两种情况下简并四波混频的基本特性.当夹角较大时,在光折变类光纤内部形成了两个四波混频作用区域,获得了比小角度情况提高4倍的大相位共轭反射率.给出了Ce:KNSBN光折变类光纤中,在入射夹角分别为小角度和大角度两种情况下,相位共轭光反射率分别随信号光光强、两束泵浦光光强比变化的实验结果,并用理论公式进行了拟合,理论分析和实验结果相符.还研究了Ce:KNSBN光折变类光纤四波混频光栅模式和相位共轭光时间响应特性.光折变类光纤的相位共轭响应时间较快,可为秒量级.     

Absorption and dispersion by a multiple driven two-level atom

We investigate the absorption and dispersion properties of a two-level atom driven by a polychromatic field. The driving field is composed of a strong resonant (carrier) frequency component and a large number of symmetrically detuned sideband fields (modulators). A rapid increase in the absorption at the central frequency and the collapse of the response of the system from multiple frequencies to a single frequency are predicted to occur when the Rabi frequency of the modulating fields is equal to the Rabi frequency of the carrier field. These are manifestations of the undressing or a disentanglement of the atomic and driving field states, that leads to a collapse of the atom to its ground state. Our calculation permits consideration of the question of the undressing of the driven atom by a multiple-modulated field and the predicted spectra offer a method of observing undressing. Moreover, we find that the absorption and dispersion spectra split into multiplets whose structures depend on the Rabi frequency of the modulating fields. The spectral features can jump between different resonance frequencies by changing the Rabi frequency of the modulating fields or their initial phases, which can have potential applications as a quantum frequency filter. Received 23 October 2001 and Received in final form 31 January 2002     

Testing of linear polarizer using photorefractive effect

A new method is developed to test linear polarizers using two-wave mixing in photorefractive Bi₁₂TiO₂₀ (Bismuth Titanium Oxide, BTO). The extinction ratios obtained from this method was comparable with the literature values and the method is also useful for qualitative analysis of linear polarizers. Detailed theoretical and experimental analysis is given in the paper.     

Theoretical Studies of Water''s and Methanol''s Effects on Alcoholysis of N-Benzyl-3-oxo-β-sultam

The mechanisms about the water's and methanol's effects on the alcoholysis of N-benzyl-3-oxo-β-sultam together with their differences have been studied by using density functional theory at the B3LYP/6-31G* level. The results, in comparison with a previous study on the relative reaction without the assistance of water and methanol, show that the added water or methanol can remarkably reduce the energy barrier of alcoholysis reaction of N-benzyl-3-oxo-β-sultam and the most favorite pathway is the breaking of C-N bond instead of S-N. It is also found that the reaction energy barrier of methanol-assisted alcoholysis is a little higher than that of the water-assisted one.     

The effect of In doping on optical properties of Fe:LiNBO3 crystals

Fe:LiNbO₃ and In:Fe:LiNbO₃ crystals were grown by Czochralski method. The absorption spectra were measured to investigate their defect structure. The photo damage resistance and photorefractive properties were measured. The photo damage resistance of the In:Fe:LiNbO₃ crystal in which the In concentration is above the threshold value is one order of magnitude higher than that of the Fe:LiNbO₃ crystal. The mechanisms of the violet shift of the absorption edge and the enhancement of the photorefractive effect of In:Fe:LiNbO₃ crystals were investigated.     

Flow Injection Analysis - Inductively Coupled Plasma/Mass Spectrometry: Study of Interelement Effects

Abstract

A flow injection analysis - inductively coupled plasma/mass spectrometry (FIA/ICP/MS) system is described using a Sciex Elan Model 250 ICP/MS system coupled with a peristaltic pump and injection valve. Sample volumes of 25 μl are injected and samples can be measured at the rate of one per minute. Addition of nitric acid to the carrier generally enhanced and stabilized the recorded signals. Also, the nitric acid tended to lessen interelement effects. Most interelement effects were fairly constant above 0.1 pm added element.     

Activation Energy of Proton Migration in Mn- and Fe-Doped Lithium Niobate Obtained by Holographic Methods

The activation energy of thermal fixing of photorefractive gratings is determined in congruent and nearly stoichiometric lithium niobate crystals, both doped with iron or manganese. The novel technique called holographic scattering method is compared with the standard two-wave mixing method. A measurement of the angular distribution of the self scattered intensity and its possible analytical function is presented. The mathematical problems of the holographic scattering method are discussed applying the angular distribution functions.     

Observation of the bright photovoltaic spatial soliton in fiber-like photorefractive crystal

We have observed two-dimensional bright photorefractive spatial soliton for the first time in a Ce:KNSBN fiber-like crystal at wave-length of 514.5 nm with the intensity range between 2.83 × 10³ W/cm² and 4.71 × 10³ W/cm², then compared it with the one formed in a bulk sample. By comparison we have found that the intensity of forming a soliton in a fiber-like crystal is 7 9 times that in a bulk crystal due to stronger scattering light and complicated multi-wave interaction. By comparison we have also found that the transverse dimensions of a soliton formed in a fiber-like crystal are about 4% smaller than the ones in a bulk crystal when the experimental geometry remains the same, then we have exploited the theory including the contribution of scattering field to interpret the experimental phenomenon.