Contrast Of Fringe Pattern Research Articles

Modeling window smoothing effect hidden in fringe projection profilometry

The reconstruction using MEMS micro-vibration mirrors is the most promising. However, the influence mechanism of the line laser, which serves as the sole light source of MEMS-based systems, on reconstruction is unclear. To fill this theoretical gap, we propose the first interpretable laser influence model called the window smoothing model. This model reveals the window smoothing effect of laser beam scanning and quantifies its impact on modulation intensity through a decay factor. Given the absence of lens defocusing issues, the window smoothing effect becomes the primary factor affecting the contrast of fringe patterns. Therefore, a novel method using laser parameters to evaluate system accuracy is introduced. Leveraging these insights, we further propose an optimal fringe number calibration method, also based on laser parameters, to maximize the reconstruction accuracy of any given system. Finally, experimental results validate the effectiveness of the proposed method. As the first model tailored for MEMS systems, the window smoothing model is interpretable, highly accurate, and universal. Therefore, this model can provide new insights and a theoretical foundation for achieving high-performance MEMS-based reconstruction.

Rapid 3D reconstruction method based on the polarization-enhanced fringe pattern of an HDR object

Measurement of high dynamic range objects is an obstacle in structured light 3D measurement. They entail both over-exposed and low-exposed pixels in a single exposure. This paper proposed a polarization-enhanced fringe pattern (PEFP) method that a high dynamic range image can be obtained within a single exposure time. The degree of linear polarization (DOLP) is calculated using the polarization properties of reflected light and a linear polarizer in fixed azimuth in this method. The DOLP is efficiently estimated by the projected polarization-state-encode (PSE) pattern, and it does not need to change the state of the polarizer. The DOLP depends on light intensity rather than the reflectivity of the object surfaces indicated in experimental results. The contrast of fringe patterns was enhanced, and the quality of fringe patterns was improved by the proposed method. More sufficient 3D point clouds and high-quality shape can be recovered using this method.

Visualization of magnetic domain structure in FeSi based high permeability steel plates by neutron imaging

In the present work, a combined study with polarized neutron imaging (PNI) and neutron-grating interferometry based dark field imaging (DFI) experiments on grain oriented high permeability steel sample with 3% Si and 0.35 mm thickness is reported. With the combination of these two experimental techniques it was possible to obtain the complex picture of magnetic domain distribution and domain walls in the electric steel samples. With the PNI technique, the observed fringe pattern contrast may be correlated with basic magnetic domains. These magnetic domains are oriented anti-parallel with respect to each other and the different magnetic field in each domain may lead to fringe pattern contrast. The magnetic domains are disrupted at the grain boundaries, observed as discontinuities in the fringe pattern contrast. In comparison, with DFI measurements, we visualized scattering contrast from magnetic domain walls. A clear correlation between basic domains (from PNI) and domain walls (using DFI) is observed. In the current study we also demonstrate the potential of combining two differential experimental techniques to visualize and obtain collective information about magnetic domains and domain walls.

Tilted and axis-shift Lloyd's mirror system for recording low-density and large-area holographic grating

It is difficult to record holographic gratings of low density (<100 lines/mm) and large area simultaneously using traditional holographic system. In order to produce both low-density and large-area holographic gratings, a tilted and axis-shift (TAS) Lloyd's mirror system was designed for recording such holographic gratings. The recording area will increase largely especially for gratings of low density, by setting the angle between the Lloyd's mirror and the substrate larger than 90°, and meanwhile, by enlarging the intersection angle of incident light and mirror surface. Insuring the projected area onto the substrate by reflex equal to the incident area directly onto the substrate, the optical axis was shifted to realize the maximization of utilization of interference area. The contrast of fringe pattern was analyzed by the coherence for the laser beam in the space and time scale. The TAS Lloyd's mirror system for 60 lines/mm grating in the contrast of 0.8 was optimized, and as a result, the interference area was increased by about 150 times comparing to the traditional Lloyd's mirror system using the Lloyd's mirror of same dimensions.

Photorefractive Fourier transform profilometer for the measurement of 3-D object shapes

In the present work dynamic moiré-like fringe patterns, produced by photorefraction with low spatial frequencies, applied for profile determination of small objects is proposed. Basically, a Fourier transform profilometry technique is developed for an automated profile determination. This means, as far as we know, a new experimental procedure that exploits the real time holographic two wave mixing in Bi12TiO20 crystal sample. Besides, the mainly advantages of this procedure are, comparatively to the classical fringe projection method using the Michelson interferometer, best fringe pattern contrast, less speckle noise, absence of noises produced by spurious reflections and, the most significant, a pure sinusoidal shape obtained by dynamic holographic moiré-like process using photorefraction.

Improvement of the signal-to-noise ratio in interferometry using multi-frame high-dynamic-range and normalization algorithms

Using both high dynamic range (HDR) and normalization methodologies, we show a method to improve the fringe pattern contrast in interferometric measurements normally used for phase recovering. In a simulated interferogram that mimics the main effects that can be found in an interferometric process (stray-light, photon noise, electronic noise, scattering phenomena, etc.) it was possible to improve the contrast of the fringes and to decrease the root mean square error by more than 35%. The method proposed is applied to experimental interferograms to measure wavefront error and retardance changes on liquid crystal (LC) devices. It is done by using a Mach–Zehnder set-up in which we used different polarization areas. The proposed method increases the quality of the phase recovered and decreases the root mean square error by 50%.

Electronic speckle pattern shearing interferometer with a photopolymer holographic grating.

A photopolymer holographic grating is used to produce the two sheared images in an electronic speckle pattern shearing interferometer. A ground glass screen following the grating eliminates unwanted diffraction orders and removes the requirement for the CCD camera to resolve the diffraction grating's pitch. The sheared images on the ground glass are further imaged onto the CCD camera. The fringe pattern contrast was estimated to be above 90%. A validation of the system was done by comparing the theoretical phase difference distribution with the experimental data from the three-point bending test.