KEYWORDS: Tissues, Objectives, Image resolution, Light sources and illumination, Microscopy, Visualization, Lenses, In vivo imaging, Point spread functions, Optical microsystems
We have developed a compact scattering-based light sheet microscopy (sLSM) probe capable of imaging unstained tissues with cellular resolution. In the compact sLSM probe, a custom miniature objective lens was developed to achieve a high lateral resolution, large field of view (FOV), and small field curvature. The measured resolution of the custom objective was 1.65 to 1.97 μm across the FOV of ±1.0 mm. The compact probe had dimensions of 4 cm in width and height and 10 cm in length. The compact sLSM probe achieved an axial resolution better than 5.6 μm over a depth range of 206.2 μm and a lateral resolution of 1.9 μm. Preliminary results showed that the compact sLSM probe could visualize cellular details of fixed human anal epithelial tissues in a similar manner to a bench light sheet microscopy device using off-the-shelf objective lenses.
We developed and tested a system for measuring the through-focus point spread function (PSF) for IOLs and converting it to the modulation transfer function (MTF). The system consists of a light source, eye model, a test IOL, a 10X magnifier, and a 16-bit CCD camera. By capturing the image of the IOL through a range of focus positions, the PSF can be found and then converted to MTF. Unlike basic monofocal lenses, multifocal IOLs can focus at two or more positions, while extended depth of field (EDOF) IOLs lenses provide a continuum of foci. These advanced IOLs are beneficial as they more closely resemble the natural range of focus of the eye. The modulation transfer function (MTF) is a standard approach for IOL characterization, but existing MTF measurement methodology is not optimized for multifocal or EDOF IOLs. As IOLs continue to evolve, using the MTF to predict image quality is vital to implanting the most appropriate lens in the patient’s eyes.
We have recently developed a low-cost (material cost = $1,500), smartphone-compatible confocal endomicroscope. By using a custom, hyper-chromatic objective lens, the confocal endomicroscope generated cross-sectional confocal images over a depth range of 110 µm. The confocal endomicroscope achieved lateral resolution of 2 µm and axial resolution of 4 µm. The imaging speed was 4 fps. Preliminary results from the pilot study of imaging the human cervix in vivo in Uganda showed that the confocal endomicroscope could visualize distinctive, bright objects with a similar distribution to squamous epithelial cell nuclei.
We have developed an axially spectrally-encoded confocal endomicroscope that can visualize multiple depths of the tissue in a single image frame. We developed a custom hyperchromatic objective lens (focal length = 4.8 mm; NA = 0.68) to focus different wavelengths from a broadband light source into different axial depths of the tissue. The confocal endomicroscope achieved lateral and axial resolution of 2 μm and 4 μm, respectively over a lateral field of 468 μm and an axial depth range of 100 μm. The material cost was < $1500. Preliminary confocal images of human tissues in vivo clearly visualized cellular details.
We have developed a low-cost (material cost < $2,000) chromatic confocal endomicroscope capable of cross-sectional imaging of the tissue at lateral and axial resolution of 1.55μm and 9.5μm, respectively.
In this paper, we demonstrate deep learning-based denoising of high-speed (180 fps) confocal images obtained with our low-cost SECM device. The CARE network was trained with 3090 high- and low-SNR image pairs on the Google Colab platform and tested with 45 unseen image pairs. The CARE prediction showed significant increase of SSIM and PSNR, and reduction of the banding noise while maintaining the cellular details. The preliminary results show the potential of using a deep learning-based denoising approach to enable high-speed SECM imaging.
We developed a smartphone-based epifluorescence microscope for fresh tissue imaging. The smartphone microscope optics was optimally designed to achieve similar resolution (0.56 μm) and FOV (520 μm) as the bench 40x microscope, commonly used during the histopathologic analysis. Preliminary images obtained from an excised human pancreatic tissue stained with a rapid staining fluorescence dye (PARPi-FL) clearly visualized individual tumor cells.
The polymerization dynamics and microstructure of the fibrin network is vital to hemostasis. During cardiac surgery, heparin is administered to prevent bleeding and reversed using protamine at the end of surgery. Residual heparin and inadequate reversal following surgery impair fibrin integrity, likely associated with major postoperative blood loss. In this study, we apply a recent approach, SECM, to evaluate fibrin integrity in blood clots during heparin administration and protamine reversal in cardiac surgery patients. SECM’s capability for video rate microscopy over large fields of view with a spatial resolution of 0.4x1.0µm permits the dynamic assessment of fibrin polymerization and 3D microstructure. Plasma from 10 patients was collected during cardiac surgery at baseline and following protamine reversal. In addition, the dose-dependent response of heparin was studied by spiking 6 normal plasma samples at heparin doses of 0.1-2USP/mL. All samples were tested using SECM and clot polymerization parameters including fibrin time (FT) and fibrin density (FD) were derived. In cardiac surgical patients, FD was lower after protamine reversal (p<0.05) compared to baseline despite similar FT, suggesting that fibrin microstructure is not restored immediately after surgery. In spiked samples, fibrin polymerization was delayed with higher FT (p<0.05), fibrin strands were longer, and the FD was lower (p<0.05) with increasing heparin dose. Similar to surgical samples, FD was not restored following protamine reversal (p<0.01) in spiked samples. These studies show that the loss of fibrin integrity following cardiac surgery can be quantified using SECM, which may provide new insights on mechanisms of postoperative bleeding.
Utilizing spatial wavelength encoding, spectrally encoded endoscopy (SEE) makes it possible to create miniature, small diameter endoscopic probes that can allow easy access to hard-to-reach locations within the body. Previously described SEE probes have been side-viewing, which limits their use for guiding the navigation of narrow passages. Forward-viewing SEE (FVSEE) probes are advantageous as they provide a look ahead that facilitates navigation and surveillance of a wider field of view (FOV). In this work, we present a novel FVSEE probe. The 500-µm illumination optics are designed in such a way that the shortest wavelength (460 nm) propagates along the optical axis, while an angle of approximately 56° is formed between the longest wavelength (720 nm) and the optical axis. Two-dimensional illumination was accomplished by rotating the illumination optics at a speed of 15 rps using a miniature torque coil. Reflected light from the sample was collected by 8 multimode detection fibers that were arranged into a circular array around the illumination optics. The proximal ends of the detection fibers were polished at a 17° angle, resulting in a total angle of detection of approximately 100°. Light coming out from the distal end of the detection fibers, which were rearranged into a linear array, was detected using a custom spectrometer with a tall-pixel linear CCD camera. The FVSEE probe was used to conduct a preclinical imaging of a swine joint. The results were compared to a commercial chip-on-the-tip mini-endoscope and showed a better spatial resolution and a wider FOV using the FVSEE probe.
Utilizing spatial wavelength encoding, spectrally encoded endoscopy (SEE) makes it possible to create miniature, small diameter endoscopic probes that can allow easy access to hard-to-reach locations within the body. Previously described SEE probes have been side-viewing, which limits their use for guiding the navigation of narrow passages. Forward-viewing SEE probes are advantageous as they provide a look ahead that facilitates navigation and surveillance of a wider field of view. In this work, we present a novel forward-viewing SEE probe. The 500-µm illumination optics are designed in such a way that the shortest wavelength (460 nm) propagates along the optical axis, while an angle of approximately 56° is formed between the longest wavelength (720 nm) and the optical axis. Two-dimensional illumination was accomplished by rotating the illumination optics at a speed of 15 rps using a miniature torque coil. Reflected light from the sample was collected by 8 multimode detection fibers that were arranged into a circular array around the illumination optics. The proximal ends of the detection fibers were polished at a 17° angle, resulting in a total angle of detection of approximately 100°. Light coming out from the distal end of the detection fibers, which were rearranged into a linear array, was detected using a custom spectrometer with a tall-pixel linear CCD camera. Similar to the theoretical value, an effective FOV of 23 mm at a focal distance of 10 mm was measured by imaging a grid pattern. Preliminary results demonstrate the potential of the forward-viewing SEE probe for a variety of medical imaging applications.
Dukho Do, DongKyun Kang, Nima Tabatabaei, Catriona Grant, Norman Nishioka, Mireille Rosenberg, Paul Hesterberg, Qian Yuan, John Garber, Aubrey Katz, Wayne Shreffler, Guillermo Tearney
Eosinophilic Esophagitis (EoE) is an inflammatory disease caused by inhaled or ingested food allergies, and characterized by the infiltration of eosinophils in the esophagus. The gold standard for diagnosing EoE is to conduct endoscopy and obtain multiple biopsy specimens from different portions of the esophagus; an exam is considered positive if more than 15 eosinophils per high power field (HPF) in any of the biopsies. This method of diagnosis is problematic because endoscopic biopsy is expensive and poorly tolerated and the esophageal eosinophil burden needs to be monitored frequently during the course of the disease. Spectrally encoded confocal microscopy (SECM) is a high-speed confocal microscopy technology that can visualize individual eosinophils in large microscopic images of the human esophagus, equivalent to more than 30,000 HPF. Previously, we have demonstrated that tethered capsule SECM can be conducted in unsedated subjects with diagnosed EoE. However, speckle noise and the relatively low resolution in images obtained with the first capsule prototypes made it challenging to distinguish eosinophils from other cells. In this work, we present a next-generation tethered SECM capsule, which has been modified to significantly improve image quality. First, we substituted the single mode fiber with a dual-clad fiber to reduce speckle noise. A gradient-index multimode fiber was fusion spliced at the tip of the dual-clad fiber to increase the effective numerical aperture of the fiber from 0.09 to 0.15, expanding the beam more rapidly to increase the illumination aperture at the objective. These modifications enabled the new SECM capsule to achieve a lateral resolution of 1.8 µm and an axial resolution of 16.1 µm, which substantially improves the capacity of this probe to visualize cellular features in human tissue. The total size of the SECM capsule remained 6.75 mm in diameter and 31 mm in length. We are now in the process of testing this new SECM capsule in humans. Early results using this new SECM capsule suggest that this technology has the potential to be an effective tool for the diagnosis of EoE.
Eosinophilic Esophagitis (EoE) is caused by food allergies, and defined by histological presence of eosinophil cells in the esophagus. The current gold standard for EoE diagnosis is endoscopy with pinch biopsy to detect more than 15 eosinophils/ High power field (HPF). Biopsy examinations are expensive, time consuming and are difficult to tolerate for patients. Spectrally encoded confocal microscopy (SECM) is a high-speed reflectance confocal microscopy technology capable of imaging individual eosinophils as highly scattering cells (diameter between 8 µm to 15 µm) in the epithelium. Our lab has developed a tethered SECM capsule that can be swallowed by unsedated patients. The capsule acquires large area confocal images, equivalent to more than 30,000 HPFs, as it traverses through the esophagus. In this paper, we present the outcome of a clinical study using the tethered SECM capsule for diagnosing EoE. To date, 32 subjects have been enrolled in this study. 88% of the subjects swallowed the capsules without difficulty and of those who swallowed the capsule, 95% preferred the tethered capsule imaging procedure to sedated endoscopic biopsy. Each imaging session took about 12 ± 2.4 minutes during which 8 images each spanning of 24 ± 5 cm2 of the esophagus were acquired. SECM images acquired from EoE patients showed abundant eosinophils as highly scattering cells in squamous epithelium. Results from this study suggest that the SECM capsule has the potential to become a less-invasive, cost-effective tool for diagnosing EoE and monitoring the response of this disease to therapy.
Spectrally encoded confocal microscopy (SECM) is a high-speed confocal endomicroscopy technology that can image extremely large regions of human tissue at cellular resolution within a short imaging time. Previously, we have developed a 7-mm-diameter SECM endoscopic capsule and successfully demonstrated imaging of human esophagus in vivo. Even though we were able to successfully capture images with the previous capsule, it suffered from two limitations: (1) the capsule had a small diameter, which provided a limited contact between SECM capsule and esophagus; and (2) speckle noise in SECM images made it challenging to appreciate cellular features.
In this paper, we present a new SECM capsule, termed SECM half-inch tethered endoscopic capsule (HITEC), which addresses the two aforementioned technical challenges. With the SECM HITEC, a dual-clad fiber was used to reduce the speckle noise. Miniature GRIN optics was used to increase the NA of the fiber from 0.09 to 0.25, which made it possible to build a SECM capsule with large diameter (12.7 mm) while maintaining a short rigid length (22 mm). A water-immersion objective lens was custom designed and manufactured to provide high NA of 0.7.
We have manufactured the SECM HITEC catheter and tested its optical and mechanical performance. Lateral and axial resolution was measured as 1.2 µm and 13 µm, respectively. We have imaged swine esophageal tissues ex vivo, and SECM images clearly visualized cell nuclei. Non-uniform rotational distortion (NURD) was small, less than 5%.
Preliminary results suggest that SECM HITEC provides sufficient optical and mechanical performance for tissue imaging. In a future clinical study, we will test the feasibility of utilizing SECM HITEC for improved cellular imaging human of the human esophagus in vivo.
Spectrally encoded endoscopy (SEE) is a miniature endoscopic technology that can acquire images of internal organs through a hair-thin probe. While most previously described SEE probes have been side viewing, forward-view (FV)-SEE is advantageous in certain clinical applications as it provides more natural navigation of the probe and has the potential to provide a wider field of view. Prior implementations of FV-SEE used multiple optical elements that increase fabrication complexity and may diminish the robustness of the device. In this paper, we present a new design that uses a monolithic optical element to realize FV-SEE imaging. The optical element is specially designed spacer, fabricated from a 500-μm-glass rod that has a mirror surface on one side and a grating stamped on its distal end. The mirror surface is used to change the incident angle on the grating to diffract the shortest wavelength of the spectrum so that it is parallel to the optical axis. Rotating the SEE optics creates a circular FV-SEE image. Custom-designed software processes FV-SEE images into circular images, which are displayed in real-time. In order to demonstrate this new design, we have constructed the FV-SEE optical element using a 1379 lines/mm diffraction grating. When illuminated with a source with a spectral bandwidth of 420-820 nm, the FV-SEE optical element provides 678 resolvable points per line. The imaging performance of the FV-SEE device was tested by imaging a USAF resolution target. SEE images showed that this new approach generates high quality images in the forward field with a field of view of 58°. Results from this preliminary study demonstrate that we can realize FV-SEE imaging with simple, monolithic, miniature optical element. The characteristics of this FV-SEE configuration will facilitate the development of robust miniature endoscopes for a variety of medical imaging applications.
Unacceptably large percentage (20-40%) of breast cancer lumpectomy patients are required to undergo multiple surgeries when positive margins are found upon post-operative histologic assessment. If the margin status can be determined during surgery, surgeon can resect additional tissues to achieve tumor-free margin, which will reduce the need for additional surgeries. Spectrally encoded confocal microscopy (SECM) is a high-speed reflectance confocal microscopy technology that has a potential to image the entire surgical margin within a short procedural time. Previously, SECM was shown to rapidly image a large area (10 mm by 10 mm) of human esophageal tissue within a short procedural time (15 seconds). When used in lumpectomy, SECM will be able to image the entire margin surface of ~30 cm2 in around 7.5 minutes. SECM images will then be used to determine margin status intra-operatively. In this paper, we present results from a study of testing accuracy of SECM for diagnosing malignant breast tissues. We have imaged freshly-excised breast specimens (N=46) with SECM. SECM images clearly visualized histomorphologic features associated with normal/benign and malignant breast tissues in a similar manner to histologic images. Diagnostic accuracy was tested by comparing SECM diagnoses made by three junior pathologists with corresponding histologic diagnoses made by a senior pathologist. SECM sensitivity and specificity were high, 0.91 and 0.93, respectively. Intra-observer agreement and inter-observer agreement were also high, 0.87 and 0.84, respectively. Results from this study showed that SECM has a potential to accurately determine margin status during breast cancer lumpectomy.
Three-dimensional (3-D) visualization of the fine structures within the lung parenchyma could advance our understanding of alveolar physiology and pathophysiology. Current knowledge has been primarily based on histology, but it is a destructive two-dimensional (2-D) technique that is limited by tissue processing artifacts. Micro-CT provides high-resolution three-dimensional (3-D) imaging within a limited sample size, but is not applicable to intact lungs from larger animals or humans. Optical reflectance techniques offer the promise to visualize alveolar regions of the large animal or human lung with sub-cellular resolution in three dimensions. Here, we present the capabilities of three optical reflectance techniques, namely optical frequency domain imaging, spectrally encoded confocal microscopy, and full field optical coherence microscopy, to visualize both gross architecture as well as cellular detail in fixed, phosphate buffered saline-immersed rat lung tissue. Images from all techniques were correlated to each other and then to corresponding histology. Spatial and temporal resolution, imaging depth, and suitability for in vivo probe development were compared to highlight the merits and limitations of each technology for studying respiratory physiology at the alveolar level.
Spectrally encoded confocal microscopy (SECM) and optical frequency domain imaging (OFDI) are two reflectancebased
imaging technologies that may be utilized for high-resolution microscopic screening of internal organs. SECM
provides en face images of tissues with a high lateral resolution of 1-2 μm, and a penetration depth of up to 300 μm.
OFDI generates cross-sectional images of tissue architecture with a resolution of 10-20 μm and a penetration depth of 1-
2 mm. Since the two technologies yield complementary microscopic information on two different size scales (SECM-cellular
and OFDI-architectural) that are commonly used for histopathologic evaluation, their combination may allow for
more accurate optical diagnosis. Here, we report the integration of these two imaging modalities in a single bench top
system. SECM images of swine small intestine showed the presence of goblet cells, and OFDI images revealed the finger-shaped villous architecture. In clinical study of 9 gastroesophageal biopsies from 8 patients, a diverse set of architectural and cellular features was observed, including squamous mucosa with mild hyperplasia and gastric antral mucosa with gastric pits and crypts. The capability of this multimodality device to enable the visualization of microscopic features on these two size scales supports our hypothesis that improved diagnostic accuracy may be obtained by merging these two technologies into a single instrument.
New confocal microscopy having no mechanical beam scanning devices is proposed. The proposed system can get two-dimensional information of a specimen in real-time by using spectral encoding technique and slit aperture. Spectral encoding technique is used to encode one- dimensional lateral information of the specimen in wavelength by a diffraction grating and a broadband light source. The modeling of the optical system is conducted. The effect of slit width variation on the axial response of the system is evaluated by numerical simulation based on the wave optics. Proper width of the slit aperture which plays a crucial role of the out-of-focus blur rejection is determined by a compromise between axial resolution and signal intensity from the simulation result. Design variables and governing equations of the system are derived on the assumption of a lateral sampling resolution of 50 nm. The system is designed to have a mapping error less than the half pixel size, to be diffraction-limited and to have the maximum illumination efficiency. The designed system has a FOV of 12.8 μm x 9.6 μm, a theoretical axial FWHM of 1.1 μm and a lateral magnification of -367.8.
Lateral resolution enhancement in confocal self-interference microscopy (CSIM) is evaluated. CSIM, which uses the birefringence of the calcite plate to generate self-interference pattern, sharpens the central lobe of the effective spot. Numerical simulation results of two-dimensional imaging performances are presented. Two-point resolution of 149nm is achieved, which is enhanced by nearly 100% compared to that of confocal microscopy.
We describe the design and the implementation of reflection confocal scanning microscopy (CSM) using an acousto-optical deflector (AOD) for the fast horizontal scan and a galvanometer mirror (GM) for the slow vertical scan. In the beam scanning system it is important to maintain the lateral and the axial performance during scanning operation. We propose a simple method to design a scanning system using the finite ray tracing and the diffraction theory. We define a
cost function which contains the effect of aberrations on the performance of microscopy. We construct the designed system and evaluate its performance. The OSLO simulation shows that the performances of CSM are not changed with deflection angle. So we conclude that the beam scanning system is properly designed. In addition, we propose an image formation method and show images obtained with the system.
The errors can cause the serious loss of the performance of a precision machine system. In this paper, we propose the method of allocating the alignment tolerances of the components and apply this method to Confocal Scanning Microscopy (CSM) to get the optimal tolerances.
CSM uses confocal aperture, which blocks the out-of-focus information. Thus, it provides images with superior resolution and has unique property of optical sectioning. Recently, due to these properties, it has been widely used for measurement in biological field, medical science, material science and semiconductor industry.
In general, tight tolerances are required to maintain the performance of a system, but a high cost of manufacturing and assembling is required to preserve the tight tolerances. The purpose of allocating the optimal tolerances is minimizing the cost while keeping the performance of the system. In the optimal problem, we set the performance requirements as constraints and maximized the tolerances.
The Monte Carlo Method, a statistical simulation method, is used in tolerance analysis. Alignment tolerances of optical components of the confocal scanning microscopy are optimized, to minimize the cost and to maintain the observation performance of the microscopy. We can also apply this method to the other precision machine system.
KEYWORDS: Confocal microscopy, Optical transfer functions, Objectives, Signal detection, Point spread functions, Luminescence, Photodetectors, Contrast transfer function, Mirrors, Spherical lenses
In fluorescence mode confocal microscopes, only 0.02% of emitted signal can be detected in best case. So, we proposed reflecting optical system to increase signal intensity detected in photon detector. In this paper, we evaluate the proposed reflecting optical system using optical transfer function. To evaluate the proposed system, we used the modeling method based on wave optics. We first calculated point spread function of total system, and calculated optical transfer function of total system. When we use the proposed reflecting optical system, we can increase the signal intensity detected in photon detector. Amount of increased signal intensity depends on the ratio of NA of objective in the original confocal microscopy to NA of objective in reflecting optical system. We also simulated axial response of total system. FWHM of axial response increased a little when using reflecting optical system. The amount of increased FWHM also depends on the ratio of NA, mentioned above. Maximum increase in FWHM of axial response is about 5%.
Tolerance analysis for focusing unit of near field recording system is presented. The assembling and manufacturing tolerances of SIL and OL are simulated using CODE V. In addition, we proposed to move collimated lens (CL) back and forth to compensate and control these tolerances, especially in optical axis direction. And we proposed, a new doublet solid immersion lens (DSIL) for near field optical system, which can minimize the tilting, decenter, defocus misalignment problems between objective lens and solid immersion lens in existing near field optical system. The objective lens, which confines the beam, and secondary lens which increases the numerical aperture, join together to make one module cemented lens system.
Confocal scanning microscopy (CSM) has been used in biological application, materials science, semiconductor quality measurement and other non-destructive microscopic application. Small spot of light illuminates a sample, and a small detector that is ideally a point detector collects the reflected or transmitted light having the information of specimen. An image distribution can be reconstructed by a correlation analysis of spots with the high bandwidth. The mechanism for two-dimensional beam scanning and optical sectioning has an important role in CSM as the three-dimensional profiler. The parasitic motion of focus on the detector gives rise to the fatal distortion of an image profile named the extinction effect while using acousto-optical (AO) deflector. The intensity profile for the open loop scanning should be matched with its response for the standard. The non-linearity can be minimized with the optical sectioning or the optical probe of the closed loop control. This paper shows the mathematical expression of the light such as the extinction curve in the optical fields of system using AO deflector, the axial/lateral response experimentally when the error sources change, and the methods of optical sectioning. We propose the progressive methods for the high quality image as the following. At first, for having the corrected image, small spot and long scan range, this paper shows that the optimal design having the multi-objects can be used by choosing the unitary lens device in CSM. At second, in order to compensate for the intensity cancellation at the end profile that may be the cause of waviness for the optical image, this paper shows that it is efficient to schedule the frequency of scan. According to characteristics of the extinction curve and axial/lateral response having the error property, we can define the frequency and sensitivity of as their robustness. Finally, the axial response gives an important motive for the optical section, and the limit of object depth. The edge enhancement may be a fatal defeat to the reconstruction of image and sensitive to the conditions of specimen such as slope, irregular reflectivity, shape, etc. That means that the intensity profile for the open loop scanning method should be matched with its response to a perfect mirror as specimen, which can be minimized with the optical sectioning or the optical probe of the closed loop control.
KEYWORDS: Sensors, Signal detection, Algorithm development, Polarizers, Signal processing, Detection and tracking algorithms, Optical alignment, Manufacturing, Polarizing prisms, 3D modeling
In this paper, we present a 3-step auto-alignment algorithm for the incident angle of an ellipsometer without auxiliary equipment. The 3-step algorithm uses only a 3-axis precision stage (two rotation and one translation) for ellipsometric incident angle alignment, and consists of two incident angles and its following corrective process. The corrective process is to position the spot on the center of the detector's aperture plane, and consists of accessing and centering on the detector's aperture. In the first step, the polarizer and analyzer arm are set at a proper incident angle and the spot is centered on the detector's aperture by the corrective process. In the second step, the polarizer and analyzer arm are set at a measured incident angle and the spot is centered on the detector's aperture by the corrective process. In the third step, height error and angle errors of the specimen are calculated with the stage's angle from the first and second steps. Finally, locating the specimen stage at an errorless position completes incident angle alignment. We modeled 3-D optical paths using a homogeneous transformation matrix (HTM), and simulated the developed alignment algorithm. The results showed that the developed alignment algorithm works well. Experiment results also revealed good agreement on the simulation. The developed alignment algorithm may be applied to other alignment problems, such as tilt alignment of lithography.
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