The shallow subsurface defects are difficult to be identified and quantified by ultrasonic time-of-flight diffraction(TOFD)due to the low resolution induced by pulse width and beam spreading.In this paper,Sparse-SAFT ...The shallow subsurface defects are difficult to be identified and quantified by ultrasonic time-of-flight diffraction(TOFD)due to the low resolution induced by pulse width and beam spreading.In this paper,Sparse-SAFT is proposed to improve the time resolution and lateral resolution in TOFD imaging by combining sparse deconvolution and synthetic aperture focusing technique(SAFT).The mathematical model in the frequency domain is established based on the l1 and l2 norm constraints,and the optimization problem is solved for enhancing time resolution.On this basis,SAFT is employed to improve lateral resolution by delay-and-sum beamforming.The simulated and experimental results indicate that the lateral wave and tip-diffracted waves can be decoupled with Sparse-SAFT.The shallow subsurface defects with a height of 3.0 mm at the depth of 3.0 mm were detected quantitatively,and the relative measurement errors of flaw heights and depths were no more than 10.3%.Compared to conventional SAFT,the time resolution and lateral resolution are enhanced by 72.5 and 56%with Sparse-SAFT,respectively.Finally,the proposed method is also suitable for improving resolution to detect the defects beyond dead zone.展开更多
Optical-resolution photoacoustic microscopy(OR-PAM)has rapidly developed and is capable of characterizing optical absorption properties of biological tissue with high contrast and high resolution(micrometer-scale late...Optical-resolution photoacoustic microscopy(OR-PAM)has rapidly developed and is capable of characterizing optical absorption properties of biological tissue with high contrast and high resolution(micrometer-scale lateral resolution).However,the conventional excitation source of rapidly diverging Gaussian beam imposes limitations on the depth of focus(DOF)in OR-PAM,which in turn affects the depth-resolving ability and detection sensitivity.Here,we proposed a flexible DOF,depth-invariant resolution photoacoustic microscopy(FDIR-PAM)with nondiffraction of Airy beams.The spatial light modulator was incorporated into the optical pathway of the excitation source with matched switching phase patterns,achieving the flexibly adjustable modulation parameters of the Airy beam.We conducted experiments on phantoms and intravital tissue to validate the effectiveness of the proposed approach for high sensitivity and highresolution characterization of variable topology of tissue,offering a promising DOF of 926μm with an invariant lateral resolution of 3.2μm,which is more than 17-fold larger compared to the Gaussian beam.In addition,FDIR-PAM successfully revealed clear individual zebrafish larvae and the pigment pattern of adult zebrafishes,as well as fine morphology of cerebral vasculature in a large depth range with high resolution,which has reached an evident resolving capability improvement of 62%mean value compared with the Gaussian beam.展开更多
In order to improve the resolution of digital holography with a common-dimension charge-coupled device (CCD) sensor, the point spread functions are briefly derived for the commonly used and practical post-magnificatio...In order to improve the resolution of digital holography with a common-dimension charge-coupled device (CCD) sensor, the point spread functions are briefly derived for the commonly used and practical post-magnification, pre-magnification, and image-plane digital holographic microscopic systems. The ultimate resolutions of these systems are analyzed and compared. The results show that the ultimate lateral resolution of pre-magnification digital holography is superior to that of post-magnification digital holography in the same conditions. We also demonstrate that the ultimate lateral resolution of image-plane digital holography has no correlation with the photosensitive dimension of the CCD sensor, and it is not significantly related to the pixel size of the sensor. Moreover, both the ultimate resolution and the imaging quality of image-plane digital holography are superior to that of pre- and post-magnification digital holographic microscopy. High-resolution imaging, whose resolution is close to the ultimate resolution of the microscope objective, can be achieved by image-plane digital holography even with a submillimeter-dimension sensor. This system, by which perfect imaging can be achieved, is optimal for commonly used digital holographic microscopy. Experimental results demonstrate the correctness of the theoretical analysis.展开更多
基金National Key Research and Development Program of China(Grant No.2019YFA0709003)National Natural Science Foundation of China(Grant No.51905079)Liaoning Revitalization Talents Program(Grant No.XLYC1902082).
文摘The shallow subsurface defects are difficult to be identified and quantified by ultrasonic time-of-flight diffraction(TOFD)due to the low resolution induced by pulse width and beam spreading.In this paper,Sparse-SAFT is proposed to improve the time resolution and lateral resolution in TOFD imaging by combining sparse deconvolution and synthetic aperture focusing technique(SAFT).The mathematical model in the frequency domain is established based on the l1 and l2 norm constraints,and the optimization problem is solved for enhancing time resolution.On this basis,SAFT is employed to improve lateral resolution by delay-and-sum beamforming.The simulated and experimental results indicate that the lateral wave and tip-diffracted waves can be decoupled with Sparse-SAFT.The shallow subsurface defects with a height of 3.0 mm at the depth of 3.0 mm were detected quantitatively,and the relative measurement errors of flaw heights and depths were no more than 10.3%.Compared to conventional SAFT,the time resolution and lateral resolution are enhanced by 72.5 and 56%with Sparse-SAFT,respectively.Finally,the proposed method is also suitable for improving resolution to detect the defects beyond dead zone.
基金supported by the National Natural Science Foundation of China(Grant Nos.62105255 and 62275210)the Xidian University Specially Funded Project for Interdisciplinary Exploration(Grant No.TZJH2024043)+1 种基金the Key Research and Development Program of Shaanxi Province(Grant No.2023-YBSF-293)the National Young Talent Program and Shaanxi Young Top-notch Talent Program,and the Fundamental Research Funds for CentralUniversities(Grant No.ZYTS23187).
文摘Optical-resolution photoacoustic microscopy(OR-PAM)has rapidly developed and is capable of characterizing optical absorption properties of biological tissue with high contrast and high resolution(micrometer-scale lateral resolution).However,the conventional excitation source of rapidly diverging Gaussian beam imposes limitations on the depth of focus(DOF)in OR-PAM,which in turn affects the depth-resolving ability and detection sensitivity.Here,we proposed a flexible DOF,depth-invariant resolution photoacoustic microscopy(FDIR-PAM)with nondiffraction of Airy beams.The spatial light modulator was incorporated into the optical pathway of the excitation source with matched switching phase patterns,achieving the flexibly adjustable modulation parameters of the Airy beam.We conducted experiments on phantoms and intravital tissue to validate the effectiveness of the proposed approach for high sensitivity and highresolution characterization of variable topology of tissue,offering a promising DOF of 926μm with an invariant lateral resolution of 3.2μm,which is more than 17-fold larger compared to the Gaussian beam.In addition,FDIR-PAM successfully revealed clear individual zebrafish larvae and the pigment pattern of adult zebrafishes,as well as fine morphology of cerebral vasculature in a large depth range with high resolution,which has reached an evident resolving capability improvement of 62%mean value compared with the Gaussian beam.
文摘In order to improve the resolution of digital holography with a common-dimension charge-coupled device (CCD) sensor, the point spread functions are briefly derived for the commonly used and practical post-magnification, pre-magnification, and image-plane digital holographic microscopic systems. The ultimate resolutions of these systems are analyzed and compared. The results show that the ultimate lateral resolution of pre-magnification digital holography is superior to that of post-magnification digital holography in the same conditions. We also demonstrate that the ultimate lateral resolution of image-plane digital holography has no correlation with the photosensitive dimension of the CCD sensor, and it is not significantly related to the pixel size of the sensor. Moreover, both the ultimate resolution and the imaging quality of image-plane digital holography are superior to that of pre- and post-magnification digital holographic microscopy. High-resolution imaging, whose resolution is close to the ultimate resolution of the microscope objective, can be achieved by image-plane digital holography even with a submillimeter-dimension sensor. This system, by which perfect imaging can be achieved, is optimal for commonly used digital holographic microscopy. Experimental results demonstrate the correctness of the theoretical analysis.
