Plasma-enhanced atomic layer deposition (PEALD) is gaining interest in thin films for laser applications, and post-annealing treatments are often used to improve thin film properties. However, research to improve thin...Plasma-enhanced atomic layer deposition (PEALD) is gaining interest in thin films for laser applications, and post-annealing treatments are often used to improve thin film properties. However, research to improve thin film properties is often based on an expensive and time-consuming trial-and-error process. In this study, PEALD-HfO2 thin film samples were deposited and treated under different annealing atmospheres and temperatures. The samples were characterized in terms of their refractive indices, layer thicknesses and O/Hf ratios. The collected data were split into training and validation sets and fed to multiple back-propagation neural networks with different hidden layers to determine the best way to construct the process–performance relationship. The results showed that the three-hidden-layer back-propagation neural network (THL-BPNN) achieved stable and accurate fitting. For the refractive index, layer thickness and O/Hf ratio, the THL-BPNN model achieved accuracy values of 0.99, 0.94 and 0.94, respectively, on the training set and 0.99, 0.91 and 0.90, respectively, on the validation set. The THL-BPNN model was further used to predict the laser-induced damage threshold of PEALD-HfO2 thin films and the properties of the PEALD-SiO2 thin films, both showing high accuracy. This study not only provides quantitative guidance for the improvement of thin film properties but also proposes a general model that can be applied to predict the properties of different types of laser thin films, saving experimental costs for process optimization.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
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
Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device perf...Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device performance.Nevertheless,the physical picture of interlayer coupling effect during incorporation of monolayer(1L-)hBN is not explicit yet.In this article,spectroscopic ellipsometry was used to experimentally obtain the broadband excitonic and critical point properties of WS_(2)/MoS_(2)and WS_(2)/hBN/MoS_(2)van der Waals heterostructures.We find that 1L-hBN can only slightly block the interlayer electron transfer from WS_(2)layer to MoS_(2)layer.Moreover,insertion of 1L-hBN weakens the interlayer coupling effect by releasing quantum confinement and reducing efficient dielectric screening.Consequently,the exciton binding energies in WS_(2)/hBN/MoS_(2)heterostructures blueshift comparing to those in WS_(2)/MoS_(2)heterostructures.In this exciton binding energies tuning process,the reducing dielectric screening effect plays a leading role.In the meantime,the quasi-particle(QP)bandgap remains unchanged before and after 1L-hBN insertion,which is attributed to released quantum confinement and decreased dielectric screening effects canceling each other.Unchanged QP bandgap as along with blueshift exciton binding energies lead to the redshift exciton transition energies in WS_(2)/hBN/MoS_(2)heterostructures.展开更多
Different laminated structures of TiO_(2)/SiO_(2) composite film were prepared via atomic layer deposition(ALD)on alumina substrates.The effect of the annealing temperature in the air on the surface morphologies,cryst...Different laminated structures of TiO_(2)/SiO_(2) composite film were prepared via atomic layer deposition(ALD)on alumina substrates.The effect of the annealing temperature in the air on the surface morphologies,crystal structures,binding energies,and ingredient content of these films was investigated using X-ray diffraction,field emission scanning electron microscopy,and X-ray photoelectron spectroscopy.Results showed that the binding energy of Ti and Si increased with decrease of the Ti content,and the TiO_(2)/SiO_(2) nanolaminated films exhibited a complex bonding structure.As the annealing temperature increased,the thickness of the nanolaminated films decreased,and the density and surface roughness increased.An increase in the crystallization temperature was proportional to the SiO_(2) content in TiO_(2)/SiO_(2) composite film.The annealing temperature and thin thickness strongly affected the phase structure of the ALD TiO_(2) thin film.To be specific,the TiO_(2) thin film transformed into an anatase phase from an amorphous phase after an increase in the annealing temperature from 400℃ to 550℃,and the TiO_(2) film exhibited an anatase phase until the annealing temperature reached 850℃,owing to its extremely small thickness.The annealing process caused the Al ions in the substrate to diffuse into the films and bond with 0.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
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
基金This work was supported by the Program of Shanghai Academic Research Leader(No.23XD1424100)the CAS Project for Young Scientists in Basic Research(No.YSBR-081)+1 种基金the National Natural Science Foundation of China(No.61975215)the Science and Technology Planning Project of the Shanghai Municipal Science&Technology Commission(No.21DZ1100400).
文摘Plasma-enhanced atomic layer deposition (PEALD) is gaining interest in thin films for laser applications, and post-annealing treatments are often used to improve thin film properties. However, research to improve thin film properties is often based on an expensive and time-consuming trial-and-error process. In this study, PEALD-HfO2 thin film samples were deposited and treated under different annealing atmospheres and temperatures. The samples were characterized in terms of their refractive indices, layer thicknesses and O/Hf ratios. The collected data were split into training and validation sets and fed to multiple back-propagation neural networks with different hidden layers to determine the best way to construct the process–performance relationship. The results showed that the three-hidden-layer back-propagation neural network (THL-BPNN) achieved stable and accurate fitting. For the refractive index, layer thickness and O/Hf ratio, the THL-BPNN model achieved accuracy values of 0.99, 0.94 and 0.94, respectively, on the training set and 0.99, 0.91 and 0.90, respectively, on the validation set. The THL-BPNN model was further used to predict the laser-induced damage threshold of PEALD-HfO2 thin films and the properties of the PEALD-SiO2 thin films, both showing high accuracy. This study not only provides quantitative guidance for the improvement of thin film properties but also proposes a general model that can be applied to predict the properties of different types of laser thin films, saving experimental costs for process optimization.
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(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the National Natural Science Foundation of China(Nos.11674062,61775042,and 61774040)the Fudan University-CIOMP Joint Fund(Nos.FC2019-004,FC2019-006,and FC2018-002)+2 种基金the National Key R&D Program of China(No.2018YFA0703700)the Shanghai Municipal Science and Technology Commission(No.18JC1410300)the Shanghai Municipal Natural Science Foundation(No.20ZR1403200).
文摘Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device performance.Nevertheless,the physical picture of interlayer coupling effect during incorporation of monolayer(1L-)hBN is not explicit yet.In this article,spectroscopic ellipsometry was used to experimentally obtain the broadband excitonic and critical point properties of WS_(2)/MoS_(2)and WS_(2)/hBN/MoS_(2)van der Waals heterostructures.We find that 1L-hBN can only slightly block the interlayer electron transfer from WS_(2)layer to MoS_(2)layer.Moreover,insertion of 1L-hBN weakens the interlayer coupling effect by releasing quantum confinement and reducing efficient dielectric screening.Consequently,the exciton binding energies in WS_(2)/hBN/MoS_(2)heterostructures blueshift comparing to those in WS_(2)/MoS_(2)heterostructures.In this exciton binding energies tuning process,the reducing dielectric screening effect plays a leading role.In the meantime,the quasi-particle(QP)bandgap remains unchanged before and after 1L-hBN insertion,which is attributed to released quantum confinement and decreased dielectric screening effects canceling each other.Unchanged QP bandgap as along with blueshift exciton binding energies lead to the redshift exciton transition energies in WS_(2)/hBN/MoS_(2)heterostructures.
基金supported by the National Special Support Program for Young Top-notch TalentNational Natural Science Foundation of China(No.61975215)+2 种基金Youth Innovation Promotion Association of the Chinese Academy of SciencesShanghai Young Top-notch Talent ProgramStrategic Priority Research Program of the Chinese Academy of Sciences(No.XDB16030400)。
文摘Different laminated structures of TiO_(2)/SiO_(2) composite film were prepared via atomic layer deposition(ALD)on alumina substrates.The effect of the annealing temperature in the air on the surface morphologies,crystal structures,binding energies,and ingredient content of these films was investigated using X-ray diffraction,field emission scanning electron microscopy,and X-ray photoelectron spectroscopy.Results showed that the binding energy of Ti and Si increased with decrease of the Ti content,and the TiO_(2)/SiO_(2) nanolaminated films exhibited a complex bonding structure.As the annealing temperature increased,the thickness of the nanolaminated films decreased,and the density and surface roughness increased.An increase in the crystallization temperature was proportional to the SiO_(2) content in TiO_(2)/SiO_(2) composite film.The annealing temperature and thin thickness strongly affected the phase structure of the ALD TiO_(2) thin film.To be specific,the TiO_(2) thin film transformed into an anatase phase from an amorphous phase after an increase in the annealing temperature from 400℃ to 550℃,and the TiO_(2) film exhibited an anatase phase until the annealing temperature reached 850℃,owing to its extremely small thickness.The annealing process caused the Al ions in the substrate to diffuse into the films and bond with 0.
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(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.