Journals >Acta Photonica Sinica
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2021
Volume: 50 Issue 6
25 Article(s)
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Efficient Processing of Super-hydrophobic Biomimetic Structures on Stainless Steel Surfaces by Spatiotemporal Interference of Two Femtosecond Laser Beams Based on Spatial Light Modulator
Hui SHI, Yuhan LIN, Tianqing JIA, Kaiqiang CAO, Yuchan ZHANG, Ruozhong HAN, and Zhenrong SUN
The femtosecond laser spatiotemporal interference method based on spatial light modulator is developed. By changing the 800 nm femtosecond laser fluence and the cumulative pulse number， the 5 mm×5 mm two-scale biomimetic shark skin surface micro-nano structures were processed on 316 mirror stainless steel with higThe femtosecond laser spatiotemporal interference method based on spatial light modulator is developed. By changing the 800 nm femtosecond laser fluence and the cumulative pulse number， the 5 mm×5 mm two-scale biomimetic shark skin surface micro-nano structures were processed on 316 mirror stainless steel with high efficiency and quality. The wettability of the structures fabricated with different laser parameters were also analyzed. When the laser fluence is 1.37 J/cm2 and the cumulative pulse number is 30~40， the carbon content on the surface of stainless steel increases by up to 13.22%， and the wettability of which is changed from hydrophilic （contact angle is 88°） to super-hydrophobic. The water contact angle is as high as 165°. In this study， a flexible and efficient femtosecond laser spatiotemporal interference method is developed to obtain a stable super-hydrophobic surface， which provides a new idea for the processing of biomimetic structures..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 91 (2021)
Highly Efficient Fabrication of Superhydrophilic Structures on Silicon Surface by the Interference of Two Femtosecond Laser Beams
Yanli LI, Xin JIA, Kaiqiang CAO, Fengzhuo ZHANG, Long CHEN, and Tianqing JIA
Hybrid micro/nanostructures with an area of 10 mm×10 mm are fabricated in 30 s by using the two-beam interference of femtosecond laser combined with the cylindrical lens line scanning technique， which greatly improved the laser processing efficiency. The silicon surface structures contain long-periodic microstructHybrid micro/nanostructures with an area of 10 mm×10 mm are fabricated in 30 s by using the two-beam interference of femtosecond laser combined with the cylindrical lens line scanning technique， which greatly improved the laser processing efficiency. The silicon surface structures contain long-periodic microstructures determined by two-beam interference and the periodic nanostructures induced by femtosecond laser. The hybrid micro/nanostructures greatly improve the surface roughness. Under the effect of capillarity， the ablated silicon surface shows superhydrophilicity in air， and the contact angle drops from 40° to 0°. The X-ray photoelectron spectra of the silicon surface shows that the content of Si-OH and H2O molecules increases by 22.3% and 13.6%， respectively， which further improves the hydrophilicity of silicon surface. With the increase of laser fluence and the decrease of scanning speed， the contact angle of the ablated silicon surface decreases gradually. This provides a new method for the efficient fabrication of large-area superhydrophilic structures， and has potential applications in the fields of heat conduction， biochip， etc..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 100 (2021)
Atomic and Molecular Physics
Power Frequency Electric Field Measurement Based on Electromagnetic Induced Transparent Spectrum under Radio Frequency Field
Chungang ZHANG, Wei LI, Hao ZHANG, Mingyong JING, and Linjie ZHANG
The two-photon （852 nm and 509 nm） excitation was used to achieve the preparation of the 53S1/2 Rydberg state of cesium atoms. The electromagnetically induced transparency spectrum of Rydberg atoms in which the radio frequency electric fields in the AC Stark effect was studied. By changing the amplitude of the radio frThe two-photon （852 nm and 509 nm） excitation was used to achieve the preparation of the 53S1/2 Rydberg state of cesium atoms. The electromagnetically induced transparency spectrum of Rydberg atoms in which the radio frequency electric fields in the AC Stark effect was studied. By changing the amplitude of the radio frequency electric fields， the dependance of the Stark frequency shift of Rydberg atoms on the amplitude of the electric field was investigated. In the experiments， the power frequency electric fields were modulated to the radio frequency electric fields. The traceable measurement of the field strength of the power frequency electric field was realized. The field strength sensitivity can reach 0.37 V/cm， and the amplitude measurement dynamic range can reaches 37.2 dB. Moreover， the frequency measurement of power frequency electric fields is demonstrated， and the uncertainty of frequency measurement is smaller than 0.1%..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 154 (2021)
Control of Polarization States of Atomic High-order Harmonic Generation
Zhijiang LI, Guoli WANG, Zhihong JIAO, Xiaoyong LI, and Xiaoxin ZHOU
The polarization of high-order harmonics radiated from He driven by counter-rotating two-color laser field， which consists of a elliptically polarized fundamental field and its counter-rotating circular third harmonic pulse， are investigated by numerically solving the two-dimensional time-dependent Schrödinger equThe polarization of high-order harmonics radiated from He driven by counter-rotating two-color laser field， which consists of a elliptically polarized fundamental field and its counter-rotating circular third harmonic pulse， are investigated by numerically solving the two-dimensional time-dependent Schrödinger equation with split operator method. The simulations show that the polarization state of harmonics can be fully controlled from circular polarization， through elliptically， to linearly polarized harmonics， by adjusting the ellipticity， intensity and phase of the fundamental field. This research is helpful for the generation of extreme utilityvehicle and X-ray sources with controllable polarization states in the experiment..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 161 (2021)
Image Processing
An Evaluation Method of Optical Camouflage Effect Based on Contour Deformation Degree
Jun YU, Haoyang LIU, Yunhui ZHANG, Zhiyi HU, and Miao CHU
Aiming at the problem of target contour deformation in the effect evaluation of optical camouflage， this paper proposes a binary statistical moment algorithm based on contour deformation degree. Firstly， the original background image of a camouflage target is binarized， followed that the background image is evenly segmAiming at the problem of target contour deformation in the effect evaluation of optical camouflage， this paper proposes a binary statistical moment algorithm based on contour deformation degree. Firstly， the original background image of a camouflage target is binarized， followed that the background image is evenly segmented， and then the contour features of the target are extracted， so that a binary statistical matrix of the contour feature vector is constructed. Finally， both the Euclidean distance and Cosine normalization are adopted to calculate the binary statistical moment， so as to obtain the contour deformation degree of the target. The experimental results show that， the proposed algorithm can effectively extract the contour features of the target； the contour deformation index reaches 0.905±0.004 and 0.77±0.80； compared with the traditional Hu moment algorithm， the principal component factor is increased by 27% and 7% respectively， and the algorithm efficiency is improved by 69.8%. The optical camouflage effect can be effectively evaluated from the perspective of the target contour..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 188 (2021)
Combining MRF Energy and DCE-MRI Time-domain Features for Breast Tumors Segmentation Algorithm
Haoyang ZHOU, Bao FENG, Feifei QI, Zhuangsheng LIU, and Wansheng LONG
To solve the low contrast， blurred boundry and intensity inhomogeous of the breast cancer lesions in the dynamic contrast-enhanced magnetic resonance imaging images， an integrated active contour model is proposed by combining markov random field energy with time-domain features. First， the edge-stop function of active To solve the low contrast， blurred boundry and intensity inhomogeous of the breast cancer lesions in the dynamic contrast-enhanced magnetic resonance imaging images， an integrated active contour model is proposed by combining markov random field energy with time-domain features. First， the edge-stop function of active contour model is derived from a fuzzy c-means cluster which treat the intensity and variation of time-domain as the feature. Then， markov random field energy is constructed to improve the difference between the lesions and other tissues. Finally， the region term is derived from k-nearest neighbor method which treat markov random field energy as dataset. The evolution of the contour curve stops at the boundary of lesions， and the energy function constructed by region term and edge term is minimized.The experiment proved that markov random field energy and time-domain feature can improve the contrast between the breast tumours and other tissues. Compared with state of the art of active contours models， the result segmented by the proposed method is more similar to the artificial segmentation， so that the proposed method is meaningful for breast cancer segmentation..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 197 (2021)
Introduction for Special Issue
[in Chinese]
Hongbo SUN, and Qidai CHEN
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 1 (2021)
Lasers and Laser Optics
Experimental Research on High Power Cascade Co-pumping Erbium-Ytterbium Co-doped Fiber Laser
Dan WANG, Qun HAN, Panpan NIU, and Tiegen LIU
The amplified spontaneous emission in the Yb band and thermal effect are the main obstacles to the power scaling of high-power Er/Yb-codoped fiber lasers. In order to obtain a high-power and high-efficiency fiber laser， a liquid cooling structure and the cascade co-pumping method are used to carry out experimental reseThe amplified spontaneous emission in the Yb band and thermal effect are the main obstacles to the power scaling of high-power Er/Yb-codoped fiber lasers. In order to obtain a high-power and high-efficiency fiber laser， a liquid cooling structure and the cascade co-pumping method are used to carry out experimental research on the erbium-ytterbium co-doped fiber laser. The results show that by using a 2.1 m large core diameter erbium-ytterbium co-doped fiber， a maximum output of 21.6 W at 1 548.9 nm is obtained with a pump power of 47.5 W， and the pump conversion efficiency is 45.7%. The slope efficiency before and after the Yb band oscillation is established are 48.4% and 56.2%， respectively..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 138 (2021)
Study on Optical Force Characteristics of Triangular Metal Nanoparticles
Xiaolei WANG, Guangke JIANG, Yuxin DONG, Siliang LIU, Liping GONG, Jiehui ZHAO, Zhuqing ZHU, and Bing GU
Based on Maxwell's stress tensor theory， the photodynamic properties of polygonal gold nanoparticles in a focused field were studied. Taking triangular gold nanoparticles as an example， the trapping characteristics of triangular gold nanoparticles in focusing field with circular symmetric energy distribution and wiBased on Maxwell's stress tensor theory， the photodynamic properties of polygonal gold nanoparticles in a focused field were studied. Taking triangular gold nanoparticles as an example， the trapping characteristics of triangular gold nanoparticles in focusing field with circular symmetric energy distribution and with triangular energy distribution were studied respectively from the stress conditions of the particles in the focusing field. The results show that the triangular gold nanoparticles with side length of 50~350 nm can be stably captured by using the circular symmetric focusing field. When the triangular focusing field is used， the triangular gold nanoparticles with side length of 100~350 nm can be stably captured under the condition that the particles enter the focusing field at an angle matching the shape of the focusing field. The trapping properties of triangular gold nanoparticles were compared between the circular symmetric focusing field and the triangular focusing field， and we found that the trapping force of the triangular focusing field in the x direction was stronger than that of the circular symmetric focusing field. In the y direction， the capturing range of the triangular focusing field is larger than that of the circular symmetric focusing field. In this work， we studied the optical trapping properties of triangular metal nanoparticles in different focused fields， and laid a theoretical foundation for the application of optical manipulation based on non-spherical metal particles in Raman super-resolution imaging， particle micro-processing and other fields..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 144 (2021)
Optical Devices
A Planar Artificial Compound Eye Based on Metalens Array
Li ZHOU, Xiaohu ZHANG, Xiaogang LIN, Chao GAO, and Yongcai GUO
In order to realize an optical imaging system with light-weight， integration and large field of view， a planar artificial compound eye structure based on the utilization of a metalens array is proposed. It uses TiO2 nanopillars with different orientation angles to manipulate the electro-magnetic wave based on the gromeIn order to realize an optical imaging system with light-weight， integration and large field of view， a planar artificial compound eye structure based on the utilization of a metalens array is proposed. It uses TiO2 nanopillars with different orientation angles to manipulate the electro-magnetic wave based on the grometric phase principles. It makes the surface of the metalens array and the image plane both planar， and does not need the non-spherical processing required by the traditional curved compound eyes. With the superposition of the off-axis phase onto the traditional matalens’ focusing phase， the effect produced by the illumination of the non-paraxial light beams on the imaging quality is effectively canceled and a large field of view is achieved. The designed compound eye is mainly composed of an array of 11×11 metalenses. It has the size of the 165 μm×165 μm and overall height of 18.6 μm， with the field of view of 140°×140°. The simulation results indicates that the the proposed compound eye structure achieves good image quality even under the illumination at a large off-axis angle （50°）..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 168 (2021)
Performance Research and Fabrication of 1 310 nm Superluminescent Diodes with High Power
Tuo WANG, Hongmei CHEN, Huimin JIA, Zhonghui YAO, Dan FANG, Cheng JIANG, Ziyang ZHANG, Kexue LI, Jilong TANG, and Zhipeng WEI
In order to optimize the performance of the 1 310 nm superluminescent diode， such as increase the output power of the device. In this simulation， the parameters of waveguide structure， and the heat dissipation for 1 310 nm superluminescent diode with the J-type waveguide have been investigated. The research results shoIn order to optimize the performance of the 1 310 nm superluminescent diode， such as increase the output power of the device. In this simulation， the parameters of waveguide structure， and the heat dissipation for 1 310 nm superluminescent diode with the J-type waveguide have been investigated. The research results show that the waveguide etching depth， bending angle and thickness of the insulating layer were important for achieve high power output. Based on the research results， the superluminescent diode device structure and fabrication process were optimized， and J-type superluminescent diode with a ridge width of 5 μm， a bending angle of 8°， an etching depth of 1.7 μm and an insulating layer thickness of 300 nm was prepared. The superluminescent diode with 1.5 mm straight waveguide length has realized a high output power （42.2 mW） and wide bandwidth （10 nm） under 500 mA continuous-wave operation at room temperature..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 179 (2021)
Scattering
Regulation of Hierarchical Structure on Surface-enhanced Raman Scattering Characteristics of Nanoporous Metals
Ronghui CAI, Ruirui SONG, and Ling ZHANG
Hierarchical nanoporous materials with high-density "hot spots" were obtained by constructing secondary mesopores on the single-stage nanoporous metal ligaments. The finite difference time domain method was used to simulate the local electromagnetic field intensity and distribution of hierarchical nanoporous Hierarchical nanoporous materials with high-density "hot spots" were obtained by constructing secondary mesopores on the single-stage nanoporous metal ligaments. The finite difference time domain method was used to simulate the local electromagnetic field intensity and distribution of hierarchical nanoporous structures， and the SERS characteristics of dealloyed hierarchical nanoporous metals were detected with the help of Raman spectroscopy. Combined experimental results with theoretical analysis， it can be seen that the local electromagnetic field intensity and hot spots density of the hierarchical nanoporous metals are higher than that of the single-stage nanoporous metals， resulting in better SERS activity. The detection limit of hierarchical nanoporous gold and hierarchical nanoporous copper for crystal violet molecules can reach 10-11 mol·L-1， and the SERS enhancement factor is about two orders of magnitude higher than that of single-stage nanoporous metals. The study indicates that the introduction of secondary structure can greatly improve the local electromagnetic field intensity of single-stage nanoporous metals， which provides a new method for preparing of high-performance SERS substrate..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 217 (2021)
Special Issue for Ultrafast Laser Precision Machining of Hard and Brittle Materials
Femtosecond Laser Single-pass High Quality Direct Cutting Thin Quartz Glass Process Based on Filament Effect（Invited）
Kai LIAO, Wenjun WANG, Xuesong MEI, and Bin LIU
A one-step direct cutting method of 200 μm quartz glass using high-repetition frequency femtosecond laser combined with scanning galvanometer based on filament effect was proposed. Through the optimization of the processing process parameters， the fast and high-quality cutting of thin quartz glass is realized. The procA one-step direct cutting method of 200 μm quartz glass using high-repetition frequency femtosecond laser combined with scanning galvanometer based on filament effect was proposed. Through the optimization of the processing process parameters， the fast and high-quality cutting of thin quartz glass is realized. The processing speed can be achieved 10 mm/s， the edge chipping is less 7.5 μm， and the roughness of the cross section is achieved 1 μm. The method realizes the simultaneous improvement of thin glass cutting efficiency and quality， and has a good application prospect in the field of laser processing..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 3 (2021)
Advances in the Preparation of Functional Surfaces with Special Wettability by Femtosecond Laser Ablation（Invited）
Sizhu WU, Xiaodong LÜ, Chuanzong LI, Chenchu ZHANG, Jianquan LI, Yi XIAO, and Dong WU
Functional surfaces with special wettability have played an important role in society and our daily life. Meanwhile， femtosecond laser has become an important tool to prepare a special wetting surface because of its unique manufacturing advantages. This article discusses the method of fabricating various microstructureFunctional surfaces with special wettability have played an important role in society and our daily life. Meanwhile， femtosecond laser has become an important tool to prepare a special wetting surface because of its unique manufacturing advantages. This article discusses the method of fabricating various microstructures by femtosecond laser， that is based on the connection between biological surface microstructures in nature and their practical applications. Then， three aspects of the preparation of the surface with special wettability via femtosecond laser are reviewed which are the “Janus” surfaces， the smart response surperhydrophobic surfaces， and the slippery surfaces. By summarizing the research results of the surface with special wettability prepared by femtosecond laser， this review provides a reference for the research， application， and future research direction of special wetting surfaces using a femtosecond laser..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 15 (2021)
Femtosecond Laser Direct Writing for Polarization Convertors and Geometric Phase Elements（Invited）
Lei WANG, Yi WANG, Lin WANG, Shuai XU, Hua FAN, and Ligang NIU
There is a growing popularity of the miniaturization and integration of various optical elements. In particular， the meta-optics has attracted great interests by manupulating the electric-magnectic properties of materials. Herein， we reviewed the recent advances on the fabrication and characterization of polarization cThere is a growing popularity of the miniaturization and integration of various optical elements. In particular， the meta-optics has attracted great interests by manupulating the electric-magnectic properties of materials. Herein， we reviewed the recent advances on the fabrication and characterization of polarization convertors and geometric phase elements by femtosecond laser direct wirting. Firstly， the mechanism of meta-optics will provide. Then， we will review the fabrication technologies for meta-optics by femtseond laser direct writing in photoresist， laser ablation on metal film， and femtosecond laser-induced nanogratings in the bulk. Finally， we will comment on the challenges of femtosecond laser micro/nanotechnologies for meta-optics..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 38 (2021)
Temporal-spatial Dynamics of Femtosecond Time Resolved Plasma in Femtosecond Laser Induced Microstructure（Invited）
Fengqin HUANG, Tianlun SHEN, Jinhai SI, Tao CHEN, and Xun HOU
Temporal-spatial evolutions of transient plasma in single pulse femtosecond （fs） laser induced microstructure in fused silica were investigated using fs time-resolved pump-probe shadowgraphy. The relation between the spatial distribution of transient electron density and the distribution of fs laser-induced microstructTemporal-spatial evolutions of transient plasma in single pulse femtosecond （fs） laser induced microstructure in fused silica were investigated using fs time-resolved pump-probe shadowgraphy. The relation between the spatial distribution of transient electron density and the distribution of fs laser-induced microstructure in fused silica were also studied. In this study， the fs laser was focused by two kinds of microscope objectives with different Numerical Aperture （NA）. The results showed that the transient peak electron density indued by focused fs laser was increased and then decreased as delay time of probe beam increased. When the NA of the microscope objective was 0.45， the spatial position of transient peak electron density induced by fs laser did not moved as delay time increased， which basically kept at the nonlinear focus. The fs laser-induced microstructure in the sample was punctate. When the NA of the microscope objective was 0.3， the spatial position of transient peak electron density induced by fs laser moved from the sample surface to the inside of the sample as delay time increased. The fs laser-induced microstructure in the sample was long strips. In addition， we found that the spatial position of fs laser-induced maximum transient electron density was consistent with the position of laser-induced microstructure when fs laser was focused by the two different microscope objective. Those results imply that fs time-resolved pump-probe shadowgraphy may be used for online monitoring fs laser processing process， which can provide references for directional control of ultrafast laser-induced material microstructure and optimization of machining parameters..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 50 (2021)
Fabrication of Time Capsules by Femtosecond Laser-induced Birefringence（Invited）
Lin WANG, Hua FAN, Zhenze LI, Yi WANG, Yishi XU, Lei WANG, and Qidai CHEN
Femtosecond laser-induced birefringent voxels were explored by using birefringent microscope and optical microscope. It shows that the retardance increases as the pulse number increases. Two types of structures are found. Type X structures require at least 20 pulses and single pulse energy no more than 854 nJ. More， thFemtosecond laser-induced birefringent voxels were explored by using birefringent microscope and optical microscope. It shows that the retardance increases as the pulse number increases. Two types of structures are found. Type X structures require at least 20 pulses and single pulse energy no more than 854 nJ. More， the pulse duration must limited between 300 fs and 600 fs. Additionally， the data storage process is presented by taking Chinese characters of "Acta Photonica Sinica" as example. Time capsules containing the history of Jilin Province， the history of Jilin University， and the history of Tsinghua University are prepared..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 58 (2021)
Water-assisted Femtosecond Laser Silicon Carbide Micro-hole Machining（Invited）
Sijia XU, Yanhao YU, and Qidai CHEN
A water-assisted femtosecond laser silicon carbide micro-hole machining method is proposed， and a 200 μm diameter micro-hole is processed on a 350 μm thick silicon carbide sample. The difference between processing micro-holes in air and water-assisted processing of micro-holes is discussed. Water reduces the temperaturA water-assisted femtosecond laser silicon carbide micro-hole machining method is proposed， and a 200 μm diameter micro-hole is processed on a 350 μm thick silicon carbide sample. The difference between processing micro-holes in air and water-assisted processing of micro-holes is discussed. Water reduces the temperature of the processing area， greatly reducing the occurrence of oxidation reactions. The debris produced by processing is taken away by the water， avoiding the formation of HAZ and reducing the roughness of the sample. The processed micro-holes have smooth sidewalls and no HAZ， which has practical application value in industry. The processing method makes it a reality to process silicon carbide micropores with good morphology， and is expected to be applied to the industrial processing of silicon carbide..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 66 (2021)
Fabrication of High Temperature Resistant Geometric Phase Element Inside Sapphire by Femtoesecond Laser（Invited）
Yiming LU, Bingrong GAO, Xueqing LIU, and Qidai CHEN
Aiming at the problems of difficult processing， low precision and poor effect of fabricating geometric phase elements in crystal materials， a femtosecond laser-induced nano-grating technology was proposed to fabricate the internal geometric phase diffraction elements. The femtosecond laser near-threshold processing metAiming at the problems of difficult processing， low precision and poor effect of fabricating geometric phase elements in crystal materials， a femtosecond laser-induced nano-grating technology was proposed to fabricate the internal geometric phase diffraction elements. The femtosecond laser near-threshold processing method effectively improves the processing accuracy and the fabricating accuracy is 340 nm. By adjusting the polarization of the scanning laser， the direction of the induced nano-grating can be accurately controlled， leading to the change of the slow axis direction of the crystalline birefringence. Based on this method， the geometric phase Fresnel zone plate in sapphire has been fabricated. The device has a good morphology with no cracks and excellent optical performance， which can be used for focusing in high-temperature environments..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 71 (2021)
Influence of Laser Pulse Width on the Performance of Glass Waveguide（Invited）
Yingde WANG, Yanhao YU, Zhennan TIAN, and Qidai CHEN
By changing the laser pulse width， the optical waveguide is directly written in boro-aluminosilicate glass， and the effects of the pulse width on the section morphology of the optical waveguide， the size of the mode field and the transmission ratio of the directional coupler are studied. In the experiment， a single modBy changing the laser pulse width， the optical waveguide is directly written in boro-aluminosilicate glass， and the effects of the pulse width on the section morphology of the optical waveguide， the size of the mode field and the transmission ratio of the directional coupler are studied. In the experiment， a single mode/multi-mode critical power laser with a pulse width of 239 fs is used to fabricate the waveguide. The cross section size of the waveguide changes from 5.4 μm×4.2 μm （239 fs） to 5.1 μm×2.4 μm （700 fs）. The size of the mode field changed from 6.2 μm×6 μm （239 fs） to 5.8 μm×4.8 μm（700 fs） and the transmission modes were single mode. The shape of the mode field gradually changed from round to ellipse. The transmission ratio of the directional coupler changes from 97.8% （239 fs） to 70.2% （700 fs） in the horizontal polarization and from 99.2% （239 fs） to 79.7% （700 fs） in the vertical polarization. Experiments have found that the laser with a pulse width of more than 600fs is not conducive to the preparation of waveguides with stable performance..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 78 (2021)
Fabrication of Sapphire Grating by Femtosecond Laser Assisted Etching（Invited）
Jiaxin ZHENG, Bingrong GAO, Yafei XUE, Ziyi LUO, Shanguo HAN, Xueqing LIU, and Qidai CHEN
By using femtosecond laser assisted etching technology， a grating structure with adjustable period， duty cycle and height is achieved on sapphire surface. It solves the problem of poor surface quality in femtosecond laser processing of hard and brittle materials， such as low processing accuracy caused by debris accumulBy using femtosecond laser assisted etching technology， a grating structure with adjustable period， duty cycle and height is achieved on sapphire surface. It solves the problem of poor surface quality in femtosecond laser processing of hard and brittle materials， such as low processing accuracy caused by debris accumulation， and difficulty in preparing deep structures. The roughness of the sapphire grating structure was reduced from 78 nm （after direct laser writing） to 7 nm （after dry etching）， and the sapphire microstructures with a period of 800 nm and a aspect ratio of 4 were fabricated. The femtosecond laser assisted etching technology can prepare a high smoothness grating on sapphire surface， and the result proves that this technology can significantly improve the diffraction efficiency of each diffraction order..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 84 (2021)
A Study on Ablation Quality of Silicon by Femtosecond Laser Pulse Trains
Tianqi CHEN, Jian YANG, and Tianqing JIA
In order to improve the ablation quality of high fluence femtosecond laser， a Fabry-Perot cavity was used to generate femtosecond laser pulse trains whose pulse interval can be tuned continuously from 1 to 3 500 ps， and the ablation quality of silicon by single femtosecond pulses and pulse trains with different pulse iIn order to improve the ablation quality of high fluence femtosecond laser， a Fabry-Perot cavity was used to generate femtosecond laser pulse trains whose pulse interval can be tuned continuously from 1 to 3 500 ps， and the ablation quality of silicon by single femtosecond pulses and pulse trains with different pulse intervals were systematically investigated. According to the experiment results， pulse trains with intervals around 50~100 ps achieved the most ideal ablation crater. The coronal redeposition materials at the edge of the crater were greatly reduced and the thickness reduced to 40% of that of single femtosecond pulses. In the meanwhile， there is almost no adhered dust or thermal damage on the surrounding substrate， and the quality factor increased from 0.52 to 0.89. The femtosecond laser pulse trains reported in this paper， on account of the interaction of subsequent pulses and ejected material， when the pulse interval is in the range of 50~100 ps， the subsequent pulses of which can fully atomize the ejected material， thus reduce the coronal redeposition materials and contamination and damage of high-temperature dust and improve the ablation quality..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 108 (2021)
Characteristics and Mechanism of CVD Single Crystal Diamond Processed by Picosecond Laser
Qiuling WEN, Xinyu WEI, Hualu WANG, Changcai CUI, Jing LU, Zhongwei HU, and Feng JIANG
In order to explore the ablation characteristics and the material removal mechanism of diamond in picosecond laser processing， an experimental study of picosecond laser processing microgrooves on CVD single crystal diamond was carried out. The field emission scanning electron microscopy was used to observe the externalIn order to explore the ablation characteristics and the material removal mechanism of diamond in picosecond laser processing， an experimental study of picosecond laser processing microgrooves on CVD single crystal diamond was carried out. The field emission scanning electron microscopy was used to observe the external and internal morphologies of the diamond microgrooves. The experimental results show that micro-chippings and micro-cracks were emerged at the edge of the diamond microgrooves， and nano-rippes with periods of approximately 255 nm and 495 nm were formed at the sidewall and bottom of the microgrooves. The ablation threshold， ablation rate and material removal rate of diamond were obtained by measuring the width， depth and volume of the diamond microgrooves. Raman analysis shows that graphite was generated at the bottom of the microgroove. This indicates that the ablation process of picosecond laser processing diamond proceeds via a surface graphitization. the graphite peak red shifts as the laser energy increases. Theoretical results show that the thickness of the graphite layer at the bottom of the diamond is about 88.7 nm. The temperature field of the picosecond laser ablation of diamond was simulated. The simulation results show that the laser energy is mainly distributed on the surface of the diamond， while the laser energy diffuses into the diamond through heat conduction is very small. Therefore， the heat-affected zone of the picosecond laser processing diamond is extremely small， resulting in the thickness of the graphite layer is less than 100 nm..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 118 (2021)
Short-pulse Laser-induced Plasma Micro-etching of High-temperature and High Pressure Single Crystal Diamond
Xizhao LU, Jialin CHEN, Qiuling WEN, Jing LU, and Feng JIANG
A short-pulse （<200 ns） infrared （1 064 nm） Laser Induced Plasma Assisted Ablation （LIPAA） is considered as a micro-processing technology to ablate a single crystal diamond. The mechanism of different infrared laser parameters which include laser fluence， pulse width， repetition rate etc. influence on the micro-struA short-pulse （<200 ns） infrared （1 064 nm） Laser Induced Plasma Assisted Ablation （LIPAA） is considered as a micro-processing technology to ablate a single crystal diamond. The mechanism of different infrared laser parameters which include laser fluence， pulse width， repetition rate etc. influence on the micro-structure linewidth and depth was explored as well as the distance between single crystal diamond and copper target. While the pulse width is greater than 4 ns， the laser interacted on the good crystal orientation of the single crystal diamond with the prominent photothermal effect， and the laser fluence of the induced metal plasma cluster reaches a certain threshold， combined with the short pulse laser energy action， the surface temperature of the single crystal diamond rises rapidly to 600°C and above. At this time， the diamond surface layer has an etched micro-structure. When the laser with a pulse width of less than 4 ns bombards the surface of the target， the short-pulse laser bombards the target to induce metal plasma clusters. At this time， back sputtering of related metal targets and back etching and graphitization can also be achieved. The metal deposition and groove profiles are impacted on the pulse width and repetition rate of infrared laser. The experimental results prove that LIPAA is a new and reliable diamond micro-structure processing technology..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 129 (2021)
Thin Films
Influence of Substrate Temperature on Properties of ZnSe Thin Films Deposited by Electron-beam Evaporation
Guangyu ZHAO, Li XU, Jie FAN, Jiabin ZHANG, Yunping LAN, Yonggang ZOU, and Xiaohui MA
In order to study the influence of substrate temperature on the microstructure and optical properties of ZnSe thin films， a single layer of ZnSe thin films was prepared on K9 glass substrate by electron beam evaporation. By studying the X-ray diffraction spectrum， transmission spectrum characteristics， surface morpholoIn order to study the influence of substrate temperature on the microstructure and optical properties of ZnSe thin films， a single layer of ZnSe thin films was prepared on K9 glass substrate by electron beam evaporation. By studying the X-ray diffraction spectrum， transmission spectrum characteristics， surface morphology and roughness of the thin film， the variation rules of the microstructure and optical properties of the thin film under different substrate temperatures were analyzed. The experimental results show that the ZnSe films prepared in the range of substrate temperature from 20℃ to 200℃ are all single crystal films with （111） crystallographic texture. With the increase of substrate temperature， the kinetic energy obtained by atoms on the substrate increases， resulting in the increase of grain size， internal strain and dislocation density of the films. The optical properties of thin films are also different at different substrate temperatures. With the increase of substrate temperature， the refractive index and extinction coefficient decrease， the optical band gap increases， and the surface roughness of thin films decreases. It is concluded that the decrease of refractive index is caused by the increase of the proportion of the pores in the film， and the decrease of extinction coefficient is caused by the increase of crystallinity and the reduction of internal defects..
Acta Photonica Sinica
- Publication Date: Jun. 25, 2021
- Vol. 50, Issue 6, 209 (2021)
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