Photoinduced bireffingence with large optical nonlinearity in a bacteriorhodopsin/polymer composite Him is observed. A high refractive index change of 8.5× 10^-5 photoinduced by 476nm pumping beam is reached at t...Photoinduced bireffingence with large optical nonlinearity in a bacteriorhodopsin/polymer composite Him is observed. A high refractive index change of 8.5× 10^-5 photoinduced by 476nm pumping beam is reached at the low intensity of 6.SmW/cm^2. Based on it, a broadband all-optical photonic switch is realized with an optical controlling switch system. Because of controlling beam＇s selectivity in switching, the transporting beams of different wavelengths with different intensities and shapes can be modulated by adjusting the wavelength and intensity of the controlling beam.展开更多
Using the molecular dynamics method, the stability of small He-vacancy clusters is studied under the condition of the high He and low vacancy densities. The result shows that there is a competition between He atoms de...Using the molecular dynamics method, the stability of small He-vacancy clusters is studied under the condition of the high He and low vacancy densities. The result shows that there is a competition between He atoms detrapped and self-interstitial atoms （SIAs） emitted during the clustering of He atoms. When the He number is above a critical value of 9, the SIA emission is predominant. The SIA emission can result in deep capture of He atoms since the binding energy of He to a He-vacancy cluster is increased with the number of SIAs created. The cluster thus grows up. In addition, more SIAs are created when the temperature is elevated. The average volume of a He atom is increased. The cluster expansion takes place at high temperature.展开更多
We have explicitly identified coloured conical emission （CCE） and noncollinear optical parametric generation （OPC） by spectrum characterizations. With an experimental setup providing different pump pulse durations...We have explicitly identified coloured conical emission （CCE） and noncollinear optical parametric generation （OPC） by spectrum characterizations. With an experimental setup providing different pump pulse durations, CCE and noncollinear OPG are observed both alternatively and simultaneously. Comparisons between CCE and noncollinear OPC are studied. Accumulation behaviour of modulational instabilities is observed in our two-crystal cascaded configuration, which results in enhancement or depression of the CCE formation.展开更多
A formula is developed to describe the propagation of beams driven by few-cycle Gaussian pulse in a media with group velocity dispersion （GVD）. With the method, the spatiotemporal evolution of the pulsed beam can be...A formula is developed to describe the propagation of beams driven by few-cycle Gaussian pulse in a media with group velocity dispersion （GVD）. With the method, the spatiotemporal evolution of the pulsed beam can be straightforwardly quantified as long as the monochromatic beam solutions in free space, which have been widely investigated in previous works, are known. The method makes it possible to analytically deal with the few-cycle pulsed beams with transverse profiles other than the Gaussian one, which is, to our knowledge, the one mainly investigated previously, in GVD media.展开更多
The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and impr...The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L10 FePt films. Moreover, the coercivity increases when a thin Fe layer covers the FePt layer. Beyond a critical thickness, however, the Fe cover layer quickens the magnetization reversal of Fe49Pt51/Fe bi-layers by their exchange coupling.展开更多
Partially deuterated KDP is an ideal nonlinear crystal for second-harmonic generation （SHG） of femtosecond lasers at 1 μm, which features with vanished group-velocity mismatch at its retracing point of phase-matchi...Partially deuterated KDP is an ideal nonlinear crystal for second-harmonic generation （SHG） of femtosecond lasers at 1 μm, which features with vanished group-velocity mismatch at its retracing point of phase-matching. We numerically investigate the characteristics of SHG with femtosecond lasers in a partially deuterated KDP, which shows that group-velocity dispersion plays an important role. This spectrally non-critical phase-matching configuration can support both high efficiency and large acceptance bandwidth.展开更多
We perform a comparative st udy on the electroluminescence （EL） and photoluminescence （PL） of Si nanocrystaldoped SiO2 （nc-Si：SiO2） and SiO2, and clarify whether the contribution from Si nanocrystals in the EL ...We perform a comparative st udy on the electroluminescence （EL） and photoluminescence （PL） of Si nanocrystaldoped SiO2 （nc-Si：SiO2） and SiO2, and clarify whether the contribution from Si nanocrystals in the EL of nc-Si：SiO2 truly exists. The results unambiguously indicate the presence of EL of Si nanocrystals. The difference of peak positions between the EL and PL spectra are discussed. It is found that the normal method of passivation to enhance the PL of Si nanocrystals is not equally effective for the EL, hence new methods need to be explored to promote the EL of Si nanocrystals.展开更多
Sn/Yb codoped silica optical fiber preform is prepared by the modified chemical vapor deposition （MCVD） followed by the solution-doping method. Ultraviolet （UV） optical absorption, photoluminescence （PL） spectra...Sn/Yb codoped silica optical fiber preform is prepared by the modified chemical vapor deposition （MCVD） followed by the solution-doping method. Ultraviolet （UV） optical absorption, photoluminescence （PL） spectra under 978-nm laser diode （LD） pumping, and refractive index change after exposure to 266-nm laser pulses are obtained. There is only a little change in the PL spectra while a positive refractive index change up to 2×10^-4 is observed after 30-min exposure to 266-nm laser pulses. The results show that both of the peculiar photosensitivity of Smdoped silica and the gain property of Yb-doped silica fiber are preserved in the Sn/Yb codoped silica optical fiber preform. The experimental data suggest that the photosensitivity of the fiber preform under high energy density laser irradiation should be mainly due to the bond-breaking of oxygen deficient defects, while under relatively low energy density laser irradiation, the refractive index change probably originates from the photoconversion of optically active defects.展开更多
Magnetic tunnel junctions （MTJs） with one proper oxidized FeOx layer placed between the Al oxide barrier and the top CoFe pinned layer show large tunnelling-magnetoresistance （TMR） signals as high as 39% after ann...Magnetic tunnel junctions （MTJs） with one proper oxidized FeOx layer placed between the Al oxide barrier and the top CoFe pinned layer show large tunnelling-magnetoresistance （TMR） signals as high as 39% after anneal at 380℃. The increased TMR signal may originate from the as-deposited Fe/FeOx （non-magnetic） layers changing to Fe＋magnetic FeOy layer （some Fe3O4 and mostly other kind of magnetic Fe oxide） after high temperature anneal. The maximum TMR value （TMR ） and the corresponding temperature Ts where the TMRmax occurs upon annealing are closely associated with the oxidation time of the AlOx and FeOx layers, too long oxidation for the Fe layers is detrimental for the TMR value. In addition to the enhanced AlOx barrier quality upon anneal, the improved thermal stability is also attributed to the Mn diffusion retardation by the presence of the FeOx layer which acts as an antidiffusion layer. For MTJs without the interposed FeOx layer, the TMR signal reduction at 300℃ originates from the Mnlr/CoFe partially decoupling and CoFe/AlOx interface polarization loss due to the significant Mn diffusion.展开更多
Cascaded nonlinear phase shifts may be imposed on the interacting waves during second-harmonic generation （SHG） in a quasi-Phase-matched （QPM） structure, whieh are severe in high-intensity regime and may result in...Cascaded nonlinear phase shifts may be imposed on the interacting waves during second-harmonic generation （SHG） in a quasi-Phase-matched （QPM） structure, whieh are severe in high-intensity regime and may result in lower conversion efficiency. We propose a configuration of QPM structure with reduced domain-length, which may depress the nonlinear phase shifts to some extent and lead to an improvement on the conversion efficiency. The numerical analyses on the conversion efficiency as well as the relative phase angle are discussed in detail for better understanding of the SHG process.展开更多
The focusing properties of fractal zone plates （FZPs） with different structure parameters are studied experimentally. The axial irradiance of FZPs is deduced at n=4. The experimental results are in good agreement wi...The focusing properties of fractal zone plates （FZPs） with different structure parameters are studied experimentally. The axial irradiance of FZPs is deduced at n=4. The experimental results are in good agreement with the theoretical prediction. A method to fabricate FZPs with variable structure parameters is mentioned, and the liquid-crystal-on-silicon device is used to implement this experiment. The experimental results indicate that the focal depth of lower order FZPs is larger than that of higher order FZPs.展开更多
Stimulated Raman scattering （SRS） of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from...Stimulated Raman scattering （SRS） of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from the surface ripple of nonlinear crystal, can be significantly enhanced due to SRS, and the gain of instability increases with the spatial period of modulation. Numerical simulations based on the nonlinear coupled-wave equations verify the validity of the perturbation approach.展开更多
We investigate the structure and exchange coupling in TbFeCo/FePt bilayer films. It is found that FePt has the L10 structure and the easy axis of the FePt film is perpendicular to the film plane. Results of the vibrat...We investigate the structure and exchange coupling in TbFeCo/FePt bilayer films. It is found that FePt has the L10 structure and the easy axis of the FePt film is perpendicular to the film plane. Results of the vibrating sample magnetometer and the magneto-optical Kerr effect measurements show a strong perpendicular exchange coupling between the ferrimagnetic TbFeCo layer and the hard ferromagnetic FePt layer. The magnetization direction of each layer and the process of magnetization reversal are discussed in detail. The switching field dependence on the exchange coupling has been modelled by micromagnetic simulation and the interlayer coupling constant is about -0.9 erg/cm^2 according to this simulation.展开更多
A series of Co/Alq3 granular film samples are prepared using co-evaporating technique. The microstructures and magnetic properties are investigated. The Kerr spectra and optical constants of Cox（Alq3）1-x （0.19 ≤ x...A series of Co/Alq3 granular film samples are prepared using co-evaporating technique. The microstructures and magnetic properties are investigated. The Kerr spectra and optical constants of Cox（Alq3）1-x （0.19 ≤ x ≤ 1） granular films are measured using a magneto-optical Kerr spectrometer and a spectroscopic ellipsometer in the 1.5-4.5 eV photon energy range. The Kerr rotation reaches the maximum value of 0.5° in the x = 0.65 sample. The relationship between enhanced Kerr rotation and optical constants is discussed, and the concentration dependence of MOKE spectra is also investigated.展开更多
The effect of transverse coupling in a photorefractive oscillator is studied. From the study the condition for stable optical patterns of multimode oscillation is given analytically and verified by numerical simulatio...The effect of transverse coupling in a photorefractive oscillator is studied. From the study the condition for stable optical patterns of multimode oscillation is given analytically and verified by numerical simulation. Under the stable condition, the period-doubling route to spatiotemporal chaos is observed.展开更多
Due to group velocity mismatch, the generation of the cascaded fifth-order nonlinear phase shifts with femtosecond pulse will inevitably cause the severe pulse distortion. By theoretical study and numerical simulation...Due to group velocity mismatch, the generation of the cascaded fifth-order nonlinear phase shifts with femtosecond pulse will inevitably cause the severe pulse distortion. By theoretical study and numerical simulations, we show that undistorted femtosecond pulse which is impressed the cascaded fifth-order nonlinear phase shifts can be obtained at large values of the phase mismatching △κL.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 50533010.
文摘Photoinduced bireffingence with large optical nonlinearity in a bacteriorhodopsin/polymer composite Him is observed. A high refractive index change of 8.5× 10^-5 photoinduced by 476nm pumping beam is reached at the low intensity of 6.SmW/cm^2. Based on it, a broadband all-optical photonic switch is realized with an optical controlling switch system. Because of controlling beam＇s selectivity in switching, the transporting beams of different wavelengths with different intensities and shapes can be modulated by adjusting the wavelength and intensity of the controlling beam.
基金Supported by the National Natural Science Foundation of China under Grant No 10376008.
文摘Using the molecular dynamics method, the stability of small He-vacancy clusters is studied under the condition of the high He and low vacancy densities. The result shows that there is a competition between He atoms detrapped and self-interstitial atoms （SIAs） emitted during the clustering of He atoms. When the He number is above a critical value of 9, the SIA emission is predominant. The SIA emission can result in deep capture of He atoms since the binding energy of He to a He-vacancy cluster is increased with the number of SIAs created. The cluster thus grows up. In addition, more SIAs are created when the temperature is elevated. The average volume of a He atom is increased. The cluster expansion takes place at high temperature.
基金Supported the National Natural Science Foundation of China under Grant Nos 60538010 and 10576009, and the Science and Technology Commission of Shanghai under Grant Nos 05JC14005 and 05SG02.
文摘We have explicitly identified coloured conical emission （CCE） and noncollinear optical parametric generation （OPC） by spectrum characterizations. With an experimental setup providing different pump pulse durations, CCE and noncollinear OPG are observed both alternatively and simultaneously. Comparisons between CCE and noncollinear OPC are studied. Accumulation behaviour of modulational instabilities is observed in our two-crystal cascaded configuration, which results in enhancement or depression of the CCE formation.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60538010, 10576009 and 10674050, the Programme for Innovative Research Team of Higher Education in Guangdong （06CXTD005）, the Specialized Research Fund for the Doctoral Programme of Higher Education of China （20060574006）, and the National High-Technology Research and Development Programme of China under Grant No 2007AAXXX507.
文摘A formula is developed to describe the propagation of beams driven by few-cycle Gaussian pulse in a media with group velocity dispersion （GVD）. With the method, the spatiotemporal evolution of the pulsed beam can be straightforwardly quantified as long as the monochromatic beam solutions in free space, which have been widely investigated in previous works, are known. The method makes it possible to analytically deal with the few-cycle pulsed beams with transverse profiles other than the Gaussian one, which is, to our knowledge, the one mainly investigated previously, in GVD media.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 60490290,60678008 and 50771032)the National Basic Research Program of China (Grant No 2009CB929201)the Science Foundation of the Science and Technology Committee of Shanghai (Grant No 06DJ14007)
文摘The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L10 FePt films. Moreover, the coercivity increases when a thin Fe layer covers the FePt layer. Beyond a critical thickness, however, the Fe cover layer quickens the magnetization reversal of Fe49Pt51/Fe bi-layers by their exchange coupling.
基金Supported by the Ph.D. Programme Foundation of Ministry of Education of China, the Project on 0ptical Science and Technology of Shanghai （012261065）, and the National Natural Science Foundation of China under Grant No 10376009.
文摘Partially deuterated KDP is an ideal nonlinear crystal for second-harmonic generation （SHG） of femtosecond lasers at 1 μm, which features with vanished group-velocity mismatch at its retracing point of phase-matching. We numerically investigate the characteristics of SHG with femtosecond lasers in a partially deuterated KDP, which shows that group-velocity dispersion plays an important role. This spectrally non-critical phase-matching configuration can support both high efficiency and large acceptance bandwidth.
基金Supported by the National Natural Science Foundation of China under Grant No 60638010, and the Ministry of Education of China under Grant No 20060246028.
文摘We perform a comparative st udy on the electroluminescence （EL） and photoluminescence （PL） of Si nanocrystaldoped SiO2 （nc-Si：SiO2） and SiO2, and clarify whether the contribution from Si nanocrystals in the EL of nc-Si：SiO2 truly exists. The results unambiguously indicate the presence of EL of Si nanocrystals. The difference of peak positions between the EL and PL spectra are discussed. It is found that the normal method of passivation to enhance the PL of Si nanocrystals is not equally effective for the EL, hence new methods need to be explored to promote the EL of Si nanocrystals.
基金supported by the National Natural Science Foundation of China (Nos. 10074011 and 60378034)the Ministry of Science and Technology of China (Nos. 02JD14001 and 03DJ14001).
文摘Sn/Yb codoped silica optical fiber preform is prepared by the modified chemical vapor deposition （MCVD） followed by the solution-doping method. Ultraviolet （UV） optical absorption, photoluminescence （PL） spectra under 978-nm laser diode （LD） pumping, and refractive index change after exposure to 266-nm laser pulses are obtained. There is only a little change in the PL spectra while a positive refractive index change up to 2×10^-4 is observed after 30-min exposure to 266-nm laser pulses. The results show that both of the peculiar photosensitivity of Smdoped silica and the gain property of Yb-doped silica fiber are preserved in the Sn/Yb codoped silica optical fiber preform. The experimental data suggest that the photosensitivity of the fiber preform under high energy density laser irradiation should be mainly due to the bond-breaking of oxygen deficient defects, while under relatively low energy density laser irradiation, the refractive index change probably originates from the photoconversion of optically active defects.
文摘Magnetic tunnel junctions （MTJs） with one proper oxidized FeOx layer placed between the Al oxide barrier and the top CoFe pinned layer show large tunnelling-magnetoresistance （TMR） signals as high as 39% after anneal at 380℃. The increased TMR signal may originate from the as-deposited Fe/FeOx （non-magnetic） layers changing to Fe＋magnetic FeOy layer （some Fe3O4 and mostly other kind of magnetic Fe oxide） after high temperature anneal. The maximum TMR value （TMR ） and the corresponding temperature Ts where the TMRmax occurs upon annealing are closely associated with the oxidation time of the AlOx and FeOx layers, too long oxidation for the Fe layers is detrimental for the TMR value. In addition to the enhanced AlOx barrier quality upon anneal, the improved thermal stability is also attributed to the Mn diffusion retardation by the presence of the FeOx layer which acts as an antidiffusion layer. For MTJs without the interposed FeOx layer, the TMR signal reduction at 300℃ originates from the Mnlr/CoFe partially decoupling and CoFe/AlOx interface polarization loss due to the significant Mn diffusion.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10776005, 60725418 and 10576009, and the National Basic Research Programme of China under Grant No 2007CB815104.
文摘Cascaded nonlinear phase shifts may be imposed on the interacting waves during second-harmonic generation （SHG） in a quasi-Phase-matched （QPM） structure, whieh are severe in high-intensity regime and may result in lower conversion efficiency. We propose a configuration of QPM structure with reduced domain-length, which may depress the nonlinear phase shifts to some extent and lead to an improvement on the conversion efficiency. The numerical analyses on the conversion efficiency as well as the relative phase angle are discussed in detail for better understanding of the SHG process.
基金Supported by the National High Technology Development Program of China under Grant No 2002AA84TS11, the National Natural Science Foundation of China under Grant No 6987704 and the China Academy of Engineering Physics under Grant No 10176007.
文摘The focusing properties of fractal zone plates （FZPs） with different structure parameters are studied experimentally. The axial irradiance of FZPs is deduced at n=4. The experimental results are in good agreement with the theoretical prediction. A method to fabricate FZPs with variable structure parameters is mentioned, and the liquid-crystal-on-silicon device is used to implement this experiment. The experimental results indicate that the focal depth of lower order FZPs is larger than that of higher order FZPs.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10376009, 10576009 and 60538010.
文摘Stimulated Raman scattering （SRS） of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from the surface ripple of nonlinear crystal, can be significantly enhanced due to SRS, and the gain of instability increases with the spatial period of modulation. Numerical simulations based on the nonlinear coupled-wave equations verify the validity of the perturbation approach.
基金Supported by the National Natural Science Foundation under Grant Nos 60490290, 10404019, and 10374019, the Science and Technology Committee of Shanghai under Grant No 04D214001, and the Ministry of Education of China.
文摘We investigate the structure and exchange coupling in TbFeCo/FePt bilayer films. It is found that FePt has the L10 structure and the easy axis of the FePt film is perpendicular to the film plane. Results of the vibrating sample magnetometer and the magneto-optical Kerr effect measurements show a strong perpendicular exchange coupling between the ferrimagnetic TbFeCo layer and the hard ferromagnetic FePt layer. The magnetization direction of each layer and the process of magnetization reversal are discussed in detail. The switching field dependence on the exchange coupling has been modelled by micromagnetic simulation and the interlayer coupling constant is about -0.9 erg/cm^2 according to this simulation.
基金Supported by the National Natural Science Foundation of China under Grant 60501002.
文摘A series of Co/Alq3 granular film samples are prepared using co-evaporating technique. The microstructures and magnetic properties are investigated. The Kerr spectra and optical constants of Cox（Alq3）1-x （0.19 ≤ x ≤ 1） granular films are measured using a magneto-optical Kerr spectrometer and a spectroscopic ellipsometer in the 1.5-4.5 eV photon energy range. The Kerr rotation reaches the maximum value of 0.5° in the x = 0.65 sample. The relationship between enhanced Kerr rotation and optical constants is discussed, and the concentration dependence of MOKE spectra is also investigated.
基金the National Natural Science Foundation of China(Grant No.60076025).
文摘The effect of transverse coupling in a photorefractive oscillator is studied. From the study the condition for stable optical patterns of multimode oscillation is given analytically and verified by numerical simulation. Under the stable condition, the period-doubling route to spatiotemporal chaos is observed.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 60088003 and 10276012)National High-Tech Committee of China, and National Project 973 of China (Grant No. G19990752023).
文摘Due to group velocity mismatch, the generation of the cascaded fifth-order nonlinear phase shifts with femtosecond pulse will inevitably cause the severe pulse distortion. By theoretical study and numerical simulations, we show that undistorted femtosecond pulse which is impressed the cascaded fifth-order nonlinear phase shifts can be obtained at large values of the phase mismatching △κL.
