Photoacoustic detection has shown excellent performance in measuring thickness and detecting defects in metal nanofilms.However,existing research on ultrafast lasers mainly focuses on using picosecond or nanosecond la...Photoacoustic detection has shown excellent performance in measuring thickness and detecting defects in metal nanofilms.However,existing research on ultrafast lasers mainly focuses on using picosecond or nanosecond lasers for large-scale material processing and measurement.The theoretical study of femtosecond laser sources for photoacoustic nondestructive testing(NDT)in nanoscale thin film materials receives much less emphasis,leading to a lack of a complete physical model that covers the entire process from excitation to measurement.In this study,we developed a comprehensive physical model that combines the two-temperature model with the acoustic wave generation and detection model.On the basis of the physical model,we established a simulation model to visualize the ultrafast lasermaterial interaction process.The damage threshold of the laser source is determined,and the effect of key parameters(laser fluence,pulse duration,and wavelength)for AlCu nanofilms on the femtosecond photoacoustic NDT process is discussed using numerical results from the finite element model.The numerical results under certain parameters show good agreement with the experimental results.展开更多
A ferroelectric liquid crystal polarization rotator(FLCPR)has been widely used in polarization measurement due to its fast and stable modulation characteristics.The accurate characterization of the modulation performa...A ferroelectric liquid crystal polarization rotator(FLCPR)has been widely used in polarization measurement due to its fast and stable modulation characteristics.The accurate characterization of the modulation performance of FLCPR directly affects the measurement accuracy of the instrument based on liquid crystal modulation.In this study,FLCPR is accurately characterized using a self-developed high-speed Stokes polarimeter.Strong linear and weak circular birefringence are observed during modulation processes,and all the optical parameters of FLCPR are dependent on driving voltage.A dual FLCPR-based Mueller matrix polarimeter is designed on the basis of the Stokes polarimeter.The designed polarimeter combines the advantages of the high modulation frequency of FLCPR and the ultrahigh temporal resolution of the fast polarization measurement system in the Stokes polarimeter.The optimal configuration of the designed polarizer is predicted in accordance with singular value decomposition.A simulated thickness measurement of a 24 nm standard SiO2 thin film is performed using the optimal configuration.Results show that the relative error in thickness measurement caused by using the unsatisfactory modulation characteristics of FLCPR reaches up to−4.34%.This finding demonstrates the importance of the accurate characterization of FLCPR in developing a Mueller matrix polarizer.展开更多
Remote measurement of object orientation is often required in many applications.Out of the six degrees of freedom(DoF)that determine object orientation in space,the roll angle is the most difficult to measure using op...Remote measurement of object orientation is often required in many applications.Out of the six degrees of freedom(DoF)that determine object orientation in space,the roll angle is the most difficult to measure using optical methods.In this letter,we propose a remote Stokes roll-angle sensor that measures roll angles from the detected Stokes vectors of modulated polarized light retroreflected from a sensing unit comprised simply of a retarder and a planar reflection mirror.Experimental results have shown that the proposed sensor can realize absolute roll angle measurement in an unprecedented range of 180°with a maximum absolute error of less than 0.25°and a measurement resolution of better than 0.01°.The proposed sensor adopts a coaxial design and takes the advantages of compactness,simplicity and low cost,and moreover,can be further expanded to a three-DoF angle sensor due to the sensitivity of the sensing unit to other two kinds of angles(pitch and yaw).展开更多
基金funded by the National Natural Science Foundation of China(Grant Nos.52375541,52022034,52130504,and 62175075)the National Key Research and Development Plan of China(Grant No.2022YFF0709104)+2 种基金the Key Research and Development Plan of Hubei Province,China(Grant No.2020BAA8)the Interdisciplinary Research Program of Huazhong University of Science and Technology,China(Grant No.2023JCYJ047)the Innovation Project of Optics Valley Laboratory,China(Grant No.OVL2023PY003).
文摘Photoacoustic detection has shown excellent performance in measuring thickness and detecting defects in metal nanofilms.However,existing research on ultrafast lasers mainly focuses on using picosecond or nanosecond lasers for large-scale material processing and measurement.The theoretical study of femtosecond laser sources for photoacoustic nondestructive testing(NDT)in nanoscale thin film materials receives much less emphasis,leading to a lack of a complete physical model that covers the entire process from excitation to measurement.In this study,we developed a comprehensive physical model that combines the two-temperature model with the acoustic wave generation and detection model.On the basis of the physical model,we established a simulation model to visualize the ultrafast lasermaterial interaction process.The damage threshold of the laser source is determined,and the effect of key parameters(laser fluence,pulse duration,and wavelength)for AlCu nanofilms on the femtosecond photoacoustic NDT process is discussed using numerical results from the finite element model.The numerical results under certain parameters show good agreement with the experimental results.
基金This work was funded by the National Natural Science Foundation of China(Grant Nos.51575214,51525502,51975232,51727809,and 51805193)the National Key Research and Development Plan(Grant No.2017YFF0204705)+1 种基金the Natural Science Foundation of Hubei Province of China(Grant No.2018CFA057)the National Science and Technology Major Project of China(Grant No.2017ZX02101006-004).
文摘A ferroelectric liquid crystal polarization rotator(FLCPR)has been widely used in polarization measurement due to its fast and stable modulation characteristics.The accurate characterization of the modulation performance of FLCPR directly affects the measurement accuracy of the instrument based on liquid crystal modulation.In this study,FLCPR is accurately characterized using a self-developed high-speed Stokes polarimeter.Strong linear and weak circular birefringence are observed during modulation processes,and all the optical parameters of FLCPR are dependent on driving voltage.A dual FLCPR-based Mueller matrix polarimeter is designed on the basis of the Stokes polarimeter.The designed polarimeter combines the advantages of the high modulation frequency of FLCPR and the ultrahigh temporal resolution of the fast polarization measurement system in the Stokes polarimeter.The optimal configuration of the designed polarizer is predicted in accordance with singular value decomposition.A simulated thickness measurement of a 24 nm standard SiO2 thin film is performed using the optimal configuration.Results show that the relative error in thickness measurement caused by using the unsatisfactory modulation characteristics of FLCPR reaches up to−4.34%.This finding demonstrates the importance of the accurate characterization of FLCPR in developing a Mueller matrix polarizer.
基金the National Science Foundation of China(NSFC)(51775217,51727809,51525502,and 51805193)the National Science and Technology Major Project of China(2017ZX02101006-004).
文摘Remote measurement of object orientation is often required in many applications.Out of the six degrees of freedom(DoF)that determine object orientation in space,the roll angle is the most difficult to measure using optical methods.In this letter,we propose a remote Stokes roll-angle sensor that measures roll angles from the detected Stokes vectors of modulated polarized light retroreflected from a sensing unit comprised simply of a retarder and a planar reflection mirror.Experimental results have shown that the proposed sensor can realize absolute roll angle measurement in an unprecedented range of 180°with a maximum absolute error of less than 0.25°and a measurement resolution of better than 0.01°.The proposed sensor adopts a coaxial design and takes the advantages of compactness,simplicity and low cost,and moreover,can be further expanded to a three-DoF angle sensor due to the sensitivity of the sensing unit to other two kinds of angles(pitch and yaw).
