ABSTRACT
High-speed three-dimensional (3D) imaging is essential for revealing the structure and functions of biological specimens. Confocal laser scanning microscopy has been widely employed for this purpose. However, it requires a time-consuming image-stacking procedure. As a solution, we previously developed light needle microscopy using a Bessel beam with a wavefront-engineered approach [Biomed. Opt. Express13, 1702 (2022)10.1364/BOE.449329]. However, this method applies only to multiphoton excitation microscopy because of the requirement to reduce the sidelobes of the Bessel beam. Here, we introduce a beam that produces a needle spot while eluding the intractable artifacts due to the sidelobes. This beam can be adopted even in one-photon excitation fluorescence 3D imaging. The proposed method can achieve real-time, rapid 3D observation of 200-nm particles in water at a rate of over 50 volumes per second. In addition, fine structures, such as the spines of neurons in fixed mouse brain tissue, can be visualized in 3D from a single raster scan of the needle spot. The proposed method can be applied to various modalities in biological imaging, enabling rapid 3D image acquisition.
ABSTRACT
Single-shot laser ablation is performed on the surface of a transparent glass material using a radially polarized femtosecond beam. Theoretical and experimental investigation revealed the significant role of the material interface under high-numerical-aperture conditions. The longitudinal electric field at the focus was remarkably enhanced due to the total reflection on the interface when a radially polarized beam was focused on the back surface of the glass from the inside using an immersion lens. This focusing condition enabled the fabrication of a small ablation hole sized 67 nm. This study offers a novel, to the best of our knowledge, approach to realize laser nanoprocessing with radially polarized beams.
ABSTRACT
We demonstrate the femtosecond-laser processing of self-suspended monolayer graphene grown by chemical vapor deposition, resulting in multipoint drilling with holes having a diameter of <100 nm. Scanning transmission electron microscopy revealed the formation of many nanopores on the laser-irradiated graphene. Furthermore, atomic-level defects as well as nanopores were found in the graphene membrane by high-resolution transmission electron microscopy, while the overall crystal structure remained intact. Raman spectroscopy showed an increase in the defect density with an increase in the number of laser shots, suggesting that the nanopore formation triggered the creation of the <100 nm holes. The approach presented herein can offer an experimental insight into the simulation of atomic dynamics in graphene under femtosecond-laser irradiation. The thorough examination of the atomic defect formation and secondary effect of surface cleaning observed in this study would help develop engineering methods for graphene and other two-dimensional materials in the future.
ABSTRACT
We propose single-path single-shot phase-shifting digital holographic microscopy (SSP-DHM) in which the quantitative phase information of an object wave is acquired without a laser light source. Multiple phase-shifted holograms are simultaneously obtained using a linear polarizer, a liquid crystal on a silicon spatial light modulator (LCoS-SLM), and a polarization-imaging camera. Complex amplitude imaging of a USAF1951 test target and phase imaging of transparent HeLa cells are performed to show its quantitative phase-imaging ability. We also conduct an experiment for the motion-picture imaging of transparent particles to highlight the single-shot imaging ability of SSP-DHM.
ABSTRACT
We propose a phase-shifting interferometry technique using only two in-line phase-shifted self-interference holograms. There is no requirement for additional recording or estimation in the measurement. The proposed technique adopts a mathematical model for self-interference digital holography. The effectiveness of the proposed technique is demonstrated by experiments on incoherent digital holographic microscopy and color-multiplexed fluorescence digital holography with computational coherent superposition. Two-color-multiplexed four-step phase-shifting incoherent digital holography is realized for the first time, to the best of our knowledge, using the proposed technique.
ABSTRACT
Ultrafast laser ablation was applied to process 10-nm self-supporting membranes. The membranes were processed over tens of square micrometers by single-shot irradiation of two visible laser pulses, followed by the realization of periodic sub-microstructures. The fabricated geometry is dependent on the intensity distribution of the superposed input pulses, providing flexibility and facilitating practical micro- and nanoengineering. Ease of designing the processing parameters and speed of processing are the significant advantages of this method compared to focused ion beam (FIB) milling.
ABSTRACT
The longitudinal electric field produced by focusing a radially polarized beam is applied in confocal laser scanning microscopy by introducing a higher-order transverse mode, combined with a technique of polarization conversion for signal detection. This technique improves signal detection corresponding to the longitudinally polarized field under a small confocal pinhole, enabling full utilization of the small focal spot characteristic of the longitudinal field. Detailed numerical and experimental studies demonstrate the enhanced spatial resolution in confocal imaging that detects a scattering signal using a higher-order radially polarized beam. Our method can be widely applied in various imaging techniques that detect coherent signals such as second-harmonic generation microscopy.
ABSTRACT
The creation of ultraviolet optical vortex beams with the topological charge of $ \vert l \vert = 1 $|l|=1 at the wavelength of 325 nm was demonstrated from a He-Cd metal vapor laser with a spot defect mirror. The measured $ {{\rm M}^2} $M2 factor was close to the theoretical value of two of the $ {{\rm LG}_{01}} $LG01 Laguerre-Gaussian mode. Some interference experiments showed that the obtained vortex beams were stable enough for practical applications such as holographic lithography.
ABSTRACT
Tight focusing of a radially polarized beam is used for single-shot laser ablation of metals. The strong longitudinal field is generated at the focus, and its contribution to the ablation process is comprehensively examined for various metal materials. In the presence of the longitudinal field at the focus, a fabricated crater at the surface exhibits either a spot shape or a doughnut shape, depending on the material. The experimental results indicate that the strong longitudinal electric field on metal surfaces is capable of promoting material removal, which may provide a novel processing scheme in ultrafast laser microprocessing with enhanced spatial resolution.
ABSTRACT
We demonstrate that the spatial resolution in confocal laser scanning microscopy is remarkably improved by simple image subtraction between images acquired by higher-order transverse modes of a cylindrical vector beam, referred to as radially and azimuthally polarized Laguerre-Gaussian mode beams. Two types of combinations of vector mode beams suitable for subtraction imaging are derived by a systematical study based on numerical calculations. The spatial resolution of about 100 nm is experimentally achieved without the degradation of image quality.