Papers by Keyword: Speckle

Abstract: An optical scheme using two correlationless beams to suppress the speckle of the pico-projection system is proposed. By using two broadband beam splitters (BBS) and two high reflection mirrors, the originally incident laser beam is split into two beams. The mutual correlation coefficient between two split beams is very close to zero. We use the haze reflection based on the random scattering model to simulate light reflected from the rough surface. In simulations, light is respectively reflected from the same size flat and rough surfaces and both recorded images are compared with each other. The image from flat surface is very clear on the detector plane. On the contrary, the image from rough surface is very fuzzy and the edge is hard to figure out. The simulations show that the speckle contrast ratio (CR) is reduced from 1.0 to 0.707. We find out a solution of the speckle CR less than 0.71 when the distance between two BBSs is 2.4 mm and the thickness of each BBS is 0.4 mm. Finally, we carry out an experiment and verify the simulating results. By our analysis from the experimental data, the speckle CR can be reduced about 25% which is close to the theoretical value of 29.3%.

Abstract: Speckle pattern interferometry can be used to measure he displacement, strain and vibration, surface deformation and surface roughness. And dynamic laser speckle measurement with high accuracy has been widely used in measurement of surface deformation. Tool breakage is the main bottleneck of high-speed intermittent cutting development, therefore, obtaining stress distribution of milling tools is a base of improving the tool design and tool life. Using a speckle measurement method of double pulsed digital based on FPGA, which involves the laser cutter, tools and CCD, transforms the high-speed dynamic measurement to quasi-static measurement. As a result, we can get two speckle images of front and back milling cutter surface and calculate the deformation ,strain and stress distribution of the tool surface with analysis.

Abstract: Optical Full Field Techniques (OFFT) are more and more utilized by mechanical laboratories. Among these methods, interferometry techniques (mainly composed of Speckle/Grating Interferometry or Speckle/Grating Shearography) are more difficult to use in a mechanical lab context, because of their sensitivity to external vibrations (except shearography), and because of the global lack of optical culture of mechanical engineers. Speckle-based methods are of great practical interest for the users, but their signal to noise ratio (SNR) is affected by the rigid body motion of the specimen. Here, the speckle decorrelation is minimized at local scale directly using the SNR. First, a shearography experiment is modeled to characterize the recorrelation procedure for a rigid body motion, a constant strain map and finally a high degree of localization. The mean noise level is found to be 6 times higher than a fully-correlated phase map for a 1 pixel speckle size. Last, a first application to a single-ply fabric composite lamina is shown. Resulting strain maps are of high quality with a very low spatial resolution (4 pixels). The local bending / global tension coupling effect is clearly put in evidence.

Abstract: Our recent work [1] theoretically revealed that speckles can be formed when nanofluids containing a modest volume fraction of nanoparticles are illuminated by a monochromatic laser beam. This paper focuses on the key issues, including the experimental setup, the particle volume fraction of the nanofluid, the flow velocity of the nanofluid and the diameter of the pipe, in measuring the velocities of nanoparticles in nanofluids with laser speckle velocimetry (LSV). First an experimental setup is established according to the optical characteristics of nanoparticle and the measuring principles of particle image velocimetry (PIV) and LSV. Then a conclusion is made from the experimental results that clear speckle patterns can be formed when the particle volume fraction is between 0.0005% and 0.002% is able to form. Finally, in order to make it applicable to utilize LSV to measure the velocities of nanoparticles in nanofluids that flow in pipe, nanofluids can not flow too fast and the diameter of the pipe should not be too small.

Abstract: The two-dimensional deformation of wood with different grains under shearing loads was measured using an electronic speckle pattern interferometry (ESPI) technique. The radical, tangential and end sections of Douglas firs (Pseudotsuga menziesii) were used as specimens. Results revealed that the deformation values significantly vary for every part of the specimens, and the ring directions of earlywood and latewood, which compose the annual rings, have an effect on the two-dimensional deformation of wood.

Abstract: The two-dimensional deformation of wood under shearing loads is measured using an electronic speckle pattern interferometry (ESPI) technique. The radical and tangential sections of Douglas firs are used as specimens in the longitudinal direction. Results reveal that large two-dimensional deformation of the wood can be measured using the ESPI technique, the deformation values significantly vary for every part of the specimens, and the ring directions of earlywood and latewood, which compose the annual rings, have an effect on the two-dimensional deformation of wood.

Abstract: This study is concerned with the fundamental characteristics of a new nondestructive measuring technique of the tooth roughness with precisely. In the dental clinics, the estimation of roughness of tooth surfaces with a hand explorer is one of the important tests for the finishing the crown re-shaping and resin fillings. If the tooth surface is rough enough to hold dental plaque, it occasio-nally causes dental diseases around it. Therefore, it is important to measure the roughness of the tooth surfaces for the prevention of furthermore distraction of the tooth. Laser speckle measurement is used as an evaluation method for objectively measuring the surface roughness with non-contact. In this study, a laser speckle measurement system for measuring the surface roughness is constructed. Comparison measurement is carried out for the tooth pieces with the various unidirectional roughness and the metallic test pieces with the standard roughness. The experimental results using the actual measuring system show some important points as follows. Firstly, there is a good correla-tion between the laser speckle pattern and the tooth roughness as well as that of the metallic test pieces. Secondly, the reflection from the tooth shows a different tendency in comparison with the reflection from the metallic test pieces.