None Ge Yun-Ran, None Zheng Kang, None Ding Chun-Ling, None Hao Xiang-Ying, None Jin Rui-Bo
Optical nonreciprocity has been a popular research topic in recent years. Semiconductor quantum wells (SQWs) have a key role in many high-performance optoelectronic devices. In this paper, we propose a theoretical scheme to achieve nonmagnetic optical nonreciprocity based on the four-wave mixing effect in SQW nanostructures. Using the experimentally available parameters, the nonreciprocal behavior of the probe field in both front and back directions through this SQW is achieved, where both nonreciprocal transmission and nonreciprocal phase shift have high transmission rates. Furthermore, by embedding this SQW nanostructure into a Mach-Zender interferometer, a reconfigurable nonreciprocal device based on high transmission nonreciprocal phase shift that can be used as an isolator or a circulator is designed and analyzed. The device can be realized as a two-port optical isolator with an isolation ratio of 92.39 dB and an insertion loss of 0.25 dB, and as a four-port optical circulator with a fidelity of 0.9993, a photon survival probability of 0.9518 and a low insertion loss with suitable parameters. Semiconductor media have the advantage of easier integration and tunable parameters, and this scheme can provide theoretical guidance for the implementation of nonreciprocal and nonreciprocal photonic devices based on semiconductor solid-state media.
{"title":"Highly Effcient Nonreciprocity based on the Four Wave Mixing in a Semiconductor Quantum Well","authors":"None Ge Yun-Ran, None Zheng Kang, None Ding Chun-Ling, None Hao Xiang-Ying, None Jin Rui-Bo","doi":"10.7498/aps.73.20231212","DOIUrl":"https://doi.org/10.7498/aps.73.20231212","url":null,"abstract":"Optical nonreciprocity has been a popular research topic in recent years. Semiconductor quantum wells (SQWs) have a key role in many high-performance optoelectronic devices. In this paper, we propose a theoretical scheme to achieve nonmagnetic optical nonreciprocity based on the four-wave mixing effect in SQW nanostructures. Using the experimentally available parameters, the nonreciprocal behavior of the probe field in both front and back directions through this SQW is achieved, where both nonreciprocal transmission and nonreciprocal phase shift have high transmission rates. Furthermore, by embedding this SQW nanostructure into a Mach-Zender interferometer, a reconfigurable nonreciprocal device based on high transmission nonreciprocal phase shift that can be used as an isolator or a circulator is designed and analyzed. The device can be realized as a two-port optical isolator with an isolation ratio of 92.39 dB and an insertion loss of 0.25 dB, and as a four-port optical circulator with a fidelity of 0.9993, a photon survival probability of 0.9518 and a low insertion loss with suitable parameters. Semiconductor media have the advantage of easier integration and tunable parameters, and this scheme can provide theoretical guidance for the implementation of nonreciprocal and nonreciprocal photonic devices based on semiconductor solid-state media.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136203616","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
None Song Yu-Xin, None Li Yu-Qi, None Wang Ling-Han, None Zhang Xiao-Lan, None Wang Chong, None Wang Qin-Sheng
Transition metal dichalcogenides have emerged as a prominent class of two-dimensional layered materials, capturing sustained attention from researchers due to their unique structures and properties. These distinctive characteristics render transition metal dichalcogenides highly versatile in numerous fields, including optoelectronics, nanoelectronics, energy storage devices, and electrocatalysis. In particular, the ability to modulate the doping characteristics of these materials plays a crucial role in improving the photoelectric response performance of devices, making it imperative to investigate and understand such effects. In recent years, the electrochemical ion intercalation technique has emerged as a novel approach for precise doping control of two-dimensional materials. Building upon this advancement, this paper aims to demonstrate the effective doping control of transition metal dichalcogenides devices by utilizing the electrochemical ion intercalation method specifically on thick WS2 layers. The results reveal a remarkable enhancement in electrical conductivity, approximately 200 times higher than the original value, alongside the achievement of efficient and reversible control over the photoelectric response performance through the manipulation of gate voltage. One of the key findings of this paper is the successful demonstration of the reversible cyclic control of the photoelectric response in WS2 devices through ion intercalation, regulated by the gate voltage. This dynamic control mechanism showcases the potential for finely tuning and tailoring the performance of photoelectric devices made from two-dimensional materials. The ability to achieve reversible control is especially significant as it allows for a versatile range of applications, enabling devices to be adjusted according to specific requirements and operating conditions. The implications of this work extend beyond the immediate findings and present a foundation for future investigations into response control of photoelectric devices constructed using two-dimensional materials through the utilization of the ion intercalation method. By establishing the feasibility and efficacy of this technique in achieving controlled doping and precise modulation of photoelectric response, researchers can explore its potential applications in various technological domains. Furthermore, this research serves as a stepping stone for the development of advanced doping strategies, enabling the design and fabrication of high-performance devices with enhanced functionalities. In summary, this work showcases the significance of doping control in transition metal dichalcogenide devices and demonstrates the potential of the electrochemical ion intercalation method for achieving precise modulation of their photoelectric response performance. The observed enhancements in electrical conductivity and the ability to reversibly control the photoelectric response highlight th
{"title":"Modulation of photocurrent response in WS<sub>2</sub> optoelectronic devices with Li intercalation","authors":"None Song Yu-Xin, None Li Yu-Qi, None Wang Ling-Han, None Zhang Xiao-Lan, None Wang Chong, None Wang Qin-Sheng","doi":"10.7498/aps.72.20231000","DOIUrl":"https://doi.org/10.7498/aps.72.20231000","url":null,"abstract":"Transition metal dichalcogenides have emerged as a prominent class of two-dimensional layered materials, capturing sustained attention from researchers due to their unique structures and properties. These distinctive characteristics render transition metal dichalcogenides highly versatile in numerous fields, including optoelectronics, nanoelectronics, energy storage devices, and electrocatalysis. In particular, the ability to modulate the doping characteristics of these materials plays a crucial role in improving the photoelectric response performance of devices, making it imperative to investigate and understand such effects.<br>In recent years, the electrochemical ion intercalation technique has emerged as a novel approach for precise doping control of two-dimensional materials. Building upon this advancement, this paper aims to demonstrate the effective doping control of transition metal dichalcogenides devices by utilizing the electrochemical ion intercalation method specifically on thick WS<sub>2</sub> layers. The results reveal a remarkable enhancement in electrical conductivity, approximately 200 times higher than the original value, alongside the achievement of efficient and reversible control over the photoelectric response performance through the manipulation of gate voltage. One of the key findings of this paper is the successful demonstration of the reversible cyclic control of the photoelectric response in WS<sub>2</sub> devices through ion intercalation, regulated by the gate voltage. This dynamic control mechanism showcases the potential for finely tuning and tailoring the performance of photoelectric devices made from two-dimensional materials. The ability to achieve reversible control is especially significant as it allows for a versatile range of applications, enabling devices to be adjusted according to specific requirements and operating conditions.<br>The implications of this work extend beyond the immediate findings and present a foundation for future investigations into response control of photoelectric devices constructed using two-dimensional materials through the utilization of the ion intercalation method. By establishing the feasibility and efficacy of this technique in achieving controlled doping and precise modulation of photoelectric response, researchers can explore its potential applications in various technological domains. Furthermore, this research serves as a stepping stone for the development of advanced doping strategies, enabling the design and fabrication of high-performance devices with enhanced functionalities.<br>In summary, this work showcases the significance of doping control in transition metal dichalcogenide devices and demonstrates the potential of the electrochemical ion intercalation method for achieving precise modulation of their photoelectric response performance. The observed enhancements in electrical conductivity and the ability to reversibly control the photoelectric response highlight th","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135212838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
None Fan Chao-Yang, None Li Chao-Feng, None Yang Su-Hui, None Liu Xin-Yu, None Liao Ying-Qi
The echo of underwater lidar often contains a significant quantity of scattering clutters. In order to effectively suppress this scattering clutter and improve the ranging accuracy of underwater lidar, a novel denoising method based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and wavelet threshold denoising is proposed.The CEEMDAN-wavelet threshold denoising algorithm uses the correlation coefficient to select intrinsic mode function (IMF) components obtained from the CEEMDAN decomposition. The IMFs, which are more closely related to the original signal, are selected. Then, the wavelet thresholding denoising algorithm is applied to each of the selected IMFs to perform additional denoising. For each IMF component, specific threshold values are calculated based on their frequency and amplitude characteristics. Subsequently, the wavelet coefficients of the IMF components are processed by using these threshold values. Finally, the denoised IMF components are combined and reconstructed to obtain the final denoised signal. Applying the wavelet threshold denoising algorithm to IMF components can effectively remove noise components that cannot be removed by traditional CEEMDAN partial reconstruction methods. By using the threshold value calculated based on the characteristics of each IMF component, the wavelet thresholding denoising process is improved in comparison with directly using a single threshold value. This approach enhances the algorithm’s adaptability and enables more effective removal of noise from the signal.We apply the proposed method to underwater ranging experiments. A 532 nm intensity-modulated continuous wave laser is used as a light source. Ranging is performed for a target in water with varying attenuation coefficients. A white polyvinyl chloride (PVC) reflector is used as a target. When the correlation extreme value is directly used to determine the delay at a distance of 3.75 attenuation length, it results in a ranging error of 19.2 cm. However, after applying the proposed method, the ranging error is reduced to 6.2 cm, thus effectively improving the ranging accuracy. These results demonstrate that the method has a significant denoising effect in underwater lidar system.
{"title":"Suppression of scattering clutter in underwater LiDAR based on CEEMDAN-wavelet threshold denoising algorithm","authors":"None Fan Chao-Yang, None Li Chao-Feng, None Yang Su-Hui, None Liu Xin-Yu, None Liao Ying-Qi","doi":"10.7498/aps.72.20231035","DOIUrl":"https://doi.org/10.7498/aps.72.20231035","url":null,"abstract":"<sec>The echo of underwater lidar often contains a significant quantity of scattering clutters. In order to effectively suppress this scattering clutter and improve the ranging accuracy of underwater lidar, a novel denoising method based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and wavelet threshold denoising is proposed.</sec><sec>The CEEMDAN-wavelet threshold denoising algorithm uses the correlation coefficient to select intrinsic mode function (IMF) components obtained from the CEEMDAN decomposition. The IMFs, which are more closely related to the original signal, are selected. Then, the wavelet thresholding denoising algorithm is applied to each of the selected IMFs to perform additional denoising. For each IMF component, specific threshold values are calculated based on their frequency and amplitude characteristics. Subsequently, the wavelet coefficients of the IMF components are processed by using these threshold values. Finally, the denoised IMF components are combined and reconstructed to obtain the final denoised signal. Applying the wavelet threshold denoising algorithm to IMF components can effectively remove noise components that cannot be removed by traditional CEEMDAN partial reconstruction methods. By using the threshold value calculated based on the characteristics of each IMF component, the wavelet thresholding denoising process is improved in comparison with directly using a single threshold value. This approach enhances the algorithm’s adaptability and enables more effective removal of noise from the signal.</sec><sec>We apply the proposed method to underwater ranging experiments. A 532 nm intensity-modulated continuous wave laser is used as a light source. Ranging is performed for a target in water with varying attenuation coefficients. A white polyvinyl chloride (PVC) reflector is used as a target. When the correlation extreme value is directly used to determine the delay at a distance of 3.75 attenuation length, it results in a ranging error of 19.2 cm. However, after applying the proposed method, the ranging error is reduced to 6.2 cm, thus effectively improving the ranging accuracy. These results demonstrate that the method has a significant denoising effect in underwater lidar system.</sec>","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135400417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
None Xiao You-Peng, None Wang Huai-Ping, None Feng Lin
One of the research hotspots in thin film solar cell technology is to seek the suitable absorber layer materials to replace cadmium telluride and copper indium gallium selenium. Recently, germanium selenide (GeSe) with excellent photoelectric property has entered the field of vision of photovoltaic researchers. The main factors affecting the performance of heterojunction solar cell are the material properties of each functional layer, the device configuration, and the interface characteristics at the heterostructure. In this study, we exploited GeSe as the absorber layer, assembled with stable TiO2 as electron transport layer and Cu2O as hole transport layer, respectively, to construct a heterojunction solar cell with the FTO/TiO2/GeSe/Cu2O/Metal structure. The TiO2 and Cu2O can form small spike-like conduction band offset and valence band offset with the absorber layer, respectively, which do not hinder majority carrier transport but can effectively suppress carrier recombination at the heterointerface. Subsequently, the wxAMPS software was used to simulate and analyze the effects of functional layer material parameters, heterointerface characteristics, and operating temperature on the performance parameters of the proposed solar cell. Considering the practical application, the relevant material parameters were selected carefully. After optimization, at 300 K, the proposed GeSe heterojunction solar cell has reached an open circuit voltage of 0.752 V, a short circuit current of 40.71 mAcm-2, a filling factor of 82.89%, and a conversion efficiency of 25.39%. The results anticipate that the GeSe based heterojunction solar cell with a structure of FTO/TiO2/GeSe/Cu2O/Au have the potential to become a high-efficiency, low toxicity, and low-cost photovoltaic device. Simulation analysis also provides some reference for the design and preparation of heterojunction solar cell.
{"title":"Numerical simulation of Germanium selenide heterojunction solar cell","authors":"None Xiao You-Peng, None Wang Huai-Ping, None Feng Lin","doi":"10.7498/aps.72.20231220","DOIUrl":"https://doi.org/10.7498/aps.72.20231220","url":null,"abstract":"One of the research hotspots in thin film solar cell technology is to seek the suitable absorber layer materials to replace cadmium telluride and copper indium gallium selenium. Recently, germanium selenide (GeSe) with excellent photoelectric property has entered the field of vision of photovoltaic researchers. The main factors affecting the performance of heterojunction solar cell are the material properties of each functional layer, the device configuration, and the interface characteristics at the heterostructure. In this study, we exploited GeSe as the absorber layer, assembled with stable TiO<sub>2</sub> as electron transport layer and Cu<sub>2</sub>O as hole transport layer, respectively, to construct a heterojunction solar cell with the FTO/TiO<sub>2</sub>/GeSe/Cu<sub>2</sub>O/Metal structure. The TiO<sub>2</sub> and Cu<sub>2</sub>O can form small spike-like conduction band offset and valence band offset with the absorber layer, respectively, which do not hinder majority carrier transport but can effectively suppress carrier recombination at the heterointerface. Subsequently, the wxAMPS software was used to simulate and analyze the effects of functional layer material parameters, heterointerface characteristics, and operating temperature on the performance parameters of the proposed solar cell. Considering the practical application, the relevant material parameters were selected carefully. After optimization, at 300 K, the proposed GeSe heterojunction solar cell has reached an open circuit voltage of 0.752 V, a short circuit current of 40.71 mAcm<sup>-2</sup>, a filling factor of 82.89%, and a conversion efficiency of 25.39%. The results anticipate that the GeSe based heterojunction solar cell with a structure of FTO/TiO<sub>2</sub>/GeSe/Cu<sub>2</sub>O/Au have the potential to become a high-efficiency, low toxicity, and low-cost photovoltaic device. Simulation analysis also provides some reference for the design and preparation of heterojunction solar cell.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135400649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The substantial undercooling and rapid solidification of liquid quinary Zr57Cu20Al10Ni8Ti5 alloy are achieved by electromagnetic levitation (EML) technique. The amorphous solidification mechanism is revealed with molecular dynamics (MD) simulation. It is observed in EML experiment that the containerlessly solidified alloy is characterized by a core-shell structure, with mainly amorphous phase becoming the core and crystalline ZrCu, Zr2Cu and Zr8Cu5 phases forming the shell. The volume fraction of amorphous core structure increases with undercooling and attains a value up to 81.3% at the maximum experimental undercooling of 300 K, which indicates that the critical undercooling required for complete amorphous solidification is 334 K. TEM analyses show that the alloy microstructure is mainly composed of Zr8Cu5 phase, whereas the ZrCu phase and Zr2Cu phase are suppressed when liquid undercooling approaches this threshold. Once the critical undercooling is reached, amorphous solidification prevails over the crystallization of Zr8Cu5 phase. In addition, a small quantity of amorphous phases are found in the crystalline shell and a little trace of Zr8Cu5 nano-cluster is detected among the amorphous core. It is further verified by MD simulation that the formation of amorphous phase in the shell is caused by the microsegregation-induced solutal undercooling when liquid alloy attains the critical undercooling, while the nano-clusters within the core is mainly ascribed to the micro-thermal fluctuation effect inside highly undercooled liquid phase.
{"title":"Microscopic structure evolution and amorphous solidification mechanism of liquid quinary Zr<sub>57</sub>Cu<sub>20</sub>Al<sub>10</sub>Ni<sub>8</sub>Ti<sub>5</sub> Alloy","authors":"None Xu Shan-Sen, None Chang Jian, None Zhai Bin, None Zhu Xiannian, None Wei Bing-Bo","doi":"10.7498/aps.72.20231169","DOIUrl":"https://doi.org/10.7498/aps.72.20231169","url":null,"abstract":"The substantial undercooling and rapid solidification of liquid quinary Zr<sub>57</sub>Cu<sub>20</sub>Al<sub>10</sub>Ni<sub>8</sub>Ti<sub>5</sub> alloy are achieved by electromagnetic levitation (EML) technique. The amorphous solidification mechanism is revealed with molecular dynamics (MD) simulation. It is observed in EML experiment that the containerlessly solidified alloy is characterized by a core-shell structure, with mainly amorphous phase becoming the core and crystalline ZrCu, Zr<sub>2</sub>Cu and Zr<sub>8</sub>Cu<sub>5</sub> phases forming the shell. The volume fraction of amorphous core structure increases with undercooling and attains a value up to 81.3% at the maximum experimental undercooling of 300 K, which indicates that the critical undercooling required for complete amorphous solidification is 334 K. TEM analyses show that the alloy microstructure is mainly composed of Zr<sub>8</sub>Cu<sub>5</sub> phase, whereas the ZrCu phase and Zr<sub>2</sub>Cu phase are suppressed when liquid undercooling approaches this threshold. Once the critical undercooling is reached, amorphous solidification prevails over the crystallization of Zr<sub>8</sub>Cu<sub>5</sub> phase. In addition, a small quantity of amorphous phases are found in the crystalline shell and a little trace of Zr<sub>8</sub>Cu<sub>5</sub> nano-cluster is detected among the amorphous core. It is further verified by MD simulation that the formation of amorphous phase in the shell is caused by the microsegregation-induced solutal undercooling when liquid alloy attains the critical undercooling, while the nano-clusters within the core is mainly ascribed to the micro-thermal fluctuation effect inside highly undercooled liquid phase.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135401843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
None Shi Liang-Zhu, None Zhang Meng, None Chu Yu-Xi, None Liu Bo-Wen, None Hu Ming-Lie
Deep ultraviolet (DUV) femtosecond laser combines the advantages of high single-photon energy of DUV laser and high peak power of femtosecond laser, which is widely used in scientific research, biomedicine, material processing and so on. However, there is a problem in the process of generating DUV femtosecond laser based on nonlinear frequency conversion which the group velocity mismatch caused by dispersion will make the temporal walk-off of the nonlinear frequency conversion larger than the pulse duration of the femtosecond laser, which makes the generation of the DUV femtosecond laser very difficult. In this paper,based on a Yb-doped fiber femtosecond laser, the delay line was optimized to precisely compensate the spatial and temporal walk-off, so DUV femtosecond laser with a center wavelength of 206 nm and a repetition rate of 1 MHz is obtained, whose maximum output power is 102 mW. The maximum conversion efficiency is 4.25% from near infrared to DUV. The RMS power stability is 0.88% within 3 hours, and the peak-to-peak power stability is 3.75%. The evolution of laser spectra and beam quality during the process of second harmonic generation (SHG), FHG and SFG has been systematically studied. The experiment results provide a basis for the generation of DUV femtosecond laser from femtosecond fiber lasers.
{"title":"206 nm deep ultraviolet laser from fifth harmonic generation of femtosecond fiber laser","authors":"None Shi Liang-Zhu, None Zhang Meng, None Chu Yu-Xi, None Liu Bo-Wen, None Hu Ming-Lie","doi":"10.7498/aps.72.20230877","DOIUrl":"https://doi.org/10.7498/aps.72.20230877","url":null,"abstract":"Deep ultraviolet (DUV) femtosecond laser combines the advantages of high single-photon energy of DUV laser and high peak power of femtosecond laser, which is widely used in scientific research, biomedicine, material processing and so on. However, there is a problem in the process of generating DUV femtosecond laser based on nonlinear frequency conversion which the group velocity mismatch caused by dispersion will make the temporal walk-off of the nonlinear frequency conversion larger than the pulse duration of the femtosecond laser, which makes the generation of the DUV femtosecond laser very difficult. In this paper,based on a Yb-doped fiber femtosecond laser, the delay line was optimized to precisely compensate the spatial and temporal walk-off, so DUV femtosecond laser with a center wavelength of 206 nm and a repetition rate of 1 MHz is obtained, whose maximum output power is 102 mW. The maximum conversion efficiency is 4.25% from near infrared to DUV. The RMS power stability is 0.88% within 3 hours, and the peak-to-peak power stability is 3.75%. The evolution of laser spectra and beam quality during the process of second harmonic generation (SHG), FHG and SFG has been systematically studied. The experiment results provide a basis for the generation of DUV femtosecond laser from femtosecond fiber lasers.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135402172","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Protein function is related to its structure and dynamics. Molecular dynamics simulation is an important tool in the study of protein dynamics by exploring its conformational space, however, conformational sampling is a nontrivial issue, since the risk of missing key details due to under-sampling. In recent years, deep learning methods, such as auto-encoder, can couple with MD to explore conformational space of proteins. After training with the MD trajectories, auto-encoder can generate new conformations quickly by inputting random numbers in low dimension space. However, some issues still remain, such as requirements for the quality of the training set, the limitation of explorable area and the undefined sampling direction. In this work, we have built a supervised auto-encoder, in which some reaction coordinates are used to guide conformational exploration alone certain directions. We have also tried expanding the explorable area by training with the data generated by the model. Two multi-domain proteins, bacteriophage T4 lysozyme and adenylate kinase, were used to illustrate the method. In the case of the training set consisting of only under-sampled simulated trajectories, the supervised auto-encoder can still explore alone the given reaction coordinates. The explored conformational space can cover all the experimental structures of the proteins and be extended to regions far from the training sets. Having been verified by molecular dynamics and secondary structure calculations, most of the conformations explored were found to be plausible. The supervised auto-encoder provides a way to efficiently expand the conformational space of a protein with limited computational resources, although some suitable reaction coordinates is required. By integrate appropriate reaction coordinates or experimental data, the supervised auto-encoder may serve as an efficient tool for exploring conformational space of proteins.
{"title":"Explore Conformational Space of Proteins with Supervised Auto-Encoder","authors":"None Chen Guanglin, None Zhang Zhiyong","doi":"10.7498/aps.72.20231060","DOIUrl":"https://doi.org/10.7498/aps.72.20231060","url":null,"abstract":"Protein function is related to its structure and dynamics. Molecular dynamics simulation is an important tool in the study of protein dynamics by exploring its conformational space, however, conformational sampling is a nontrivial issue, since the risk of missing key details due to under-sampling. In recent years, deep learning methods, such as auto-encoder, can couple with MD to explore conformational space of proteins. After training with the MD trajectories, auto-encoder can generate new conformations quickly by inputting random numbers in low dimension space. However, some issues still remain, such as requirements for the quality of the training set, the limitation of explorable area and the undefined sampling direction. In this work, we have built a supervised auto-encoder, in which some reaction coordinates are used to guide conformational exploration alone certain directions. We have also tried expanding the explorable area by training with the data generated by the model. Two multi-domain proteins, bacteriophage T4 lysozyme and adenylate kinase, were used to illustrate the method. In the case of the training set consisting of only under-sampled simulated trajectories, the supervised auto-encoder can still explore alone the given reaction coordinates. The explored conformational space can cover all the experimental structures of the proteins and be extended to regions far from the training sets. Having been verified by molecular dynamics and secondary structure calculations, most of the conformations explored were found to be plausible. The supervised auto-encoder provides a way to efficiently expand the conformational space of a protein with limited computational resources, although some suitable reaction coordinates is required. By integrate appropriate reaction coordinates or experimental data, the supervised auto-encoder may serve as an efficient tool for exploring conformational space of proteins.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135402200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dong-Bin Jiang, Ying Zhang, Da-Peng Jiang, Bin Zhu, Gang Li, Li Sun, Zheng Huang, Feng Lu, Na Xie, Kai-Nan Zhou, Jing-Qin Su
Spectral gain narrowing is one of the key factors affecting broadband amplification of ultrashort pulses. In this paper, the spectral gain characteristics in broadband amplification are studied theoretically and experimentally by using the characteristic of Nd,Gd:SrF2 crystal, i.e. the emission spectrum that has a certain width at the higher stimulated emission cross section. Through the numerical simulation, the evolution law of output spectrum of the laser gain medium under different spectral gain lineshapes and different gain values is studied in detail. Theoretical calculation shows that the spectral gain is narrowed obviously with the increase of gain value of the traditional Gaussian emission spectrum, and that increasing the spectral bandwidth at the maximum stimulated emission cross section can obviously suppress the spectral gain narrowing. Furthermore, the spectral gain narrowing characteristics of the Nd,Gd:SrF2 crystal are studied experimentally. A Ф 13 mm×150 mm Nd,Gd:SrF2 crystal is used as the gain medium which is pumped by flash lamps in the experimental study. The experimental results show that the output spectra of Nd,Gd:SrF2 crystals are not obviously narrowed when the full width at half maximum (FWHM) of spectral width of the input laser is 5 nm and the gain is 140 times. The experimental results are consistent with the theoretical calculation and analysis. The crystal can work normally at a repetition rate of 0.2 Hz and 1.0 Hz in the experiment, but due to the influence of thermal effect, the gain will decrease to a certain extent with the increase of pump energy and repetition rate. The research results lay the foundation for the application of fluoride crystal in broadband chirped pulse amplification.
{"title":"Nd, Gd:SrF<sub>2</sub> crystal spectrum gain characteristic in broadband laser amplification","authors":"Dong-Bin Jiang, Ying Zhang, Da-Peng Jiang, Bin Zhu, Gang Li, Li Sun, Zheng Huang, Feng Lu, Na Xie, Kai-Nan Zhou, Jing-Qin Su","doi":"10.7498/aps.72.20230972","DOIUrl":"https://doi.org/10.7498/aps.72.20230972","url":null,"abstract":"Spectral gain narrowing is one of the key factors affecting broadband amplification of ultrashort pulses. In this paper, the spectral gain characteristics in broadband amplification are studied theoretically and experimentally by using the characteristic of Nd,Gd:SrF<sub>2</sub> crystal, i.e. the emission spectrum that has a certain width at the higher stimulated emission cross section. Through the numerical simulation, the evolution law of output spectrum of the laser gain medium under different spectral gain lineshapes and different gain values is studied in detail. Theoretical calculation shows that the spectral gain is narrowed obviously with the increase of gain value of the traditional Gaussian emission spectrum, and that increasing the spectral bandwidth at the maximum stimulated emission cross section can obviously suppress the spectral gain narrowing. Furthermore, the spectral gain narrowing characteristics of the Nd,Gd:SrF<sub>2</sub> crystal are studied experimentally. A <i>Ф</i> 13 mm×150 mm Nd,Gd:SrF<sub>2</sub> crystal is used as the gain medium which is pumped by flash lamps in the experimental study. The experimental results show that the output spectra of Nd,Gd:SrF<sub>2</sub> crystals are not obviously narrowed when the full width at half maximum (FWHM) of spectral width of the input laser is 5 nm and the gain is 140 times. The experimental results are consistent with the theoretical calculation and analysis. The crystal can work normally at a repetition rate of 0.2 Hz and 1.0 Hz in the experiment, but due to the influence of thermal effect, the gain will decrease to a certain extent with the increase of pump energy and repetition rate. The research results lay the foundation for the application of fluoride crystal in broadband chirped pulse amplification.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135508550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
None Wang Long, None Wang Liu-Ying, None Liu Gu, None Tang Xiu-Jian, None Ge Chao-Qun, None Wang Bin, None Xu Ke-Jun, None Wang Xin-Jun
Multi-spectral compatible stealth materials become an imperative development trend, especially visible and infrared compatible stealth materials have become a top priority in the field of optoelectronic stealth technology. However, the demands of infrared stealth and visible stealth on spectral response are different, which makes it difficult to reconcile the design of functional coupling materials. Therefore, it is crucial to develop selective control technology of optical characteristics. A visible and infrared compatible stealth superstructure thin film is proposed based on the FTO/Ag/FTO stacked film structure. A collaborative design method for high visible transmission and low infrared radiation is established, and the mechanism of microstructure characteristics affecting visible transmission and infrared reflection spectra is explained. The highly transparent infrared stealth thin film is optimized, and its compatibility stealth performance is tested and characterized through the use of visible transmission spectroscopy, infrared reflection spectroscopy, and thermal imaging characterization techniques. It has shown that visible transmission depends on the coupling and matching effect between the semiconductor dielectric layer and the metal layer, while infrared radiation suppression mainly depends on the metal layer. As the thickness of FTO film increases, the visible transmission peak undergoes a red shift, leading to a flattening of the transmission spectrum curve, the average transmission first increases and then gradually decreases. As the thickness of Ag thin film layer increases, the transmission peak of visible undergoes a blue shift, causing the transmission spectrum curve to tend a high-frequency transmission state, narrowing the frequency domain of visible transmission and gradually decreasing the average transmittance. At the same time, the infrared reflectance increases with the increase of Ag film thickness, but the change amplitude significantly decreases when the Ag film thickness is greater than 18 nm. When the thickness of the optimized FTO/Ag/FTO film structure is 40/12/40 nm, it has a high level of background perspective reproduction and high-temperature infrared radiation suppression ability. The average transmittance of 0.38~0.78 μm visible light band is 82.52%, and the average reflectance of 3~14 μm mid-far infrared band is 81.46%. The radiation temperature of the sample is 49 ℃ and 75.8 ℃ lower in mid infrared and far infrared than that of the quartz sheet at 150 ℃, respectively. The new stealth film can be attached to the camouflage coating surface of special vehicles to achieve visible and infrared compatible stealth, and can be used for cockpit windows to ensure thermal insulation, temperature control, and infrared stealth without affecting the field of view. This study can provide a new approach for the design and application of visible and infrared compatible stealth materials.
{"title":"Design of high transparent infrared stealth thin films based on FTO/Ag/FTO structure","authors":"None Wang Long, None Wang Liu-Ying, None Liu Gu, None Tang Xiu-Jian, None Ge Chao-Qun, None Wang Bin, None Xu Ke-Jun, None Wang Xin-Jun","doi":"10.7498/aps.72.20231084","DOIUrl":"https://doi.org/10.7498/aps.72.20231084","url":null,"abstract":"Multi-spectral compatible stealth materials become an imperative development trend, especially visible and infrared compatible stealth materials have become a top priority in the field of optoelectronic stealth technology. However, the demands of infrared stealth and visible stealth on spectral response are different, which makes it difficult to reconcile the design of functional coupling materials. Therefore, it is crucial to develop selective control technology of optical characteristics. A visible and infrared compatible stealth superstructure thin film is proposed based on the FTO/Ag/FTO stacked film structure. A collaborative design method for high visible transmission and low infrared radiation is established, and the mechanism of microstructure characteristics affecting visible transmission and infrared reflection spectra is explained. The highly transparent infrared stealth thin film is optimized, and its compatibility stealth performance is tested and characterized through the use of visible transmission spectroscopy, infrared reflection spectroscopy, and thermal imaging characterization techniques. It has shown that visible transmission depends on the coupling and matching effect between the semiconductor dielectric layer and the metal layer, while infrared radiation suppression mainly depends on the metal layer. As the thickness of FTO film increases, the visible transmission peak undergoes a red shift, leading to a flattening of the transmission spectrum curve, the average transmission first increases and then gradually decreases. As the thickness of Ag thin film layer increases, the transmission peak of visible undergoes a blue shift, causing the transmission spectrum curve to tend a high-frequency transmission state, narrowing the frequency domain of visible transmission and gradually decreasing the average transmittance. At the same time, the infrared reflectance increases with the increase of Ag film thickness, but the change amplitude significantly decreases when the Ag film thickness is greater than 18 nm. When the thickness of the optimized FTO/Ag/FTO film structure is 40/12/40 nm, it has a high level of background perspective reproduction and high-temperature infrared radiation suppression ability. The average transmittance of 0.38~0.78 μm visible light band is 82.52%, and the average reflectance of 3~14 μm mid-far infrared band is 81.46%. The radiation temperature of the sample is 49 ℃ and 75.8 ℃ lower in mid infrared and far infrared than that of the quartz sheet at 150 ℃, respectively. The new stealth film can be attached to the camouflage coating surface of special vehicles to achieve visible and infrared compatible stealth, and can be used for cockpit windows to ensure thermal insulation, temperature control, and infrared stealth without affecting the field of view. This study can provide a new approach for the design and application of visible and infrared compatible stealth materials.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135550323","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
None Li Xin, None Zeng Ming, None Liu Hui, None Ning Zhong-Xi, None Yu Da-Ren
With the rapid development of commercial space in recent years, the low-power and low-cost propulsion systems are needed more and more urgently. Compared with conventional chemical propulsion, electric propulsion has a higher specific impulse. Compared with the conventional xenon propellant, iodine propellant that does not require high pressure storage, is cheap and close to the relative atomic mass and ionization energy of xenon. Electron cyclotron resonance source has the advantages of no internal electrode, low pressure ionization, high plasma density and compact structure, which is suitable for low power electric propulsion. Therefore, the study of low power iodine propellant electron cyclotron resonance plasma source is of great significance. In this study, a set of corrosion-resistant feed system with balanced and stable output of iodine vapor is designed. Then the iodine-corrosion-resistant electron cyclotron resonance thruster is designed completely. A corrosion-resistant coaxial cavity structure is used to feed the microwave to the thruster, and the channel magnetic field is changed into a cusped field to generate more electron cyclotron resonance (ECR) layers. Finally, the combined ignition experiment is successfully conducted, showing the first plasma source using electron cyclotron resonance to ionize iodine propellant that can be used for electric propulsion in the world. The analyses of experiments, static magnetic field, microwave electric field distribution show that the unstable plasma plume scintillation at low power and low flow is caused by the conversion between ordinary wave electron plasmon resonance heating mode and extraordinary wave electron cyclotron resonance heating mode. The decrease of ionization rate at a high flow rate is caused by electron loss, wall loss and electronegativity of iodine propellant. Based on this principle, an improvement scheme is proposed. The plasma source has no obvious damage after discharge, which indicates that it has the potential of long life. This work preliminarily proves that the low power electron cyclotron resonance electric propulsion scheme of low power iodine propellant is feasible.
{"title":"Iodine Electron Cyclotron Resonance Plasma Source for Electric Propulsion","authors":"None Li Xin, None Zeng Ming, None Liu Hui, None Ning Zhong-Xi, None Yu Da-Ren","doi":"10.7498/aps.72.20230785","DOIUrl":"https://doi.org/10.7498/aps.72.20230785","url":null,"abstract":"With the rapid development of commercial space in recent years, the low-power and low-cost propulsion systems are needed more and more urgently. Compared with conventional chemical propulsion, electric propulsion has a higher specific impulse. Compared with the conventional xenon propellant, iodine propellant that does not require high pressure storage, is cheap and close to the relative atomic mass and ionization energy of xenon. Electron cyclotron resonance source has the advantages of no internal electrode, low pressure ionization, high plasma density and compact structure, which is suitable for low power electric propulsion. Therefore, the study of low power iodine propellant electron cyclotron resonance plasma source is of great significance. In this study, a set of corrosion-resistant feed system with balanced and stable output of iodine vapor is designed. Then the iodine-corrosion-resistant electron cyclotron resonance thruster is designed completely. A corrosion-resistant coaxial cavity structure is used to feed the microwave to the thruster, and the channel magnetic field is changed into a cusped field to generate more electron cyclotron resonance (ECR) layers. Finally, the combined ignition experiment is successfully conducted, showing the first plasma source using electron cyclotron resonance to ionize iodine propellant that can be used for electric propulsion in the world. The analyses of experiments, static magnetic field, microwave electric field distribution show that the unstable plasma plume scintillation at low power and low flow is caused by the conversion between ordinary wave electron plasmon resonance heating mode and extraordinary wave electron cyclotron resonance heating mode. The decrease of ionization rate at a high flow rate is caused by electron loss, wall loss and electronegativity of iodine propellant. Based on this principle, an improvement scheme is proposed. The plasma source has no obvious damage after discharge, which indicates that it has the potential of long life. This work preliminarily proves that the low power electron cyclotron resonance electric propulsion scheme of low power iodine propellant is feasible.","PeriodicalId":10252,"journal":{"name":"Chinese Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135401004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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