Multispectral and polarization cameras that can simultaneously acquire the spatial,spectral,and polarization characteristics of an object have considerable potential applications in target detection,biomedical imaging...Multispectral and polarization cameras that can simultaneously acquire the spatial,spectral,and polarization characteristics of an object have considerable potential applications in target detection,biomedical imaging,and remote sensing.In this work,we develop a common-aperture optical system that can capture multispectral and polarization information.An off-axis three-mirror optical system is mounted on the front end of the proposed system and used as a common-aperture telescope in the visible light(400 nm-750 nm)and long-wave infrared(LWIR,8μm-12μm)waveband.The system can maintain a wide field of view(4.5°)and it can demonstrate an enhanced identification ability.The off-axis three-mirror system gets rid of central obscuration while further yielding stable system resolution and energy.Light that has passed through the front-end common-aperture reflection system is divided into the visible light and LWIR waveband by a beamsplitter.The two wavebands then converge on two detectors through two groups of lenses.Our simulation results indicate that the proposed system can obtain clear images in each waveband to meet the diverse imaging requirements.展开更多
To achieve excellent tracking accuracy,a coarse-fine dual-stage control system is chosen for inertially stabilized platform.The coarse stage is a conventional inertially stabilized platform,and the fine stage is a sec...To achieve excellent tracking accuracy,a coarse-fine dual-stage control system is chosen for inertially stabilized platform.The coarse stage is a conventional inertially stabilized platform,and the fine stage is a secondary servo mechanism to control lens motion in the imaging optical path.Firstly,the dual-stage dynamics is mathematically modeled as a coupling multi-input multi-output(MIMO)control system.Then,by incorporating compensation of adaptive model to deal with parameter variations and nonlinearity,a systematic robust H∞control scheme is designed,which can achieve good tracking performance,as well as improve system robustness against model uncertainties.Lyapunov stability analysis confirmed the stability of the overall control system.Finally,simulation and experiment results are provided to demonstrate the feasibility and effectiveness of the proposed control design method.展开更多
Diamond-like carbon （DLC） thin film is one of the most widely used optical thin films. The fraction of chemical bondings has a great influence on the properties of the DLC film. In this work, DLC thin films are prep...Diamond-like carbon （DLC） thin film is one of the most widely used optical thin films. The fraction of chemical bondings has a great influence on the properties of the DLC film. In this work, DLC thin films are prepared by ion-beam sputtering deposition in Ar and CH4 mixtures with graphite as the target. The influences of the ion-beam voltage on the surface morphology, chemical structure, mechanical and infrared optical properties of the DLC films are investigated by atomic force microscopy （AFM）, Raman spectroscopy, nanoindentation, and Fourier transform infrared （FTIR） spec- troscopy, respectively. The results show that the surface of the film is uniform and smooth. The film contains sp2 and sp3 hybridized carbon bondings. The film prepared by lower ion beam voltage has a higher sp3 bonding content. It is found that the hardness of DLC films increases with reducing ion-beam voltage, which can be attributed to an increase in the fraction of sp3 carbon bondings in the DLC film. The optical constants can be obtained by the whole infrared optical spectrum fitting with the transmittance spectrum. The refractive index increases with the decrease of the ion-beam voltage, while the extinction coefficient decreases.展开更多
The oxygen-related defects in CZ silicon during electron irradiation(1.5 MeV)and subsequent annealing in the range of 150-600℃were investigated by means of FTIR.In the electron irradiation CZ-Si,vacancy-oxygen comple...The oxygen-related defects in CZ silicon during electron irradiation(1.5 MeV)and subsequent annealing in the range of 150-600℃were investigated by means of FTIR.In the electron irradiation CZ-Si,vacancy-oxygen complex is one of the dominant defects and its concentration is proportional to electron dose but not related to oxygen concentration.In this work,it was focused on the identification of the weak band at 860 cm^(-1)which was originated from asymmetrical stretching vibrations of an oxygen atom in the negative VO complex.It exhibits the same thermal stability with neutral VO band at 830 cm^(-1).In addition,the intensity of 889 cm-1 band has never been observed to exceed that of the A-center,implying that only a partial transformation of VO into VO_(2)does occur.展开更多
Solid-state samples based on modified polymethyl methacrylate （MPMMA） with methanol doped with the dye pyrromethene 650 （PM650） axe prepared. The effects of a volume percentage of methanol on the laser characteris...Solid-state samples based on modified polymethyl methacrylate （MPMMA） with methanol doped with the dye pyrromethene 650 （PM650） axe prepared. The effects of a volume percentage of methanol on the laser characteristics of the sample, including spectra properties, slope efficiency, photostability and tunable properties, are investigated. The broadband dye laser output wavelength is around 655 nm and a highest slope efficiency of 32.23% is achieved. Pumping the samples at a repetition rate of 5 Hz with a pulse energy of as high as 100 mJ （the fluence is 0.26 J/cm2）, the longest lifetime （168000 shots） is obtained in the sample （MMA：methanol=18：2）, and the corresponding normalized photostability reaches 109.19 GJ/mol. When the sample （MMA：methanol=18：2） is placed in a Shoshan-type oscilla- tor, the naxrow-linewidth operation is a continuous tuning range （up to 64 nm）. The results indicate that the laser characteristics of solid-state dyes can be greatly enhanced by using modified PMMA with methanol serving as the solid host.展开更多
In this paper,various aberrations have been analyzed.Not only the effects of aberration on geometrical center position are taken into account,but also the deviation of displayed star position energy center caused by a...In this paper,various aberrations have been analyzed.Not only the effects of aberration on geometrical center position are taken into account,but also the deviation of displayed star position energy center caused by aberration is analyzed.These two aspects have been taken into comprehensive evaluation and star position correction.The correction method based on polar coordinates is proposed,and cumbersome partition correction and calculated quantity based on two-dimensional coordinates can be simplified.The experimental results show that the correction processing based on polar coordinates is simpler and easier compared with any other correction methods.In addition,the correction results are significantly more accurate.展开更多
The fiber optic sensing technology provides data support in structural health monitoring of the macro facilities,including design,construction,and maintenance of bridges,tunnels,ports and other infrastructures.In this...The fiber optic sensing technology provides data support in structural health monitoring of the macro facilities,including design,construction,and maintenance of bridges,tunnels,ports and other infrastructures.In this paper,a distributed vibration sensing system is proved to be responsive to a single touch over a 1.8-m-long equivalent fiber segment,covering a vibration frequency from 5 Hz to 25 kHz.The sensing fiber was arranged as an S type layout on the bridge to recognize the standing state,windblown disturbance,and walking vibration.Moreover,the knocking and climbing events are recognized fiber laying spinning lines and hanging on the fences,respectively.The demonstration shows an accurate positioning and sensitive vibration monitoring applied on the automated three-dimensional(3D) printed bridge,which is applicable to all kinds of 3D printed facilities as intelligent sensory neuro-networks.展开更多
A four-state model considering the relative velocity distribution function for calculating the cross section of laserinduced collisional energy transfer in a Sr Li system is presented and profiles of laser-induced col...A four-state model considering the relative velocity distribution function for calculating the cross section of laserinduced collisional energy transfer in a Sr Li system is presented and profiles of laser-induced collision cross section are obtained. The resulting spectra obtained from different intermediate states are strongly asymmetrical in an opposite asymmetry. Both of the two intermediate states have contributions to the final state, and none of the intermediate states should be neglected. The peak of the laser-induced collisional energy transfer （LICET） profile shifts toward the red and the FWHM becomes narrower obviously with laser field intensity increasing. A cross section of 1.2 × 10^-12 cm2 at a laser field intensity of 2.17 ×107 V/m is obtained, which indicates that this collision process can be an effective way to transfer energy selectively from a storage state to a target state. The existence of saturation for cross section with the increase of the laser intensity shows that the high-intensity redistribution of transition probabilities is an important feature of this process, which is not accounted for in a two-state treatment.展开更多
A non-destructive technique for subsurface measurements is proposed by combining light scattering method with laser confocal scanning tomography. The depth and distribution of subsurface defect layers are represented ...A non-destructive technique for subsurface measurements is proposed by combining light scattering method with laser confocal scanning tomography. The depth and distribution of subsurface defect layers are represented in term of scattered light intensity pattern, and three types of fused silica specimens are fabricated by different grinding and polishing processes to verify the validity and effectiveness. By using the direct measurement method with such technique, micron-scale cracks and scratches can be easily distinguished, and the instructional subsurface defect depths of 55, 15, and 4 μm are given in real time allowing for an in-process observation and detection.展开更多
While infrared （IR） hard protective film of ZnS optical window is used in high temperature environment, its optical and mechanical stabilities are the premise of the IR optical system. IR hard protective film is dep...While infrared （IR） hard protective film of ZnS optical window is used in high temperature environment, its optical and mechanical stabilities are the premise of the IR optical system. IR hard protective film is deposited on ZnS optical windows by chemical vapor deposition （CVD）, and ablation experiments are done to the maximum temperature the film can endure. The effects of ablation temperature on the optical and mechanical properties of the protective films are investigated by surface profiler, Fourier-transform infrared （FTIR） spectrometry, IR ellipsometer, and Metallographic microscope. It is shown that the optical and mechanical properties of ZnS hard protective film change little before 500 ℃, and film refractive index and optical thickness reduce while ablation temperature surpassing 500 ℃, forming crater-like ablation structure, which leads to the reduction of film combination significantly.展开更多
Design and preparation of multilayer optical coatings are investigated on laser crystal Nd：YVO4, YVO4, and frequency doubling crystal KTP substrate. Multilayer optical coatings are deposited on one surface of the cry...Design and preparation of multilayer optical coatings are investigated on laser crystal Nd：YVO4, YVO4, and frequency doubling crystal KTP substrate. Multilayer optical coatings are deposited on one surface of the crystals using the ion beam sputtering technique, and the other surface is coated with a single SiO2 as protective layer. For the YVO4 crystal after coating, the reflectivity at 1 064 and 532 nm are greater than 99.9% and 99.8%, respectively, and the transmissivity at 808 nm is greater than 91.5%. For the KTP crystal after coating, the reflectivity at 1064 nm is greater than 99.95%, and the transmissivity at 532 nm is greater than 99.5%. After thermal annealing, the transmissivity can be improved. The obtained coated crystals can be used in high Dower solid-state lasers.展开更多
A recently developed time-resolved coherent anti-Stokes Raman scattering(tr-CARS) technique allows the measurement of vibrational coherences with high frequency differences with the ambient environment.The method is b...A recently developed time-resolved coherent anti-Stokes Raman scattering(tr-CARS) technique allows the measurement of vibrational coherences with high frequency differences with the ambient environment.The method is based on the short spatial extension of femtosecond pulses with a broadband tunable nonlinear optical parametric amplifier(NOPA) and an internal time delay between the probe and pump/Stokes pulse pair in the CARS process.The different beat frequencies between Raman modes can be selectively detected as oscillations in the tr-CARS transient signal with the broadband tunable NOPA.In this work,we aim at the Raman C-H stretching vibrations from 2800 cm 1 to 3000 cm 1,within which the different vibrational modes in both ethanol and methanol are selectively excited and simultaneously detected.The high time resolution of the experimental set-up allows one to monitor the vibrational coherence dynamics and to observe the quantum beat phenomena on a terahertz scale.This investigation indicates that the femtosecond tr-CARS technique is a powerful tool for the real-time monitoring and detection of molecular and biological agents,including airborne contaminants such as bacterial spores,viruses and their toxins.展开更多
A variant of all-resonant CARS named electronic-resonant enhancement CARS （ERE-CARS） is applied to measure the methanol-water solution concentration at room temperature. The measurements are performed using the ERE-...A variant of all-resonant CARS named electronic-resonant enhancement CARS （ERE-CARS） is applied to measure the methanol-water solution concentration at room temperature. The measurements are performed using the ERE-CARS signal of the Raman vibrations near the C--H stretching modes （at 2835 and 2942 cm^-1） in methanol. By changing the timing （△t〉0） of the laser pulses of this non-degenerate four wave mixing technique, the concentration information based on the vibrational dynamics of the C--H bonds can be successfully detected as the frequency-spread dephasing rate duiing the first few hundred fs in the ERE-CARS signal with high sensitivity and accuracy. Femtosecond time-resolved ERE-CARS technique is applied to the concentration analysis of a mixture of the organic solution. This investigation indicates that femtosecond time-resolved ERE-CARS technique might be a powerful tool for real-time detection for solution concentration of different liquids.展开更多
The metal aluminum （Al） is widely used because it has high reflectivity from the ultraviolet to the infrared band. But the new deposited Al films is exposed to the atmosphere, it forms transparent Al2O3 films on its...The metal aluminum （Al） is widely used because it has high reflectivity from the ultraviolet to the infrared band. But the new deposited Al films is exposed to the atmosphere, it forms transparent Al2O3 films on its surface at once. In this letter, the Al films is deposited on the quartz substrate by electron beam evaporation. The effect of Al films oxidation on refractive index and extinction coefficient is investigated by spectroscopic ellipsometry （SE）. The optical constants of Al films change with the increase of oxidation time. The two parameters become stable when these films are exposed in air more than 2 days.展开更多
Germanium （Ge） films are prepared on BK7 glass and multispectral zinc sulfide （m-ZnS） substrates by ion beam assisted deposition （IBAD）. The effects of substrate temperature, deposition rate, and ion energy on t...Germanium （Ge） films are prepared on BK7 glass and multispectral zinc sulfide （m-ZnS） substrates by ion beam assisted deposition （IBAD）. The effects of substrate temperature, deposition rate, and ion energy on the microstructure and optical properties of the films are investigated. It can be concluded that Ge film deposited with higher rate or ion energy has more optical absorption, while ion energy below 150 eV helps to reduce film absorption. Film refractive index increases with film deposition rate and bombardment ion energy while it is below 300 eV. And higher growth rate or bombardment ion energy can weaken film diffraction intensity.展开更多
SiO2 films are deposited on Si substrates by an ion beam sputtering technique and continuously annealed in a quartz culture dish in air at various annealing temperature ranging from 20 to 750 ℃ with a step of 100 ℃ ...SiO2 films are deposited on Si substrates by an ion beam sputtering technique and continuously annealed in a quartz culture dish in air at various annealing temperature ranging from 20 to 750 ℃ with a step of 100 ℃ for a fixed time of 24 h. The effects of thermal treatment on optical anisotropy properties of SiO2 films are investigated by spectroscopic ellipsometry. When the annealing temperature is 550℃, the optical anisotropy properties of SiO2 film is minimum. The obtained results indicate that the optical anisotropy properties of SiO2 films can be improved by a proper thermal annealing process.展开更多
A multi-lens retroreflector with field curvature compensation was designed and used in an alignment-free distributed-cavity laser with a long working distance for resonant beam charging applications.The multi-lens des...A multi-lens retroreflector with field curvature compensation was designed and used in an alignment-free distributed-cavity laser with a long working distance for resonant beam charging applications.The multi-lens design,which makes use of off-the-shelf components,also allows a large field of view[FoV]without requirement of large element aperture.By implementing this design,an end-pumped 1063 nm Nd:GdVO4 laser could deliver over 5 W continuous-wave output power over a large range of working distances(1-5 m)and with ±30°receiver FoV under an incident diode pump power of 16.6 W.The output power fluctuation was less than 10%when moving and tilting the receiver over such a large range,without requiring any realignment of the cavity.展开更多
基金Project supported by the National Natural Science Foundation of china(Grant No.61471039)
文摘Multispectral and polarization cameras that can simultaneously acquire the spatial,spectral,and polarization characteristics of an object have considerable potential applications in target detection,biomedical imaging,and remote sensing.In this work,we develop a common-aperture optical system that can capture multispectral and polarization information.An off-axis three-mirror optical system is mounted on the front end of the proposed system and used as a common-aperture telescope in the visible light(400 nm-750 nm)and long-wave infrared(LWIR,8μm-12μm)waveband.The system can maintain a wide field of view(4.5°)and it can demonstrate an enhanced identification ability.The off-axis three-mirror system gets rid of central obscuration while further yielding stable system resolution and energy.Light that has passed through the front-end common-aperture reflection system is divided into the visible light and LWIR waveband by a beamsplitter.The two wavebands then converge on two detectors through two groups of lenses.Our simulation results indicate that the proposed system can obtain clear images in each waveband to meet the diverse imaging requirements.
基金Project (61174203) supported by the National Natural Science Foundation of China
文摘To achieve excellent tracking accuracy,a coarse-fine dual-stage control system is chosen for inertially stabilized platform.The coarse stage is a conventional inertially stabilized platform,and the fine stage is a secondary servo mechanism to control lens motion in the imaging optical path.Firstly,the dual-stage dynamics is mathematically modeled as a coupling multi-input multi-output(MIMO)control system.Then,by incorporating compensation of adaptive model to deal with parameter variations and nonlinearity,a systematic robust H∞control scheme is designed,which can achieve good tracking performance,as well as improve system robustness against model uncertainties.Lyapunov stability analysis confirmed the stability of the overall control system.Finally,simulation and experiment results are provided to demonstrate the feasibility and effectiveness of the proposed control design method.
基金Project supported by the National Natural Science Foundation of China(Grant No.61235011)the Science Foundation of the Science and Technology Commission of Tianjin Municipality,China(Grant Nos.13JCYBJC17300 and 12JCQNIC01200)
文摘Diamond-like carbon （DLC） thin film is one of the most widely used optical thin films. The fraction of chemical bondings has a great influence on the properties of the DLC film. In this work, DLC thin films are prepared by ion-beam sputtering deposition in Ar and CH4 mixtures with graphite as the target. The influences of the ion-beam voltage on the surface morphology, chemical structure, mechanical and infrared optical properties of the DLC films are investigated by atomic force microscopy （AFM）, Raman spectroscopy, nanoindentation, and Fourier transform infrared （FTIR） spec- troscopy, respectively. The results show that the surface of the film is uniform and smooth. The film contains sp2 and sp3 hybridized carbon bondings. The film prepared by lower ion beam voltage has a higher sp3 bonding content. It is found that the hardness of DLC films increases with reducing ion-beam voltage, which can be attributed to an increase in the fraction of sp3 carbon bondings in the DLC film. The optical constants can be obtained by the whole infrared optical spectrum fitting with the transmittance spectrum. The refractive index increases with the decrease of the ion-beam voltage, while the extinction coefficient decreases.
基金The work was financially supported by the National Natural Science Foundation of China(No.50472034)Natural Science Foundation of Hebei Province(No.E2005000048)Specialized Research Fundforthe Doctoral Program of Higher Education(No.20050080006).
文摘The oxygen-related defects in CZ silicon during electron irradiation(1.5 MeV)and subsequent annealing in the range of 150-600℃were investigated by means of FTIR.In the electron irradiation CZ-Si,vacancy-oxygen complex is one of the dominant defects and its concentration is proportional to electron dose but not related to oxygen concentration.In this work,it was focused on the identification of the weak band at 860 cm^(-1)which was originated from asymmetrical stretching vibrations of an oxygen atom in the negative VO complex.It exhibits the same thermal stability with neutral VO band at 830 cm^(-1).In addition,the intensity of 889 cm-1 band has never been observed to exceed that of the A-center,implying that only a partial transformation of VO into VO_(2)does occur.
基金Project supported by the National Natural Science Foundation of China (Grant No.61008023)the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology,China (Grant No.HIT.NSRIF.2009009)
文摘Solid-state samples based on modified polymethyl methacrylate （MPMMA） with methanol doped with the dye pyrromethene 650 （PM650） axe prepared. The effects of a volume percentage of methanol on the laser characteristics of the sample, including spectra properties, slope efficiency, photostability and tunable properties, are investigated. The broadband dye laser output wavelength is around 655 nm and a highest slope efficiency of 32.23% is achieved. Pumping the samples at a repetition rate of 5 Hz with a pulse energy of as high as 100 mJ （the fluence is 0.26 J/cm2）, the longest lifetime （168000 shots） is obtained in the sample （MMA：methanol=18：2）, and the corresponding normalized photostability reaches 109.19 GJ/mol. When the sample （MMA：methanol=18：2） is placed in a Shoshan-type oscilla- tor, the naxrow-linewidth operation is a continuous tuning range （up to 64 nm）. The results indicate that the laser characteristics of solid-state dyes can be greatly enhanced by using modified PMMA with methanol serving as the solid host.
文摘In this paper,various aberrations have been analyzed.Not only the effects of aberration on geometrical center position are taken into account,but also the deviation of displayed star position energy center caused by aberration is analyzed.These two aspects have been taken into comprehensive evaluation and star position correction.The correction method based on polar coordinates is proposed,and cumbersome partition correction and calculated quantity based on two-dimensional coordinates can be simplified.The experimental results show that the correction processing based on polar coordinates is simpler and easier compared with any other correction methods.In addition,the correction results are significantly more accurate.
基金supported by the National Natural Science Foundation of China (No.6210031560)the Natural Science Foundation of Hebei Province (No.A2020202013)the Natural Science Foundation of Tianjin City (No.21JCQNJC00780)。
文摘The fiber optic sensing technology provides data support in structural health monitoring of the macro facilities,including design,construction,and maintenance of bridges,tunnels,ports and other infrastructures.In this paper,a distributed vibration sensing system is proved to be responsive to a single touch over a 1.8-m-long equivalent fiber segment,covering a vibration frequency from 5 Hz to 25 kHz.The sensing fiber was arranged as an S type layout on the bridge to recognize the standing state,windblown disturbance,and walking vibration.Moreover,the knocking and climbing events are recognized fiber laying spinning lines and hanging on the fences,respectively.The demonstration shows an accurate positioning and sensitive vibration monitoring applied on the automated three-dimensional(3D) printed bridge,which is applicable to all kinds of 3D printed facilities as intelligent sensory neuro-networks.
文摘A four-state model considering the relative velocity distribution function for calculating the cross section of laserinduced collisional energy transfer in a Sr Li system is presented and profiles of laser-induced collision cross section are obtained. The resulting spectra obtained from different intermediate states are strongly asymmetrical in an opposite asymmetry. Both of the two intermediate states have contributions to the final state, and none of the intermediate states should be neglected. The peak of the laser-induced collisional energy transfer （LICET） profile shifts toward the red and the FWHM becomes narrower obviously with laser field intensity increasing. A cross section of 1.2 × 10^-12 cm2 at a laser field intensity of 2.17 ×107 V/m is obtained, which indicates that this collision process can be an effective way to transfer energy selectively from a storage state to a target state. The existence of saturation for cross section with the increase of the laser intensity shows that the high-intensity redistribution of transition probabilities is an important feature of this process, which is not accounted for in a two-state treatment.
基金supported by the National Natural Science Foundation of China(No.10825521)the National"863"Program of China(No.2006AA12Z139)the Shanghai Committee of Science and Technology (No.07DZ22302)
文摘A non-destructive technique for subsurface measurements is proposed by combining light scattering method with laser confocal scanning tomography. The depth and distribution of subsurface defect layers are represented in term of scattered light intensity pattern, and three types of fused silica specimens are fabricated by different grinding and polishing processes to verify the validity and effectiveness. By using the direct measurement method with such technique, micron-scale cracks and scratches can be easily distinguished, and the instructional subsurface defect depths of 55, 15, and 4 μm are given in real time allowing for an in-process observation and detection.
文摘While infrared （IR） hard protective film of ZnS optical window is used in high temperature environment, its optical and mechanical stabilities are the premise of the IR optical system. IR hard protective film is deposited on ZnS optical windows by chemical vapor deposition （CVD）, and ablation experiments are done to the maximum temperature the film can endure. The effects of ablation temperature on the optical and mechanical properties of the protective films are investigated by surface profiler, Fourier-transform infrared （FTIR） spectrometry, IR ellipsometer, and Metallographic microscope. It is shown that the optical and mechanical properties of ZnS hard protective film change little before 500 ℃, and film refractive index and optical thickness reduce while ablation temperature surpassing 500 ℃, forming crater-like ablation structure, which leads to the reduction of film combination significantly.
文摘Design and preparation of multilayer optical coatings are investigated on laser crystal Nd：YVO4, YVO4, and frequency doubling crystal KTP substrate. Multilayer optical coatings are deposited on one surface of the crystals using the ion beam sputtering technique, and the other surface is coated with a single SiO2 as protective layer. For the YVO4 crystal after coating, the reflectivity at 1 064 and 532 nm are greater than 99.9% and 99.8%, respectively, and the transmissivity at 808 nm is greater than 91.5%. For the KTP crystal after coating, the reflectivity at 1064 nm is greater than 99.95%, and the transmissivity at 532 nm is greater than 99.5%. After thermal annealing, the transmissivity can be improved. The obtained coated crystals can be used in high Dower solid-state lasers.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60878018 and 61008023)the Program of Excellentat Harbin Institute of Technology
文摘A recently developed time-resolved coherent anti-Stokes Raman scattering(tr-CARS) technique allows the measurement of vibrational coherences with high frequency differences with the ambient environment.The method is based on the short spatial extension of femtosecond pulses with a broadband tunable nonlinear optical parametric amplifier(NOPA) and an internal time delay between the probe and pump/Stokes pulse pair in the CARS process.The different beat frequencies between Raman modes can be selectively detected as oscillations in the tr-CARS transient signal with the broadband tunable NOPA.In this work,we aim at the Raman C-H stretching vibrations from 2800 cm 1 to 3000 cm 1,within which the different vibrational modes in both ethanol and methanol are selectively excited and simultaneously detected.The high time resolution of the experimental set-up allows one to monitor the vibrational coherence dynamics and to observe the quantum beat phenomena on a terahertz scale.This investigation indicates that the femtosecond tr-CARS technique is a powerful tool for the real-time monitoring and detection of molecular and biological agents,including airborne contaminants such as bacterial spores,viruses and their toxins.
基金supported by the National Natural Science Foundation of China (Grant No. 61008023)the Program of Excellent at Harbin Institute of Technology
文摘A variant of all-resonant CARS named electronic-resonant enhancement CARS （ERE-CARS） is applied to measure the methanol-water solution concentration at room temperature. The measurements are performed using the ERE-CARS signal of the Raman vibrations near the C--H stretching modes （at 2835 and 2942 cm^-1） in methanol. By changing the timing （△t〉0） of the laser pulses of this non-degenerate four wave mixing technique, the concentration information based on the vibrational dynamics of the C--H bonds can be successfully detected as the frequency-spread dephasing rate duiing the first few hundred fs in the ERE-CARS signal with high sensitivity and accuracy. Femtosecond time-resolved ERE-CARS technique is applied to the concentration analysis of a mixture of the organic solution. This investigation indicates that femtosecond time-resolved ERE-CARS technique might be a powerful tool for real-time detection for solution concentration of different liquids.
文摘The metal aluminum （Al） is widely used because it has high reflectivity from the ultraviolet to the infrared band. But the new deposited Al films is exposed to the atmosphere, it forms transparent Al2O3 films on its surface at once. In this letter, the Al films is deposited on the quartz substrate by electron beam evaporation. The effect of Al films oxidation on refractive index and extinction coefficient is investigated by spectroscopic ellipsometry （SE）. The optical constants of Al films change with the increase of oxidation time. The two parameters become stable when these films are exposed in air more than 2 days.
文摘Germanium （Ge） films are prepared on BK7 glass and multispectral zinc sulfide （m-ZnS） substrates by ion beam assisted deposition （IBAD）. The effects of substrate temperature, deposition rate, and ion energy on the microstructure and optical properties of the films are investigated. It can be concluded that Ge film deposited with higher rate or ion energy has more optical absorption, while ion energy below 150 eV helps to reduce film absorption. Film refractive index increases with film deposition rate and bombardment ion energy while it is below 300 eV. And higher growth rate or bombardment ion energy can weaken film diffraction intensity.
文摘SiO2 films are deposited on Si substrates by an ion beam sputtering technique and continuously annealed in a quartz culture dish in air at various annealing temperature ranging from 20 to 750 ℃ with a step of 100 ℃ for a fixed time of 24 h. The effects of thermal treatment on optical anisotropy properties of SiO2 films are investigated by spectroscopic ellipsometry. When the annealing temperature is 550℃, the optical anisotropy properties of SiO2 film is minimum. The obtained results indicate that the optical anisotropy properties of SiO2 films can be improved by a proper thermal annealing process.
基金This work was supported by the National Natural Science Foundation of China(Nos.61975146 and 62075159)Major Scientific and Technological Innovation Projects of Key R&D Plans in Shandong Province(No.2019JZZY020206)+1 种基金National Key R&D Program of China(No.2017YFF0104603)Foundation for Distinguished Young Scholars of China Academy of Space Technology(2021).
文摘A multi-lens retroreflector with field curvature compensation was designed and used in an alignment-free distributed-cavity laser with a long working distance for resonant beam charging applications.The multi-lens design,which makes use of off-the-shelf components,also allows a large field of view[FoV]without requirement of large element aperture.By implementing this design,an end-pumped 1063 nm Nd:GdVO4 laser could deliver over 5 W continuous-wave output power over a large range of working distances(1-5 m)and with ±30°receiver FoV under an incident diode pump power of 16.6 W.The output power fluctuation was less than 10%when moving and tilting the receiver over such a large range,without requiring any realignment of the cavity.
