This paper describes a tunable dual-wavelength Ti:sapphire laser system with quasi-continuous-wave and high-power outputs. In the design of the laser, it adopts a frequency-doubled Nd:YAG laser as the pumping source...This paper describes a tunable dual-wavelength Ti:sapphire laser system with quasi-continuous-wave and high-power outputs. In the design of the laser, it adopts a frequency-doubled Nd:YAG laser as the pumping source, and the birefringence filter as the tuning element. Tunable dual-wavelength outputs with one wavelength range from 700 nm to 756.5 nm, another from 830 nm to 900mn have been demonstrated. With a pump power of 23 W at 532 nm, a repetition rate of 7 kHz and a pulse width of 47.6 ns, an output power of 5.1 W at 744.8 nm and 860.9 nm with a pulse width of 13.2 ns and a line width of 3 nm has been obtained, it indicates an optical-to-optical conversion efficiency of 22.2%.展开更多
A Kerr-lens mode-locked Ti:sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The charac...A Kerr-lens mode-locked Ti:sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti:sapphire l^ser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37 ps to 2.11 ps, and 36 fs pulses are achieved atter extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr6dinger equation, and the simulation results are in good agreement with the experimental results.展开更多
Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamen...Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.展开更多
A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. Using a fused-silica prism as the dispersion element, a tuning range of 740-855 nm is obtai...A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. Using a fused-silica prism as the dispersion element, a tuning range of 740-855 nm is obtained. At an incident pump energy of 774mJ, the maximum output energy of 104mJ at 790nm with a pulse width of 100μs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, it is the highest pulse energy at 790 nm with pulse width of hundred micro-seconds for an all-solid-state laser. The linewidth of output is 0.5 nm, and the beam quality factor M2 is 1.16. The high-pulse-energy high-beam-quality tunable Ti:sapphire laser in the range of 740-855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe2BO3F2 measured in a wider wavelength range and to assess Miller's rule quantitatively.展开更多
We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses a...We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW.The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.展开更多
We demonstrate a 100-TW-class femtosecond Ti:sapphire laser running at a repetition rate of 0.1Hz based on a 20TW/10 Hz laser facility (XL-Ⅱ).Pumping the new stage amplifier with a 25J green Nd:glass laser,we success...We demonstrate a 100-TW-class femtosecond Ti:sapphire laser running at a repetition rate of 0.1Hz based on a 20TW/10 Hz laser facility (XL-Ⅱ).Pumping the new stage amplifier with a 25J green Nd:glass laser,we successfully improve the laser energy to 3.4J with duration of 29 fs,corresponding to a peak power of 11 7 TW.展开更多
We experimentally demonstrate that a tunable supercontinuum(SC) can be generated in a Yb3+-doped microstructure fiber by the concept of wavelength conversion with a Ti:sapphire femtosecond(fs) laser as the pump....We experimentally demonstrate that a tunable supercontinuum(SC) can be generated in a Yb3+-doped microstructure fiber by the concept of wavelength conversion with a Ti:sapphire femtosecond(fs) laser as the pump.Experimental results show that an emission light around 1040 nm in an anomalous dispersion region is first generated and amplified by fs pulses in the normal dispersion region. Then, SC spectra from 1100 to 1380 nm and 630 to 840 nm can be achieved by combined effects of higher-order soliton fission and Raman soliton self-frequency shift in the anomalous dispersion region and self-phase modulation, dispersive wave, and four-wave mixing in the normal dispersion region. It is also demonstrated that the 20 nm change of pump results in a 280 nm broadband shift of soliton and the further red-shift of soliton is limited by OH-absorption at 1380 nm.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
We studied the evolution of wavefront aberration(WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification(CPA) system. The results verified that the WFA of the amplified laser beam has l...We studied the evolution of wavefront aberration(WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification(CPA) system. The results verified that the WFA of the amplified laser beam has little relation with the change of the pump beam energies. Transverse parasitic lasing that might occur in CPA hardly affects the wavefront of the signal beam. Thermal effects were also considered in this study, and the results show that the thermal effect cumulated in multiple amplification processes also has no obvious influence on the wavefront of the signal beam for a single-shot frequency. The results presented in this paper confirmed experimentally that the amplification in a Ti:sapphire CPA system has little impact on the WFA of the signal beam and it is very helpful for wavefront correction of single-shot PW and multi-PW laser systems based on Ti:sapphire.展开更多
We report a high repetition frequency, high power stability and low laser noise laser-diode(LD) end-pumped Nd: YAG ceramic passively Q-switched laser at 1123 nm based on a Ti_(3)C_(2)T_(x)-polyvinyl alcohol(PVA) film ...We report a high repetition frequency, high power stability and low laser noise laser-diode(LD) end-pumped Nd: YAG ceramic passively Q-switched laser at 1123 nm based on a Ti_(3)C_(2)T_(x)-polyvinyl alcohol(PVA) film as a saturable absorber(SA). A Brewster polarizer(BP) and a birefringent crystal(BC) are incorporated to enable frequency selection and filtering for the passively Q-switched 1123 nm pulsed laser to improve the power stability and reduce the noise. When the pump power is 5.1 W, an average output power of 457.9 m W is obtained, corresponding to a repetition frequency of 1.09 MHz,a pulse width of 56 ns, a spectral line width of 0.65 nm, a power instability of ±0.92%, and a laser noise of 0.89%.The successful implementation of the “Ti_(3)C_(2)T_(x)-PVA film passively Q-switching” combined with “frequency selection and filtering of BP + BC” technology path provides a valuable reference for developing pulsed laser with high repetition frequency, high stability and low noise.展开更多
The spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the one- dimensional (1D) and two-dimensional (2D) Frantz-Nodvik equations. The simulation indicates that th...The spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the one- dimensional (1D) and two-dimensional (2D) Frantz-Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti:sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti:sapphire chirped pulse amplifier system.展开更多
We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio th...We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio through numerical simulation. The simulation results demonstrate that the linewidth of external-cavity semiconductor lasers can be reduced by increasing the external cavity length and feedback ratio, and adding more external feedback points can further narrow the linewidth and enhance the side mode suppression ratio. This research provides insight into the external cavity distributed feedback mechanism and can guide the design of high-performance external cavity semiconductor lasers. .展开更多
Transparent brittle materials such as glass and sapphire are widely concerned and applied in consumer electronics, optoelectronic devices, etc. due to their excellent physical and chemical stability and good transpare...Transparent brittle materials such as glass and sapphire are widely concerned and applied in consumer electronics, optoelectronic devices, etc. due to their excellent physical and chemical stability and good transparency. Growing research attention has been paid to developing novel methods for high-precision and high-quality machining of transparent brittle materials in the past few decades. Among the various techniques, laser machining has been proved to be an effective and flexible way to process all kinds of transparent brittle materials. In this review, a series of laser machining methods, e.g. laser full cutting, laser scribing, laser stealth dicing, laser filament, laser induced backside dry etching (LIBDE), and laser induced backside wet etching (LIBWE) are summarized. Additionally, applications of these techniques in micromachining, drilling and cutting, and patterning are introduced in detail. Current challenges and future prospects in this field are also discussed.展开更多
Using an infrared thermographic technique, the temperature field during laser welding of TA15 is quantitatively measured and investigated. The ilffluenee of two welding parameters on the weld temperature distribution ...Using an infrared thermographic technique, the temperature field during laser welding of TA15 is quantitatively measured and investigated. The ilffluenee of two welding parameters on the weld temperature distribution is analyzed and the meehanisnl is discussed. New conclusions are drawn that are different from conventional weld temperature distributions. For the face of the weld, changes in welding speed induce changes in the temperature distribution because of different heat inputs and the cooling effect. Sinfilar temperature features in the welds are observed for all speeds, which exhibit a relatively low temperature area below 1 500 ℃ between the high temperature area in the position of laser incidence and the sub-high temperature area at the end of the molten pool. For the ilffluenee of laser power on the face of the weld, the temperature on the weld is higher for P = 2.8 kW compared to P = 2.0 kW, especially the temperature in the sub-high temperature area. However, for the temperature field of the back of the weld, the ilffluenee of welding speeds is quite different compared to the results for the face of the weld. The highest temperature does not locate in the keyhole area, but instead in the middle of the molten pool. And there are different temperature features at different speeds. When v = 6 m/min, the temperature field is like a uniform color belt and the temperature along the center of the weld fluctuates between 300 and 450 ℃. When v = 4 m/rain, the transient temperature distribution is not uniform and is unstable at different times. However, for v = 2.4 m/rain and lower speeds, the temperature field becomes stable. The ilffluenee of laser power on the back of the weld temperature field is more complex. The measured temperature does not increase with increasing laser power, which seems to eolffliet with the conventional thermal conduction theory-. This may be related with the characteristics of the keyhole area.展开更多
In this paper, Ni-based alloy composite coating reinforced by Ti (C, N) particles was fabricated on the mild steel through laser cladding technology. The microstrncture of laser cladding layer was analyzed by means ...In this paper, Ni-based alloy composite coating reinforced by Ti (C, N) particles was fabricated on the mild steel through laser cladding technology. The microstrncture of laser cladding layer was analyzed by means of optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The wear resistance test of the coating was evaluated using an M-2000 tester. The results showed that the Ni-based composite coating had an ability of rapid solidification to form dendritic crystals microstructure consisting of Ti ( C, N) particulates uniformly distributed in the matrix. It was found that some Ti( C,N) particles are similar to be round in shape, and the others are irregular. Laser cladding layer reinforced by Ti( C, N) particulates was found to possess good wear resistance property.展开更多
Fe-based alloy coatings reinforced by Ti( C, N) particles was produced through CO2 laser cladding technology. The microstructure of laser cladding coating was analyzed by means of X-ray diffraction ( XRD ), transm...Fe-based alloy coatings reinforced by Ti( C, N) particles was produced through CO2 laser cladding technology. The microstructure of laser cladding coating was analyzed by means of X-ray diffraction ( XRD ), transmission electron microscopy (TEM) , selected area electron diffraction ( SAED ) , scanning electron microscopy (SEM) and electron probe microscopic analyzer ( EPMA ). The mechanical property of the layer was measured by using microhardness meter. The results show that Ti ( C0. 3 N0. 7 ) panicles are introduced by an in-situ metallurgical reaction between TiN particle and graphite powder during laser cladding process. Titanium carbonitrides particles existed in the layer are fairly fine, ranging from 0. 1 μm to 5.0 μm, and evenly dispersed in the metal α-Fe matrix. Most of them take on nearly rhombus shape, and some of them are irregular in shape. The microhardness of laser cladding layer ranges from 770 HV0. 3 to 850 HV0. 3.展开更多
基金Project supported in part by the National Natural Science Foundation of China (Grant Nos 10474071, 60637010, 60671036 and 60278001) and Tianjin Applied Fundamental Research Project, China (07JCZDJC05900).
文摘This paper describes a tunable dual-wavelength Ti:sapphire laser system with quasi-continuous-wave and high-power outputs. In the design of the laser, it adopts a frequency-doubled Nd:YAG laser as the pumping source, and the birefringence filter as the tuning element. Tunable dual-wavelength outputs with one wavelength range from 700 nm to 756.5 nm, another from 830 nm to 900mn have been demonstrated. With a pump power of 23 W at 532 nm, a repetition rate of 7 kHz and a pulse width of 47.6 ns, an output power of 5.1 W at 744.8 nm and 860.9 nm with a pulse width of 13.2 ns and a line width of 3 nm has been obtained, it indicates an optical-to-optical conversion efficiency of 22.2%.
基金Project supported by the National Basic Research Program of China (Grant No. 2006CB806002)the National High Technology Research and Development Program of China (Grant No. 2007AA03Z447)+3 种基金National Natural Science Foundation of China (Grant Nos. 60678012 and 60838004)the Foundation for Key Program of Ministry of Education, China (Grant No. 108032)FANEDD(Grant No. 2007B34)NCET (Grant No. NCET-07-0597)
文摘A Kerr-lens mode-locked Ti:sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti:sapphire l^ser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37 ps to 2.11 ps, and 36 fs pulses are achieved atter extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr6dinger equation, and the simulation results are in good agreement with the experimental results.
基金National Natural Science Foundation of China(51575013,51275011)National Key R&D Program of China(2018 YFB1107500)
文摘Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61275157 and 61475040the National Key Scientific Instrument and Equipment Development,Project under Grant No 2012YQ120048+1 种基金the National Development Project for Major Scientific Research Facility under Grant No ZDYZ2012-2the National Key Research and Development Program of China under Grant No 2016YFB0402003
文摘A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. Using a fused-silica prism as the dispersion element, a tuning range of 740-855 nm is obtained. At an incident pump energy of 774mJ, the maximum output energy of 104mJ at 790nm with a pulse width of 100μs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, it is the highest pulse energy at 790 nm with pulse width of hundred micro-seconds for an all-solid-state laser. The linewidth of output is 0.5 nm, and the beam quality factor M2 is 1.16. The high-pulse-energy high-beam-quality tunable Ti:sapphire laser in the range of 740-855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe2BO3F2 measured in a wider wavelength range and to assess Miller's rule quantitatively.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFB0402105)
文摘We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW.The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11074298,91126008,10804128 and 10925421the National Basic Research Program of China under Grant No 2007CB815104the Instrument Developing Project of Chinese Academy of Sciences under Grant No 2010004.
文摘We demonstrate a 100-TW-class femtosecond Ti:sapphire laser running at a repetition rate of 0.1Hz based on a 20TW/10 Hz laser facility (XL-Ⅱ).Pumping the new stage amplifier with a 25J green Nd:glass laser,we successfully improve the laser energy to 3.4J with duration of 29 fs,corresponding to a peak power of 11 7 TW.
基金Supported by the National Natural Science Foundation of China under Grant No 61735011the Natural Science Foundation of Hebei Province under Grant Nos F2016203389 and F2018105036+2 种基金the Science and Technology Research Project of College and University in Hebei Province under Grant No BJ2017108the Open Subject of Jiangsu Key Laboratory of Meteorological Observation and Information Processing under Grant No KDXS1107the Science and Technology Project of Tangshan City under Grant No 17130257a
文摘We experimentally demonstrate that a tunable supercontinuum(SC) can be generated in a Yb3+-doped microstructure fiber by the concept of wavelength conversion with a Ti:sapphire femtosecond(fs) laser as the pump.Experimental results show that an emission light around 1040 nm in an anomalous dispersion region is first generated and amplified by fs pulses in the normal dispersion region. Then, SC spectra from 1100 to 1380 nm and 630 to 840 nm can be achieved by combined effects of higher-order soliton fission and Raman soliton self-frequency shift in the anomalous dispersion region and self-phase modulation, dispersive wave, and four-wave mixing in the normal dispersion region. It is also demonstrated that the 20 nm change of pump results in a 280 nm broadband shift of soliton and the further red-shift of soliton is limited by OH-absorption at 1380 nm.
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.
基金Project supported by the National Natural Science Foundation of China(Grant No.61775223)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB1603)
文摘We studied the evolution of wavefront aberration(WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification(CPA) system. The results verified that the WFA of the amplified laser beam has little relation with the change of the pump beam energies. Transverse parasitic lasing that might occur in CPA hardly affects the wavefront of the signal beam. Thermal effects were also considered in this study, and the results show that the thermal effect cumulated in multiple amplification processes also has no obvious influence on the wavefront of the signal beam for a single-shot frequency. The results presented in this paper confirmed experimentally that the amplification in a Ti:sapphire CPA system has little impact on the WFA of the signal beam and it is very helpful for wavefront correction of single-shot PW and multi-PW laser systems based on Ti:sapphire.
基金Project supported by the Serving Local Special Project of Shaanxi Provincial Department of Education of China (Grant No. 19JC040)the National Natural Science Foundation of China (Grant No. 61905193)。
文摘We report a high repetition frequency, high power stability and low laser noise laser-diode(LD) end-pumped Nd: YAG ceramic passively Q-switched laser at 1123 nm based on a Ti_(3)C_(2)T_(x)-polyvinyl alcohol(PVA) film as a saturable absorber(SA). A Brewster polarizer(BP) and a birefringent crystal(BC) are incorporated to enable frequency selection and filtering for the passively Q-switched 1123 nm pulsed laser to improve the power stability and reduce the noise. When the pump power is 5.1 W, an average output power of 457.9 m W is obtained, corresponding to a repetition frequency of 1.09 MHz,a pulse width of 56 ns, a spectral line width of 0.65 nm, a power instability of ±0.92%, and a laser noise of 0.89%.The successful implementation of the “Ti_(3)C_(2)T_(x)-PVA film passively Q-switching” combined with “frequency selection and filtering of BP + BC” technology path provides a valuable reference for developing pulsed laser with high repetition frequency, high stability and low noise.
基金Project supported by 100 Talents Program of Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant Nos.61475169,61521093,and 11127901)the Youth Innovation Promotion Association of Chinese Academy of Sciences
文摘The spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the one- dimensional (1D) and two-dimensional (2D) Frantz-Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti:sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti:sapphire chirped pulse amplifier system.
文摘We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio through numerical simulation. The simulation results demonstrate that the linewidth of external-cavity semiconductor lasers can be reduced by increasing the external cavity length and feedback ratio, and adding more external feedback points can further narrow the linewidth and enhance the side mode suppression ratio. This research provides insight into the external cavity distributed feedback mechanism and can guide the design of high-performance external cavity semiconductor lasers. .
基金National Natural Science Foundation of China (51575114 and 51805093)National Key R&D Program of China (2018YFB1107700)Guangzhou Science and Technology Project (201607010156).
文摘Transparent brittle materials such as glass and sapphire are widely concerned and applied in consumer electronics, optoelectronic devices, etc. due to their excellent physical and chemical stability and good transparency. Growing research attention has been paid to developing novel methods for high-precision and high-quality machining of transparent brittle materials in the past few decades. Among the various techniques, laser machining has been proved to be an effective and flexible way to process all kinds of transparent brittle materials. In this review, a series of laser machining methods, e.g. laser full cutting, laser scribing, laser stealth dicing, laser filament, laser induced backside dry etching (LIBDE), and laser induced backside wet etching (LIBWE) are summarized. Additionally, applications of these techniques in micromachining, drilling and cutting, and patterning are introduced in detail. Current challenges and future prospects in this field are also discussed.
文摘Using an infrared thermographic technique, the temperature field during laser welding of TA15 is quantitatively measured and investigated. The ilffluenee of two welding parameters on the weld temperature distribution is analyzed and the meehanisnl is discussed. New conclusions are drawn that are different from conventional weld temperature distributions. For the face of the weld, changes in welding speed induce changes in the temperature distribution because of different heat inputs and the cooling effect. Sinfilar temperature features in the welds are observed for all speeds, which exhibit a relatively low temperature area below 1 500 ℃ between the high temperature area in the position of laser incidence and the sub-high temperature area at the end of the molten pool. For the ilffluenee of laser power on the face of the weld, the temperature on the weld is higher for P = 2.8 kW compared to P = 2.0 kW, especially the temperature in the sub-high temperature area. However, for the temperature field of the back of the weld, the ilffluenee of welding speeds is quite different compared to the results for the face of the weld. The highest temperature does not locate in the keyhole area, but instead in the middle of the molten pool. And there are different temperature features at different speeds. When v = 6 m/min, the temperature field is like a uniform color belt and the temperature along the center of the weld fluctuates between 300 and 450 ℃. When v = 4 m/rain, the transient temperature distribution is not uniform and is unstable at different times. However, for v = 2.4 m/rain and lower speeds, the temperature field becomes stable. The ilffluenee of laser power on the back of the weld temperature field is more complex. The measured temperature does not increase with increasing laser power, which seems to eolffliet with the conventional thermal conduction theory-. This may be related with the characteristics of the keyhole area.
文摘In this paper, Ni-based alloy composite coating reinforced by Ti (C, N) particles was fabricated on the mild steel through laser cladding technology. The microstrncture of laser cladding layer was analyzed by means of optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The wear resistance test of the coating was evaluated using an M-2000 tester. The results showed that the Ni-based composite coating had an ability of rapid solidification to form dendritic crystals microstructure consisting of Ti ( C, N) particulates uniformly distributed in the matrix. It was found that some Ti( C,N) particles are similar to be round in shape, and the others are irregular. Laser cladding layer reinforced by Ti( C, N) particulates was found to possess good wear resistance property.
文摘Fe-based alloy coatings reinforced by Ti( C, N) particles was produced through CO2 laser cladding technology. The microstructure of laser cladding coating was analyzed by means of X-ray diffraction ( XRD ), transmission electron microscopy (TEM) , selected area electron diffraction ( SAED ) , scanning electron microscopy (SEM) and electron probe microscopic analyzer ( EPMA ). The mechanical property of the layer was measured by using microhardness meter. The results show that Ti ( C0. 3 N0. 7 ) panicles are introduced by an in-situ metallurgical reaction between TiN particle and graphite powder during laser cladding process. Titanium carbonitrides particles existed in the layer are fairly fine, ranging from 0. 1 μm to 5.0 μm, and evenly dispersed in the metal α-Fe matrix. Most of them take on nearly rhombus shape, and some of them are irregular in shape. The microhardness of laser cladding layer ranges from 770 HV0. 3 to 850 HV0. 3.