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Speckle Methods in Experimental Mechanics
Published in Rajpal S. Sirohi, Speckle Metrology, 2020
Instead of using the full aperture of the lens, a mask containing two or more apertures is placed at the entrance pupil of the lens. This modifies the optical transfer function of the lens. From the speckle metrology point of view, the speckle size increases at the image plane. Also the depth of focus or depth of field increases. Furthermore, each speckle pattern is modulated by Young’s-type fringes. During filtering these Young’s fringes diffract light in well-defined directions. Therefore there is no need to place an aperture at the filtering plane while carrying out whole-field filtering. Because there is considerably more light available in these so-called diffraction halos, there is an enormous gain in the signal-to-noise ratio, resulting in almost unit contrast fringes [17]. There are other advantages as well. For example, both u and υ in-plane components can be measured simultaneously. Multiplexing using theta modulation or/and frequency modulation is possible [18].
Optical Profiling Techniques for MEMS Measurement
Published in Wolfgang Osten, Optical Inspection of Microsystems, 2019
Klaus Körner, Johann Krauter, Aiko Ruprecht, Tobias Wiesendanger
Recently, a new proposal has been reported for topography measurement on the microscopic scale to increase the application range of the fringe projection technique with only one grating [40]; this has some advantages compared with other approaches. Instead of using optics with a rather low numerical aperture, objectives with a high numerical aperture are used to reduce the depth of focus to a reasonable range. Extended objects are now illuminated and imaged with some parts that are in focus and other parts that are considerably blurred. Using the additional depth scanning of the measurement system or of the object, the surface topography is determined, as in white-light interferometry, but on a coarser scale. Therefore, similar acquisition and evaluation algorithms can be used for this special type of fringe projection technique.
Research Methods of Nanostructures and Nanomaterials
Published in Zulkhair A. Mansurov, Carbon Nanomaterials in Biomedicine and the Environment, 2020
Zulkhair A. Mansurov, Nina. N. Mofa, Tatyana A. Shabanova
The advantage of SEM in comparison with the optical microscope which utilizes light is its depth of focus and resolving capability. For the optical microscope, the depth of focus is the distance above and below the image plane over which the image appears in focus. As the magnification increases in the optical microscope, the depth of focus decreases. The three-dimensional appearance of the specimen image is a direct result of the large depth of field of the SEM. It is this large depth of fields that is the most attractive feature of the scanning electron microscope. The steep surface and edges (cliffs) tend to be brighter than flat surfaces resulting in images with good three-dimensional contrast [5].
Repeatability and reproducibility of anterior lens zonule length measurement using ArcScan insight 100 very high-frequency ultrasound
Published in Expert Review of Medical Devices, 2023
Zehui Zhu, Han Zou, Hongzhe Li, Xueer Wu, Yiyi Wang, Zhangliang Li, Yune Zhao
Previous in vivo studies on zonules mainly depended on ultrasound biomicroscopy (UBM). The UBM technique produces precise biometric measurements of the anterior ocular segments, including the structures behind the iris. During the UBM examination, subjects must be supine, which has the potential to influence the measurement results [8,9]. Insight 100 is a newly developed ultrasound device that works on the same principle as UBM but with a mechanically controlled transducer, which facilitates easier usage [6,10]. Subjects, in a sitting position, were examined through a disposable eyepiece, which helps to prevent cross-contamination (Figure 1). The alignment position and depth of focus can be set manually, thus enabling the acquisition of high-quality scans of the anterior lens zonule.
Design of multi-auxetic microstructures for sound absorbing applications
Published in Advanced Composite Materials, 2023
The polyurethane-based multi-auxetic foams were prepared by a facile and scalable method, using a mechanically triaxial thermal compression method and precise laser cutting method with long focal lens, as illustrated in Figure 1(a-c). Through this laser cutting strategy that enables precise control, the normal polyurethane foam (NF) is cut with different diameters every halfway through in the direction of its height, as shown in Figure 1(b). Since the thickness of the NF is thicker than the depth of focus of the single-focal condenser lens mounted on the CO2 laser cutting machine, the problem of uneven NF cutting occurs during the manufacturing process. Therefore, the NF is cut by replacing it with a long-focal lens, limiting the power of the CO2 laser to 27% of 100 W, and setting the speed of the laser head to 50 mm/s. Then, to manipulate the microstructure of the NF, a mechanical thermal compression process was conducted using a frame at 150° for 1 h. Triaxially processed NF was compressed from 0% to 50% in all directions of a cylindrical frame mold.
Synthetic wavelength scanning interferometry for 3D surface profilometry with extended range of height measurement using multi-colour LED light sources
Published in Journal of Modern Optics, 2023
Priyanka Mann, Vishesh Dubey, Azeem Ahmad, Ankit Butola, Dalip Singh Mehta
Interference takes place only when the two optical path lengths are equal and interference fringes can be observed, as far as the optical path difference introduced by the object step height is within the coherence length of the tuned light source. This microscope objective lens is attached to a piezo-electric transducer (PZT) (Piezo, Jena, MIPOS 3) to generate the phase-shifted interferograms. The PZT is driven by an amplifier which is controlled by the computer, and it shifts the inbuilt reference mirror in the vertical direction to generate the optical path difference and introduces the phase shift between the reference and the object beams. Since the vertical movement of the objective lens was less than the depth of focus of the objective lens; therefore, the sample remains within focus throughout the whole measurement. Phase-shifted colour interferograms are stored in the computer for further processing.