This was an outlook on the prediction of the infrared laser potentiality from concentration dependences of the 2F5/2 experimental decay time in Yb3+-doped solid-state crystals mainly on cubic crystals with 99.99% pur...This was an outlook on the prediction of the infrared laser potentiality from concentration dependences of the 2F5/2 experimental decay time in Yb3+-doped solid-state crystals mainly on cubic crystals with 99.99% purity which could be extended to laser ceramics of the same composition.展开更多
Based on a theoretical model of Q-switched laser with the influences of the driving signal sent to the Pockels cell and the doping concentration of the gain medium taken into account,a method of achieving high energy ...Based on a theoretical model of Q-switched laser with the influences of the driving signal sent to the Pockels cell and the doping concentration of the gain medium taken into account,a method of achieving high energy sub-nanosecond Q-switched lasers is proposed and verified in experiment.When a Nd:YVO4 crystal with a doping concentration of 0.7 at.%is used as a gain medium and a driving signal with the optimal high-level voltage is applied to the Pockels cell,a stable single-transverse-mode electro-optical Q-switched laser with a pulse width of 0.77 ns and a pulse energy of 1.04 mJ operating at the pulse repetition frequency of 1 kHz is achieved.The precise tuning of the pulse width is also demonstrated.展开更多
Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi2) assisted excimer laser crystallization (ELC). The process to prepare a sample includes two steps. One step cons...Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi2) assisted excimer laser crystallization (ELC). The process to prepare a sample includes two steps. One step consists of the formation of NiSi2 precipitates by heat-treating the dehydrogenated amorphous silicon (a-Si) coated with a thin layer of Ni. And the other step consists of the formation of poly-Si grains by means of ELC. According to the test results of scanning electron microscopy (SEM), another grain growth model named two-interface grain growth has been proposed to contrast with the conventional Ni-metal-induced lateral crystallization (Ni-MILC) model and the ELC model. That is, an additional grain growth interface other than that in conventional ELC is formed, which consists of NiSi2 precipitates and a-Si. The processes for grain growth according to various excimer laser energy densities delivered to the a-Si film have been discussed. It is discovered that grains with needle shape and most of a uniform orientation are formed which grow up with NiSi2 precipitates as seeds. The reason for the formation of such grains which are different from that of Ni-MILC without migration of Ni atoms is not clear. Our model and analysis point out a method to prepare grains with needle shape and mostly of a uniform orientation. If such grains are utilized to make thin-film transistor, its characteristics may be improved.展开更多
Single crystal of Yb x Y 1- x Al 3(BO 3) 4 (Yb∶YAB) was grown by using flux method based on the potassium trimolybdate. 160 mW efficient continuous wave green output was obtained from a fibre coupled ...Single crystal of Yb x Y 1- x Al 3(BO 3) 4 (Yb∶YAB) was grown by using flux method based on the potassium trimolybdate. 160 mW efficient continuous wave green output was obtained from a fibre coupled 976 nm laser diode. The conversion efficiency is larger than 11 3%, and the electrical input green conversion efficiency is 3 9%. Tunable green output from 513 0 to 545 8 nm is also demonstrated with a quartz birefringent filter. By enhancing the incident pump power, 1 1 W cw green output can be reached.展开更多
We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd:CaGdAI04 (Nd:CGA) as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser ...We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd:CaGdAI04 (Nd:CGA) as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser pulses as short as 850fs at 1079nm are obtained with a repetition rate of 124.6 MHz. The measured threshold pump power is 1.45 W. A maximum average output power of 122mW is obtained under the pump power of 5.9 W. These results show that Nd:CGA could be a promising laser medium for generating femtosecond ultrashort pulse at about 1 μm.展开更多
Semiconductor and laser single crystals are usually brittle and hard,which need to be ground to have satisfactory surface integrity and dimensional precision prior to their applications.Improvement of the surface inte...Semiconductor and laser single crystals are usually brittle and hard,which need to be ground to have satisfactory surface integrity and dimensional precision prior to their applications.Improvement of the surface integrity of a ground crystal can shorten the time of a subsequent polishing process,thus reducing the manufacturing cost.The development of cost-effective grinding technologies for those crystals requires an in-depth understanding of their deformation and removal mechanisms.As a result,a great deal of research efforts were directed towards studying this topic in the past two or three decades.In this review,we aimed to summarize the deformation and removal characteristics of representative semiconductor and laser single crystals in accordance with the scale of mechanical loading,especially at extremely small scales.Their removal mechanisms were critically examined based on the evidence obtained from highresolution TEM analyses.The relationships between machining conditions and removal behaviors were discussed to provide a guidance for further advancing of the grinding technologies for those crystals.展开更多
We report the repetitively Q-switched laser operation of the Yb-doped calcium niobium gallium garnet disordered garnet crystal, achieved with an acousto-optic modulator in a compact plano-concave resonator that is end...We report the repetitively Q-switched laser operation of the Yb-doped calcium niobium gallium garnet disordered garnet crystal, achieved with an acousto-optic modulator in a compact plano-concave resonator that is endpumped by a 935-nm diode laser. An average output power of 1.96 W is produced at pulse repetition rate of50 k Hz at emission wavelengths around 1035 nm, with a slope efficiency of 16%. The highest pulse energy of 269 μJ is generated at pulse repetition rate of 1 k Hz, with pulse width 12.1 ns and peak power 20.53 kW.展开更多
Multi-conjugation adaptive optics(MCAOs) have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view(FOV).The atmospheric tomographic phase reconst...Multi-conjugation adaptive optics(MCAOs) have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view(FOV).The atmospheric tomographic phase reconstruction and projection of three-dimensional turbulence volume onto wavefront correctors,such as deformable mirrors(DMs) or liquid crystal wavefront correctors(LCWCs),is a very important step in the data processing of an MCAO's controller.In this paper,a method according to the wavefront reconstruction performance of MCAO is presented to evaluate the optimized configuration of multi laser guide stars(LGSs) and the reasonable conjugation heights of LCWCs.Analytical formulations are derived for the different configurations and are used to generate optimized parameters for MCAO.Several examples are given to demonstrate our LGSs configuration optimization method.Compared with traditional methods,our method has minimum wavefront tomographic error,which will be helpful to get higher imaging resolution at large FOV in MCAO.展开更多
The effect of laser energy density on the crystallization of hydrogenated intrinsic amorphous silicon (a-Si:H) thin films was studied both theoretically and experimentally. The thin films were irritated by a freque...The effect of laser energy density on the crystallization of hydrogenated intrinsic amorphous silicon (a-Si:H) thin films was studied both theoretically and experimentally. The thin films were irritated by a frequency-doubled (λ= 532 nm) Nd:YAG pulsed nanosecond laser. An effective density functional theory model was built to reveal the variation of bandgap energy influenced by thermal stress after laser irradiation. Experimental results establish correlation between the thermal stress and the shift of transverse optical peak in Raman spectroscopy and suggest that the relatively greater shift of the transverse optical (TO) peak can produce higher stress. The highest crystalline fraction (84.5%) is obtained in the optimized laser energy density (1000 mJ/cm2) with a considerable stress release. The absorption edge energy measured by the UV- visible spectra is in fairly good agreement with the bandgap energy in the density functional theory (DFT) simulation.展开更多
By using the re-derived formulae for both line-strength of electricdipole transition and simple J-mixing coefficients within the 4f shell in a rare-earthion, the spectroscopic properties of the luminescent material Eu...By using the re-derived formulae for both line-strength of electricdipole transition and simple J-mixing coefficients within the 4f shell in a rare-earthion, the spectroscopic properties of the luminescent material Eu3+ =Y2O3 and laser crystals Tb3+:=YAlO3 and Nd3+:YVO4, are investigated in detail. On the basis of three fitting Ω parameters and the effective reduced matrix elements, the spectral linestrengths, spontaneous emission probabilities, fluorescent branching ratios and lifetimeare calculated. The better agreement between theoretical results and experimental dataindicates the importance of J-mixing in the spectroscopic study of laser crystals.展开更多
Eye-safe 1.5~1.6 μm lasers have important applications in optical fiber communication, medicine, laser-range-finding, lidar, etc. Er^3+ and Yb^3+ co-doped crystal pumped by diode laser around 976 nm is an attracti...Eye-safe 1.5~1.6 μm lasers have important applications in optical fiber communication, medicine, laser-range-finding, lidar, etc. Er^3+ and Yb^3+ co-doped crystal pumped by diode laser around 976 nm is an attractive method for obtaining 1.5~1.6 μm laser in compact device with high output beam quality. In this paper, the recent research and progress of several important Er^3+ and Yb^3+ co-doped laser crystals at 1.5~1.6 μm in authors’ lab are reported.展开更多
Single, composite crystal and ceramic continuous wave (CW) 946-nm Nd:YAG lasers are demonstrated, respectively. The ceramic laser behaves better than the crystal laser. With 5-mm long ceramic, a CW output power of ...Single, composite crystal and ceramic continuous wave (CW) 946-nm Nd:YAG lasers are demonstrated, respectively. The ceramic laser behaves better than the crystal laser. With 5-mm long ceramic, a CW output power of 1.46 W is generated with an optical conversion efficiency of 13.9%, while the slope efficiency is 17.9%. The optimal ceramic length for a 946- nm laser is also calculated.展开更多
The laser irradiation effect on the SERS intensity for Ag film is discussed using crystal violet (CV) as a probe. The thickness of silver film,the etching time of the glass slide by gaseous hydrogen fluoride, and the ...The laser irradiation effect on the SERS intensity for Ag film is discussed using crystal violet (CV) as a probe. The thickness of silver film,the etching time of the glass slide by gaseous hydrogen fluoride, and the laser irradiation time for different amounts of CV on silver films were investigated. The laser burn out model was proposed to explain the dependence of the SERS intensity of CV on the laser irradiation time.展开更多
A CaF2-CeF3 disordered crystal containing 1.06% of Er^3+ ions was grown by the temperature gradient technique.Optical absorption and emission spectra recorded at room temperature and at 10 K, luminescence decay curve...A CaF2-CeF3 disordered crystal containing 1.06% of Er^3+ ions was grown by the temperature gradient technique.Optical absorption and emission spectra recorded at room temperature and at 10 K, luminescence decay curve recorded at room temperature, and extended x-ray-absorption fine structure spectra were analyzed with an intention to assess the laser potential related to the ^4I13/2→^4I15/2 transition of Er^3+. In addition, the thermal diffusivity of the crystal was measured at room temperature. The analysis of room-temperature spectra revealed that the ^4I13/2 emission is long-lived with a radiative lifetime value of 5.5 ms, peak emission cross section of 0.73 × 10^-20 cm^2, and large spectral width pointing at the tunability of the emission wavelength in the region stretching from approximately 1480 nm to 1630 nm. The energies of the crystal field components for the ground and excited multiplets determined from low-temperature absorption and emission spectra made it possible to predict successfully the spectral position and shape of the room-temperature ^4I13/2→^4I15/2 emission band. Based on the correlation of the optical spectra and dynamics of the luminescence decay, it was concluded that in contrast to Yb^3+ ions in heavily doped CaF2 erbium ions in the CaF2-CeF3 crystal reside in numerous sites with dissimilar relaxation rates.展开更多
This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Re...This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Research has been carried out on the laser-induced crystallization of thin films and nanostructures.The in situ transmission electron microscopy(TEM)monitoring of the crystallization of amorphous precursors in nanodomains is discussed herein.The directed assembly of silicon nanoparticles and the modulation of their optical properties by phase switching is presented.The vapor-liquid-solid mechanism has been adopted as a bottom-up approach in the synthesis of semiconducting nanowires(NWs).In contrast to furnace heating methods,laser irradiation offers high spatial selectivity and precise control of the heating mechanism in the time domain.These attributes enabled the investigation of NW nucleation and the early stage of nanostructure growth.Site-and shape-selective,on-demand direct integration of oriented NWs was accomplished.Growth of discrete silicon NWs with nanoscale location selectivity by employing near-field laser illumination is also reported herein.Tuning the properties of 2D transition metal dichalcogenides(TMDCs)by modulating the free carrier type,density,and composition can offer an exciting new pathway to various practical nanoscale electronics.In situ Raman probing of laser-induced processing of TMDC flakes was conducted in a TEM instrument.展开更多
Direct growth and patterning of atomically thin two-dimensional(2D)materials on various substrates are essential steps towards enabling their potential for use in the next generation of electronic and optoelectronic d...Direct growth and patterning of atomically thin two-dimensional(2D)materials on various substrates are essential steps towards enabling their potential for use in the next generation of electronic and optoelectronic devices.The conventional gas-phase growth techniques,however,are not compatible with direct patterning processes.Similarly,the condensed-phase methods,based on metal oxide deposition and chalcogenization processes,require lengthy processing times and high temperatures.Here,a novel self-limiting laser crystallization process for direct crystallization and patterning of 2D materials is demonstrated.It takes advantage of significant differences between the optical properties of the amorphous and crystalline phases.Pulsed laser deposition is used to deposit a thin layer of stoichiometric amorphous molybdenum disulfide(MoS2)film(∼3 nm)onto the fused silica substrates.A tunable nanosecond infrared(IR)laser(1064 nm)is then employed to couple a precise amount of power and number of pulses into the amorphous materials for controlled crystallization and direct writing processes.The IR laser interaction with the amorphous layer results in fast heating,crystallization,and/or evaporation of the materials within a narrow processing window.However,reduction of the midgap and defect states in the as crystallized layers decreases the laser coupling efficiency leading to higher tolerance to process parameters.The deliberate design of such laser 2D material interactions allows the selflimiting crystallization phenomena to occur with increased quality and a much broader processing window.This unique laser processing approach allows high-quality crystallization,direct writing,patterning,and the integration of various 2D materials into future functional devices.展开更多
The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A sm...The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A small amount of β-Si3N4 formed at 1250℃ and increased slowly until the α- β transformation happened at 1700℃, whereas α-Si3N4 appeared at 1300℃ andincreased rapidly between 1500-1600℃. The formation of β phase at the lower temperature was caused by the nitridation of free Si due to the preexisted β-nuclei in the Si3N4 particles, whereasthe α phase was formed by solid crystallization from the amorphous matrix. There were α and β SiC formed at 1700℃ due to the presence of Sio and Co gases in the system. FTIR analysis shows that two new IR absorption at 1356 and 1420 cm-1, and an overall strong absorption in wide wavenumber range resulted from the powders annealed at 1600 and 1700℃ respectively展开更多
Adaptive optics(AO) systems are widespread and considered as an essential part of any large aperture telescope for obtaining a high resolution imaging at present.To enlarge the imaging field of view(FOV),multi-las...Adaptive optics(AO) systems are widespread and considered as an essential part of any large aperture telescope for obtaining a high resolution imaging at present.To enlarge the imaging field of view(FOV),multi-laser guide stars(LGSs) are currently being investigated and used for the large aperture optical telescopes.LGS measurement is necessary and pivotal to obtain the cumulative phase distortion along a target in the multi-LGSs AO system.We propose a high precision phase reconstruction algorithm to estimate the phase for a target with an uncertain turbulence profile based on the interpolation.By comparing with the conventional average method,the proposed method reduces the root mean square(RMS) error from 130 nm to 85 nm with a 30% reduction for narrow FOV.We confirm that such phase reconstruction algorithm is validated for both narrow field AO and wide field AO.展开更多
The single and coupled photonic crystal nanocavity lasers are fabricated in the InGaAsP material system and their static and dynamic features are compared. The coupled-cavity lasers show a larger lasing e^ciency and g...The single and coupled photonic crystal nanocavity lasers are fabricated in the InGaAsP material system and their static and dynamic features are compared. The coupled-cavity lasers show a larger lasing e^ciency and generate an output power higher than the single-cavity lasers, results that are consistent with the theoretical results obtained by rate equations. In dynamic regime, the single-cavity lasers produce pulses as short as 113 ps, while the coupled-cavity lasers show a significantly longer lasing duration. These results indicate that the photonic crystal laser is a promising candidate for the light source in high-speed photonic integrated circuit.展开更多
We demonstrate the temperature-dependent fluorescence properties of Pr:LiGdF4 crystal tor the first time, to the best of our knowledge, and its blue diode pumped cw red laser at 720 nm at room temperature. The fluore...We demonstrate the temperature-dependent fluorescence properties of Pr:LiGdF4 crystal tor the first time, to the best of our knowledge, and its blue diode pumped cw red laser at 720 nm at room temperature. The fluorescence lifetime and polarized emission cross sections in the visible range are measured and calculated in a temperature range from 77K to 300 K, and the variations of the fluorescence lifetime and spectra are discovered. The reasons for these changes are explained accordingly. The output wavelength of the 720nm laser is first reported on the laser performance by using a fiber-coupled laser diode at the wavelength of 442nm as the pump source, and the maximum cw output power is about 303roW.展开更多
文摘This was an outlook on the prediction of the infrared laser potentiality from concentration dependences of the 2F5/2 experimental decay time in Yb3+-doped solid-state crystals mainly on cubic crystals with 99.99% purity which could be extended to laser ceramics of the same composition.
基金the National Key Research and Development Program of China(Grant No.2017YFB0405203)the Shanxi“1331 Project”Key Subjects Construction,China(Grant No.1331KSC).
文摘Based on a theoretical model of Q-switched laser with the influences of the driving signal sent to the Pockels cell and the doping concentration of the gain medium taken into account,a method of achieving high energy sub-nanosecond Q-switched lasers is proposed and verified in experiment.When a Nd:YVO4 crystal with a doping concentration of 0.7 at.%is used as a gain medium and a driving signal with the optimal high-level voltage is applied to the Pockels cell,a stable single-transverse-mode electro-optical Q-switched laser with a pulse width of 0.77 ns and a pulse energy of 1.04 mJ operating at the pulse repetition frequency of 1 kHz is achieved.The precise tuning of the pulse width is also demonstrated.
基金Project supported by the National High Technology Development Program of China (Grant No 2002AA303250) and by the National Natural Science Foundation of China (Grant No 60576056).
文摘Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi2) assisted excimer laser crystallization (ELC). The process to prepare a sample includes two steps. One step consists of the formation of NiSi2 precipitates by heat-treating the dehydrogenated amorphous silicon (a-Si) coated with a thin layer of Ni. And the other step consists of the formation of poly-Si grains by means of ELC. According to the test results of scanning electron microscopy (SEM), another grain growth model named two-interface grain growth has been proposed to contrast with the conventional Ni-metal-induced lateral crystallization (Ni-MILC) model and the ELC model. That is, an additional grain growth interface other than that in conventional ELC is formed, which consists of NiSi2 precipitates and a-Si. The processes for grain growth according to various excimer laser energy densities delivered to the a-Si film have been discussed. It is discovered that grains with needle shape and most of a uniform orientation are formed which grow up with NiSi2 precipitates as seeds. The reason for the formation of such grains which are different from that of Ni-MILC without migration of Ni atoms is not clear. Our model and analysis point out a method to prepare grains with needle shape and mostly of a uniform orientation. If such grains are utilized to make thin-film transistor, its characteristics may be improved.
文摘Single crystal of Yb x Y 1- x Al 3(BO 3) 4 (Yb∶YAB) was grown by using flux method based on the potassium trimolybdate. 160 mW efficient continuous wave green output was obtained from a fibre coupled 976 nm laser diode. The conversion efficiency is larger than 11 3%, and the electrical input green conversion efficiency is 3 9%. Tunable green output from 513 0 to 545 8 nm is also demonstrated with a quartz birefringent filter. By enhancing the incident pump power, 1 1 W cw green output can be reached.
基金Supported by the National Key Basic Research Program of China under Grant No 2013CB922402the International Joint Research Program,and the National Natural Science Foundation of China under Grant Nos 61210017 and 11434016
文摘We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd:CaGdAI04 (Nd:CGA) as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser pulses as short as 850fs at 1079nm are obtained with a repetition rate of 124.6 MHz. The measured threshold pump power is 1.45 W. A maximum average output power of 122mW is obtained under the pump power of 5.9 W. These results show that Nd:CGA could be a promising laser medium for generating femtosecond ultrashort pulse at about 1 μm.
基金The authors would like to acknowledge the financial supports from Australia Research Council(ARC)under Discovery Projects program(DP180103275)It is also supported by the Scientific Research Funds of Huaqiao University(605-50Y19022)Certain images in this publication have been obtained by the author(s)from the Wikipedia/Wikimedia website,where they were made available under a Creative Commons licence or stated to be in the public domain.Please see individual captions in this publications for details.To the extent that the law allows,IOP Publishing disclaim any liability that any person may suffer as a result of accessing,using or forwarding the image(s).Any reuse rights should be checked and permission should be sought if necessary from the Wikipedia/Wikimedia and/or the copyright owner(as appropriate)before using or forwarding the image(s).
文摘Semiconductor and laser single crystals are usually brittle and hard,which need to be ground to have satisfactory surface integrity and dimensional precision prior to their applications.Improvement of the surface integrity of a ground crystal can shorten the time of a subsequent polishing process,thus reducing the manufacturing cost.The development of cost-effective grinding technologies for those crystals requires an in-depth understanding of their deformation and removal mechanisms.As a result,a great deal of research efforts were directed towards studying this topic in the past two or three decades.In this review,we aimed to summarize the deformation and removal characteristics of representative semiconductor and laser single crystals in accordance with the scale of mechanical loading,especially at extremely small scales.Their removal mechanisms were critically examined based on the evidence obtained from highresolution TEM analyses.The relationships between machining conditions and removal behaviors were discussed to provide a guidance for further advancing of the grinding technologies for those crystals.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11274188 and 11574170
文摘We report the repetitively Q-switched laser operation of the Yb-doped calcium niobium gallium garnet disordered garnet crystal, achieved with an acousto-optic modulator in a compact plano-concave resonator that is endpumped by a 935-nm diode laser. An average output power of 1.96 W is produced at pulse repetition rate of50 k Hz at emission wavelengths around 1035 nm, with a slope efficiency of 16%. The highest pulse energy of 269 μJ is generated at pulse repetition rate of 1 k Hz, with pulse width 12.1 ns and peak power 20.53 kW.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174274,11174279,61205021,11204299,61475152,and 61405194)the State Key Laboratory of Applied Optics,Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences
文摘Multi-conjugation adaptive optics(MCAOs) have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view(FOV).The atmospheric tomographic phase reconstruction and projection of three-dimensional turbulence volume onto wavefront correctors,such as deformable mirrors(DMs) or liquid crystal wavefront correctors(LCWCs),is a very important step in the data processing of an MCAO's controller.In this paper,a method according to the wavefront reconstruction performance of MCAO is presented to evaluate the optimized configuration of multi laser guide stars(LGSs) and the reasonable conjugation heights of LCWCs.Analytical formulations are derived for the different configurations and are used to generate optimized parameters for MCAO.Several examples are given to demonstrate our LGSs configuration optimization method.Compared with traditional methods,our method has minimum wavefront tomographic error,which will be helpful to get higher imaging resolution at large FOV in MCAO.
基金Project supported by the Shanghai Leading Academic Disciplines,China(Grant No.S30107)
文摘The effect of laser energy density on the crystallization of hydrogenated intrinsic amorphous silicon (a-Si:H) thin films was studied both theoretically and experimentally. The thin films were irritated by a frequency-doubled (λ= 532 nm) Nd:YAG pulsed nanosecond laser. An effective density functional theory model was built to reveal the variation of bandgap energy influenced by thermal stress after laser irradiation. Experimental results establish correlation between the thermal stress and the shift of transverse optical peak in Raman spectroscopy and suggest that the relatively greater shift of the transverse optical (TO) peak can produce higher stress. The highest crystalline fraction (84.5%) is obtained in the optimized laser energy density (1000 mJ/cm2) with a considerable stress release. The absorption edge energy measured by the UV- visible spectra is in fairly good agreement with the bandgap energy in the density functional theory (DFT) simulation.
文摘By using the re-derived formulae for both line-strength of electricdipole transition and simple J-mixing coefficients within the 4f shell in a rare-earthion, the spectroscopic properties of the luminescent material Eu3+ =Y2O3 and laser crystals Tb3+:=YAlO3 and Nd3+:YVO4, are investigated in detail. On the basis of three fitting Ω parameters and the effective reduced matrix elements, the spectral linestrengths, spontaneous emission probabilities, fluorescent branching ratios and lifetimeare calculated. The better agreement between theoretical results and experimental dataindicates the importance of J-mixing in the spectroscopic study of laser crystals.
基金Supported by the National Natural Science Foundation of China (No. 50590405 and 50802094)the Major Programs of the Chinese Academy of Sciences (No. SZD08001-1)+1 种基金the Natural Science Foundation of Fujian Province (No. 2008J0173)the Knowledge Innovation Program of the Chinese Academy of Sciences
文摘Eye-safe 1.5~1.6 μm lasers have important applications in optical fiber communication, medicine, laser-range-finding, lidar, etc. Er^3+ and Yb^3+ co-doped crystal pumped by diode laser around 976 nm is an attractive method for obtaining 1.5~1.6 μm laser in compact device with high output beam quality. In this paper, the recent research and progress of several important Er^3+ and Yb^3+ co-doped laser crystals at 1.5~1.6 μm in authors’ lab are reported.
基金Project supported by the National Natural Science Foundation of China(Grant No.61405171)the Natural Science Foundation of Shandong Province,China(Grant No.ZR2012FQ014)the Science and Technology Program of the Shandong Higher Education Institutions of China(Grant No.J13LJ05)
文摘Single, composite crystal and ceramic continuous wave (CW) 946-nm Nd:YAG lasers are demonstrated, respectively. The ceramic laser behaves better than the crystal laser. With 5-mm long ceramic, a CW output power of 1.46 W is generated with an optical conversion efficiency of 13.9%, while the slope efficiency is 17.9%. The optimal ceramic length for a 946- nm laser is also calculated.
文摘The laser irradiation effect on the SERS intensity for Ag film is discussed using crystal violet (CV) as a probe. The thickness of silver film,the etching time of the glass slide by gaseous hydrogen fluoride, and the laser irradiation time for different amounts of CV on silver films were investigated. The laser burn out model was proposed to explain the dependence of the SERS intensity of CV on the laser irradiation time.
基金Project supported by Shanghai Engineering Research Center for Sapphire Crystals,China(Grant No.14DZ2252500)the Fund of Key Laboratory of Optoelectronic Materials Chemistry and Physics Chinese Academy of Sciences(Grant No.2008DP17301)+4 种基金the Fundamental Research Funds for the Central Universities of Chinathe National Natural Science Foundation of China and China Academy of Engineering Physics Joint Fund(Grant No.U1530152)the National Natural Science Foundation of China(Grant Nos.61475177 and 61621001)the Natural Science Foundation of Shanghai Municiple,China(Grant No.13ZR1446100)the MOE Key Laboratory of Advanced Micro-Structured Materials of China
文摘A CaF2-CeF3 disordered crystal containing 1.06% of Er^3+ ions was grown by the temperature gradient technique.Optical absorption and emission spectra recorded at room temperature and at 10 K, luminescence decay curve recorded at room temperature, and extended x-ray-absorption fine structure spectra were analyzed with an intention to assess the laser potential related to the ^4I13/2→^4I15/2 transition of Er^3+. In addition, the thermal diffusivity of the crystal was measured at room temperature. The analysis of room-temperature spectra revealed that the ^4I13/2 emission is long-lived with a radiative lifetime value of 5.5 ms, peak emission cross section of 0.73 × 10^-20 cm^2, and large spectral width pointing at the tunability of the emission wavelength in the region stretching from approximately 1480 nm to 1630 nm. The energies of the crystal field components for the ground and excited multiplets determined from low-temperature absorption and emission spectra made it possible to predict successfully the spectral position and shape of the room-temperature ^4I13/2→^4I15/2 emission band. Based on the correlation of the optical spectra and dynamics of the luminescence decay, it was concluded that in contrast to Yb^3+ ions in heavily doped CaF2 erbium ions in the CaF2-CeF3 crystal reside in numerous sites with dissimilar relaxation rates.
基金The research was performed at the Laser Thermal Laboratory by Drs David J Hwang,Sang-gil Ryu,Eunpa Kim,Jung Bin In,and the current students,Letian Wang,Yoonsoo Rho and Matthew Eliceiri.Professors Andrew M Minor,Junqiao Wu,Oscar D Dubon,Drs Bin Xiang,Frances I Allen,and Changhyun Ko of UCB Materials Science and Engineering,and Dr Carlo Carraro of UCB Chem.Engineering contributed to the work.The research was supported by DARPA/MTO under TBN grant N66001-08-1-2041,the US Department of Energy SBIR grant(DE-FG02-07ER84813),Samsung GRO,and NSF CMMI-1363392.The in situ experiments were performed at the National Center for Electron Microscopy at the Lawrence Berkeley National Laboratory,which is supported by the Office of Science,Office of Basic Energy Sciences,Scientific User Facilities Division,of the US Department of Energy under Contract No.DE-AC02-05CH11231.The laser-induced nanowire growth and doping was conducted on the LACVD apparatus in the UC Berkeley Marvell Nanofabrication Laboratory.
文摘This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Research has been carried out on the laser-induced crystallization of thin films and nanostructures.The in situ transmission electron microscopy(TEM)monitoring of the crystallization of amorphous precursors in nanodomains is discussed herein.The directed assembly of silicon nanoparticles and the modulation of their optical properties by phase switching is presented.The vapor-liquid-solid mechanism has been adopted as a bottom-up approach in the synthesis of semiconducting nanowires(NWs).In contrast to furnace heating methods,laser irradiation offers high spatial selectivity and precise control of the heating mechanism in the time domain.These attributes enabled the investigation of NW nucleation and the early stage of nanostructure growth.Site-and shape-selective,on-demand direct integration of oriented NWs was accomplished.Growth of discrete silicon NWs with nanoscale location selectivity by employing near-field laser illumination is also reported herein.Tuning the properties of 2D transition metal dichalcogenides(TMDCs)by modulating the free carrier type,density,and composition can offer an exciting new pathway to various practical nanoscale electronics.In situ Raman probing of laser-induced processing of TMDC flakes was conducted in a TEM instrument.
基金This work is supported by the Intermural Grant Program(IGP)at Auburn University.
文摘Direct growth and patterning of atomically thin two-dimensional(2D)materials on various substrates are essential steps towards enabling their potential for use in the next generation of electronic and optoelectronic devices.The conventional gas-phase growth techniques,however,are not compatible with direct patterning processes.Similarly,the condensed-phase methods,based on metal oxide deposition and chalcogenization processes,require lengthy processing times and high temperatures.Here,a novel self-limiting laser crystallization process for direct crystallization and patterning of 2D materials is demonstrated.It takes advantage of significant differences between the optical properties of the amorphous and crystalline phases.Pulsed laser deposition is used to deposit a thin layer of stoichiometric amorphous molybdenum disulfide(MoS2)film(∼3 nm)onto the fused silica substrates.A tunable nanosecond infrared(IR)laser(1064 nm)is then employed to couple a precise amount of power and number of pulses into the amorphous materials for controlled crystallization and direct writing processes.The IR laser interaction with the amorphous layer results in fast heating,crystallization,and/or evaporation of the materials within a narrow processing window.However,reduction of the midgap and defect states in the as crystallized layers decreases the laser coupling efficiency leading to higher tolerance to process parameters.The deliberate design of such laser 2D material interactions allows the selflimiting crystallization phenomena to occur with increased quality and a much broader processing window.This unique laser processing approach allows high-quality crystallization,direct writing,patterning,and the integration of various 2D materials into future functional devices.
文摘The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A small amount of β-Si3N4 formed at 1250℃ and increased slowly until the α- β transformation happened at 1700℃, whereas α-Si3N4 appeared at 1300℃ andincreased rapidly between 1500-1600℃. The formation of β phase at the lower temperature was caused by the nitridation of free Si due to the preexisted β-nuclei in the Si3N4 particles, whereasthe α phase was formed by solid crystallization from the amorphous matrix. There were α and β SiC formed at 1700℃ due to the presence of Sio and Co gases in the system. FTIR analysis shows that two new IR absorption at 1356 and 1420 cm-1, and an overall strong absorption in wide wavenumber range resulted from the powders annealed at 1600 and 1700℃ respectively
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174274,11174279,61205021,11204299,61475152,and 61405194)State Key Laboratory of Applied Optics,Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences
文摘Adaptive optics(AO) systems are widespread and considered as an essential part of any large aperture telescope for obtaining a high resolution imaging at present.To enlarge the imaging field of view(FOV),multi-laser guide stars(LGSs) are currently being investigated and used for the large aperture optical telescopes.LGS measurement is necessary and pivotal to obtain the cumulative phase distortion along a target in the multi-LGSs AO system.We propose a high precision phase reconstruction algorithm to estimate the phase for a target with an uncertain turbulence profile based on the interpolation.By comparing with the conventional average method,the proposed method reduces the root mean square(RMS) error from 130 nm to 85 nm with a 30% reduction for narrow FOV.We confirm that such phase reconstruction algorithm is validated for both narrow field AO and wide field AO.
基金Supported by the National Key Basic Research Special Fund/CNKBRSF of China under Grant Nos 2012CB933501,2016YFA0301102,2016YFB0401804 and 2016YFB0402203the National Natural Science Foundation of China under Grant Nos61535013,61321063 and 61137003+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant Nos XDB24010100,XDB24010200,XDB24020100 and XDB24030100the One Hundred Person Project of the Chinese Academy of Sciences
文摘The single and coupled photonic crystal nanocavity lasers are fabricated in the InGaAsP material system and their static and dynamic features are compared. The coupled-cavity lasers show a larger lasing e^ciency and generate an output power higher than the single-cavity lasers, results that are consistent with the theoretical results obtained by rate equations. In dynamic regime, the single-cavity lasers produce pulses as short as 113 ps, while the coupled-cavity lasers show a significantly longer lasing duration. These results indicate that the photonic crystal laser is a promising candidate for the light source in high-speed photonic integrated circuit.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51025210,51102156 and 51272131the Young and Middle-Aged Scientists Research Awards Fund of Shandong Province under Grant No BS2011CL024
文摘We demonstrate the temperature-dependent fluorescence properties of Pr:LiGdF4 crystal tor the first time, to the best of our knowledge, and its blue diode pumped cw red laser at 720 nm at room temperature. The fluorescence lifetime and polarized emission cross sections in the visible range are measured and calculated in a temperature range from 77K to 300 K, and the variations of the fluorescence lifetime and spectra are discovered. The reasons for these changes are explained accordingly. The output wavelength of the 720nm laser is first reported on the laser performance by using a fiber-coupled laser diode at the wavelength of 442nm as the pump source, and the maximum cw output power is about 303roW.