Phase-shifting determination and pattern recognition using a modified Sagnac interferometer with multiple reflections.

This work has implemented a diverse modification of the Sagnac interferometer to accommodate various measurement requirements, including phase shifting, pattern recognition, and a morphological analysis. These modifications were introduced to validate the adaptability and versatility of the system. To enable phase shifting using the multiple light reflection technique, a half-wave plate (HWP) was utilized with rotations at 0, π/8, π/4, and 3π/8 radians, generating four interference patterns. It is possible to observe a distinct circular fringe width as the polarized light experiences diffraction at the interferometer's output as it travels through a circular aperture with various diameters ranging from 0.4 to 1 mm. Further modifications were made to the setup by inserting a pure glass and a fluoride-doped tin oxide (FTO) transparent substrate into the common path. This modification aimed to detect and analyze a horizontal fringe pattern. Subsequently, the FTO substrate was replaced with a bee leg to facilitate morphology recognition. A deep learning-based image processing technique was employed to analyze the bee leg morphology. The experimental results showed that the proposed scheme succeeded in achieving the phase shift, measuring hole diameters with errors smaller than 1.6%, separating distinct transparent crystals, and acquiring the morphological view of a bee's leg. The method also has successfully achieved an accurate surface area and background segmentation with an accuracy over 87%. Overall, the outcomes demonstrated the potential of proposed interferometers for various applications, and the advantages of the optical sensors were highlighted, particularly in microscopic applications.

NiO thickness measurement using a rectangular-type Sagnac interferometer as the material transport layer in a perovskite solar cell.

This work aims to utilize a phase-shifting technique in a rectangular-type Sagnac interferometer (RTSI) to measure the thickness of a thin film of nickel (II) oxide (NiO) in an electron transport layer (ETL) in perovskite solar cell preparation. The NiO layer is deposited on a fluorine-doped tin oxide (FTO) glass substrate. In the RTSI setup, the signal output from the interferometer is divided into the reference and testing arms using a nonpolarizing beam splitter (NPBS). The balanced photodetectors then detect the signal, with the FTO/NiO layer placed in the testing arm and pure FTO in the reference arm. By analyzing the signal intensities at polarization settings of 0° to 180°, the phase shift and thickness of the NiO layer can be determined. The thickness values of FTO and NiO films obtained through three different phase-shifting algorithms of three-, four-, and five-steps are calculated. The obtained NiO thickness values are validated against scanning electron microscopy (SEM). Finally, by considering the NiO thickness value that exhibits the lowest percentage error compared to one from SEM, it is confirmed that the three-step algorithm is the most suitable scheme for obtaining intensities at 0°, 45°, and 90°. Therefore, the proposed setup shows promise as a replacement for SEM in thickness measurements.

A flow quantification method using fluid dynamics regularization and MR tagging.

This paper presents a new method for improved flow analysis and quantification using MRI. The method incorporates fluid dynamics to regularize the flow quantification from tagged MR images. Specifically, the flow quantification is formulated as a minimization problem based on the following: 1) the Navier-Stokes equation governing the fluid dynamics; 2) the flow continuity equation and boundary conditions; and 3) the data consistency constraint. The minimization is carried out using a genetic algorithm. This method is tested using both computer simulations and MR flow experiments. The results are evaluated using flow vector fields from the computational fluid dynamics software package as a reference, which show that the new method can achieve more realistic and accurate flow quantifications than the conventional method.

A regularized flow quantification method using MRI tagging and Single Echo Acquisition imaging.

Single Echo Acquisition (SEA) imaging is a fully parallel imaging method that can be used to image rapid flow at the frame rate as high as 200 frames per second. Previous work has shown that SEA imaging can visualize turbulent flows, and discussed a preliminary tool for quantitatively analyzing 2D rapid fluid flows using SEA imaging and the HARmonic Phase (HARP) method. In this paper, the quantification method was further developed to use physical model to constrain the HARP flow analysis. Specifically, the method uses Navier-Stokes and continuity equations to regularize the flow analysis. The method is applied to the tagged SEA MR image sequence of turbulent flows to test its effectiveness. The results from the new method was demonstrated and compared with the flow field obtained from the conventional HARP method.

A new serial image registration method for contrast-enhanced MRI study.

This paper presents a new method for aligning serial images acquired in contrast-enhanced MRI studies. A unique feature of the proposed method is that it uses dynamic references, rather than a single reference image as in the conventional method, to obtain co-registration of serial images. Specifically, each image serves as a reference for its neighboring images and the overall registration of all serial images is derived subsequently. We tested the new method using a digital image phantom and in-vivo contrast-enhanced tumor MRI data, using a least-square registration criterion and a rigid-body spatial transformation. Preliminary results showed that the new method is generally more robust and accurate than the conventional method.