Digital holography(DH)has emerged as one of the most effective coherent imaging technologies.The technological developments of digital sensors and optical elements have made DH the primary approach in several research...Digital holography(DH)has emerged as one of the most effective coherent imaging technologies.The technological developments of digital sensors and optical elements have made DH the primary approach in several research fields,from quantitative phase imaging to optical metrology and 3D display technologies,to name a few.Like many other digital imaging techniques,DH must cope with the issue of speckle artifacts,due to the coherent nature of the required light sources.Despite the complexity of the recently proposed de-speckling methods,many have not yet attained the required level of effectiveness.That is,a universal denoising strategy for completely suppressing holographic noise has not yet been established.Thus the removal of speckle noise from holographic images represents a bottleneck for the entire optics and photonics scientific community.This review article provides a broad discussion about the noise issue in DH,with the aim of covering the best-performing noise reduction approaches that have been proposed so far.Quantitative comparisons among these approaches will be presented.展开更多
Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process for producing small- and medium-size structures. However, a key obstacle for the application of this techni...Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process for producing small- and medium-size structures. However, a key obstacle for the application of this technique in industry is the lack of reliability and qualification mainly because of melt pool instabilities during the laser-powder interaction, which degrade the quality of the manufactured components. In this paper, we propose multi- wavelength digital holography as a proof of concept for in situ real-time investigation of the melt pool morphology. A two-wavelength digital holographic setup was co-axially implemented in a laser beam melting facility. The solidified aluminum tracks and melt pools during the manufacturing of 316L were obtained with full- field one-shot acquisitions at short exposure times and various scanning velocities. The evaluation of the complex coherence factor of digital holograms allowed the quality assessment of the phase reconstruction. The motion blur was analyzed by scanning the dynamic melt pool.展开更多
基金support under Grant NSF/IIS-1422179Grant NSF ECCS 1545687.
文摘Digital holography(DH)has emerged as one of the most effective coherent imaging technologies.The technological developments of digital sensors and optical elements have made DH the primary approach in several research fields,from quantitative phase imaging to optical metrology and 3D display technologies,to name a few.Like many other digital imaging techniques,DH must cope with the issue of speckle artifacts,due to the coherent nature of the required light sources.Despite the complexity of the recently proposed de-speckling methods,many have not yet attained the required level of effectiveness.That is,a universal denoising strategy for completely suppressing holographic noise has not yet been established.Thus the removal of speckle noise from holographic images represents a bottleneck for the entire optics and photonics scientific community.This review article provides a broad discussion about the noise issue in DH,with the aim of covering the best-performing noise reduction approaches that have been proposed so far.Quantitative comparisons among these approaches will be presented.
文摘Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process for producing small- and medium-size structures. However, a key obstacle for the application of this technique in industry is the lack of reliability and qualification mainly because of melt pool instabilities during the laser-powder interaction, which degrade the quality of the manufactured components. In this paper, we propose multi- wavelength digital holography as a proof of concept for in situ real-time investigation of the melt pool morphology. A two-wavelength digital holographic setup was co-axially implemented in a laser beam melting facility. The solidified aluminum tracks and melt pools during the manufacturing of 316L were obtained with full- field one-shot acquisitions at short exposure times and various scanning velocities. The evaluation of the complex coherence factor of digital holograms allowed the quality assessment of the phase reconstruction. The motion blur was analyzed by scanning the dynamic melt pool.
