Rules and mechanism of damage in Al2O3 coatings irradiated by CO2 CW laser are studied in order to improve the ability of parts of equipment standing against the high power laser. Al2O3 coatings were sprayed by air pl...Rules and mechanism of damage in Al2O3 coatings irradiated by CO2 CW laser are studied in order to improve the ability of parts of equipment standing against the high power laser. Al2O3 coatings were sprayed by air plasma spray（APS） on the 45^# steel substrate, and then were irradiated by CO2 CW laser from 795 W/cm^2 to 31 830 W/cm^2. As the output power of the laser is increasing, its porosity is increasing and cracks are appearing and spreading quickly, And also the phase will transform from γ-Al2O3 to a-Al2O3 in the damaged areas. When the energy density is 17 507 W/cm^2, the coatings are destroyed completely. The thermal infection field on substrate is rather small. The laser energy is depleted by the phase transformation and cracks in Al2O3 coatings during the laser thermal shock.展开更多
In this work ITO thin film annealing was carried out using a CW CO2 laser beam for ITO thin film annealing over a 1 cm2 area with a temperature higher than 250°C to obtain ITO grains with excellent structural qua...In this work ITO thin film annealing was carried out using a CW CO2 laser beam for ITO thin film annealing over a 1 cm2 area with a temperature higher than 250°C to obtain ITO grains with excellent structural quality thin films. The obtained ITO films were characterized for crystallization, surface morphology, electrical and optical properties, which has theoretical significance and application value. ITO thin films are deposited on glass substrates by sputter coater system (RF) from a high density target (In2O3-SnO2, 90-10 wt%). After deposition, ITO thin films have been irradiated by CW CO2 laser (λ = 10.6 μm) with power ranging from 1 to 10 watt. These films were annealed at temperatures 250°C, 350°C, and 450°C in the air for 20 minutes using different laser power. The main incentive was to develop a low temperature process for ITO thin films, which typically required a 350°C anneal to crystallize and achieve optimum optical and electrical properties. The XRD results showed that 350°C temperature laser annealing could crystallize ITO with a strong (222) preferred orientation and its grain size increased from 29.27 nm to 48.63 nm. The structure, optical transmission, energy gap, resistivity and sheet resistance of the ITO thin films were systematically investigated as a function of laser post annealing temperature. It was found that the lowest resistivity was 2.9 × 10-4 Ω-cm and that sheet resistance was 14.5 Ω/sq. And the highest optical transmittance (98.65%) of ITO films was obtained at 350°C annealing temperature.展开更多
Er:CaF_(2) crystals are crucial gain media for producing 3μm mid-infrared (MIR) lasers pumped by 976 nm continuouswave (CW) lasers owing to their low phonon energy and high conversion efficiency.This study investigat...Er:CaF_(2) crystals are crucial gain media for producing 3μm mid-infrared (MIR) lasers pumped by 976 nm continuouswave (CW) lasers owing to their low phonon energy and high conversion efficiency.This study investigated the damage characteristics and mechanism of Er:CaF_(2) crystals irradiated with a 976 nm CW laser.The laser-induced damage threshold of Er:CaF_(2) crystals with different Er^(3+) doping levels was tested;the damage morphology consists of a series of regular 70? cracks related to the angle of the crystal slip system on the surface.A finite-element model was used to calculate the temperature and stress fields of the crystals.The results indicated that the damage can be attributed to surface tensile stresses caused by the temperature gradient,and crystals with higher doping concentrations were more susceptible to damage owing to stronger light absorption.These findings provide valuable insights into the development of high-power MIR lasers.展开更多
To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary...To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.展开更多
A set of fiber-coupled continuous wave (CW) diode lasers has been used to pump Tm, Ho:GdVO_4 and generate 2.048-μm laser radiation at liquid nitrogen temperature. The optical-optical efficiencies of 25%, output power...A set of fiber-coupled continuous wave (CW) diode lasers has been used to pump Tm, Ho:GdVO_4 and generate 2.048-μm laser radiation at liquid nitrogen temperature. The optical-optical efficiencies of 25%, output power of 3.5 W, and pumping threshold of 838 mW have been obtained and compared with those from Tm, Ho:YLF under identical experimental conditions.展开更多
Tm：CaF2 and Tm;Y：CaF2 single crystals were prepared by the temperature gradient technique. The spectral properties of Tm;Y：CaF2 single crystals were investigated and compared with those of Tm：CaF2. It was demonstr...Tm：CaF2 and Tm;Y：CaF2 single crystals were prepared by the temperature gradient technique. The spectral properties of Tm;Y：CaF2 single crystals were investigated and compared with those of Tm：CaF2. It was demonstrated that codoping with Y3＋ ions could efficiently improve the spectroscopic properties. Tm;Y：CaF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections, and much longer fluorescence lifetimes of the upper laser level（Tm3＋：3H4 level） than Tm：CaF2 crystals. Continuous-wave（CW） lasers around 1.97 μm were demonstrated in 4.0 at. % Tm,4.0 at. % Y：CaF2 single crystals under 792 nm laser diode（LD） pumping. The best laser performance has been demonstrated with a low threshold of 0.368 W, a high slope efficiency of 54.8%, and a maximum output power of 1.013 W.展开更多
In this paper, several photonic generating methods for optical triangular pulses were reviewed. Four frontier research methods for generating optical triangular pulses were introduced, these four methods are respectiv...In this paper, several photonic generating methods for optical triangular pulses were reviewed. Four frontier research methods for generating optical triangular pulses were introduced, these four methods are respectively based on the frequency-to-time conversion, using normally dispersive fiber, by single-stage dual-drive Mach-Zehnder modulator （MZM）, and using dual-parallel MZM. These four methods can be classified into two categories in terms of the optical source employed, such as mode-lock laser （MLL） and continuous-wave （CW） respectively. Compared with the methods based on MLL, those based on CW have many advantages, such as simpler structure, lower price, higher stability, more flexible and wider tunability. Besides, the method using single-stage drive MZM can generate versatile waveform optical pulses, which has better performance than the first two methods in tunable capability of both repetition rate and center wavelength. With the same driving signal applied, the optical source using the dual-parallel MZM can generate signal with higher frequency than that of using the single-stage MZM.展开更多
基金the Ministerial Level Advanced Research Foundation (1040020440703)
文摘Rules and mechanism of damage in Al2O3 coatings irradiated by CO2 CW laser are studied in order to improve the ability of parts of equipment standing against the high power laser. Al2O3 coatings were sprayed by air plasma spray（APS） on the 45^# steel substrate, and then were irradiated by CO2 CW laser from 795 W/cm^2 to 31 830 W/cm^2. As the output power of the laser is increasing, its porosity is increasing and cracks are appearing and spreading quickly, And also the phase will transform from γ-Al2O3 to a-Al2O3 in the damaged areas. When the energy density is 17 507 W/cm^2, the coatings are destroyed completely. The thermal infection field on substrate is rather small. The laser energy is depleted by the phase transformation and cracks in Al2O3 coatings during the laser thermal shock.
文摘In this work ITO thin film annealing was carried out using a CW CO2 laser beam for ITO thin film annealing over a 1 cm2 area with a temperature higher than 250°C to obtain ITO grains with excellent structural quality thin films. The obtained ITO films were characterized for crystallization, surface morphology, electrical and optical properties, which has theoretical significance and application value. ITO thin films are deposited on glass substrates by sputter coater system (RF) from a high density target (In2O3-SnO2, 90-10 wt%). After deposition, ITO thin films have been irradiated by CW CO2 laser (λ = 10.6 μm) with power ranging from 1 to 10 watt. These films were annealed at temperatures 250°C, 350°C, and 450°C in the air for 20 minutes using different laser power. The main incentive was to develop a low temperature process for ITO thin films, which typically required a 350°C anneal to crystallize and achieve optimum optical and electrical properties. The XRD results showed that 350°C temperature laser annealing could crystallize ITO with a strong (222) preferred orientation and its grain size increased from 29.27 nm to 48.63 nm. The structure, optical transmission, energy gap, resistivity and sheet resistance of the ITO thin films were systematically investigated as a function of laser post annealing temperature. It was found that the lowest resistivity was 2.9 × 10-4 Ω-cm and that sheet resistance was 14.5 Ω/sq. And the highest optical transmittance (98.65%) of ITO films was obtained at 350°C annealing temperature.
基金supported by the Key Foreign Cooperation Projects of the Bureau of International Cooperation of the Chinese Academy of Sciences (No. 181231KYSB20210001)the National Key Laboratory of Infrared Detection Technologies (No. IRDT-23-11)+2 种基金the National Natural Science Foundation of China (Nos. 51972229,61925508 and 62205359)the Key Research and Development Program of the Ministry of Science and Technology (No. GG20210301)the National Defense Science and Technology 173 Program (No. 2021-JCJQ-JJ-0639)。
文摘Er:CaF_(2) crystals are crucial gain media for producing 3μm mid-infrared (MIR) lasers pumped by 976 nm continuouswave (CW) lasers owing to their low phonon energy and high conversion efficiency.This study investigated the damage characteristics and mechanism of Er:CaF_(2) crystals irradiated with a 976 nm CW laser.The laser-induced damage threshold of Er:CaF_(2) crystals with different Er^(3+) doping levels was tested;the damage morphology consists of a series of regular 70? cracks related to the angle of the crystal slip system on the surface.A finite-element model was used to calculate the temperature and stress fields of the crystals.The results indicated that the damage can be attributed to surface tensile stresses caused by the temperature gradient,and crystals with higher doping concentrations were more susceptible to damage owing to stronger light absorption.These findings provide valuable insights into the development of high-power MIR lasers.
基金supported by the National Key Technology Research and Development Program under Grant No.2007BAF11B01
文摘To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.
基金This work was supported by the Scientific Research Foundation of Harbin Institute of Technology
文摘A set of fiber-coupled continuous wave (CW) diode lasers has been used to pump Tm, Ho:GdVO_4 and generate 2.048-μm laser radiation at liquid nitrogen temperature. The optical-optical efficiencies of 25%, output power of 3.5 W, and pumping threshold of 838 mW have been obtained and compared with those from Tm, Ho:YLF under identical experimental conditions.
基金financially supported by the National Natural Science Foundation of China(Nos.61422511,61635012,and 51432007)the Strategic Priority Program of the Chinese Academy of Sciences(No.XDB16030000)
文摘Tm：CaF2 and Tm;Y：CaF2 single crystals were prepared by the temperature gradient technique. The spectral properties of Tm;Y：CaF2 single crystals were investigated and compared with those of Tm：CaF2. It was demonstrated that codoping with Y3＋ ions could efficiently improve the spectroscopic properties. Tm;Y：CaF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections, and much longer fluorescence lifetimes of the upper laser level（Tm3＋：3H4 level） than Tm：CaF2 crystals. Continuous-wave（CW） lasers around 1.97 μm were demonstrated in 4.0 at. % Tm,4.0 at. % Y：CaF2 single crystals under 792 nm laser diode（LD） pumping. The best laser performance has been demonstrated with a low threshold of 0.368 W, a high slope efficiency of 54.8%, and a maximum output power of 1.013 W.
基金This work was partly supported by the National Natural Science Foundation of China （Grant Nos. 61275076, 61177069）.
文摘In this paper, several photonic generating methods for optical triangular pulses were reviewed. Four frontier research methods for generating optical triangular pulses were introduced, these four methods are respectively based on the frequency-to-time conversion, using normally dispersive fiber, by single-stage dual-drive Mach-Zehnder modulator （MZM）, and using dual-parallel MZM. These four methods can be classified into two categories in terms of the optical source employed, such as mode-lock laser （MLL） and continuous-wave （CW） respectively. Compared with the methods based on MLL, those based on CW have many advantages, such as simpler structure, lower price, higher stability, more flexible and wider tunability. Besides, the method using single-stage drive MZM can generate versatile waveform optical pulses, which has better performance than the first two methods in tunable capability of both repetition rate and center wavelength. With the same driving signal applied, the optical source using the dual-parallel MZM can generate signal with higher frequency than that of using the single-stage MZM.
