The dynamic buckling of thin copper plate induced by laser beam, was analyzed with the numerical integration and disturbance methods of controlling equation. The buckling and post-buckling of thin plate were shown, wi...The dynamic buckling of thin copper plate induced by laser beam, was analyzed with the numerical integration and disturbance methods of controlling equation. The buckling and post-buckling of thin plate were shown, with the consideration of the temperature distribution, inertia effect and initial deflection. At last, the buckling criterion about the circular plate was obtained and used to investigate the relation between the critical laser intensity and the ratio of thickness and diameter of the plate. The results fit the experimental observation and FEM simulation very well, and benefit the understanding of failure phenomenon of structures irradiated by laser beam.展开更多
Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of interfacial laye...Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of interfacial layer, yielding metallic Ga and N2 gas. The substrate can be easily removed by heating above the Ga melting point (29°C). X-ray diffraction, atomic force microscopy and photoluminescence of GaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality of the GaN films. And further discussions on the threshold energy and crack-free strategies of laser lift-off process have also been presented.展开更多
After laser quenching and tempering of three kinds of annealed tool high-speed steel(W18Cr-4V, W9Mo3Cr4V1, W6Mo5Cr4V2) test samples, the microhardness measurer was used to test the samples and some problems, such as t...After laser quenching and tempering of three kinds of annealed tool high-speed steel(W18Cr-4V, W9Mo3Cr4V1, W6Mo5Cr4V2) test samples, the microhardness measurer was used to test the samples and some problems, such as the hardness and depth of hardening-quenching layer were analyzed. Furthermore, after laser quenching and tempering of the quenched and three-time tempered high-speed steel (W18Cr4V) and its hardness analyzing, different results of laser-quenching samples were obtained under different initial heat-treating.展开更多
The characteristics of fiber laser coherent beam combination are investigated by using a 2×2 fiber laser array with a self-Fourier cavity.The experimental results show that with a certain output width the power r...The characteristics of fiber laser coherent beam combination are investigated by using a 2×2 fiber laser array with a self-Fourier cavity.The experimental results show that with a certain output width the power ratio of the center spot is increased with the increase of space duty cycle,meanwhile the number of secondary spots is decreased correspondingly.The results are in agreement with theoretic analysis.展开更多
Graphite powders were irradiated by pulsed laser at room temperature and normal pressure and then boiled in perchloric acid. Samples were characterized by high-resolution transmission electron microscopy (HRTEM), elec...Graphite powders were irradiated by pulsed laser at room temperature and normal pressure and then boiled in perchloric acid. Samples were characterized by high-resolution transmission electron microscopy (HRTEM), electron diffraction pattern (EDP), X-ray diffraction (XRD) pattern, and Raman spectroscopy. The analyses on the HRTEM images, EDP, and XRD show that the diamond particles with a size of about 5 nm are obtained. The shifting and broadening of the diamond peak in Raman spectrum indicate that there are high defect density and residual internal stress in synthetic diamond.展开更多
The vaporization threshold was measured under the irradiation of 1.064-μm, 10-ns pulsed laser. Then we calculated the vaporization temperature based on the conservation law of energy and analyzed the vaporization tim...The vaporization threshold was measured under the irradiation of 1.064-μm, 10-ns pulsed laser. Then we calculated the vaporization temperature based on the conservation law of energy and analyzed the vaporization time based on our established model. These results coincided well with the information from the micrograph of scanning electron microscope (SEM) and the spectra of the plasma. Besides, the laser ablation rate was also computed and discussed theoretically.展开更多
We present the birefringence measurements induced in K9 specimen by cracks produced by 1 064-nm Nd:YAG laser. The birefringence data are converted into units of stress, permitting the estimation of residual stress ne...We present the birefringence measurements induced in K9 specimen by cracks produced by 1 064-nm Nd:YAG laser. The birefringence data are converted into units of stress, permitting the estimation of residual stress near cracks. The laser parameters and characterization of the optical material influence the value of residual stress. Residual stress in optical materials can affect fracture; thus, this factor should be considered in any formulation that involves enhanced damage resistance of optical components used in laser-induced damage experiments. The probability of the initial damage and the direction of the energy dissipation in cracks determine the residual stress distribution. Moreover, thermal-stress coupling enlarges the asymmetry of residual stress distribution. Therefore, the physical mechanism of asymmetric damage is useful for understanding the nature of optical materials under high-power laser irradiation.展开更多
A model that considers both thermal expansion and thermo-optical effects is developed to investigate the trans- mission variation of optical coatings when they are exposed to an intense laser beam. Our results indicat...A model that considers both thermal expansion and thermo-optical effects is developed to investigate the trans- mission variation of optical coatings when they are exposed to an intense laser beam. Our results indicate that a higher gradient of the transmission spectrum curve at a certain wavelength leads to a more evident variation of the coating transmission. Three customized HfO2-SiO2 multilayer coatings with different transmission spectra are used to measure the transmitted power under the irradiation of a 1080 nm continuous-fiber laser. Excellent agreement is found between the experimental result and the theoretical prediction. Our result is helpful for the improvement of such devices in the application of high-power laser systems.展开更多
A method for fabricating three-dimensional (3D) photonic crystals (PhCs) easily and simply, by using a visible light (- 532 nm) to pass one triangular pyramid to form non-coplanar multi-beam interference, named ...A method for fabricating three-dimensional (3D) photonic crystals (PhCs) easily and simply, by using a visible light (- 532 nm) to pass one triangular pyramid to form non-coplanar multi-beam interference, named laser interference etching technique, is reported. In the experiment, we exposed a 9-μm-thick photo- resist on the silicon substrate with exposure intensities of 150, 180, and 220 mJ/cm^2, and produced the periodical nanostructures. Through varying a common angle in the triangular pyramid, other interference patterns can be obtained to fabricate various PhCs.展开更多
Crystallization is induced by pulsed laser irradiation of as-deposited amorphous Ge_2Sb_2Te_5 films. Changes of the irradiated areas have been analyzed with the reflectivity contrast. As laser fluences increasing, the...Crystallization is induced by pulsed laser irradiation of as-deposited amorphous Ge_2Sb_2Te_5 films. Changes of the irradiated areas have been analyzed with the reflectivity contrast. As laser fluences increasing, the reflectivity contrast increases from 0%-2% to 14%-16%, which indicates the structure of asdeposited films transforms from amorphous to crystalline phases. The process of crystallization driven by the movement and rearrangement of atoms is described. And also the influence of the pulse duration on the threshold of crystallization is discussed, the results show that a lower threshold of crystallization can be produced for as-deposited films irradiated by the laser with short pulse duration. However, by the laser with long pulse duration, crystallization can only be formed with a higher threshold. The crystallization of films by irradiation of laser pulses is studied by Raman spectra.展开更多
SiO2-TiO2 sol-gel films are deposited on SiO2/Si by dip-coating technique. The SiO2-TiO2 strips are fabricated by laser direct writing using an ytterbium fiber laser and followed by chemical etching. Surface structure...SiO2-TiO2 sol-gel films are deposited on SiO2/Si by dip-coating technique. The SiO2-TiO2 strips are fabricated by laser direct writing using an ytterbium fiber laser and followed by chemical etching. Surface structures, morphologies and roughness of the films and strips are characterized. The experimental results demonstrate that the SiO2-TiO2 sol-gel film is loose in structure and a shrinkage concave groove forms if the film is irradiated by laser beam. The surface roughness of both non-irradiated and laser irradiated areas increases with the chemical etching time. But the roughness of laser irradiated area increases more than that of non-irradiated area under the same etching time. After being etched for 28 s, the surface roughness value of the laser irradiated area increases from 0.3 nm to 3.1 nm.展开更多
As the output power of a chemical oxygen iodine laser (COIL) increases, the output laser beam instability appears as the far-field beam spot drift and deformation for the large Presnel number unstable resonator. In or...As the output power of a chemical oxygen iodine laser (COIL) increases, the output laser beam instability appears as the far-field beam spot drift and deformation for the large Presnel number unstable resonator. In order to interpret this phenomenon, an output beam mode simulation code was developed with the fast Fourier transform method. The calculation results show that the presence of the nonuniform gain in COIL produces a skewed output intensity distribution, which causes the mirror tilt and bulge due to the thermal expansion. With the output power of COIL increases, the mirror surfaces, especially the back surface of the scraper mirror, absorb more and more heat, which causes the drift and deformation of far field beam spot seriously. The initial misalignment direction is an important factor for the far field beam spot drifting and deformation.展开更多
We show self-coupled and cross-coupled vector beam evolution equations in the low-amplitude regime for screening solitons, which can exhibit the analytical solutions of bright-bright and dark-dark vector solitons. Our...We show self-coupled and cross-coupled vector beam evolution equations in the low-amplitude regime for screening solitons, which can exhibit the analytical solutions of bright-bright and dark-dark vector solitons. Our analysis indicates that these self-coupled vector solitons are obtained irrespective of the intensities of the two optical beams, whereas these cross-coupled vector solitons can be established when the intensities of the two optical beams are equal. Relevant examples are provided where the photorefractive crystal is lithium niobate (LiNbO3). The stability properties of these vector solitons have been investigated numerically and it has been found that they are stable.展开更多
The optical limiting behaviors of nano-gold self-assembled multi-wall carbon nanotube (MWNT) were experimentally investigated at 532 and 1064 nm, respectively. The comparison of the limiting performances between carbo...The optical limiting behaviors of nano-gold self-assembled multi-wall carbon nanotube (MWNT) were experimentally investigated at 532 and 1064 nm, respectively. The comparison of the limiting performances between carbon nanotube suspension, C60 solution, and carbon black suspension (CBS) was performed. The results show that the optical limiting characteristic of nano-gold self-assembled MWNT is better than those of C60 and CBS. The mechanisms of the optical limiting for the samples were discussed.展开更多
The influence of circular aperture on the intensity of high-order harmonic generation (HHG) with intense femtosecond laser pulse was studied both experimentally and theoretically. The intensity variety of HHG with the...The influence of circular aperture on the intensity of high-order harmonic generation (HHG) with intense femtosecond laser pulse was studied both experimentally and theoretically. The intensity variety of HHG with the diameter of circular aperture was observed in pulsed Ar gas. The result was discussed and interpreted in terms of the theory of Hankel transform. It is found that using the Gaussian beam truncated by an aperture could enhance the conversion efficiency of HHG at certain conditions.展开更多
文摘The dynamic buckling of thin copper plate induced by laser beam, was analyzed with the numerical integration and disturbance methods of controlling equation. The buckling and post-buckling of thin plate were shown, with the consideration of the temperature distribution, inertia effect and initial deflection. At last, the buckling criterion about the circular plate was obtained and used to investigate the relation between the critical laser intensity and the ratio of thickness and diameter of the plate. The results fit the experimental observation and FEM simulation very well, and benefit the understanding of failure phenomenon of structures irradiated by laser beam.
基金supported by Special Funds for Major Stale Basic Research Project G20000683863 Hi-tech Research Project,Distinguished Young Scientist Grant(60025411)+1 种基金National Nature Science Foundation of China(69976014,69636010,69806006,69987001)benefited from using the laser device of the Pulsed Laser Deposition laboratory in Nanjing University.
文摘Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of interfacial layer, yielding metallic Ga and N2 gas. The substrate can be easily removed by heating above the Ga melting point (29°C). X-ray diffraction, atomic force microscopy and photoluminescence of GaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality of the GaN films. And further discussions on the threshold energy and crack-free strategies of laser lift-off process have also been presented.
文摘After laser quenching and tempering of three kinds of annealed tool high-speed steel(W18Cr-4V, W9Mo3Cr4V1, W6Mo5Cr4V2) test samples, the microhardness measurer was used to test the samples and some problems, such as the hardness and depth of hardening-quenching layer were analyzed. Furthermore, after laser quenching and tempering of the quenched and three-time tempered high-speed steel (W18Cr4V) and its hardness analyzing, different results of laser-quenching samples were obtained under different initial heat-treating.
基金supported by the National"863"Program of China(No.2008AA03Z405)the Shanghai Rising-Star Program(No.09QB1401700).
文摘The characteristics of fiber laser coherent beam combination are investigated by using a 2×2 fiber laser array with a self-Fourier cavity.The experimental results show that with a certain output width the power ratio of the center spot is increased with the increase of space duty cycle,meanwhile the number of secondary spots is decreased correspondingly.The results are in agreement with theoretic analysis.
基金supported by the National Natural Science Foundation of China(No.50372043)the Tiarijin Science and Technol-ogy Committee(No.043101211).
文摘Graphite powders were irradiated by pulsed laser at room temperature and normal pressure and then boiled in perchloric acid. Samples were characterized by high-resolution transmission electron microscopy (HRTEM), electron diffraction pattern (EDP), X-ray diffraction (XRD) pattern, and Raman spectroscopy. The analyses on the HRTEM images, EDP, and XRD show that the diamond particles with a size of about 5 nm are obtained. The shifting and broadening of the diamond peak in Raman spectrum indicate that there are high defect density and residual internal stress in synthetic diamond.
基金This work was supported by the National Natural Science Foundation of China(No.10474059),the Provincial Natural Science Foundation of Shandong(No.Y2003A01),and the Project sponsored by SRF for ROCS,SEM,P.R.China.
文摘The vaporization threshold was measured under the irradiation of 1.064-μm, 10-ns pulsed laser. Then we calculated the vaporization temperature based on the conservation law of energy and analyzed the vaporization time based on our established model. These results coincided well with the information from the micrograph of scanning electron microscope (SEM) and the spectra of the plasma. Besides, the laser ablation rate was also computed and discussed theoretically.
基金supported by the National Natural Science Foundation of China(No.61078075)the Development Foundation of Science and Technology for China Academy of Engineering Physics(Nos.2010B0401055 and 2011B0401065)
文摘We present the birefringence measurements induced in K9 specimen by cracks produced by 1 064-nm Nd:YAG laser. The birefringence data are converted into units of stress, permitting the estimation of residual stress near cracks. The laser parameters and characterization of the optical material influence the value of residual stress. Residual stress in optical materials can affect fracture; thus, this factor should be considered in any formulation that involves enhanced damage resistance of optical components used in laser-induced damage experiments. The probability of the initial damage and the direction of the energy dissipation in cracks determine the residual stress distribution. Moreover, thermal-stress coupling enlarges the asymmetry of residual stress distribution. Therefore, the physical mechanism of asymmetric damage is useful for understanding the nature of optical materials under high-power laser irradiation.
基金supported by the State Key Laboratory of Laser Interaction with Matter under Grant No.Skllim1201-02
文摘A model that considers both thermal expansion and thermo-optical effects is developed to investigate the trans- mission variation of optical coatings when they are exposed to an intense laser beam. Our results indicate that a higher gradient of the transmission spectrum curve at a certain wavelength leads to a more evident variation of the coating transmission. Three customized HfO2-SiO2 multilayer coatings with different transmission spectra are used to measure the transmitted power under the irradiation of a 1080 nm continuous-fiber laser. Excellent agreement is found between the experimental result and the theoretical prediction. Our result is helpful for the improvement of such devices in the application of high-power laser systems.
基金The authors thank Department of Physics, Hong Kong University of Science and Technology for support.
文摘A method for fabricating three-dimensional (3D) photonic crystals (PhCs) easily and simply, by using a visible light (- 532 nm) to pass one triangular pyramid to form non-coplanar multi-beam interference, named laser interference etching technique, is reported. In the experiment, we exposed a 9-μm-thick photo- resist on the silicon substrate with exposure intensities of 150, 180, and 220 mJ/cm^2, and produced the periodical nanostructures. Through varying a common angle in the triangular pyramid, other interference patterns can be obtained to fabricate various PhCs.
文摘Crystallization is induced by pulsed laser irradiation of as-deposited amorphous Ge_2Sb_2Te_5 films. Changes of the irradiated areas have been analyzed with the reflectivity contrast. As laser fluences increasing, the reflectivity contrast increases from 0%-2% to 14%-16%, which indicates the structure of asdeposited films transforms from amorphous to crystalline phases. The process of crystallization driven by the movement and rearrangement of atoms is described. And also the influence of the pulse duration on the threshold of crystallization is discussed, the results show that a lower threshold of crystallization can be produced for as-deposited films irradiated by the laser with short pulse duration. However, by the laser with long pulse duration, crystallization can only be formed with a higher threshold. The crystallization of films by irradiation of laser pulses is studied by Raman spectra.
基金Hi-Tech Research and Development Program of China under Grant No.2005AA311030
文摘SiO2-TiO2 sol-gel films are deposited on SiO2/Si by dip-coating technique. The SiO2-TiO2 strips are fabricated by laser direct writing using an ytterbium fiber laser and followed by chemical etching. Surface structures, morphologies and roughness of the films and strips are characterized. The experimental results demonstrate that the SiO2-TiO2 sol-gel film is loose in structure and a shrinkage concave groove forms if the film is irradiated by laser beam. The surface roughness of both non-irradiated and laser irradiated areas increases with the chemical etching time. But the roughness of laser irradiated area increases more than that of non-irradiated area under the same etching time. After being etched for 28 s, the surface roughness value of the laser irradiated area increases from 0.3 nm to 3.1 nm.
文摘As the output power of a chemical oxygen iodine laser (COIL) increases, the output laser beam instability appears as the far-field beam spot drift and deformation for the large Presnel number unstable resonator. In order to interpret this phenomenon, an output beam mode simulation code was developed with the fast Fourier transform method. The calculation results show that the presence of the nonuniform gain in COIL produces a skewed output intensity distribution, which causes the mirror tilt and bulge due to the thermal expansion. With the output power of COIL increases, the mirror surfaces, especially the back surface of the scraper mirror, absorb more and more heat, which causes the drift and deformation of far field beam spot seriously. The initial misalignment direction is an important factor for the far field beam spot drifting and deformation.
基金This work was supported by the National Natural Sci-ence Foundation of China (No. 60078004)by the Director Foundation of Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences.
文摘We show self-coupled and cross-coupled vector beam evolution equations in the low-amplitude regime for screening solitons, which can exhibit the analytical solutions of bright-bright and dark-dark vector solitons. Our analysis indicates that these self-coupled vector solitons are obtained irrespective of the intensities of the two optical beams, whereas these cross-coupled vector solitons can be established when the intensities of the two optical beams are equal. Relevant examples are provided where the photorefractive crystal is lithium niobate (LiNbO3). The stability properties of these vector solitons have been investigated numerically and it has been found that they are stable.
基金The experiment was performed in Harbin Institute of Technology, State Key Laboratory of Tunable Laser Technology. This work was partially supported by the multidiscipline fund of Harbin Institute of Technology (HIT.MD.2002.01) and the fund of National Key Labo-ratory of Tunable Laser Technology. This work was also supported by the National Natural Science Foundation of China (No. 90206037), and the Research Foundation for the Doctoral Program of the Ministry of Education, P. R. China (No. 20020284022).
文摘The optical limiting behaviors of nano-gold self-assembled multi-wall carbon nanotube (MWNT) were experimentally investigated at 532 and 1064 nm, respectively. The comparison of the limiting performances between carbon nanotube suspension, C60 solution, and carbon black suspension (CBS) was performed. The results show that the optical limiting characteristic of nano-gold self-assembled MWNT is better than those of C60 and CBS. The mechanisms of the optical limiting for the samples were discussed.
基金This work was supported by the National Key Basic Research Special Foundation (NKBRSF) under Grant No. TG1999075207National Natural Science Foundation of China under Grant No. 90206003 and 90101027.
文摘The influence of circular aperture on the intensity of high-order harmonic generation (HHG) with intense femtosecond laser pulse was studied both experimentally and theoretically. The intensity variety of HHG with the diameter of circular aperture was observed in pulsed Ar gas. The result was discussed and interpreted in terms of the theory of Hankel transform. It is found that using the Gaussian beam truncated by an aperture could enhance the conversion efficiency of HHG at certain conditions.