Tomographic Background Oriented Schlieren using Plenoptic Cameras

2021 ◽  
Author(s):  
Jenna K Davis ◽  
Christopher J. Clifford ◽  
Dustin Kelly ◽  
B Thurow
Keyword(s):  
Refractive Index ◽  
Water Solution ◽  
Reconstruction Algorithm ◽  
3D Reconstructions ◽  
Single View ◽  
Plenoptic Camera ◽  
Flow Features ◽  
Ghosting Artifacts ◽  
Discrete Flow ◽  
Quantitative Results

Abstract The development of a tomographic BOS implementation system utilizing up to four plenoptic cameras is presented. A systematic set of experiments was performed using a pair of solid dimethylpolysiloxan (PDMS) cylinders immersed in a nearly refractive index matched gylcerol/water solution to represent discrete flow features with known sizes, shapes, separation distances, and orientation. A study was conducted to assess the influence of these features on the accuracy of 3D reconstructions of the refractive index field. It was determined that the limited angular information collected by a single plenoptic camera is insufficient for single-camera 3D reconstructions. In multi-camera configurations, the additional views collected by a plenoptic camera were shown to improve the overall reconstruction accuracy compared to an equivalent single view per camera reconstruction, potentially reducing the number of overall cameras needed to achieve a desired accuracy. For the imaging of two cylinders, three or more cameras are generally needed to avoid significant ghosting artifacts in the reconstruction. Quantitative results are presented that show that: (1) two separate cylinders will be individually resolved as long as measurements from one camera are able to observe separation between the cylinders; (2) the error in the reconstructed 3D refractive index field increases as the size of the feature decreases; and (3) the use of volumetric masking within the reconstruction algorithm is critical in order to improve the accuracy of the solution.

scholarly journals Compton scattering tomography for agricultural measurements

2006 ◽  
Vol 26 (1) ◽  
pp. 151-160 ◽  
Author(s):  
Paulo E. Cruvinel ◽  
Fatai A. Balogun
Keyword(s):  
Compton Scattering ◽  
Linear Correlation ◽  
Imaging Technique ◽  
Reconstruction Algorithm ◽  
Transmission Tomography ◽  
Electronic Density ◽  
New Approach ◽  
Quantitative Results ◽  
Water Contents ◽  
Better Than

This paper presents a new approach in tomographic instrumentation for agriculture based on Compton scattering, which allows for the simultaneous measurements of density and moisture of soil samples. Compton tomography is a technique that can be used to obtain a spatial map of electronic density of samples. Quantitative results can be obtained by using a reconstruction algorithm that takes into account the absorption of incident and scattered radiation. Results show a coefficient of linear correlation better than 0.81, when comparison is made between soil density measurements based on this method and direct transmission tomography. For soil water contents, a coefficient of linear correlation better than 0.79 was found when compared with measurements obtained by time domain reflectrometry (TDR). In addition, a set of Compton scatter images are presented to illustrate the efficacy of this imaging technique, which makes possible improved spatial variability analysis of pre-established planes.

scholarly journals THE VISIBILITY OF MONOCHROMATIC RADIATION AND THE ABSORPTION SPECTRUM OF VISUAL PURPLE

1922 ◽  
Vol 5 (1) ◽  
pp. 1-33 ◽  
Author(s):  
Selig Hecht ◽  
Robert E. Williams
Keyword(s):  
Refractive Index ◽  
Absorption Spectrum ◽  
Absorption Coefficient ◽  
Experimental Verification ◽  
High Intensity ◽  
Absorption Maximum ◽  
Water Solution ◽  
Wave Length ◽  
Relative Energy ◽  
Existing Data

1. After a consideration of the existing data and of the sources of error involved, an arrangement of apparatus, free from these errors, is described for measuring the relative energy necessary in different portions of the spectrum in order to produce a colorless sensation in the eye. 2. Following certain reasoning, it is shown that the reciprocal of this relative energy at any wave-length is proportional to the absorption coefficient of a sensitive substance in the eye. The absorption spectrum of this substance is then mapped out. 3. The curve representing the visibility of the spectrum at very low intensities has exactly the same shape as that for the visibility at high intensities involving color vision. The only difference between them is their position in the spectrum, that at high intensities being 48 µµ farther toward the red. 4. The possibility is considered that the sensitive substances responsible for the two visibility curves are identical, and reasons are developed for the failure to demonstrate optically the presence of a colored substance in the cones. The shift of the high intensity visibility curve toward the red is explained in terms of Kundt's rule for the progressive shift of the absorption maximum of a substance in solvents of increasing refractive index and density. 5. Assuming Kundt's rule, it is deduced that the absorption spectrum of visual purple as measured directly in water solution should not coincide with its position in the rods, because of the greater density and refractive index of the rods. It is then shown that, measured by the position of the visibility curve at low intensities, this shift toward the red actually occurs, and is about 7 or 8 µµ in extent. Examination of the older data consistently confirms this difference of position between the curves representing visibility at low intensities and those representing the absorption spectrum of visual purple in water solution. 6. It is therefore held as a possible hypothesis, capable of direct, experimental verification, that the same substance—visual purple—whose absorption maximum in water solution is at 503 µµ, is dissolved in the rods where its absorption maximum is at 511 µµ, and in the cones where its maximum is at 554 µµ (or at 540 µµ, if macular absorption is taken into account, as indeed it must be).

Investigation of limitations of optical diffraction tomography

2007 ◽  
Vol 15 (2) ◽  
Author(s):  
T. Kozacki ◽  
M. Kujawińska ◽  
P. Kniażewski
Keyword(s):  
Refractive Index ◽  
Dynamic Range ◽  
Tomographic Reconstruction ◽  
Back Propagation ◽  
Reconstruction Algorithm ◽  
Optical Diffraction ◽  
Diffraction Tomography ◽  
Refractive Index Distribution ◽  
Optical Diffraction Tomography ◽  
Index Distribution

AbstractOptical diffraction tomography (ODT) applied to measurement of optical microelements is limited by low dynamic range, i.e., only objects with small deviations of refractive-index distribution can be measured. Therefore in this paper the limitations and errors of ODT are investigated throughout extensive numerical experiments. It is shown that these errors can be reduced by introduction of additional numerical focusing in the tomographic reconstruction algorithm. Additionally, new tomographic reconstruction algorithm using back propagation in reference medium for optical microelements measurement with known design is proposed. This hybrid reconstruction algorithm allows significant extension of ODT applicability in measurement of elements having large deviations of refractive-index distribution.

scholarly journals Whispering Gallery Mode Resonator Temperature Compensation and Refractive Index Sensing in Glucose Droplets

Sensors ◽  
2021 ◽  
Vol 21 (21) ◽  
pp. 7184
Author(s):  
Inga Brice ◽  
Karlis Grundsteins ◽  
Kristians Draguns ◽  
Aigars Atvars ◽  
Janis Alnis
Keyword(s):  
Refractive Index ◽  
Water Solution ◽  
Whispering Gallery Mode ◽  
Dip Coating ◽  
Temperature Measurements ◽  
Photonic Sensor ◽  
Whispering Gallery ◽  
Resonance Shift ◽  
Glucose Water ◽  
High Level

Among the different types of photonic sensor devices, optical whispering gallery mode resonators (WGMRs) have attracted interest due to their high level of sensitivity, small size, and ability to perform real-time temperature measurements. Here we demonstrate the applicability of temperature measurements using WGMR in both air and liquid environments. We also show that WGMR allowed measurements of the refractive index variations in an evaporating glucose–water solution droplet. The thermal tuning of WGMR can be reduced by coating WGMRs with a thin layer of polymethyl methacrylate (PMMA). Dip-coating the silica microsphere multiple times significantly reduced the resonance shift, partially compensating for the positive thermo-optical coefficient of silica. The shift direction changed the sign eventually.

Influence of Inorganic Salts on the Refraction Index of Water

2014 ◽  
Vol 716-717 ◽  
pp. 118-121
Author(s):  
Xin Yi Zhao ◽  
Yu Feng Peng ◽  
Cong Cong Zhai ◽  
Xue Yun Han ◽  
Yi Zhang
Keyword(s):  
Refractive Index ◽  
Inorganic Salt ◽  
Water Solution ◽  
Refraction Index ◽  
Laser Wavelength ◽  
Index Of Refraction ◽  
Inorganic Salts ◽  
Distilled Water ◽  
Salt Solutions ◽  
Abbe Refractometer

The refractive index of double-distilled water and inorganic salt solutions of concentrations varying from 0.4 to 100 ppt (‰) have been measured at 20 Celsius degrees using Abbe refractometer, respectively. The inorganic salts such as NaCl, MgSO4, KCl and MgCl2,these forming the major constituents of seawater are used as solutes of the water solution. The effect of the concentration of these constituents on the refractive index of the solution is experimentally investigated. And meanwhile, the index of refraction studies are carried out for the laser wavelength of 405nm, 450nm, 532nm and 633nm under the case of varying concentration. The results show that the refractive index of the solution will be linearly increased with the increase of the concentration of these constituents. The index of refraction differs for the different solutes when their concentration is same at a certain wavelength.

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