- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2018
- RADAR
- SAR
- Review
- Speckle Noise
- Satellite images
- Noise filters
- Literature Survey
- speckle noise
- Image quality metrics
- Wavelet transform
- Optoelectronic Information Science and Engineering
- University of Canterbury
- M. V. Muthiah Govt. Arts College for Women
- Gandhigram Rural Institute (Deemed to be University)
- Canterbury District Health Board
-
Speckle reduction with fast electrically tunable lens and holographic diffusers in a laser projector
摘要： We proposed a speckle reduction system in the laser pico-projector. The holographic diffusers and the fast electrically tunable lens (FET lens) were adopted in the method of the speckle reduction. This research focuses on speckle reduction by the different divergence angle of the holographic diffusers. Moreover, the speckle contrast value can be further reduced by the fast electrically tunable lens. Different divergence angle of the holographic diffuser provides the different angular diversity to compare the speckle reduction ability. We propose three experimental methods to explore speckle reduction. In experiment 1, we use a holographic diffuser and the FET lens. The speckle contrast value can be reduced to 0.08353. In experiment 2, the speckle contrast value can be reduced to 0.06403 under the balance between power consumption and speckle reduction. In experiment 3, we adjust different waveforms to get lower speckle contrast value. Finally, the speckle contrast value is 0.048 at 400Hz. That is lower than 0.05 successfully. That caused the speckle phenomenon is undetectable by human eye.
关键词： laser pico-projector,speckle reduction,angular diversity,fast electrically tunable lens,holographic diffusers
更新于2025-09-12 10:27:22
-
Quality assessment of laser speckle patterns for digital image correlation by a Multi-Factor Fusion Index
摘要： Digital image correlation based on laser speckle has its unique advantages in ultra-high temperature deformation measurement. The traditional quality assessment criteria of arti?cial speckle which consider only the contrast of the speckle pattern or the morphology of the speckle particles are not suitable for laser speckle. Here, a new index, called Multi-Factor Fusion Index (MFFI), which takes the inhomogeneity of gray distribution, the mean square deviation of gray and the standard deviation of speckle particles size into consideration, is proposed to evaluate the quality of laser speckle patterns. Multi-Factor Fusion Index was compared with three commonly used criteria, the mean intensity gradient, the mean intensity of the second derivative, and the pattern quality metric combining the sum of square of subset intensity gradients (SSSIG) and the secondary auto-correlation peak height. The results showed that the proposed index had better capability of assessing the quality of laser speckle patterns. And the in?uence by external factors such as apertures, laser powers and temperatures and material factors such as roughness and light re?ectance were analyzed by MFFI. Experiments on arti?cial speckle showed that MFFI was also suitable for arti?cial speckle patterns in most cases.
关键词： Quality assessment criteria,Laser speckle characteristics,Multi-Factor Fusion Index (MFFI),Digital image correlation (DIC)
更新于2025-09-12 10:27:22
-
Differences in Optic Nerve Head Blood Flow Regulation in Normal Tension Glaucoma Patients and Healthy Controls as Assessed With Laser Speckle Flowgraphy During the Water Drinking Test
摘要： Précis: Optic nerve head (ONH) perfusion was not signi?cantly altered in subjects with normal tension glaucoma (NTG) nor in healthy individuals after performing the water drinking test (WDT), because of its limited effect on ocular perfusion pressure (OPP). Purpose: ONH blood ?ow can be maintained stable in healthy individuals because of a physiological phenomenon called autoregulation. Impairment of autoregulation has been shown especially under condition of NTG. The purpose of this study was to investigate the ONH blood ?ow autoregulation in patients with NTG by in?uencing the OPP with the WDT. Methods: The study included 9 eyes from 9 white patients with a diagnosis of NTG and 9 eyes from age-matched and sex-matched healthy individuals. In the glaucoma group, the antiglaucomatous therapy was paused 3 weeks before the investigations. Measurements of ONH blood ?ow were performed with laser speckle ?owgraphy. After baseline measurements, individuals ingested 800 mL of water in <5 minutes. Measurements were repeated after 15, 30, and 45 minutes. Results: The water ingestion led to a signi?cant rise in intraocular pressure (P < 0.001) but also mean arterial pressure (P < 0.001) in both groups. This resulted in stable OPP (P = 0.051) with no signi?cant difference between the groups (P = 0.43). ONH blood ?ow remained stable over time in both groups (P = 0.719). No signi?cant interaction of time and group was shown for all parameters. Conclusions: Our ?ndings show that the WDT does not signi?cantly in?uence the OPP and therefore has to be considered inferior to other methods used to assess blood ?ow autoregulation.
关键词： laser speckle ?owgraphy,normal tension glaucoma,water drinking test,blood ?ow regulation
更新于2025-09-12 10:27:22
-
Fourier transforms for fast and quantitative Laser Speckle Imaging
摘要： Laser speckle imaging is a powerful imaging technique that visualizes microscopic motion within turbid materials. At current two methods are widely used to analyze speckle data: one is fast but qualitative, the other quantitative but computationally expensive. We have developed a new processing algorithm based on the fast fourier transform, which converts raw speckle patterns into maps of microscopic motion and is both fast and quantitative, providing a dynamnic spectrum of the material over a frequency range spanning several decades. in this article we show how to apply this algorithm and how to measure a diffusion coefficient with it. We show that this method is quantitative and several orders of magnitude faster than the existing quantitative method. finally we harness the potential of this new approach by constructing a portable laser speckle imaging setup that performs quantitative data processing in real-time on a tablet.
关键词： Fast Fourier Transform,Real-time Analysis,Quantitative Imaging,Laser Speckle Imaging,Microscopic Motion
更新于2025-09-12 10:27:22
-
Pulse Waveform Analysis of the Ocular Blood Flow Using Laser Speckle Flowgraphy before and after Glaucoma Treatment
摘要： Although reduction in intraocular pressure (IOP) is the principle of glaucoma treatment, impaired ocular blood ?ow is believed to play a role in the progression of glaucoma. This study evaluated the e?ect of glaucoma treatment on pulse waveforms for optic nerve head (ONH) microcirculation in patients with glaucoma. Fifty-one subjects were included on the basis of the glaucoma treatment administered, which involved instillation of prostaglandin (PG) analogs (PG group; n ? 28) or trabeculectomy (trabeculectomy group; n ? 23). ONH blood ?ow, represented by the mean blur rate (MBRT) and pulse waveforms, was measured using laser speckle ?owgraphy before and 1 and 3 months after treatment. Three months after treatment, IOP exhibited a signi?cant decrease (p < 0.05). Although there was no signi?cant change in MBRT after treatment, the acceleration time index (ATI) signi?cantly decreased (p ? 0.034) in the PG group. In the trabeculectomy group, there was no signi?cant change in the MBRT after treatment, while ?uctuation (p ? 0.019) and blowout score (BOS) (p ? 0.036) exhibited signi?cant decrease and increase, respectively. Multiple regression analysis showed that mean deviation was signi?cantly associated with the rate of change in the BOS (p ? 0.013), age was a signi?cant contributing factor for the rate of change in ?uctuation in the trabeculectomy group, re?ection was signi?cantly associated with the ATI (p ? 0.037) in the in the PG group. Both glaucoma treatments can change the pulse waveforms, with MBRT remaining unchanged, and IOP reduction owing to the treatment may contribute to stable blood ?ow in the tissue area of the ONH. As impaired ocular blood ?ow plays a role in the progression of glaucomatous damage, it would be bene?cial if glaucoma treatment could improve the stability of ONH microcirculation.
关键词： prostaglandin analogs,laser speckle flowgraphy,trabeculectomy,intraocular pressure,glaucoma,ocular blood flow
更新于2025-09-12 10:27:22
-
Evaluation of blood flow on optic nerve head after pattern scan and conventional laser panretinal photocoagulation
摘要： To evaluate the changes in the blood ?ow on retina and the optic nerve head (ONH) after conventional laser treatment and to compare it to that after patterned scanning laser (PASCAL) treatment in patients with severe nonproliferative diabetic retinopathy (S-NPDR). In this prospective, cross-sectional study, the blood ?ow on retina and the ONH was assessed by laser speckle ?owgraphy using the mean blur rate (MBR) in 39 eyes with S-NPDR before, 1, 4, 8, 12 weeks after panretinal photocoagulation (PRP). Of 39 eyes, 17eyes with 17 patients treated by conventional laser and 22 eyes with 22 patients treated by PASCAL. The mean age was 55.5 ± 11.5 years in the conventional laser group, 55.6 ± 11.8 years in the PASCAL group. The MBR-vessel, which can be dominantly expressed as retinal blood ?ow, was signi?cantly reduced after PRP treated by conventional laser (P < .001), but did not change after PRP treated by PASCAL. The ratio of MBR-vessel to the baseline was signi?cantly lower in the conventional laser group only at Week 1 (P = .045). The MBR-tissue, which can be dominantly expressed as the ONH blood ?ow, did not signi?cantly change after PRP in the both group. The multiple stepwise regression analysis revealed that the laser burns was an independent factor signi?cantly correlated with the ratio of MBR-vessel at Week 1 to the baseline (b = (cid:1)0.550, P = .012). The retinal blood ?ow was signi?cantly reduced during the 12 weeks only after completion of PRP by conventional laser treatment. Our results indicate that short pulse on PRP treatment performed by the PASCAL would not signi?cantly reduce the retinal blood ?ow.
关键词： laser speckle ?owgraphy,patterned scanning laser,panretinal photocoagulation,mean blur rate,retinal blood ?ow
更新于2025-09-12 10:27:22
-
Investigation on intracavity SHG with controllable coherence in a degenerate laser
摘要： We investigate intracavity second harmonic generation (SHG) in a degenerate laser for generating green laser with controllable degree of coherence. It is shown that spatial coherence of the SHG emission can be controlled by varying the diameter of the limiting aperture in the degenerate laser resonator. The pumping power also affects the number of the oscillating transverse modes, so that influences the spatial coherence of the output laser. The laser of low coherence for speckle reduction has been demonstrated. It is shown that the laser of low spatial coherence may find applications in imaging, and laser display etc.
关键词： speckle suppression,lasers,Partially coherent,second harmonic generation,degenerate cavity
更新于2025-09-12 10:27:22
-
Interplay of temperature, thermal‐stresses and strains in laser‐assisted modification of collagenous tissues: Speckle‐contrast and OCT‐based studies
摘要： Moderate heating of collagenous tissues such as cartilage and cornea by infrared laser irradiation can produce biologically nondestructive structural rearrangements and relaxation of internal stresses resulting in the tissue reshaping. The reshaping results and eventual changes in optical and biological properties of the tissue strongly depend on the laser-irradiation regime. Here, a speckle-contrast technique based on monochromatic illumination of the tissue in combination with strain mapping by means of optical coherence elastography (OCE) is applied to reveal the interplay between the temperature and thermal stress fields producing tissue modifications. The speckle-based technique ensured en face visualization of cross correlation and contrast of speckle images, with evolving proportions between contributions of temperature increase and thermal-stresses determined by temperature gradients. The speckle-technique findings are corroborated by quantitative OCE-based depth-resolved imaging of irradiation-induced strain-evolution. The revealed relationships can be used for real-time control of the reshaping procedures (e.g., for laser shaping of cartilaginous implants in otolaryngology and maxillofacial surgery) and optimization of the laser-irradiation regimes to ensure the desired reshaping using lower and biologically safer temperatures. The figure of waterfall OCE-image demonstrates how the strain-rate maximum arising in the heating-beam center gradually splits and drifts towards the zones of maximal thermal stresses located at the temperature-profile slopes.
关键词： laser-tissue interaction,thermomechanical tissue reshaping,strain mapping,optical coherence elastography,speckle-contrast imaging
更新于2025-09-11 14:15:04
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Wavelength Independent Image Classification through a Multimode Fiber using Deep Neural Networks
摘要： Deep Neural Networks (DNNs) have been increasingly implemented in different research fields or industrial applications. Large amounts of data are processed daily in order to extract useful information using machine learning techniques. Many research groups have shown impressive results on improving resolution in microscopy and quantitative phase retrieval by training DNNs on real datasets. Recently, recovery and reconstruction of images after they have propagated through multimode optical fibers (MMFs) have also been achieved using DNNs. When images propagate through MMFs they suffer severe scrambling because the information gets distributed among the different spatial modes that the fiber supports. Furthermore, since the fiber modes propagate with different velocities, the local information of the input decorrelates after a few millimeters along the MMF, thus resulting in the formation of a speckle pattern at the output. Recovery of information from such speckle patterns is of practical interest for integrating the MMFs for endoscopic applications in medicine or for signal recovery in telecommunications.
关键词： Wavelength Independence,Image Classification,Speckle Patterns,Multimode Optical Fibers,Deep Neural Networks
更新于2025-09-11 14:15:04
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Speckle Noise Reduction by Fiber Scrambling for Improving the Measurement Precision of an Airborne Wind Lidar System
摘要： Optical guidance of coherent light in multimode fibers involves the generation of a speckle pattern at the fiber output due to the interference of the modes traveling in the fiber. Since the speckle pattern is sensitive to external perturbations (temperature, stress) as well as polarization and wavelength changes of the guided light, speckle noise is introduced limiting the quality and precision of fiber-coupled devices employed in various spectroscopic and imaging applications such as optical coherence tomography or differential absorption lidar. Speckle noise was also identified as one of the major contributors to the random error of an airborne direct-detection Doppler wind lidar which is a key instrument for the validation of the first spaceborne wind lidar Aeolus providing vertical wind profiles of the Earth. Significant reduction of the internal reference response fluctuations has been accomplished by integrating a fiber scrambler in front of the multimode fiber. The mode scrambler (GiGa Concept Inc.) is based on two counter-rotating step motors which squeeze a portion of a fiber at a time constant of a few milliseconds. Compressional and torsional stress of the fiber gives rise to local and stress-induced birefringence during these motions. This leads to a decorrelation of the modes supported by the fiber, thus homogenizing the intensity distribution at the fiber output and diminishing speckle noise. As a result, the response variations of the internal reference signal are lowered to 1.1 MHz (Mie) and 4.2 MHz (Rayleigh), which corresponds to a reduction in random wind error by a factor of about five (0.2 m/s) and two (0.8 m/s), respectively. In addition, the intensity fluctuations are decreased by 55% (Mie) and 22% (Rayleigh). Smoothing of the speckle pattern hence has a large impact on the measurement precision of the wind lidar and demonstrates the potential of fiber scramblers for improving the performance of fiber-coupled spectroscopic and imaging instruments suffering from speckle noise in general.
关键词： measurement precision,speckle noise,fiber scrambling,airborne wind lidar
更新于2025-09-11 14:15:04