Jingwen Zhang

Theoretical study of hierarchical structures and heredity effect of silicon solidifying on carbon nanotube

The growth of silicon atoms at the heterogeneous surface of carbon nanotubes (CNTs) is studied by means of molecular dynamics simulations. The results indicate that silicon atoms are concentrated to form an “annual ring” structure around CNTs. The structures of CNTs have strong correlation with the stacking sequence of silicon atoms. Heredity effect can be clearly observed during the heterogeneous nucleation. The uniform internal potential field around CNTs results in the formation of annual ring structures.

Lattice vibration and thermal diffusion of Yb doped KLu(WO4)2 single crystal

Yb doped KLu(WO4)2 (Yb:KLuW) single crystal was grown by the method of top-seeded-solution growth slow-cooling method. Its lattice vibrational modes were calculated by using space group theory, and polarized Raman spectra were measured at room temperature with different scattering geometry projections. The powder transmission of Fourier-transform infrared spectra was also performed as a supplement for Raman spectra to study the lattice vibration of the laser crystal. The main Raman peaks and infrared transmission bands were attributed to the internal mode WO6 octahedrons in the crystals. Two kinds of link ways of WO6 octahedrons implying large distortion had led the Raman peaks to shift to different positions. Large distortions of the WO6 octahedrons in the crystal had led to the splitting of some Raman peaks and even the activation of ν6 mode, which is originally a silent mode by the selection rule. As a self-Raman crystal, the linewidth of the Raman peaks ν1 and ν2 reached 12.5 and 16.6cm−1, with relaxa...

PHOTOREFRACTIVE PROPERTIES OF CU-DOPED (K0.5NA0.5)0.2(SR0.75BA0.25)0.9NB2O6 CRYSTALS WITH DIFFERENT DOPING LEVELS AND DIFFERENT DIMENSIONS

In this article, we studied the photorefractive properties of Cu-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 (Cu:KNSBN) crystals with different doping levels. The properties include two-wave mixing and self-pumped phase conjugation, absorption properties, and the growth conditions as well. We also studied the effect of the dimensions on the photorefractive properties. The mechanism of Cu-doped KNSBN and the influence of the different sites occupied by Cu+ on photorefractive properties are also discussed. All the experimental results showed that doping levels have much effect on the photorefractive properties. The crystal with a higher doping level has a higher effective charge carrier density, a larger coupling coefficient, and a faster response rate, which is suitable for fast optical information processing. Dimension has much influence on the photorefractive properties. The thinner crystal with the same doping level has a larger coupling gain coefficient, and a shorter response time.

Systematic studies on photorefractive crystal growth and properties of Cu- and Mn-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6

In this paper, photorefractive (PR) crystals of Cu and Mn- doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 were symmetrically studied. We reported the growth conditions, the absorption properties and the photorefractive properties including two wave mixing (TWM) and self-pumped phase conjugation (SPPC). The mechanism of Cu-doped KNSBN was referred briefly, and the influence of the different sites occupied by doping ions on PR properties was also discussed. All these results reveal that: (1) In Cu-doped KNSBN crystals, the photorefractive properties become better with the increase of the doping level, such as higher effective charge carrier density, larger coupling coefficient, faster response rate, higher SPPC reflectivity. (2) The thinner sample shows larger coupling gain coefficient, which is due to the light creep effect and beam fanning effect. The response time becomes shorter with the decrease of the thickness. (3) In Cu:KNSBN crystals, the coupling gain coefficient of TWM was obtained up to 35 cm-1. (4) In Cu:KNSBN and Mn:KNSBN samples, the SPPC reflectivity up to 73% have been obtained, respectively. (5) The C-site in the tungsten-bronze structure of KNSBN has an effect on the PR properties of the crystal. All these results show that doping in KNSBN is an effective method to improve the PR properties. The Cu-doped KNSBN crystal is a very promising photorefractive material.

Holographic associative memory using a coherently induced double phase conjugate mirror

We demonstrate a new method to implement holographic associative memory based on a coherently induced double phase conjugate mirror that has phase-conjugate reflectivity larger than unity for weak reference signal over a large range of pumping-reference intensity ratio. The phase conjugator, operated with a copper-doped KNSBN crystal, serves as a novel nonlinear feedback and gain element for the associative memory system. A vanadium-doped KNSBN crystal as storage medium improves the response speed of the holographic recording process. A stored image has been completely retrieved when a partial input addresses the associative memory system.

Double phase conjugation in copper-doped potassium sodium strontium barium niobate crystals.

We show a double phase conjugator with novel crystals of copper-doped potassium sodium strontium barium niobate. The phase conjugation reflectivity can reach 278% and depends on relative input positions of both incident beams. The response time with the input beam power ratio is measured and modeled as a function of input beam power ratio. The formation of the arch coupling loop is analyzed with theoretical simulation results and a positive feedback process is proposed. The influence of a self-pumped phase conjugation process on double phase conjugation fidelity is also discussed. It is necessary to avoid generating self-pumped phase conjugation to prevent the reduction of double phase conjugation fidelity.

Demonstration of the formation of four‐wave mixing interaction regions in a high‐efficiency mutually pumped phase conjugator

We show a mutually pumped phase conjugator with a high coupling efficiency in a novel crystal of copper‐doped potassium sodium strontium barium niobate. A twisting around of one another and self‐curving coupling channel is observed. A theory is developed to simulate the coupling channel. The shape of curved trajectories has also been calculated. We verify that one, two, three, and more four wave mixing interaction regions exist in photorefractive bridge mutually pumped phase conjugators with the simulations. The calculated results are essentially consistent with our experimental observations, and they may be used in other photorefractive phase conjugators after making a modification.

A novel internal linear cavity stimulated photorefractive scattering self-pumped phase conjugator

Abstract A stimulated photorefractive scattering self-pumped phase conjugator (SPS-SPPC) in a novel linear cavity in photorefractive crystals is described, in which the linear cavity is constructed by the spontaneous reflected grating and the incident surface. The spontaneous reflected grating and the self-pumped phase conjugator in this cavity are solved theoretically, the results show that this type of SPPC can be easily realized than a semilinear cavity SPS-SPPC since it offers low threshold. At last, both linear and semilinear cavity SPS-SPPC are observed in Fe-doped KTa 1− x Nb x O 3 (Fe:KTN) crystals, the experimental results demonstrate the above conclusion.

Self‐reading geometry conjugators with copper‐doped photorefractive (K0.5Na0.5)0.2(Sr0.75Ba0.25 )0.9Nb2O6 crystals and their applications

The dependence of the reflectivity on the distance of the spots corresponding to the two incident beams on crystals is measured and analyzed in self-reading geometry conjugators (SRGCS) with Cu-doped single-domain photorefractive (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 CrYStals. Double peaks in some dependence are observed and used to investigate the mechanism of SRGCS. The dynamic features of the two phase-conjugate beams and the decrease of the specular reflectivity of the probing beam in SRGCS are observed and analyzed. A bump in the probing beam’s phase-conjugate replica as a result of a short pause of the incident pumping beam is analyzed in terms of the pyroelectric effect and photovoltaic effect. A comparison of results on conjugation fidelity, response rate, and threshold between CAT self-pumped phase conjugators and SRGCS is given. Real-time vertical and horizontal high-pass filtering, real-time double-exposure interferometry, and detection of the blemishes caused by amplitude defects in optical systems are demonstrated experimentally. The corresponding theoretical analyses are also given.