Freestanding Zr filters are important devices for improving spectral purity in the extreme ultraviolet range of 7–20 nm,and their irradiation resistance directly determines their life and efficiency.We prepared multi...Freestanding Zr filters are important devices for improving spectral purity in the extreme ultraviolet range of 7–20 nm,and their irradiation resistance directly determines their life and efficiency.We prepared multilayered Zr/B4C and Zr/Si filters using magnetron sputtering.Their transmittance reached a maximum of 23%(λ=13.5 nm).Microwatt-radiation-induced structural changes in the filters were investigated at the metrology beamline(BL08B)of the National Synchrotron Radiation Laboratory.The aging of the Zr filters was measured and analyzed.The experimental results revealed that the damage was noticeable on the irradiated filter surfaces with different states,suggesting that the main factors causing the degradation of the filters were oxidation and carbon contamination at the surfaces.Furthermore,the thermal stability of the Zr filters was studied by annealing,and the heat accumulation during the damage process was estimated using finite-element numerical simulations and X-ray photoelectron spectroscopy measurements.Silicide formation at the Zr-Si-O system interfaces was found to be key to enhancing the stability of the filters.展开更多
Traditional hyperspectral imaging(HI)systems are constrained by a limited depth of field(DoF),necessitating refocusing for any out-of-focus objects.This requirement not only slows down the imaging speed but also compl...Traditional hyperspectral imaging(HI)systems are constrained by a limited depth of field(DoF),necessitating refocusing for any out-of-focus objects.This requirement not only slows down the imaging speed but also complicates the system architecture.It is challenging to trade off among speed,resolution,and DoF within an ultrasimple system.While some studies have reported advancements in extending DoF,the improvements remain insufficient.To address this challenge,we propose a novel,to our knowledge,differentiable framework that integrates an extended DoF(E-DoF)wave propagation model and an achromatic hyperspectral reconstructor powered by deep learning.Through rigorous experimental validation,we have demonstrated that the compact HI system is capable of snapshot capturing of high-fidelity images with an exceptional DoF reaching approximately 5 m,marking a significant improvement of over three orders of magnitude.Additionally,the system achieves over 90%spectral accuracy without aberration,nearly doubling the accuracy performance of existing methods.An asymmetric freeform surface design is introduced for diffractive optical elements,enabling dual functionality with design freedom and E-DoF.The sparse prior conditions for spatial texture and spectral features of hyperspectral cubic data are integrated into the reconstruction network,effectively mitigating texture blurring and chromatic aberration.It foresees that the optimal strategy for achromatic E-DoF can be adopted into other optical systems such as polarization imaging and depth measurement.展开更多
Various coatings in high-power laser facilities suffer from laser damage due to nodule defects.We propose a nodule dome removal(NDR)strategy to eliminate unwanted localized electric-field(E-field)enhancement caused by...Various coatings in high-power laser facilities suffer from laser damage due to nodule defects.We propose a nodule dome removal(NDR)strategy to eliminate unwanted localized electric-field(E-field)enhancement caused by nodule defects,thereby improving the laser-induced damage threshold(LIDT)of laser coatings.It is theoretically demonstrated that the proposed NDR strategy can reduce the localized E-field enhancement of nodules in mirror coatings,polarizer coatings and beam splitter coatings.An ultraviolet(UV)mirror coating is experimentally demonstrated using the NDR strategy.The LIDT is improved to about 1.9 and 2.2 times for the UV mirror coating without artificial nodules and the UV mirror coating with artificial nodule seeds with a diameter of 1000 nm,respectively.The NDR strategy,applicable to coatings prepared by different deposition methods,improves the LIDT of laser coating without affecting other properties,such as the spectrum,stress and surface roughness,indicating its broad applicability in high-LIDT laser coatings.展开更多
To reduce the seed length while maintaining the advantages of the cuboid KDP-type crystal,a long-seed KDP crystal with size 471 mm×480 mm×400 mm is rapidly grown.With almost the same high cutting efficiency ...To reduce the seed length while maintaining the advantages of the cuboid KDP-type crystal,a long-seed KDP crystal with size 471 mm×480 mm×400 mm is rapidly grown.With almost the same high cutting efficiency to obtain third harmonic generation oriented samples,this long-seed KDP-type crystal can be grown with a shorter seed than that of the cuboid KDP-type crystal.The full width at half maximum of the high-resolution X-ray diffraction of the(200)crystalline face is 28.8 arc seconds,indicating that the long-seed KDP crystal has good crystalline quality.In the wavelength range of 377–1022 nm,the transmittance of the long-seed KDP crystal is higher than 90%.The fluence for the 50%probability of laser-induced damage(LID)is 18.5 J/cm^2(3 ns,355 nm).Several test points survive when the laser fluence exceeds 30 J/cm^2(3 ns,355 nm),indicating the good LID performance of the long-seed KDP crystal.At present,the growth of a long-seed DKDP crystal is under way.展开更多
Multilayer dielectric gratings typically remove multiple-grating pillars after picosecond laser irradiation;however,the dynamic formation process of the removal is still unclear.In this study,the damage morphologies o...Multilayer dielectric gratings typically remove multiple-grating pillars after picosecond laser irradiation;however,the dynamic formation process of the removal is still unclear.In this study,the damage morphologies of multilayer dielectric gratings induced by an 8.6-ps laser pulse were closely examined.The damage included the removal of a single grating pillar and consecutive adjacent grating pillars and did not involve the destruction of the internal high-reflection mirror structure.Comparative analysis of the two damage morphological characteristics indicated the removal of adjacent pillars was related to an impact process caused by the eruption of localized materials from the left-hand pillar,exerting impact pressure on its adjacent pillars and eventually resulting in multiple pillar removal.A finite-element strain model was used to calculate the stress distribution of the grating after impact.According to the electric field distribution,the eruptive pressure of the dielectric materials after ionization was also simulated.The results suggest that the eruptive pressure resulted in a stress concentration at the root of the adjacent pillar that was sufficient to cause damage,corresponding to the experimental removal of the adjacent pillar from the root.This study provides further understanding of the laser-induced damage behavior of grating pillars and some insights into reducing the undesirable damage process for practical applications.展开更多
Laser resistance and stress-free mirrors,windows,polarizers,and beam splitters up to 400 mm×400 mm are required for the construction of the series SG facilities.In order to improve the coating quality,a program h...Laser resistance and stress-free mirrors,windows,polarizers,and beam splitters up to 400 mm×400 mm are required for the construction of the series SG facilities.In order to improve the coating quality,a program has been in place for the last ten years.For the small-aperture pick-off mirror,the laser-induced damage threshold(LIDT)is above 60 J/cm2(1064 nm,3 ns),and the reflected wavefront is less thanλ/4(λ=633 nm).The Brewster-angle polarizing beam splitter(Φ50×10 mm)shows the best LIDT result,up to 29.8 J cm 2(1064 nm,10 ns)for a p-polarized wave in the 2012damage competition of the XLIV Annual Boulder Damage Symposium.For the larger-aperture mirror and polarizer,the LIDT is above 23 J cm 2(1064 nm,3 ns)and 14 J cm 2(1064 nm,3 ns),respectively.The reflected wavefront is less thanλ/3(λ=633 nm)at the used angle.展开更多
Axially coordinated metal-porphyrin-functionalized multi-walled carbon nanotube （MWCNT） nanohybrids were prepared via two different synthetic approaches （a one-pot 1,3-dipolar cycloaddition reaction and a stepwise ...Axially coordinated metal-porphyrin-functionalized multi-walled carbon nanotube （MWCNT） nanohybrids were prepared via two different synthetic approaches （a one-pot 1,3-dipolar cycloaddition reaction and a stepwise approach that involved 1,3-dipolar cycloaddition followed by nucleophilic substitution）, and characterized through spectroscopic techniques. Attachment of the tin porphyrins to the surface of the MWCNTs significantly improves their solubility and ease of processing. These axially coordinated （5,10,15,20-tetraphenylporphyrinato）tin（Ⅳ） （SnTPP）- MWCNTs exhibit significant fluorescence quenching. The third-order nonlinear optical properties of the resultant nanohybrids were studied by using the Z-scan technique at 532 nm with both nanosecond and picosecond laser pulses. The results show that the nanohybrids exhibit significant reverse saturable absorption or saturable absorption when nanosecond or picosecond pulses, respectively, are employed. Improvement in the nanosecond regime nonlinear absorption is observed on proceeding to the nanohybrids and is ascribed to a combination of the outstanding properties of MWCNTs and the chemically attached metal-porphyrins.展开更多
Rapid growth processing of KDP crystals was improved by employing continuous filtration to eliminate bulk defects.The performances of the KDP crystals, including scattering defects, laser damage resistance and transmi...Rapid growth processing of KDP crystals was improved by employing continuous filtration to eliminate bulk defects.The performances of the KDP crystals, including scattering defects, laser damage resistance and transmittance, were measured and analyzed. Compared with rapid-grown KDP without continuous filtration, the transmittance in the nearinfrared was increased by at least 2%, almost all of ‘micron size' defects were eliminated and ‘sub-micron size' defects were decreased by approximately 90%. Laser damage testing revealed that the laser-induced damage thresholds(LIDTs),as well as the consistency of the LIDTs from sample to sample, were improved greatly. Moreover, it identified that‘micron size' defects were the precursors which initiated laser damage at relative lower laser fluence(4–6 J cm^(-2)),and there was a lower correlation between smaller size scattering defects and laser damage initiation. The improved consistency in the LIDTs, attributed to elimination of ‘micron size' defects, and LIDT enhancement originated from the decreased absorption of the KDP crystals.展开更多
With ever-increasing laser power,the requirements for ultraviolet(UV)coatings increase continuously.The fundamental challenge for UV laser-resistant mirror coatings is to simultaneously exhibit a high reflectivity wit...With ever-increasing laser power,the requirements for ultraviolet(UV)coatings increase continuously.The fundamental challenge for UV laser-resistant mirror coatings is to simultaneously exhibit a high reflectivity with a large bandwidth and high laser resistance.These characteristics are traditionally achieved by the deposition of laser-resistant layers on highly reflective layers.We propose a“reflectivity and laser resistance in one”design by using tunable nanolaminate layers that serve as an effective layer with a high refractive index and a large optical bandgap.An Al_(2)O_(3)-HfO_(2) nanolaminate-based mirror coating for UV laser applications is experimentally demonstrated using ebeam deposition.The bandwidth,over which the reflectance is >99.5%,is more than twice that of a traditional mirror with a comparable overall thickness.The laser-induced damage threshold is increased by a factor of ~1.3 for 7.6 ns pulses at a wavelength of 355 nm.This tunable,nanolaminate-based new design strategy paves the way toward a new generation of UV coatings for high-power laser applications.展开更多
Indium tin oxide(ITO) films have recently emerged as a new class of functional materials for nonlinear optical(NLO) devices due to their exotic properties around epsilon-near-zero(ENZ) wavelength. Here, we experimenta...Indium tin oxide(ITO) films have recently emerged as a new class of functional materials for nonlinear optical(NLO) devices due to their exotic properties around epsilon-near-zero(ENZ) wavelength. Here, we experimentally investigated and tailored the NLO absorption properties of ITO films. The NLO absorption response of ITO films is investigated by using the femtosecond Z-scan measurement technique at two different wavelengths of 1030 nm(out of ENZ region) and 1440 nm(within ENZ region). Interestingly, we observed conversion behavior from saturable absorption(SA) to reverse saturable absorption(RSA) at 1030 nm with the increasing incident laser intensity, whereas only SA behavior was observed at 1440 nm. We demonstrate that SA behavior was ascribed to ground-state free electrons bleaching in the conduction band, and RSA was attributed to three-photon absorption. Moreover, results reveal that ITO film shows more excellent SA performance at 1440 nm with a nonlinear absorption coefficient of ~-23.2 cm∕GW and a figure of merit of ~1.22 × 10^(-16) esu · cm.Furthermore, we tailored the SA and RSA behaviors of ITO films at 1030 and 1440 nm wavelengths via post-annealing treatment. The modulatable NLO absorption was ascribed to the changing of free-carrier concentration in ITO films via annealing treatment. The experimental findings offered an inroad for researchers to tailor its NLO absorption properties by changing the free-carrier concentration through chemical modification such as annealing, oxidation, or defect implantation. The superior and tunable nonlinear optical response suggests that ITO film might be employed as a new class material with potential applications in novel optical switches or optical limiters to realize the all-optical information process.展开更多
The laser-induced damage threshold(LIDT)of plate laser beam splitter(PLBS)coatings is closely related to the subsurface absorption defects of the substrate.Herein,a two-step deposition temperature method is proposed t...The laser-induced damage threshold(LIDT)of plate laser beam splitter(PLBS)coatings is closely related to the subsurface absorption defects of the substrate.Herein,a two-step deposition temperature method is proposed to understand the effect of substrate subsurface impurity defects on the LIDT of PLBS coatings.Firstly,BK7 substrates are heat-treated at three different temperatures.The surface morphology and subsurface impurity defect distribution of the substrate before and after the heat treatment are compared.Then,a PLBS coating consisting of alternating HfO2–Al2O3 mixture and SiO2 layers is designed to achieve a beam-splitting ratio(transmittance to reflectance,s-polarized light)of approximately 50:50 at 1053 nm and an angle of incidence of 45◦,and it is prepared under four different deposition processes.The experimental and simulation results show that the subsurface impurity defects of the substrate migrate to the surface and accumulate on the surface during the heat treatment,and become absorption defect sources or nodule defect seeds in the coating,reducing the LIDT of the coating.The higher the heat treatment temperature,the more evident the migration and accumulation of impurity defects.A lower deposition temperature(at which the coating can be fully oxidized)helps to improve the LIDT of the PLBS coating.When the deposition temperature is 140◦C,the LIDT(s-polarized light,wavelength:1064 nm,pulse width:9 ns,incident angle:45◦)of the PLBS coating is 26.2 J/cm2,which is approximately 6.7 times that of the PLBS coating deposited at 200◦C.We believe that the investigation into the laser damage mechanism of PLBS coatings will help to improve the LIDT of coatings with partial or high transmittance at laser wavelengths.展开更多
The spatial resolved method, which measures the laser-induced damage fluence by identifying the location of the damage point in the Gaussian beam three-dimensional direction, is demonstrated. The advantages and practi...The spatial resolved method, which measures the laser-induced damage fluence by identifying the location of the damage point in the Gaussian beam three-dimensional direction, is demonstrated. The advantages and practicality of this method have been explained. Taking a triple frequency beam splitter as an example, the defect damage fluence can be accurately calculated by the spatial resolved method. The different defect damage performance of the triple frequency splitter is distinguished under irradiations of only the 355 and 532 nm lasers. The spatial resolved method provides a way to obtain precise information of optical film defect information.展开更多
In this paper,a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared,in which a calculation method is firstly proposed to optimize the number of channels to a minimum.The...In this paper,a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared,in which a calculation method is firstly proposed to optimize the number of channels to a minimum.The induction of peristrophic multiplexing reduces the performance difference in one bulk of the grating,whereas there is no need to deliberately optimize the fabrication process.It is revealed that a discrete 2D angle deflection range of±30°is obtained and the relative diffraction efficiency of all the grating channels reaches more than 55%with a root-meansquare deviation of less than 3.4%in the same grating.The deviation of the Bragg incidence and exit angles from the expected values is less than 0.07°.It is believed that the proposed 2D angle amplifier has the potential to realize high-performance and large-angle beam steering in high-power laser beam scanning systems.展开更多
Multilayer dielectric gratings(MLDGs)are crucial for pulse compression in picosecond-petawatt laser systems.Bulged nodular defects,embedded in coating stacks during multilayer deposition,influence the lithographic pro...Multilayer dielectric gratings(MLDGs)are crucial for pulse compression in picosecond-petawatt laser systems.Bulged nodular defects,embedded in coating stacks during multilayer deposition,influence the lithographic process and performance of the final MLDG products.In this study,the integration of nanosecond laser conditioning(NLC)into different manufacturing stages of MLDGs was proposed for the first time on multilayer dielectric films(MLDFs)and final grating products to improve laser-induced damage performance.The results suggest that the remaining nodular ejection pits introduced by the two protocols exhibit a high nanosecond laser damage resistance,which remains stable when the irradiated laser fluence is more than twice the nanosecond-laser-induced damage threshold(nanosecond-LIDT)of the unconditioned MLDGs.Furthermore,the picosecond-LIDT of the nodular ej ection pit conditioned on the MLDFs was approximately 40%higher than that of the nodular defects,and the loss of the grating structure surrounding the nodular defects was avoided.Therefore,NLC is an effective strategy for improving the laser damage resistance of MLDGs.展开更多
Maximizing the energy-loading performance of gratings is a universal theme in high-energy pulse compression.However,sporadic grating designs strongly restrict the development of high-power laser engineering.This study...Maximizing the energy-loading performance of gratings is a universal theme in high-energy pulse compression.However,sporadic grating designs strongly restrict the development of high-power laser engineering.This study proposes an all-and mixed-dielectric grating design paradigm for Nd:glass-based pulse compressors.The solution regions are classified according to the line density.High diffraction efficiency solutions are described in more detail based on the dispersion amount and incident angle.Moreover,an energy scaling factor of 7.09 times larger than that of the National Ignition Facility’s Advanced Radiographic Capability(NIF-ARC)is obtained by taking advantage of the low electric field intensity at transverse magnetic polarization and a small incident angle.These results make a pioneering contribution to facilitate future 20–50-petawatt-class ultrafast laser systems.展开更多
The requirements for dichroic laser mirrors continue to increase with the development of laser technology. The challenge of a dichroic laser mirror coating is to simultaneously obtain spectral performance with signifi...The requirements for dichroic laser mirrors continue to increase with the development of laser technology. The challenge of a dichroic laser mirror coating is to simultaneously obtain spectral performance with significantly different reflection or transmission properties as well as a high laser-induced damage threshold(LIDT) at two different wavelengths. Traditional dichroic laser mirrors composed of alternating high-and low-refractive-index pure materials often has difficulty achieving excellent spectral performance and high LIDTs at two wavelengths simultaneously. We propose to use a new design with mixture layers and sandwich-like-structure interfaces to meet the challenging requirements. An Al_(2) O_(3)-HfO_(2) mixture-based dichroic laser mirror, which can be used as a harmonic separator in a fusion-class laser or a pump/signal beam separator in a petawatt-class Ti-sapphire laser system, is experimentally demonstrated using e-beam deposition. The mixture-based dichroic mirror coating shows good spectral performance, fine mechanical property, low absorption, and high LIDT. For the s-polarized 7.7 ns pulses at a wavelength of 532 nm and the p-polarized 12 ns pulses at a wavelength of 1064 nm, the LIDTs are almost doubled. The excellent performance of this new design strategy with mixture layers and sandwich-like-structure interfaces suggests its wide applicability in high-performance laser coating.展开更多
The nonlinear absorption （NLA） properties of potassium dideuterium phosphate crystals at 515 nm under difterent excitation laser intensities are investigated with the Z-scan technique. Two critical intensities are h...The nonlinear absorption （NLA） properties of potassium dideuterium phosphate crystals at 515 nm under difterent excitation laser intensities are investigated with the Z-scan technique. Two critical intensities are highlighted： the critical intensity for exciting the NLA and the critical intensity of the multiphoton absorption mechanism transition. Experimental results indicate the existence of defect states located in the band gap, which can be manipulated by varying laser intensity. A model based on the change of multiphoton absorption mechanism induced by the transformation of defect species is proposed to interpret the experiments. Modeling results are in good agreement with the experiment data.展开更多
To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was ...To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was developed under pulsed CO2laser irradiation. The model employed various heat transfer and hydrodynamic boundary and thermomechanical properties for assisting the understanding of the contributions of Marangoni convention,gravitational force, vaporization recoil pressure, and capillary force in the process of laser ablation and better prediction of laser processing. Simulation results indicated that the vaporization recoil pressure dominated the formation of the final ablation profile. The ablation depth increased exponentially with pulse duration and linearly with laser energy after homogenous evaporation. The model was validated by experimental data of pulse CO2laser ablation of fused silica. To further investigate laser beam figuring, local ablation by varying the overlap rate and laser energy was conducted, achieving down to 4 nm homogenous ablation depth.展开更多
A time-resolved high-power laser photometer, which measures the real-time variations of transmission, internal reflection, and scattering simultaneously with picosecond time resolution, was developed to investigate th...A time-resolved high-power laser photometer, which measures the real-time variations of transmission, internal reflection, and scattering simultaneously with picosecond time resolution, was developed to investigate the material response sequence during high-power nanosecond laser irradiation in thick fused silica. It was found that the transient transmission decreased sharply, accompanied by an increase in internal reflection at the rising edge of the laser pulse. The transient transmission recovered, while laser damage did not occur, but it did not recover if the scattering increased, indicating the occurrence of laser damage. The reason for the sharp decrease of transmission and the relationship between the transmission drop and laser damage were discussed.展开更多
Residual processing defects during the contact processing processes greatly reduce the anti-ultraviolet(UV)laser damage performance of fused silica optics,which significantly limited development of high-energy laser s...Residual processing defects during the contact processing processes greatly reduce the anti-ultraviolet(UV)laser damage performance of fused silica optics,which significantly limited development of high-energy laser systems.In this study,we demonstrate the manufacturing of fused silica optics with a high damage threshold using a CO_(2)laser process chain.Based on theoretical and experimental studies,the proposed uniform layer-by-layer laser ablation technique can be used to characterize the subsurface mechanical damage in three-dimensional full aperture.Longitudinal ablation resolutions ranging from nanometers to micrometers can be realized;the minimum longitudinal resolution is<5 nm.This technique can also be used as a crack-free grinding tool to completely remove subsurface mechanical damage,and as a cleaning tool to effectively clean surface/subsurface contamination.Through effective control of defects in the entire chain,the laser-induced damage thresholds of samples fabricated by the CO_(2)laser process chain were 41%(0%probability)and 65.7%(100%probability)higher than those of samples fabricated using the conventional process chain.This laser-based defect characterization and removal process provides a new tool to guide optimization of the conventional finishing process and represents a new direction for fabrication of highly damage-resistant fused silica optics for high-energy laser applications.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12375300,12275346,and U1930119)the Fundamental Research Funds for the Central Universities(Nos.22120210446 and 22120180070)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2020253).
文摘Freestanding Zr filters are important devices for improving spectral purity in the extreme ultraviolet range of 7–20 nm,and their irradiation resistance directly determines their life and efficiency.We prepared multilayered Zr/B4C and Zr/Si filters using magnetron sputtering.Their transmittance reached a maximum of 23%(λ=13.5 nm).Microwatt-radiation-induced structural changes in the filters were investigated at the metrology beamline(BL08B)of the National Synchrotron Radiation Laboratory.The aging of the Zr filters was measured and analyzed.The experimental results revealed that the damage was noticeable on the irradiated filter surfaces with different states,suggesting that the main factors causing the degradation of the filters were oxidation and carbon contamination at the surfaces.Furthermore,the thermal stability of the Zr filters was studied by annealing,and the heat accumulation during the damage process was estimated using finite-element numerical simulations and X-ray photoelectron spectroscopy measurements.Silicide formation at the Zr-Si-O system interfaces was found to be key to enhancing the stability of the filters.
基金Youth Innovation Promotion Association of the Chinese Academy of Sciences(2022246)Shanghai Sailing Program(22YF1454800,20YF145480)。
文摘Traditional hyperspectral imaging(HI)systems are constrained by a limited depth of field(DoF),necessitating refocusing for any out-of-focus objects.This requirement not only slows down the imaging speed but also complicates the system architecture.It is challenging to trade off among speed,resolution,and DoF within an ultrasimple system.While some studies have reported advancements in extending DoF,the improvements remain insufficient.To address this challenge,we propose a novel,to our knowledge,differentiable framework that integrates an extended DoF(E-DoF)wave propagation model and an achromatic hyperspectral reconstructor powered by deep learning.Through rigorous experimental validation,we have demonstrated that the compact HI system is capable of snapshot capturing of high-fidelity images with an exceptional DoF reaching approximately 5 m,marking a significant improvement of over three orders of magnitude.Additionally,the system achieves over 90%spectral accuracy without aberration,nearly doubling the accuracy performance of existing methods.An asymmetric freeform surface design is introduced for diffractive optical elements,enabling dual functionality with design freedom and E-DoF.The sparse prior conditions for spatial texture and spectral features of hyperspectral cubic data are integrated into the reconstruction network,effectively mitigating texture blurring and chromatic aberration.It foresees that the optimal strategy for achromatic E-DoF can be adopted into other optical systems such as polarization imaging and depth measurement.
基金supported by the National Natural Science Foundation of China(61975215)the Youth Innovation Promotion Association of the Chinese Academy of Sciences,Strategic Priority Research Program of the Chinese Academy of Sciences(XDA25020206)the Science and Technology Planning Project of Shanghai Municipal Science&Technology Commission(21DZ1100400).
文摘Various coatings in high-power laser facilities suffer from laser damage due to nodule defects.We propose a nodule dome removal(NDR)strategy to eliminate unwanted localized electric-field(E-field)enhancement caused by nodule defects,thereby improving the laser-induced damage threshold(LIDT)of laser coatings.It is theoretically demonstrated that the proposed NDR strategy can reduce the localized E-field enhancement of nodules in mirror coatings,polarizer coatings and beam splitter coatings.An ultraviolet(UV)mirror coating is experimentally demonstrated using the NDR strategy.The LIDT is improved to about 1.9 and 2.2 times for the UV mirror coating without artificial nodules and the UV mirror coating with artificial nodule seeds with a diameter of 1000 nm,respectively.The NDR strategy,applicable to coatings prepared by different deposition methods,improves the LIDT of laser coating without affecting other properties,such as the spectrum,stress and surface roughness,indicating its broad applicability in high-LIDT laser coatings.
基金supported by the National Natural Science Foundation of China(No.11535010)。
文摘To reduce the seed length while maintaining the advantages of the cuboid KDP-type crystal,a long-seed KDP crystal with size 471 mm×480 mm×400 mm is rapidly grown.With almost the same high cutting efficiency to obtain third harmonic generation oriented samples,this long-seed KDP-type crystal can be grown with a shorter seed than that of the cuboid KDP-type crystal.The full width at half maximum of the high-resolution X-ray diffraction of the(200)crystalline face is 28.8 arc seconds,indicating that the long-seed KDP crystal has good crystalline quality.In the wavelength range of 377–1022 nm,the transmittance of the long-seed KDP crystal is higher than 90%.The fluence for the 50%probability of laser-induced damage(LID)is 18.5 J/cm^2(3 ns,355 nm).Several test points survive when the laser fluence exceeds 30 J/cm^2(3 ns,355 nm),indicating the good LID performance of the long-seed KDP crystal.At present,the growth of a long-seed DKDP crystal is under way.
基金supported by the National Key R&D Program of China(2018YFE0115900)the Key Foreign Cooperation Projects of Bureau of International Cooperation of Chinese Academy of Sciences(181231KYSB20210001).
文摘Multilayer dielectric gratings typically remove multiple-grating pillars after picosecond laser irradiation;however,the dynamic formation process of the removal is still unclear.In this study,the damage morphologies of multilayer dielectric gratings induced by an 8.6-ps laser pulse were closely examined.The damage included the removal of a single grating pillar and consecutive adjacent grating pillars and did not involve the destruction of the internal high-reflection mirror structure.Comparative analysis of the two damage morphological characteristics indicated the removal of adjacent pillars was related to an impact process caused by the eruption of localized materials from the left-hand pillar,exerting impact pressure on its adjacent pillars and eventually resulting in multiple pillar removal.A finite-element strain model was used to calculate the stress distribution of the grating after impact.According to the electric field distribution,the eruptive pressure of the dielectric materials after ionization was also simulated.The results suggest that the eruptive pressure resulted in a stress concentration at the root of the adjacent pillar that was sufficient to cause damage,corresponding to the experimental removal of the adjacent pillar from the root.This study provides further understanding of the laser-induced damage behavior of grating pillars and some insights into reducing the undesirable damage process for practical applications.
文摘Laser resistance and stress-free mirrors,windows,polarizers,and beam splitters up to 400 mm×400 mm are required for the construction of the series SG facilities.In order to improve the coating quality,a program has been in place for the last ten years.For the small-aperture pick-off mirror,the laser-induced damage threshold(LIDT)is above 60 J/cm2(1064 nm,3 ns),and the reflected wavefront is less thanλ/4(λ=633 nm).The Brewster-angle polarizing beam splitter(Φ50×10 mm)shows the best LIDT result,up to 29.8 J cm 2(1064 nm,10 ns)for a p-polarized wave in the 2012damage competition of the XLIV Annual Boulder Damage Symposium.For the larger-aperture mirror and polarizer,the LIDT is above 23 J cm 2(1064 nm,3 ns)and 14 J cm 2(1064 nm,3 ns),respectively.The reflected wavefront is less thanλ/3(λ=633 nm)at the used angle.
基金Financial support from the National Natural Science Foundation of China （Nos. 51432006, 50925207, and 51172100）, the Ministry of Science and Technology of China for the International Science Linkages Program （No. 2011DFG52970）, the Ministry of Education of China for the Changjiang Innovation Research Team （No. IRT14R23）, the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project （No. B13025）, 100 Talents Program of CAS, and Jiangsu Innovation Research Team are gratefully acknowledged. M. G. H., M. P. C., and C. Z. thank the Australian Research Council （ARC） for support.
文摘Axially coordinated metal-porphyrin-functionalized multi-walled carbon nanotube （MWCNT） nanohybrids were prepared via two different synthetic approaches （a one-pot 1,3-dipolar cycloaddition reaction and a stepwise approach that involved 1,3-dipolar cycloaddition followed by nucleophilic substitution）, and characterized through spectroscopic techniques. Attachment of the tin porphyrins to the surface of the MWCNTs significantly improves their solubility and ease of processing. These axially coordinated （5,10,15,20-tetraphenylporphyrinato）tin（Ⅳ） （SnTPP）- MWCNTs exhibit significant fluorescence quenching. The third-order nonlinear optical properties of the resultant nanohybrids were studied by using the Z-scan technique at 532 nm with both nanosecond and picosecond laser pulses. The results show that the nanohybrids exhibit significant reverse saturable absorption or saturable absorption when nanosecond or picosecond pulses, respectively, are employed. Improvement in the nanosecond regime nonlinear absorption is observed on proceeding to the nanohybrids and is ascribed to a combination of the outstanding properties of MWCNTs and the chemically attached metal-porphyrins.
文摘Rapid growth processing of KDP crystals was improved by employing continuous filtration to eliminate bulk defects.The performances of the KDP crystals, including scattering defects, laser damage resistance and transmittance, were measured and analyzed. Compared with rapid-grown KDP without continuous filtration, the transmittance in the nearinfrared was increased by at least 2%, almost all of ‘micron size' defects were eliminated and ‘sub-micron size' defects were decreased by approximately 90%. Laser damage testing revealed that the laser-induced damage thresholds(LIDTs),as well as the consistency of the LIDTs from sample to sample, were improved greatly. Moreover, it identified that‘micron size' defects were the precursors which initiated laser damage at relative lower laser fluence(4–6 J cm^(-2)),and there was a lower correlation between smaller size scattering defects and laser damage initiation. The improved consistency in the LIDTs, attributed to elimination of ‘micron size' defects, and LIDT enhancement originated from the decreased absorption of the KDP crystals.
基金supported by the National Special Support Program for Young Top-notch TalentNational Natural Science Foundation of China(61975215 and 61505227)+1 种基金Youth Innovation Promotion Association of the Chinese Academy of Sciencesand Shanghai Young Top-notch Talent Program.
文摘With ever-increasing laser power,the requirements for ultraviolet(UV)coatings increase continuously.The fundamental challenge for UV laser-resistant mirror coatings is to simultaneously exhibit a high reflectivity with a large bandwidth and high laser resistance.These characteristics are traditionally achieved by the deposition of laser-resistant layers on highly reflective layers.We propose a“reflectivity and laser resistance in one”design by using tunable nanolaminate layers that serve as an effective layer with a high refractive index and a large optical bandgap.An Al_(2)O_(3)-HfO_(2) nanolaminate-based mirror coating for UV laser applications is experimentally demonstrated using ebeam deposition.The bandwidth,over which the reflectance is >99.5%,is more than twice that of a traditional mirror with a comparable overall thickness.The laser-induced damage threshold is increased by a factor of ~1.3 for 7.6 ns pulses at a wavelength of 355 nm.This tunable,nanolaminate-based new design strategy paves the way toward a new generation of UV coatings for high-power laser applications.
基金National Natural Science Foundation of China(11874369,U1831211)Strategic Priority Research Program of the Chinese Academy of Sciences(XDB1603)。
文摘Indium tin oxide(ITO) films have recently emerged as a new class of functional materials for nonlinear optical(NLO) devices due to their exotic properties around epsilon-near-zero(ENZ) wavelength. Here, we experimentally investigated and tailored the NLO absorption properties of ITO films. The NLO absorption response of ITO films is investigated by using the femtosecond Z-scan measurement technique at two different wavelengths of 1030 nm(out of ENZ region) and 1440 nm(within ENZ region). Interestingly, we observed conversion behavior from saturable absorption(SA) to reverse saturable absorption(RSA) at 1030 nm with the increasing incident laser intensity, whereas only SA behavior was observed at 1440 nm. We demonstrate that SA behavior was ascribed to ground-state free electrons bleaching in the conduction band, and RSA was attributed to three-photon absorption. Moreover, results reveal that ITO film shows more excellent SA performance at 1440 nm with a nonlinear absorption coefficient of ~-23.2 cm∕GW and a figure of merit of ~1.22 × 10^(-16) esu · cm.Furthermore, we tailored the SA and RSA behaviors of ITO films at 1030 and 1440 nm wavelengths via post-annealing treatment. The modulatable NLO absorption was ascribed to the changing of free-carrier concentration in ITO films via annealing treatment. The experimental findings offered an inroad for researchers to tailor its NLO absorption properties by changing the free-carrier concentration through chemical modification such as annealing, oxidation, or defect implantation. The superior and tunable nonlinear optical response suggests that ITO film might be employed as a new class material with potential applications in novel optical switches or optical limiters to realize the all-optical information process.
基金This study was supported by the National Natural Science Foundation of China(61975215)Youth Innovation Promotion Association of the Chinese Academy of Sciences,Strategic Priority Research Program of the Chinese Academy of Sciences(XDA25020206)the Science and Technology Planning Project of Shanghai Municipal Science&Technology Commission(21DZ1100400).
文摘The laser-induced damage threshold(LIDT)of plate laser beam splitter(PLBS)coatings is closely related to the subsurface absorption defects of the substrate.Herein,a two-step deposition temperature method is proposed to understand the effect of substrate subsurface impurity defects on the LIDT of PLBS coatings.Firstly,BK7 substrates are heat-treated at three different temperatures.The surface morphology and subsurface impurity defect distribution of the substrate before and after the heat treatment are compared.Then,a PLBS coating consisting of alternating HfO2–Al2O3 mixture and SiO2 layers is designed to achieve a beam-splitting ratio(transmittance to reflectance,s-polarized light)of approximately 50:50 at 1053 nm and an angle of incidence of 45◦,and it is prepared under four different deposition processes.The experimental and simulation results show that the subsurface impurity defects of the substrate migrate to the surface and accumulate on the surface during the heat treatment,and become absorption defect sources or nodule defect seeds in the coating,reducing the LIDT of the coating.The higher the heat treatment temperature,the more evident the migration and accumulation of impurity defects.A lower deposition temperature(at which the coating can be fully oxidized)helps to improve the LIDT of the PLBS coating.When the deposition temperature is 140◦C,the LIDT(s-polarized light,wavelength:1064 nm,pulse width:9 ns,incident angle:45◦)of the PLBS coating is 26.2 J/cm2,which is approximately 6.7 times that of the PLBS coating deposited at 200◦C.We believe that the investigation into the laser damage mechanism of PLBS coatings will help to improve the LIDT of coatings with partial or high transmittance at laser wavelengths.
基金supported by the National Natural Science Foundation of China(No.4317)the National Key Research and Development Project of China(No.2016YFE0104300)
文摘The spatial resolved method, which measures the laser-induced damage fluence by identifying the location of the damage point in the Gaussian beam three-dimensional direction, is demonstrated. The advantages and practicality of this method have been explained. Taking a triple frequency beam splitter as an example, the defect damage fluence can be accurately calculated by the spatial resolved method. The different defect damage performance of the triple frequency splitter is distinguished under irradiations of only the 355 and 532 nm lasers. The spatial resolved method provides a way to obtain precise information of optical film defect information.
基金supported by the National Key R&D Program of China(No.2020YFA0714500)the Shanghai Strategic Emerging Industry Development Special Fund(No.31011442501217020191D3101001)+1 种基金the National Natural Science Foundation of China(Nos.61875212 and U1831211)the International Partnership Program of Chinese Academy of Sciences(No.181231KYSB20200040)
文摘In this paper,a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared,in which a calculation method is firstly proposed to optimize the number of channels to a minimum.The induction of peristrophic multiplexing reduces the performance difference in one bulk of the grating,whereas there is no need to deliberately optimize the fabrication process.It is revealed that a discrete 2D angle deflection range of±30°is obtained and the relative diffraction efficiency of all the grating channels reaches more than 55%with a root-meansquare deviation of less than 3.4%in the same grating.The deviation of the Bragg incidence and exit angles from the expected values is less than 0.07°.It is believed that the proposed 2D angle amplifier has the potential to realize high-performance and large-angle beam steering in high-power laser beam scanning systems.
基金supported by the National Key R&D Program of China(Grant No.2018YFE0115900)the Key Foreign Cooperation Projects of Bureau of the International Cooperation of Chinese Academy of Sciences(Grant No.181231KYSB20210001)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA25020314).
文摘Multilayer dielectric gratings(MLDGs)are crucial for pulse compression in picosecond-petawatt laser systems.Bulged nodular defects,embedded in coating stacks during multilayer deposition,influence the lithographic process and performance of the final MLDG products.In this study,the integration of nanosecond laser conditioning(NLC)into different manufacturing stages of MLDGs was proposed for the first time on multilayer dielectric films(MLDFs)and final grating products to improve laser-induced damage performance.The results suggest that the remaining nodular ejection pits introduced by the two protocols exhibit a high nanosecond laser damage resistance,which remains stable when the irradiated laser fluence is more than twice the nanosecond-laser-induced damage threshold(nanosecond-LIDT)of the unconditioned MLDGs.Furthermore,the picosecond-LIDT of the nodular ej ection pit conditioned on the MLDFs was approximately 40%higher than that of the nodular defects,and the loss of the grating structure surrounding the nodular defects was avoided.Therefore,NLC is an effective strategy for improving the laser damage resistance of MLDGs.
基金This work was supported by the National Key R&D Program of China(No.2020YFA0714500)the National Natural Science Foundation of China(Nos.61875212 and U1831211)+2 种基金the Shanghai Strategic Emerging Industry Development Special Fund(No.31011442501217020191D3101001)the International Partnership Program of Chinese Academy of Sciences(No.181231KYSB20200040)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA25020314).
文摘Maximizing the energy-loading performance of gratings is a universal theme in high-energy pulse compression.However,sporadic grating designs strongly restrict the development of high-power laser engineering.This study proposes an all-and mixed-dielectric grating design paradigm for Nd:glass-based pulse compressors.The solution regions are classified according to the line density.High diffraction efficiency solutions are described in more detail based on the dispersion amount and incident angle.Moreover,an energy scaling factor of 7.09 times larger than that of the National Ignition Facility’s Advanced Radiographic Capability(NIF-ARC)is obtained by taking advantage of the low electric field intensity at transverse magnetic polarization and a small incident angle.These results make a pioneering contribution to facilitate future 20–50-petawatt-class ultrafast laser systems.
基金National Natural Science Foundation of China(61975215,U1831211)Youth Innovation Promotion Association of the Chinese Academy of Sciences,Strategic Priority Research Program of the Chinese Academy of Sciences(XDA25020000,XDB16030400)。
文摘The requirements for dichroic laser mirrors continue to increase with the development of laser technology. The challenge of a dichroic laser mirror coating is to simultaneously obtain spectral performance with significantly different reflection or transmission properties as well as a high laser-induced damage threshold(LIDT) at two different wavelengths. Traditional dichroic laser mirrors composed of alternating high-and low-refractive-index pure materials often has difficulty achieving excellent spectral performance and high LIDTs at two wavelengths simultaneously. We propose to use a new design with mixture layers and sandwich-like-structure interfaces to meet the challenging requirements. An Al_(2) O_(3)-HfO_(2) mixture-based dichroic laser mirror, which can be used as a harmonic separator in a fusion-class laser or a pump/signal beam separator in a petawatt-class Ti-sapphire laser system, is experimentally demonstrated using e-beam deposition. The mixture-based dichroic mirror coating shows good spectral performance, fine mechanical property, low absorption, and high LIDT. For the s-polarized 7.7 ns pulses at a wavelength of 532 nm and the p-polarized 12 ns pulses at a wavelength of 1064 nm, the LIDTs are almost doubled. The excellent performance of this new design strategy with mixture layers and sandwich-like-structure interfaces suggests its wide applicability in high-performance laser coating.
基金supported by the National Natural Science Foundation of China(Nos.61405219 and 11304328)
文摘The nonlinear absorption （NLA） properties of potassium dideuterium phosphate crystals at 515 nm under difterent excitation laser intensities are investigated with the Z-scan technique. Two critical intensities are highlighted： the critical intensity for exciting the NLA and the critical intensity of the multiphoton absorption mechanism transition. Experimental results indicate the existence of defect states located in the band gap, which can be manipulated by varying laser intensity. A model based on the change of multiphoton absorption mechanism induced by the transformation of defect species is proposed to interpret the experiments. Modeling results are in good agreement with the experiment data.
基金supported by the National Basic Research Program(No.2016YFB1102704)the Youth Innovation Promotion Association,CAS
文摘To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was developed under pulsed CO2laser irradiation. The model employed various heat transfer and hydrodynamic boundary and thermomechanical properties for assisting the understanding of the contributions of Marangoni convention,gravitational force, vaporization recoil pressure, and capillary force in the process of laser ablation and better prediction of laser processing. Simulation results indicated that the vaporization recoil pressure dominated the formation of the final ablation profile. The ablation depth increased exponentially with pulse duration and linearly with laser energy after homogenous evaporation. The model was validated by experimental data of pulse CO2laser ablation of fused silica. To further investigate laser beam figuring, local ablation by varying the overlap rate and laser energy was conducted, achieving down to 4 nm homogenous ablation depth.
基金supported by the National Key Research and Development Project of China(No.2016YFE0104300)
文摘A time-resolved high-power laser photometer, which measures the real-time variations of transmission, internal reflection, and scattering simultaneously with picosecond time resolution, was developed to investigate the material response sequence during high-power nanosecond laser irradiation in thick fused silica. It was found that the transient transmission decreased sharply, accompanied by an increase in internal reflection at the rising edge of the laser pulse. The transient transmission recovered, while laser damage did not occur, but it did not recover if the scattering increased, indicating the occurrence of laser damage. The reason for the sharp decrease of transmission and the relationship between the transmission drop and laser damage were discussed.
基金supported by the National Key Research and Development Project(2022YFB3403400)Shanghai Sailing Program(20YF1454800)+2 种基金National Natural Science Youth Foundation of China(62205352)Natural Science Foundation of Shanghai(21ZR1472000)Key Projects of the Joint Fund for Astronomy of the National Natural Science Funding of China(U1831211),and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.
文摘Residual processing defects during the contact processing processes greatly reduce the anti-ultraviolet(UV)laser damage performance of fused silica optics,which significantly limited development of high-energy laser systems.In this study,we demonstrate the manufacturing of fused silica optics with a high damage threshold using a CO_(2)laser process chain.Based on theoretical and experimental studies,the proposed uniform layer-by-layer laser ablation technique can be used to characterize the subsurface mechanical damage in three-dimensional full aperture.Longitudinal ablation resolutions ranging from nanometers to micrometers can be realized;the minimum longitudinal resolution is<5 nm.This technique can also be used as a crack-free grinding tool to completely remove subsurface mechanical damage,and as a cleaning tool to effectively clean surface/subsurface contamination.Through effective control of defects in the entire chain,the laser-induced damage thresholds of samples fabricated by the CO_(2)laser process chain were 41%(0%probability)and 65.7%(100%probability)higher than those of samples fabricated using the conventional process chain.This laser-based defect characterization and removal process provides a new tool to guide optimization of the conventional finishing process and represents a new direction for fabrication of highly damage-resistant fused silica optics for high-energy laser applications.
