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High speed determination of laser wavelength using Poincaré descriptors of speckle
摘要： Laser speckle can provide a powerful tool that may be used for metrology, for example measurements of the incident laser wavelength with a resolution beyond that which may be achieved in a commercial device. However, to realise highest resolution requires advanced multi-variate analysis techniques, which limit the acquisition rate of such a wavemeter. Here we show an arithmetically simple method to measure wavelength changes with dynamic speckle, based on a Poincarè descriptor of the speckle pattern. We demonstrate the measurement of wavelength changes at femtometer-level with a measurement time reduced by two orders of magnitude compared to the previous state-of-the-art, which offers promise for applications such as speckle-based laser wavelength stabilisation.
关键词： Poincaré descriptors,Speckle,Wavelength measurement
更新于2025-09-16 10:30:52
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Dilated residual learning with skip connections for real-time denoising of laser speckle imaging of blood flow in a log-transformed domain
摘要： Laser speckle contrast imaging (LSCI) is a wide-field and noncontact imaging technology for mapping blood flow. Although the denoising method based on block-matching and filtering three-dimensional (BM3D) was proposed to improve its signal-to-noise ratio (SNR) significantly, the processing time makes it difficult to realize real-time denoising. Furthermore, it is still difficult to obtain an acceptable level of SNR with a few raw speckle images given the presence of significant noise and artifacts. A feed-forward denoising convolutional neural network (DnCNN) achieves state-of-the-art performance in denoising nature images and is efficiently accelerated by GPU. However, it performs poorly in learning with original speckle contrast images of LSCI owing to the inhomogeneous noise distribution. Therefore, we propose training DnCNN for LSCI in a log-transformed domain to improve training accuracy and it achieves an improvement of 5.13 dB in the peak signal-to-noise ratio (PSNR). To decrease the inference time and improve denoising performance, we further propose a dilated deep residual learning network with skip connections (DRSNet). The image-quality evaluations of DRSNet with five raw speckle images outperform that of spatially average denoising with 20 raw speckle images. DRSNet takes 35 ms (i.e., 28 frames per second) for denoising a blood flow image with 486 × 648 pixels on an NVIDIA 1070 GPU, which is approximately 2.5 times faster than DnCNN. In the test sets, DRSNet also improves 0.15 dB in the PSNR than that of DnCNN. The proposed network shows good potential in real-time monitoring of blood flow for biomedical applications.
关键词： Blood flow,convolutional neural network (CNN),laser speckle contrast imaging (LSCI),dilated convolution,skip connection
更新于2025-09-16 10:30:52
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Total generalized variation denoising of speckled images using a primal-dual algorithm
摘要： In this paper, multiplicative noise removal problem is considered. Multiplicative noise is also commonly referred to as speckle. We propose a total generalized variation (TGV) based model which involves the multilook M for multiplicative noise removal. The objective function of our proposed model is strictly convex. Computationally, by using the dual representation of the second-order TGV regularization, our proposed model is transformed into a minimax problem. A ?rst-order primal-dual algorithm is developed to solve the minimax problem and the convergence of the proposed algorithm is strictly proved. At last, compared with several existing methods, experimental results demonstrate the effectiveness of the proposed method, in terms of signal-to-noise ratio, peak signal-to-noise ratio and mean absolute-deviation error.
关键词： Primal-dual algorithm,Total generalized variation (TGV),Multiplicative noise,Speckle
更新于2025-09-16 10:30:52
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Speckle reduction by employing two green lasers and two-dimensional vibration of lenses
摘要： A method of speckle reduction suitable for use in a laser projector was proposed in the paper. Speckle contrast ratio (SCR) reduction was achieved by combining wavelength diversity and angular diversity methods. First, wavelength diversity was demonstrated by the use of two green laser sources (a 520 nm laser diode (LD) and a 532 nm diode-pumped solid-state (DPSS) laser) at a power ratio of 4:1. Second, angular diversity was achieved via the vibration of two lenses in two orthogonal directions placed directly after the laser source. The vibrating lenses are small and do not require changes to the beam path of the laser source, allowing for more compact projector designs. The frequency of vibration of these lenses was optimized to minimize the SCR in the output image. A SCR of less than 4% was achieved without the use of optical diffusers, which significantly reduces optical losses. Optical transmission could be further increased with the optimization of optical coatings on the lenses. This result shows great promise for applications such as laser pico-projectors within the realm of heads-up displays (HUDs) and mobile devices.
关键词： two-dimensional vibration of lenses,speckle reduction,mini-/pico-projectors
更新于2025-09-16 10:30:52
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Depth of Field Extension in Laser Speckle Contrast Imaging
摘要： A new technique that can increase the depth of field (DOF) for in vivo tissue imaging is presented. Extended DOF for the imaging of strongly scattering media is realized through combining laser speckle contrast imaging (LSCI) with light field (LF) microscopy. To the best of our knowledge, it is for the first time to combine these two imaging techniques into one system to provide enhanced functionality. The entire imaging process requires only one single detection with no mechanical adjustment involved. The feasibility and capability of the proposed technique is experimentally demonstrated in volumetric flow speed measurement.
关键词： laser speckle contrast imaging,Light field,depth of field
更新于2025-09-16 10:30:52
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<p>Correlation between laser speckle flowgraphy and optical coherence tomography angiography measurements in normal and glaucomatous eyes</p>
摘要： Purpose: To investigate the relationship between laser speckle ?owgraphy (LSFG) and optical coherence tomography angiography (OCTA) measurements of the peripapillary retina and optic nerve head (ONH) in normal eyes and eyes with primary open-angle glaucoma (POAG). Patients and methods: One eye from each of 46 normal subjects and mild and moderate/advanced POAG patients were included. ONH blood ?ow acquired by LSFG, circumpapillary vessel density (cpVD, a 250 μm-wide elliptical annulus around the optic disc), and intra-papillary vessel density (ipVD, a 1.5×1.5 mm scan ?eld) acquired by OCTA were measured. Their values were compared among normal controls and patients at each stage of glaucoma using one-way ANOVA, and the correlation between measurements obtained by the two methods was examined by univariate regression analysis. Results: ONH tissue blood ?ow, tissue mean blur rate (MBR-T), and cpVD in the outer layer of the retina signi?cantly decreased with the progression of glaucoma stage, although the latter showed no signi?cant difference between normal subjects and mild-stage glaucoma patients. MBR-T was signi?cantly correlated with cpVD, but not with ipVD, in the retinal outer layer. Conclusion: A correlation was found only between MBR-T and cpVD in the retinal outer layer. A difference in MBR-T, but not in cpVD, was detected between normal controls and mild glaucoma patients.
关键词： optic nerve head,blood ?ow,laser speckle ?owgraphy,optical coherent tomography angiography
更新于2025-09-16 10:30:52
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Theory and experiments based on tracked moving flexible DOE loops for speckle suppression in compact laser projection
摘要： This paper describes a speckle suppression method using flexible diffractive optical elements (DOEs) based on binary random sequences with tracked motion. The DOE loops consist of 1D random-sequence diffractive structures with similar but different inclination angles. A mathematical approach for determining the optimal inclination angles and DOE speed for speckle suppression is developed, and a model for calculating the speckle suppression efficiency is constructed. Theoretical and experimental results show that the proposed method decreases the speckle contrast to below the sensitivity of the human eye, making it suitable for compact laser projections. The experimental results also indicate that current DOE production technology should be improved to avoid limiting the image quality.
关键词： Flexible DOE loop,Speckle suppression,Tracked motion
更新于2025-09-16 10:30:52
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Speckle evaluation in laser display: From speckle contrast to speckle influence degree
摘要： Speckle contrast (SC) is universally used to evaluate speckle in laser display, which has virtues of briefness in calculating and definitude in physical meaning. But the results characterized by SC is usually inconsistent with human visual perception. In this study, an alternative framework for speckle evaluation, speckle influence degree (SID), is developed. It considers the effects of SC, sampling rate, and image resolution on perceived speckle by human eyes. Theoretical analysis is firstly conducted. Then, speckle images of different sampling rate, SC, and image resolution are generated and calculated. Finally, SID is shown to be a more comprehensive metric that could characterize the influence of sampling rate and image resolution and that is better matched with subjective perception of human eyes than SC.
关键词： Speckle evaluation,Human visual perception,Laser display,Speckle,Speckle influence degree
更新于2025-09-12 10:27:22
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[IEEE 2019 41st Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC) - Berlin, Germany (2019.7.23-2019.7.27)] 2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) - A prototype system of portable laser speckle imager based on embedded graphics processing unit platform
摘要： Laser speckle contrast imaging (LSCI) is a high-resolution full-field optical technique for measuring blood flow, which has been widely used in clinical and biomedical research. However, most of the current LSCI instruments are bulky, limiting their application settings. In this work, we proposed a prototype system of portable laser speckle imager. Different from the desktop laser speckle systems that utilize personal computer (PC), our system was designed with embedded GPU system (Jetson TX2, NVIDIA, USA) and a LCD touch screen (16.5 × 12.4 cm in size, 380 g in weight). In-vivo experiments showed that the portable GPU-based system had comparable performance with our laboratory LSCI system. Such a portable LSCI imager could be potentially used in a situation that requires for easy operation and installation, such as intraoperative monitoring or bedside diagnosis.
关键词： Laser speckle contrast imaging,portable,blood flow,embedded GPU,real-time monitoring
更新于2025-09-12 10:27:22
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Use of Laser Speckle Contrast Imaging for Successful Fingertip Replantation
摘要： Fingertip replantation is a technical challenge for microsurgeons. For successful fingertip replantation, it is important to monitor the replanted fingertip vascularity for the early detection and revision of vascular compromise. Laser speckle contrast imaging (LSCI) is a camera-based technique that measures the perfusion by illuminating the tissue with a 785-nm-wavelength divergent laser beam. This creates a speckle pattern over the illuminated area. We present a case in which postoperative monitoring of the replanted fingertip microcirculation using LSCI allowed for successful Tamai zone I fingertip replantation. Postoperative monitoring using LSCI has 3 main advantages. First, this method is harmless to the patient and the replanted fingertip. A camera-based technique enables microcirculation monitoring without touching the patient or the replanted fingertip. Second, tissue perfusion is measured in real time and recorded continuously, allowing for the rapid response to the arterial or venous occlusion to be observed. Third, using LSCI, the skin perfusion can be measured quantitatively. Although further clinical investigations will be required to confirm its efficacy, LSCI has the potential to be a useful monitoring device.
关键词： fingertip replantation,microcirculation monitoring,Laser speckle contrast imaging
更新于2025-09-12 10:27:22