Synthesis and characterization of Bi-functional photorefractive polymers with high molecular weight and low glass transition temperature

Carbazole-based bi-functional photorefractive polyacrylates were prepared via free radical polymerization and post-azo-coupling reaction. The structure of polymers was characterized by Fourier transform infrared spectroscopy(FTIR) and proton nuclear magnetic resonance(1H-NMR) spectroscopy. The differential scanning calorimetry(DSC) and the thermal gravimetric analysis(TGA) were used to characterize the thermal property of polymers. The results indicate that though the glass transition temperature(Tg) of polymers increases with increasing the ratio of NLO groups, the polymers with different ratios of NLO groups still all show low glass transition temperatures around 60 °C, and good thermal stability, which are favorable to the practical application of these polymers. The gel permeation chromatographic(GPC) result indicates that these polymers all have high-molecular-weight which is favorable to the long term stability of the material. Further, these polymers have good solubility in chloroform solvent, and the solutions can easily be fabricated into optically transparent films. Gain coefficients of 75 cm-1, 185 cm-1 and 66 cm-1 can be observed at zero external electric field without any addition agent or pre-poling for polymers P-2, P-3 and P-4 respectively. The different contents of NLO groups result in the different properties of polymers P-2, P-3 and P-4.     

Radiation effects in KMgF 3 crystals

Effects of x, g and UV irradiation on Tb 3+ and Eu 2+ doped KMgF 3 crystals were studied. Thermoluminescence (TL) excited by VUV radiation was compared to that induced by x and g rays. TL excitation spectra showed maxima at 125, 140, 155 and 180 v nm. The main TL peaks appeared after VUV irradiation at about the same temperatures and with the same thermal activation energies as after x or g irradiation, indicating that these peaks are due to the same trapping levels. In samples, which had previously been exposed to ionizing radiation, TL could also be excited with longer wavelengths that could not excite any TL in un-irradiated crystals; this is attributed to a process of phototransfer (PTTL). The x and UV excited luminescence was measured at LNT and RT and showed essentially the same main emission bands that appeared in the TL and PTTL peaks of these crystals. The dose dependence of the 730 v K TL peak in of KMgF 3 :Eu 2+ was linear up to about 2000 v Gy. The TL sensitivity of KMgF 3 :Eu 2+ was by an order of magnitude higher than that of KMgF 3 :Tb 3+ , which was by a factor of two greater than that of the known TLD-l00 phosphor.     

Combined Optical/MCD/ODMR investigations of photochromism in doubly-doped Bi 12 GeO 20

Electron paramagnetic resonance is detected optically via the change of magnetic circular dichroism under microwaves at 35 v GHz. The technique is applied to Bi 12 GeO 20 samples co-doped with vanadium and a second transition metal (Cr, Mn, Co, Cu). The optical and magnetic properties of several paramagnetic defects (V Ge 4+ and Cr Ge 4+ ) are directly correlated. The basic photochromic processes occuring in samples doped with V, Mn, and Mn+V are explained. The V Ge 4+/5+ level is positioned roughly 2.2 v eV above the valence band.     

Femtosecond Nonlinear Optical Spectroscopy of the Acoustic Vibration of Metal Nanoparticles Under High Pressure

A time-resolved femtosecond optical pump-probe setup has been combined with a high hydrostatic pressure apparatus to investigate the pressure dependence of the electron and lattice ultrafast response of silver nanoparticles embedded in a glass. The short time scale measurements shows that the time constant of the electron-phonon energy exchange is unchanged over the studied pressure range (up to 60 kbar). The frequency of the coherent acoustic vibration of the nanoparticles observed on a longer time scale is found to linearly increase with pressure in agreement with the metal elastic property changes. The acoustic mode damping is also found to be modified by pressure, suggesting alteration of the metal-glass interface properties.     

High pressure study of the surface plasmon resonance in AG nanoparticles

The optical absorption spectra of a composite material formed by silver nanoparticles of 12.1 nm radius embedded in a phosphate glass have been studied as a function of hydrostatic pressure up to 11 GPa. The confinement induces a strong absorption peak, the surface plasmon resonance, which is red shifted by the application of pressure. Upon pressure release, a hysterisis is observed persisting even at ambient conditions. The pressure-induced changes in the properties of both the glass and the silver contribute to the observed behaviour, the irreversibility of which, is attributed to the pressure induced irreversible densification of glass.     

一类2(1H)-喹喔啉衍生物的紫外光谱研究

研究了一类喹喔啉衍生物 ,1 烷基 3 甲基 2 (1H) 喹喔啉 2 酮 (1 alkyl 3 methyl 2 (1H) quinoxalin 2 one,简称AMQ ,其中alkyl =H ,CH3,C2 H5,n C3H7,n C5H1 1 ,n C1 6 H33)的紫外吸收光谱。这类化合物可应用于药物 ,如用作α 氨基羟甲基异恶唑丙酸 (AMPA)受体拮抗剂、杀菌剂等 ;还可用作植物生长调节剂、荧光探针等领域。结果表明 :化合物中氮原子上烷基链的增长对该类喹喔啉衍生物的紫外吸收光谱基本没有影响 ,谱图中峰形大体相同。紫外吸收谱图中 ,在 32 7和 340nm左右有两个吸收强度相当的一对肩峰 ,2 80nm处有一个吸收强度稍弱的峰 ;340nm左右的吸收峰主要是n→Π 跃迁所致 ,其中也含有Π→Π 跃迁的成分 ;32 7和2 80nm左右强吸收峰是Π→Π 跃迁所致。     

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