We demonstrate the growth of terahertz quantum cascade laser （THz QCL） by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystal...We demonstrate the growth of terahertz quantum cascade laser （THz QCL） by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystalline quality of the THz QCL active region, From the cross-sectional transmission electron microscopy image, sharp interfaces are observed and the deduced cascade period thickness is consistent with the result of x-ray diffraction. The test device is lasing at 3.39THz and operating up to lOOK in pulsed mode. At IOK, the maximum output power is greater than 1 mW with a threshold current density of 738 A/cm^2.展开更多
A high-gradient radiofrequency(RF)gun operated in continuous-wave(CW)mode is required in various accelerating applications.Due to the high RF power loss,a traditional normal-conducting(NC)RF electron gun has difficult...A high-gradient radiofrequency(RF)gun operated in continuous-wave(CW)mode is required in various accelerating applications.Due to the high RF power loss,a traditional normal-conducting(NC)RF electron gun has difficulty meeting the requirement of generating a high-repetition-rate electron beam.The development of a scheme for a CW NC-RF gun is urgently required.Demonstrated as a photoinjector of a high-repetition-rate free-electron laser(FEL),an electron gun operated in CW mode and the VHF band is designed.An analysis of the reentrant gun cavity is presented in this paper to increase the gradient and decrease the power density and power dissipation.Referring to the analysis results,the design of a162.5 MHz gun cavity is optimized by a multi-objective evolutionary algorithm to achieve better performance in CW mode.Multipacting and thermal analyses are also deliberated in the design to coordinate with RF and mechanical design.The optimized 162.5 MHz gun cavity can be operated in CW mode to generate a high-repetition-rate beam with voltage up to 1 MV and gradient up to 32.75 MV/m at the cathode.展开更多
Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric met...Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric methane monitoring.The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode,and the influence of laser injection efficiency on measurement precision is further analyzed.The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode.In the experiment,DFB laser is used to calibrate the system with standard methane concentration,and the measurement residual is less than±4×10^(-4)μs^(-1).The methane concentration in the air is monitored in real time for two days.The results show the consistency of the concentration changes over the two days,which further demonstrates the reliability of the system for the measurement of trace methane.By analyzing the influence of mode matching,it not only assists the adjustment of the optical path,but also further improves the sensitivity of the system measurement.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
Frequency-Modulation Continuous-Wave Synthetic Aperture Radar(FMCW SAR)has shown great potential in the applications of civil and military fields because of its easy deployment and low cost.However,most of these work ...Frequency-Modulation Continuous-Wave Synthetic Aperture Radar(FMCW SAR)has shown great potential in the applications of civil and military fields because of its easy deployment and low cost.However,most of these work and analysis are concentrated on airborne FMCW SAR,where the characteristics of the imaging geometry and signal are much similar to that of traditional pulsed-SAR.As a result,a series of test campaigns of automobile-based FMCW SAR were sponsored by Institute of Electronics,Chinese Academy of Sciences(IECAS)in the autumn of 2012.In this paper,we analyze the imaging issues of FMCW SAR in automobile mode(named as near range mode),where a vehicle is used as moving platform and a large looking angle is configured.The imaging geometry and signal properties are analyzed in detail.We emphasize the difference of the near range mode from the traditional airborne SAR mode.Based on the analysis,a focusing approach is proposed in the paper to handle the data focusing in the case.Simulation experiment and real data of automobile FMCW SAR are used to validate the analysis.展开更多
We report a diode end-pumped continuous wave (CW) passively mode-locked Nd:YVO4 laser with a homemade semiconductor saturable absorber mirror (SESAM). The maximum average output power is 5.3 W at the incident pump pow...We report a diode end-pumped continuous wave (CW) passively mode-locked Nd:YVO4 laser with a homemade semiconductor saturable absorber mirror (SESAM). The maximum average output power is 5.3 W at the incident pump power of 17 W, which corresponds to an optical-optical conversion efficiency of 31.2% and slope efficiency of 34.7%. The corresponding optical spectrum has a 0.2-nm full width at half maximum (FWHM). and the pulse repetition rate is 83 MHz.展开更多
文摘We demonstrate the growth of terahertz quantum cascade laser （THz QCL） by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystalline quality of the THz QCL active region, From the cross-sectional transmission electron microscopy image, sharp interfaces are observed and the deduced cascade period thickness is consistent with the result of x-ray diffraction. The test device is lasing at 3.39THz and operating up to lOOK in pulsed mode. At IOK, the maximum output power is greater than 1 mW with a threshold current density of 738 A/cm^2.
文摘A high-gradient radiofrequency(RF)gun operated in continuous-wave(CW)mode is required in various accelerating applications.Due to the high RF power loss,a traditional normal-conducting(NC)RF electron gun has difficulty meeting the requirement of generating a high-repetition-rate electron beam.The development of a scheme for a CW NC-RF gun is urgently required.Demonstrated as a photoinjector of a high-repetition-rate free-electron laser(FEL),an electron gun operated in CW mode and the VHF band is designed.An analysis of the reentrant gun cavity is presented in this paper to increase the gradient and decrease the power density and power dissipation.Referring to the analysis results,the design of a162.5 MHz gun cavity is optimized by a multi-objective evolutionary algorithm to achieve better performance in CW mode.Multipacting and thermal analyses are also deliberated in the design to coordinate with RF and mechanical design.The optimized 162.5 MHz gun cavity can be operated in CW mode to generate a high-repetition-rate beam with voltage up to 1 MV and gradient up to 32.75 MV/m at the cathode.
基金This research is financial supported by the Natural National Science Foundation of China(Grant Nos.11874364,41877311,and 42005107)the National Key Research and Development Program of China(Grant No.2017YFC0805004)the CAS&Bengbu Technology Transfer Project(Grant No.ZKBB202102).
文摘Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric methane monitoring.The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode,and the influence of laser injection efficiency on measurement precision is further analyzed.The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode.In the experiment,DFB laser is used to calibrate the system with standard methane concentration,and the measurement residual is less than±4×10^(-4)μs^(-1).The methane concentration in the air is monitored in real time for two days.The results show the consistency of the concentration changes over the two days,which further demonstrates the reliability of the system for the measurement of trace methane.By analyzing the influence of mode matching,it not only assists the adjustment of the optical path,but also further improves the sensitivity of the system measurement.
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.
文摘Frequency-Modulation Continuous-Wave Synthetic Aperture Radar(FMCW SAR)has shown great potential in the applications of civil and military fields because of its easy deployment and low cost.However,most of these work and analysis are concentrated on airborne FMCW SAR,where the characteristics of the imaging geometry and signal are much similar to that of traditional pulsed-SAR.As a result,a series of test campaigns of automobile-based FMCW SAR were sponsored by Institute of Electronics,Chinese Academy of Sciences(IECAS)in the autumn of 2012.In this paper,we analyze the imaging issues of FMCW SAR in automobile mode(named as near range mode),where a vehicle is used as moving platform and a large looking angle is configured.The imaging geometry and signal properties are analyzed in detail.We emphasize the difference of the near range mode from the traditional airborne SAR mode.Based on the analysis,a focusing approach is proposed in the paper to handle the data focusing in the case.Simulation experiment and real data of automobile FMCW SAR are used to validate the analysis.
基金This work was supported in part by the National "863"project of China under Grant No. 2002AA311190China Ministry of Science and technology.
文摘We report a diode end-pumped continuous wave (CW) passively mode-locked Nd:YVO4 laser with a homemade semiconductor saturable absorber mirror (SESAM). The maximum average output power is 5.3 W at the incident pump power of 17 W, which corresponds to an optical-optical conversion efficiency of 31.2% and slope efficiency of 34.7%. The corresponding optical spectrum has a 0.2-nm full width at half maximum (FWHM). and the pulse repetition rate is 83 MHz.
