Objective Lens Research Articles

Microsphere oblique illumination for enhanced optical nano-imaging

Microsphere nano-imaging is a promising technique for label-free and real-time imaging, making optical sub-diffraction resolution possible. Due to the limited size and high surface curvature of microspheres, the magnified imaging suffers from the limited depth of field and low contrast. The performance of this technique depends not only on the geometric parameters of microspheres but also on the illumination conditions of an optical system. In this work, a specially designed filter is added to the microscope to adjust the illumination angle and area on the microsphere. Experimental results demonstrate that with the filter, the imaging contrast is increased by 2.77 times, and the resolution is improved from 125 nm to 100 nm. It also increases the depth of field, extending it from 519 nm to 900 nm coupled with a 20× objective lens. This effective light manipulation strategy establishes suitable illumination conditions to enhance the imaging contrast and resolution. It is also applicable to improve the performance of microspheres in other optical applications.

Surface slope measurement of steep silicon V-grooves using high NA Linnik interferometry

Abstract Optical topography measurements are of high interest in a lot of industrial and academic fields. One of the most common associated measurement methods is coherence scanning interferometry, but even though it provides sub-nanometer axial resolution, its lateral resolution is diffraction limited. Not only the feature size is a limiting factor for optical measurements, but also steep surface slopes may lead to problems, since the acceptance angle of the objective lens limits the maximum surface slope angles that can be measured. Here we use a Linnik-type interferometer with objective lenses of numerical apertures of 0.95 in order to maximize the measurable surface slope angle. We demonstrate that silicon V-groove structures with a slope angle of 54.74° can be measured. We compare the directly measured surface slope angle with an angle calculated from light that is reflected two times by the V-grooves. To verify our measurement we compare the measurement results to rigorous FEM simulations.

Co-linear Hexa-Mirror-Based Multi-Periodic Structured Illumination Microscopy.

Structured illumination microscopy (SIM) is a robust wide-field optical nanoscopy technique. Several approaches are implemented to improve SIM's resolution capability (∼2-fold). However, achieving a high resolution with a large field of view (FOV) is still challenging. We present tilt-mirror-based multi-periodic SIM for large-FOV super-resolution microscopy. The sample is illuminated by a multi-periodic structured pattern generated by six-beam interference using a custom-designed mirror mount. We achieve 3.16-fold resolution improvement while using a 20×/0.40 numerical-aperture objective that supports a large FOV (0.53 mm × 0.34 mm). This overcomes the high-space-bandwidth product challenge, achieving 9.98-fold improvement. mMP-SIM decouples illumination and collection paths, enabling scalable super-resolution over a large FOV. By using a 28×/0.80 numerical-aperture objective lens, an optical resolution of 170 nm over a 0.40 mm × 0.25 mm imaging area is demonstrated. The proof-of-principle experimental demonstration is performed for both fluorescent beads and a biosample like U2OS (human bone osteosarcoma) cells.

Ultra-small spectral confocal displacement sensors based on GRIN lenses

Spectral confocal displacement sensors have been widely used in various precision measurement fields such as aerospace, biology, and medicine due to their advantages of high accuracy, non-contact, fast response, and high resolution. In this paper, a new method of spectral confocal measurement of a ultra-compact probe based on a GRIN lens, to our knowledge, is proposed. Through ray tracing analysis, it is found that the axial dispersion is close to linear in a specific wavelength range, and a theoretical model of spectral confocal measurement with the GRIN lens is deduced. A GRIN lens with a diameter of 1 mm and a length of 6.59 mm was prepared by the ion-exchange method and used as a dispersive objective lens in a homemade spectral confocal measurement system. The system was calibrated to have an axial measurement range of 440 µm, an axial resolution better than 0.5 µm, a maximum standard deviation of 0.749 µm, and a relative error of less than 2%. In addition, the system was successfully applied to 3D surface contour scanning, demonstrating its potential for 3D scanning. The results show that the system has the advantages of simple structure, low cost, easy integration, and excellent performance.

Enabling real-time reconstruction for large field-of-view single-molecule localization microscopy using discrete field-dependent point-spread function

Single-molecule localization microscopy (SMLM) is a powerful super-resolution imaging technique that offers resolution far beyond the optical diffraction limit. The commonly used high numerical-aperture (NA) objective lenses in SMLM can only provide a nearly ideal point-spread function (PSF) at the center of the field-of-view (FOV), whereas the off-axis PSF is often distorted due to optical aberrations. Since precision and accuracy of three-dimensional (3D) spatial localization of single molecules heavily depend on the system’s PSF, the FOV of 3D SMLM is often restricted to about 50 µm × 50 µm limiting its applications in visualizing intra-/intercellular interactions and high-throughput single-molecule analysis. Here we present a systematic study to show the influence of optical aberrations on large FOV 3D SMLM using unmodified, astigmatic, and double-helix PSFs. Our results show that optical aberrations introduce significant localization errors during image reconstruction and thereby produce unreliable imaging results at the corner of the FOV. To maximize SMLM’s FOV, we proposed and verified the potential of using discrete field-dependent PSFs to retain precise and accurate single-molecule localization and compare their reconstruction results using simulated resolution test patterns and biological structures. Moreover, GPU acceleration empowers a discrete PSF calibration model with high localization speed, which can provide real-time SMLM image reconstruction. We envision these results will further guide the development of strategies that can provide real-time and reliable image reconstruction in large FOV 3D SMLM.

Active axial motion compensation in multiphoton-excited fluorescence microscopy.

In living organisms, the natural motion caused by heartbeat, breathing, or muscle movements leads to the deformation of tissue caused by translation and stretching of the tissue structure. This effect results in the displacement or deformation of the plane of observation for intravital microscopy and causes motion-induced aberrations of the resulting image data. This, in turn, places severe limitations on the time during which specific events can be observed in intravital imaging experiments. These limitations can be overcome if the tissue motion can be compensated such that the plane of observation remains steady. We have developed a mathematical shape space model that can predict the periodic motion of a cylindrical tissue phantom resembling blood vessels. This model is then used to rapidly calculate the future position of the plane of observation of a two-photon laser scanning fluorescence microscope. The focal plane is continuously adjusted to the calculated position with a piezo-actuated objective lens holder. We demonstrate active motion compensation for non-harmonic axial displacements of the vessel phantom with a field of view up to 400 µm × 400 µm, vertical amplitudes of more than 100 µm, and at a rate of 0.5 Hz.

Asymmetric reflection quantitative phase microscopy with a scalable field of view using dynamic speckle illumination.

Dynamic speckle illumination-based quantitative phase microscopy (QPM) offers the capability to eliminate coherent noise and achieve depth selection; however, the low coherence of the illumination restricts the flexibility in objective lens selection. An asymmetric reflective quantitative phase microscopy method is proposed in this Letter. The speckle field correlation is maintained through identical exit pupil diameters in the objectives of both interference arms. Moreover, a light source system with a delay line compensates for the optical path difference introduced by the asymmetric objectives, thereby achieving a high-contrast interferogram. Experimental measurements on a resolution target and a transparent sample demonstrate the dynamic phase imaging and depth-selection capabilities of the system across different fields of view.

A Microfluidic-Based Cell-Stretching Culture Device That Allows for Easy Preparation of Slides for Observation with High-Magnification Objective Lenses.

Microfluidic-based cell-stretching devices are vital for studying the molecular pathways involved in cellular responses to mechanobiological processes. Accurate evaluation of these responses requires detailed observation of cells cultured in this cell-stretching device. This study aimed to develop a method for preparing microscope slides to enable high-magnification imaging of cells in these devices. The key innovation is creating a peelable bond between the cell culture membrane and the upper channel, allowing for easy removal of the upper layer and precise cutting of the membrane for high-magnification microscopy. Using the fabricated device, OP9 cells (15,000 cells/channel) were stretched, and the effects of focal adhesion proteins and the intracellular distribution of YAP1 were examined under a fluorescence microscope with 100× and 60× objectives. Stretch stimulation increased integrinβ1 expression and promoted integrin-vinculin complex formation by approximately 1.4-fold in OP9 cells. Furthermore, YAP1 nuclear localization was significantly enhanced (approximately 1.3-fold) during stretching. This method offers a valuable tool for researchers using microfluidic-based cell-stretching devices. The advancement of imaging techniques in microdevice research is expected to further drive progress in mechanobiology research.

V-shaped PSF for 3D imaging over an extended depth of field in wide-field microscopy.

Single-shot 3D optical microscopy that can capture high-resolution information over a large volume has broad applications in biology. Existing 3D imaging methods using point-spread-function (PSF) engineering often have limited depth of field (DOF) or require custom and often complex design of phase masks. We propose a new, to the best of our knowledge, PSF approach that is easy to implement and offers a large DOF. The PSF appears to be axially V-shaped, engineered by replacing the conventional tube lens with a pair of axicon lenses behind the objective lens of a wide-field microscope. The 3D information can be reconstructed from a single-shot image using a deep neural network. Simulations in a 10× magnification wide-field microscope show the V-shaped PSF offers excellent 3D resolution (<2.5 µm lateral and ∼15 µm axial) over a ∼350 µm DOF at a 550 nm wavelength. Compared to other popular PSFs designed for 3D imaging, the V-shaped PSF is simple to deploy and provides high 3D reconstruction quality over an extended DOF.

Fist‐sized aerial volumetric display with femtosecond laser drawing

AbstractImages drawn in the air will be effective for the projection of a person or an avatar in telecommunication and man–machine communication. Direct drawing with femtosecond laser pulses can generate images anywhere without any special materials; therefore, there are fewer restrictions on image display location. The biggest challenge in research and development is to increase the display size. To increase the display size, it is necessary to make the objective lens have a longer focal length (lower numerical aperture), but increasing the focal length is accompanied by a decrease in excitation efficiency due to an increase in the focused size. Therefore, by measuring the luminous intensity and luminous size using lenses with several focal lengths, the possibility of realizing a display with a centimeter‐sized (fist‐sized) volume using a lens with a focal length of 100 mm was found. By reconstructing the optical system of the aerial volumetric display using a lens with a focal length of 100 mm, a drawing range of 68 mm on average in the lateral direction and 42 mm in the axial direction was achieved.

Development of Micro/Nano Pattern Arrays with Grating-Based Periodic Structures using the Direct Laser Lithography System

Introduction: This research delves into utilizing the Direct Laser Lithography System to produce micro/nanopattern arrays with grating-based periodic structures. Initially, refining the variation in periodic structures within these arrays becomes a pivotal pursuit. This demands a deep comprehension of how structural variation aligns with specific applications, particularly in photonics and material science. Methods: Advancements in hardware, software, or process optimization techniques hold potential for reaching this objective. Using an optical beam, this system enables the engraving of moderate periodic and quasi-periodic structures, enhancing pattern formation in a three-dimensional environment. Through cost-effective direct-beam interferometry systems utilizing 405 nm GaN and 290 to 780 nm AlInGaN semiconductor laser diodes, patterns ranging from in period were created, employing 300 nm gratings. Results: The system's cost-efficiency and ability to achieve high-resolution permit the creation of both regular and irregular grating designs. By employing an optical head assembly from a bluray disc recorder, housing a semiconductor laser diode and an objective lens with an NA of 0.85, this system displays promising potential in progressing the fabrication of micro/nanopattern arrays. Conclusion: Assessing their optical, mechanical, and electrical properties and exploring potential applications across varied fields like optoelectronics, photovoltaics, sensors, and biomedical devices represent critical strides for further exploration and advancement.

Silicon-via (Si-via) hole metrology and inspection by grayfield edge diffractometry

Silicon-via (Si-via) hole metrology and inspection by grayfield edge diffractometry

Study on Real-time Monitoring Method for Dust-scattered Stray Light in the Spectral Imaging CoronaGraph of the Chinese Meridian Project Phase II

Abstract The dust-scattered stray light in an inner-occulted coronagraph mainly arises from dust particles on the surfaces of the objective lens. Due to the random accumulation of dust on the lens surfaces, it is challenging to monitor this type of stray light and no application can be used for its real-time monitor in the past. In this study, we provide a system and method to overcome this issue, and these have been applied to the Spectral Imaging CoronaGraph (SICG) of the Chinese Meridian Project. The method is based on the relation between the sizes of dust particles and its stray light level at the imaging plane established in the laboratory and the relation between the real size of dust particles and the occupancies on the imaging plane. To monitor the stray light levels accounted for by dusts, one needs only an image of the objective lens that can be provided by the auxiliary imaging system that specially comes with SICG. Our tests show that the errors of the method are less or about 2%, giving a strong confidence in its accuracy. It provides a handy tool to monitor the dust level of the objective lens of SICG and has significantly improved the efficiency of the pipeline of stray light control.

Spectro‐Spatial Unmixing in Optical Microspectroscopy for Thickness Determination of Layered Materials

AbstractVan der Waals materials and devices incorporating them exhibit highly thickness‐dependent properties. The small lateral dimensions of mechanically exfoliated 2D‐layered flakes, however, remarkably complicate their precise thickness determination. Quantitative analysis of reflectance measurements using optical microspectroscopy is proven to be as precise as spectroscopic ellipsometry while providing an easily adaptable and non‐destructive method for thickness determination. The use of magnifying objective lenses allows obtaining the reflectance within a measurement spot of only a few microns in diameter. When the dimensions of exfoliated flakes are even smaller, however, the acquired reflectance is a superposition of those of the material of interest and the subjacent materials. To overcome this limitation, a facile approach to reduce the resolvable structure size by combining the evaluation of the reflectance measurement via transfer matrix method with spatial information extracted from optical micrographs is introduced. The efficacy when characterizing micrometer‐sized flakes is exemplarily demonstrated for thickness determination of highly oriented pyrolytic graphite and a thin film of silicon dioxide. It is shown that a maximum error of less than 10% is achieved even when the flake only covers 20% of the measurement spot.

Two Hundred Nanometer Thin Multifocal Graphene Oxide Metalens for Varying Magnification Broadband Imaging.

Conventional microscopes, which rely on multiple objective lenses for varying magnifications, are bulky, complex, and costly, making them difficult to integrate into compact devices. They require frequent manual adjustments, complicating the imaging process and increasing maintenance burdens. This paper explores the potential of single ultrathin graphene metalens to address this issue. We propose and demonstrate a 200 nm thin multiaxial focus graphene metalens with high-quality focusing, designed using spatial multiplexing and fabricated by one-step laser nanoprinting. A five-focal graphene metalens has been created, achieving clear imaging with varying magnifications across a broadband covering the entire visible wavelength. The graphene metalens has significantly reduced the size of the imaging system by orders of magnitude and holds profound potential for facilitating the integration and miniaturization of optical microscopic systems.

All-reflective freeform microscope objective for ultra-broadband microscopy.

Conventional refractive microscope objective lenses have limited applicability to a range of imaging modalities due to the dispersive nature of their optical elements. Designing a conventional refractive microscope objective that provides well-corrected imaging over a broad spectral range can be challenging, if not impossible. In contrast, reflective optics are inherently achromatic, so a system composed entirely of reflective elements is free from chromatic aberrations and, as a result, can image over an ultra-wide spectral range with perfect color correction. This study explores the design space of unobscured high numerical aperture, all-reflective microscope objectives. In particular, using freeform optical elements we obviate the need for a center obscuration, rendering the objective's modulation transfer function comparable to that of refractive lens systems of similar numerical aperture. We detail the design process of the reflective objective, from determining the design specifications to the system optimization and sensitivity analysis. The outcome is an all-reflective freeform microscope objective lens with a 0.65 numerical aperture that provides diffraction-limited imaging and is compatible with the geometric constraints of commercial microscope systems.

A Simple Morphometric Analysis of Preoperative Therapy Response for Esophageal Adenocarcinoma.

Histologic assessment of tumor regression grade (TRG) on esophagogastrectomy specimens after neoadjuvant therapy is an excellent predictor of local recurrence rate and long-term survival in esophageal adenocarcinomas. Although several grading systems exist globally, the modified Ryan system suggested by the College of American Pathologists (CAP) is widely used in North America. Most systems rely on quantitative percentage estimation of the residual tumor with or without additional qualitative descriptors, which is relatively subjective with poor interobserver agreement. To test a morphometric-based approach using the microscopic objective lens to estimate the size of the largest focus of the residual tumor. A total of 69 esophageal specimens post neoadjuvant therapy were evaluated. Tumor size was morphometrically determined by the microscopic field, using an Olympus microscope with ×10/×22 eyepieces. Residual viable tumor was categorized into 4 groups, using ×2, ×4, and ×10 objectives: less than or equal to an ×10 field; larger than an ×10 field but less than or equal to an ×4 field; larger than an ×4 field but less than an ×2 field; and larger than or equal to an ×2 field. Morphometric measurements significantly correlated with the CAP treatment effect scores. There was no significant difference in overall survival between larger than or equal to ×2 and ×2 to ×4 groups; however, a 3-tier system (TRG1: ≤ ×10, TRG2: > ×10 and ≤ ×4, and TRG3: > ×4) showed significant survival differences (P = .01). Significant differences in the percentage of lymphovascular and perineural invasion, advanced TNM stage, and lymph node metastasis were identified among the 3 groups. The proposed 3-tier morphometric approach based on microscopic field size is a simple and easy-to-use method, which helps stratify patients into 3 groups with distinct histopathologic features and overall survival.

Near-Field Nano-Focusing and Nano-Imaging of Dielectric Microparticle Lenses.

Compared with traditional far-field objective lenses, microparticle lenses have a distinct advantage of nonobservance of the diffraction limit, which has attracted extensive attention for its application in subwavelength photolithography and super-resolution imaging. In this article, a complete simulation model for a microparticle lens assisted microscopic imaging system was built to analyze the imaging characteristics of any shape of microparticle lens. With this model, we simulated the resolution of a conventional objective lens, a microsphere lens and a hollow microsphere lens, which verified the correctness of our simulation model and demonstrated the super-resolution imaging ability of microsphere lenses. Secondly, the focusing and imaging characteristics of four typical microparticle lenses are illustrated, and how the focal spot affects imaging resolution and imaging quality is analyzed. Upon this conclusion, we reformed and upgraded the microsphere lens with several parameters for smaller focal spots and higher imaging resolution. Finally, three types of microparticle lenses were designed through the optimized parameters and their focusing and imaging characteristics were demonstrated with a minimum FWHM of 140 nm at the focal plane and a highest imaging resolution around 70 nm (~λ/6). Our work opens up a new perspective of super-resolution imaging with near-field microparticle lens.

Computer-generated holography enables high-uniformity, high-efficiency depth-of-focus extension in endoscopic OCT.

Fiber-form optics extends the high-resolution tomographic imaging capabilities of optical coherence tomography (OCT) to the inside of the human body, i.e., endoscopic OCT. However, it still faces challenges due to the trade-off between probe size, resolution, and depth of focus (DOF). Here we introduce a method for extending the DOF in endoscopic OCT with high uniformity and efficiency. On the basis of multi-level diffractive optics, we leverage the multi-dimensional light-field modulation capabilities of computer-generated holography (CGH) to achieve precise control of the intensity distribution of the off-axis portion of the OCT probe light. Our method eliminates the need for an objective lens, allowing for direct fabrication at the distal facet of a single-mode fiber using femtosecond laser two-photon 3D printing. The superiority of our method has been verified through numerical simulation, beam measurement, and imaging results obtained with our home-built endoscopic OCT system.

Femtosecond laser direct writing of fiber bragg grating with high-speed and high-resolution scanning technique

Femtosecond laser direct writing of fiber bragg grating with high-speed and high-resolution scanning technique