Speckle noise reduction strategies in laser-based projection imaging, fluorescence microscopy, and digital holography with uniform illumination, improved image sharpness, and resolution

摘要

There has been immense advancement in laser-based projection imaging, fluorescence microscopy, singlemolecule localization nanoscopy, and digital holography. These techniques mostly employ lasers as light sources attributable to their high spatial and temporal coherence, high brightness, directionality, wide color gamut, and high color purity. However, high coherence properties of the laser source also cause spurious fringes, speckle noise, and inhomogeneous illumination, thus degrade the quality of images acquired from the aforementioned techniques. Additionally, such factors affect the phase measurement accuracy of digital holographic systems. Recently, the partially spatially coherent light-based illumination system for speckle-free imaging has been demonstrated in various laser projection imaging, fluorescence microscopy, and holographic techniques. Here, we review various strategies adopted for speckle-free laser projection imaging, fluorescence microscopy, singlemolecule localization nanoscopy, and digital holography with uniform illumination, improved image sharpness, and high resolution. After the rigorous literature review of various reported schemes and methods, we find that the most suitable light source for the aforementioned techniques is a partially spatially coherent monochromatic light, i.e., a pseudo-thermal light source which provides uniform illumination with least speckle noise and without any spurious fringes. In addition to this, other remarkable properties of laser light, i.e., its high monochromaticity, high brightness, and high directionality, are utilized for realizing all aforementioned techniques.