Femtosecond time-resolved interferometric microscopy

We describe optical interferometry with 100 fs time resolution and a spatial resolution of approximately one micrometer. Using a pump-probe scheme and a 2D-Fourier transformation algorithm, we are able to retrieve from the interferograms very small changes in the phase and the amplitude of the reflected probe pulses. The performance of the technique is illustrated by measurements of transient and permanent surface modifications of crystalline GaAs after exposure to intense femtosecond laser pulses with fluences near the ablation threshold. PACS 78.47.+p; 42.65.Re; 42.15.Eq; 68.35.Ja     

Inverse scattering for high-resolution interferometric microscopy

We extend the applicability of inverse scattering for optical coherence tomography (OCT) to the case of high numerical aperture focusing optics. We include the effects of tight focusing so that the approach is applicable to any interferometric microscopy method. The applicability to modalities, such as OCT and optical coherence microscopy, enables computed reconstruction of three-dimensional volumes from en face temporal ranging data. Simulations show that the computed structure outside of the focal plane exhibits spatially invariant resolution on par with the resolution achieved at the focal plane.     

Phase retrieval in low-coherence interferometric microscopy

We present compensating methods that address inherent errors in quantitative phase reporting for low-coherence interferometric techniques. A brief theoretical treatment of the problem and experimental validation using spectral domain phase microscopy demonstrate mitigation of the degrading effects of phase leakage on accurate measurement of optical path length in the vicinity of closely spaced reflectors. This result has direct implications for phase-sensitive interferometry techniques, such as Doppler imaging, as well as amplitude-based quantitative reporting. Corrected phase retrieval is demonstrated for conversion of interferometric phase to optical path length in cell surface deflections of beating cardiomyocytes.     

Single-exposure super-resolved interferometric microscopy by red-green-blue multiplexing

We present single-exposure super-resolved interferometric microscopy (SESRIM) as a novel approach capable of providing one-dimensional (1-D) super-resolution (SR) imaging in holographic microscopy using a single illumination shot. The single-exposure SR working principle is achieved by combining angular and wavelength multiplexing incoming from a set of tilted beams with different wavelengths where each wavelength is tuned with the red-green-blue (RGB) channels of a color CCD. Thus, the information included in each color channel is retrieved by holographic recording using a single-color CCD capture and by analyzing the RGB channels. Finally, 1-D SR imaging is obtained after the digital postprocessing stage yielding the generation of a synthetic aperture. Experimental results are reported validating the proposed SESRIM approach while an extension of the proposed approach to the two-dimensional case is considered.     

近场扫描干涉无孔径显微术

本文介绍了国外研究的一种新型近场扫描无孔径干涉显微镜的原理及结构。这种显微镜的分辨率可达到１ｎｍ，开辟了在亚纳米尺度成像和进行光谱分析的可能性，特别是在化学和生物学研究领域具有潜在的应用前景。     

Multiaxis interferometric displacement measurement for local probe microscopy

We present an overview of design approaches for nanometrology measuring setups with a focus on interferometry techniques and associated problems. The design and development of a positioning system with interferometric multiaxis monitoring and control is presented. The system is intended to operate as a national nanometrology standard combining local probe microscopy techniques and sample position control with traceability to the primary standard of length.     

Approximate wavenumber domain algorithm for interferometric synthetic aperture microscopy

Interferometric synthetic aperture microscopy (ISAM), which can increase transverse resolution with fixed depth of field in the spectral domain optical coherence tomography (SDOCT) is analyzed. Due to the high computational complexity needed for ISAM, the approximate wavenumber domain algorithm or ωKA is applied, which can save much rebuilding time without the Stolt interpolation. The multiple scatterers simulation and improved two-dimensional (2D) imaging of fresh pig liver based on the proposed ωKA approach are demonstrated. The current simulation and experimental results prove the effectiveness of the approximate ωKA.     

Fast pixel shifting phase unwrapping algorithm in quantitative interferometric microscopy

Quantitative interferometric microscopy is an important method for observing biological samples such as cells and tissues. As a key step in phase recovery, a fast phase unwrapping algorithm is proposed. By shifting mod 2π wrapped phase map for one pixel, then multiplying the original phase map and the shifted one, the phase discontinuities could be easily determined with high speed and efficiency. The method aims at enhancing phase retrieving efficiency without any background knowledge. We test our algorithm with both numerical simulation and experiments, by focusing our attentions on wrapped quantitative phase maps of cells. The results indicate that this algorithm features fast, precise and reliable.     

Surface plasmon interferometric microscopy for three-dimensional imaging of dynamic processes

A method, which we named surface plasmon interferometric microscopy, for real-time displaying of the dynamic evolution of the refractive index (RI) of a sample in three-dimensions is demonstrated experimentally. The Fourier fringe analysis technique is employed to get the phase variations of the samples by demodulating the interference patterns captured by a CCD camera, and the 3D RI distribution can be obtained through numerical interpolation from the relation between the phase and the RI of the samples. Our method may provide an interesting way to monitor fast dynamics of physical, biological, and chemical processes in real time.     

Imaging interferometric lithography: approaching the resolution limits of optics

The resolution limits of conventional optical lithography reflect the low-pass spatial-frequency [numerical aperture (NA) /lambda] filter characteristics of the imaging system. Imaging interferometric lithography extends the resolution of optical lithography to the spatial-frequency limits of optics (2/lambda) . Off-axis illumination downshifts the high-frequency components of the mask pattern. An interferometric beam at the wafer upshifts these frequency components back to their original spatial frequencies following the lens. 2x reduction imaging interferometric lithography experiments demonstrate a continuous frequency coverage up to ~3N.A./lambda with a consequent threefold resolution enhancement.     

Two-exposure quasi-common-path point diffraction interferometric phase microscopy using a four-step algorithm

A two-exposure nearly common-path point diffraction interferometric phase microscopy (IPM) is presented using polarization modulation and one-step grating shifting to implement quantitative phase imaging. The IPM is constructed by an improved Michelson configuration with a reflective grating, and its frequency spectrum generated by a circularly polarized object beam makes double copies through a beam splitter. One copy is low-pass filtered and reflected by a reflective pinhole mirror to create a reference beam, and the other copy is converted by a polarizer and then reflected by a reflective grating to achieve a 45° linearly polarized object beam. By the combination of a polarizing cube beam splitter with 45° tilted angle and a translation of the reflective grating with a π phase shift, four interferograms with π/2 phase shift can be obtained in two exposures. The standard four-step algorithm can then be used to reconstruct the phase of the specimen. The utility of the proposed method was demonstrated with measurements on a phase plate, cells and an oil drop.     

Autocorrelation artifacts in optical coherence tomography and interferometric synthetic aperture microscopy

Interferometric synthetic aperture microscopy processing of optical coherence tomography data has been shown to allow computational focusing of en face planes that have traditionally been regarded as out of focus. It is shown that this focusing of the image also produces a defocusing effect in autocorrelation artifacts resulting from Fourier-domain data collection. This effect is verified experimentally and through simulation.     

Electro‐optical interferometric microscopy of periodic and aperiodic ferroelectric structures

The ferroelectric domain structures of periodically poled KTiOPO₄ and two‐dimensional short range ordered poled LiNbO₃ crystals are determined non‐invasively by interferometric measurements of the electro‐optically induced phase retardation. Owing to the sign reversal of the electro‐optical coefficients upon domain inversion, a π phase shift is observed for the inverted domains. The microscopic setup provides diffraction‐limited spatial resolution allowing us to reveal the nonlinear and electro‐optical modulation patterns in ferroelectric crystals in a non‐destructive manner and to determine the poling period, duty cycle and short‐range order as well as detect local defects in the domain structure. Conversely, knowing the ferroelectric domain structure, one can use electro‐optical microscopy so as to infer the distribution of the electric field therein.

     

Imaging sclera with hard X-ray microscopy

In this study, the organization of collagen fibrils within the sclera of the eye was investigated using the 7 keV hard X-ray microscope of the Pohang light source and compared to images from electron and atomic force microscopy. From the captured X-ray images, individual collagen fibrils were observed clearly in a spatial resolution much better than 100 nm, both in longitudinal sections and in transverse sections. Some of the collagen fibrils showed evidence of axial periodicity. In some regions of the samples, we could see cross-bridge like structures between adjacent collagen fibrils. The X-ray microscope also allowed the observation of keratocytes and the lamella structure of the scleral stroma. The X-ray microscope has some unique advantages in the nano-scale imaging of bio-samples relative to other established imaging techniques.     

Imaging Caenorhabditis elegans embryogenesis by third-harmonic generation microscopy

In this study, third-harmonic generation (THG) imaging measurements were performed to characterize different developmental stages of the nematode Caenorhabditis elegans (C. elegans) embryos. Femtosecond laser pulses (1028 nm) were utilized for excitation. THG image contrast modality proved as a powerful diagnostic tool, providing valuable information and offering new insights into the complex developmental process of C. elegans embryogenesis.     

原子力显微镜扫描成像DNA分子

采用Mg2+处理DNA、APTES或戊二醛修饰云母表面、DNA拉直方法制备了λ-DNA及DNA-组蛋白复合物样品.室温下原子力显微镜以轻敲模式在空气中扫描样品成像.实验结果表明:AFM扫描成像的效果与样品的制备方法有关,同时也受操作因素影响.     

Imaging photothermal microscopy for absorption measurements of optical coatings

For absorption measurement of large-aperture optical coatings, a novel method of imaging photothermal microscopy based on image lock-in technique is presented. Detailed theoretical analysis and numerical calculation are made based on the image photothermal technique. The feasibility of this imaging method is proved through the coincidence between the theoretical results of single spot method and multi-channel method. The measuring speed of this imaging method can be increased hundreds of times compared with that of the raster scanning. This technique can expand the applications of photothermal technique.     

Imaging voltage-dependent cell motions with heterodyne Mach-Zehnder phase microscopy

We describe a heterodyne Mach-Zehnder interferometric microscope capable of quantitative phase imaging of biological samples with subnanometer sensitivity and frame rates up to 10 kHz. We use the microscope to image cultured neurons and measure nanometer-scale voltage-dependent motions in cells expressing the membrane motor protein prestin.     

Imaging of 1-nm-thick films with 193-nm microscopy

We have implemented a reflected-light microscope operating in the deep ultraviolet at 193 nm. Many materials absorb strongly at this wavelength, providing greatly enhanced contrast compared with visible and near-ultraviolet microscopes. Polymer films as thin as 1 nm and SiO(2) films as thin as 3 nm have been imaged with this nonoptimized instrument. We have also calculated image contrast for several thin-film materials that are important in semiconductor processing, and we show that 193-nm light provides 60-485x better contrast than visible light (500 nm) and 4-95x better contrast than near-ultraviolet light (315 nm) for these materials.